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  • 1.
    Alvarez-Asencio, Ruben
    et al.
    KTH Royal Institute of Technology, Sweden.
    Sababi, Majid
    KTH Royal Institute of Technology, Sweden.
    Pan, Jinshan
    KTH Royal Institute of Technology, Sweden.
    Ejnermark, Sebastian
    Uddeholms AB, Sweden.
    Ekman, Lars
    Uddeholms AB, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut. KTH Royal Institute of Technology, Sweden.
    Role of microstructure on corrosion initiation of an experimental tool alloy: A Quantitative Nanomechanical Property Mapping study2014In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 89, p. 236-241Article in journal (Refereed)
    Abstract [en]

    The adhesion properties of a FeCrVN experimental tool alloy immersed in pure water and sodium chloride solution have been studied by Quantitative Nanomechanical Property Mapping to understand the influence of microstructure on corrosion initiation of this alloy. The approach used here allows early observation and identification of pre-pitting events that may lead to passivity breakdown of the alloy. Adhesion provides a good distinction between the different regions and we ascribe this to their vanadium and nitrogen contents. Finally, the prepitting is characterized by generation of small particles in specific regions of the surface with low chromium content.

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  • 2.
    Arvidsson, Martin
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Ringstad, Lovisa
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Skedung, Lisa
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Duvefelt, Kenneth
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Feeling fine - the effect of topography and friction on perceived roughness and slipperiness2017In: Biotribology, ISSN 2352-5738, Vol. 11, p. 92-101Article in journal (Refereed)
    Abstract [en]

    (1) Background. To design materials with specific haptic qualities, it is important to understand both the contribution of physical attributes from the surfaces of the materials and the perceptions that are involved in the haptic interaction. (2) Methods. A series of 16 wrinkled surfaces consisting of two similar materials of different elastic modulus and 8 different wrinkle wavelengths were characterized in terms of surface roughness and tactile friction coefficient. Sixteen participants scaled the perceived Roughness and Slipperiness of the surfaces using free magnitude estimation. Friction experiments were performed both by participants and by a trained experimenter with higher control. (3) Results and discussion. The trends in friction properties were similar for the group of participants performing the friction measurements in an uncontrolled way and the experiments performed under well-defined conditions, showing that the latter type of measurements represent the general friction properties well. The results point to slipperiness as the key perception dimension for textures below 100. μm and roughness above 100. μm. Furthermore, it is apparent that roughness and slipperiness perception of these types of structures are not independent. The friction is related to contact area between finger and material. Somewhat surprising was that the material with the higher elastic modulus was perceived as more slippery. A concluding finding was that the flat (high friction) reference surfaces were scaled as rough, supporting the theory that perceived roughness itself is a multidimensional construct with both surface roughness and friction component.

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  • 3. Asencio, RA
    et al.
    Cranston, ED
    Atkin, R
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Ionic liquid nanotribology: Stiction suppression and surface induced shear thinning2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 26, p. 9967-9976Article in journal (Refereed)
    Abstract [en]

    The friction and adhesion between pairs of materials (silica, alumina, and polytetrafluoroethylene) have been studied and interpreted in terms of the long-ranged interactions present. In ambient laboratory air, the interactions are dominated by van der Waals attraction and strong adhesion leading to significant frictional forces. In the presence of the ionic liquid (IL) ethylammonium nitrate (EAN) the van der Waals interaction is suppressed and the attractive/adhesive interactions which lead to "stiction" are removed, resulting in an at least a 10-fold reduction in the friction force at large applied loads. The friction coefficient for each system was determined; coefficients obtained in air were significantly larger than those obtained in the presence of EAN (which ranged between 0.1 and 0.25), and variation in the friction coefficients between systems was correlated with changes in surface roughness. As the viscosity of ILs can be relatively high, which has implications for the lubricating properties, the hydrodynamic forces between the surfaces have therefore also been studied. The linear increase in repulsive force with speed, expected from hydrodynamic interactions, is clearly observed, and these forces further inhibit the potential for stiction. Remarkably, the viscosity extracted from the data is dramatically reduced compared to the bulk value, indicative of a surface ordering effect which significantly reduces viscous losses.

  • 4.
    Badal Tejedor, Maria
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Niklas, Nordgren
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation.
    Schuleit, Michael
    Novartis Pharma AG, Switzerland.
    Millqvist-Fureby, Anna
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    AFM Colloidal Probe Measurements Implicate Capillary Condensation in Punch-Particle Surface Interactions during Tableting2017In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, no 46, p. 13180-13188Article in journal (Refereed)
    Abstract [en]

    Adhesion of the powders to the punches is a common issue during tableting. This phenomenon is known as sticking and affects the quality of the manufactured tablets. Defective tablets increase the cost of the manufacturing process. Thus, the ability to predict the tableting performance of the formulation blend before the process is scaled-up is important. The adhesive propensity of the powder to the tableting tools is mostly governed by the surface-surface adhesive interactions. Atomic force microscopy (AFM) colloidal probe is a surface characterization technique that allows the measurement of the adhesive interactions between two materials of interest. In this study, AFM steel colloidal probe measurements were performed on ibuprofen, MCC (microcrystalline cellulose), α-lactose monohydrate, and spray-dried lactose particles as an approach to modeling the punch-particle surface interactions during tableting. The excipients (lactose and MCC) showed constant, small, attractive, and adhesive forces toward the steel surface after a repeated number of contacts. In comparison, ibuprofen displayed a much larger attractive and adhesive interaction increasing over time both in magnitude and in jump-in/jump-out separation distance. The type of interaction acting on the excipient-steel interface can be related to a van der Waals force, which is relatively weak and short-ranged. By contrast, the ibuprofen-steel interaction is described by a capillary force profile. Even though ibuprofen is not highly hydrophilic, the relatively smooth surfaces of the crystals allow "contact flooding" upon contact with the steel probe. Capillary forces increase because of the "harvesting" of moisture - due to the fast condensation kinetics - leaving a residual condensate that contributes to increase the interaction force after each consecutive contact. Local asperity contacts on the more hydrophilic surface of the excipients prevent the flooding of the contact zone, and there is no such adhesive effect under the same ambient conditions. The markedly different behavior detected by force measurements clearly shows the sticky and nonsticky propensity of the materials and allows a mechanistic description.

  • 5.
    Badal Tejedor, Maria
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Niklas, Nordgren
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Schuleit, Michael
    Novartis Pharma AG, Switzerland.
    Pazesh, Samaneh
    Uppsala University, Sweden.
    Alderborn, Göran
    Uppsala University, Sweden.
    Millqvist-Fureby, Anna
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Determination of interfacial amorphicity in functional powders2017In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, no 4, p. 920-926Article in journal (Refereed)
    Abstract [en]

    The nature of the surfaces of particles of pharmaceutical ingredients, food powders, and polymers is a determining factor for their performance in for example tableting, powder handling, or mixing. Changes on the surface structure of the material will impact the flow properties, dissolution rate, and tabletability of the powder blend. For crystalline materials, surface amorphization is a phenomenon which is known to impact performance. Since it is important to measure and control the level of amorphicity, several characterization techniques are available to determine the bulk amorphous content of a processed material. The possibility of characterizing the degree of amorphicity at the surface, for example by studying the mechanical properties of the particles' surface at the nanoscale, is currently only offered by atomic force microscopy (AFM). The AFM PeakForce QNM technique has been used to measure the variation in energy dissipation (eV) at the surface of the particles which sheds light on the mechanical changes occurring as a result of amorphization or recrystallization events. Two novel approaches for the characterization of amorphicity are presented here. First, since particles are heterogeneous, we present a methodology to present the results of extensive QNM analysis of multiple particles in a coherent and easily interpreted manner, by studying cumulative distributions of dissipation data with respect to a threshold value which can be used to distinguish the crystalline and amorphous states. To exemplify the approach, which is generally applicable to any material, reference materials of purely crystalline α-lactose monohydrate and completely amorphous spray dried lactose particles were compared to a partially amorphized α-lactose monohydrate sample. Dissipation data are compared to evaluations of the lactose samples with conventional AFM and SEM showing significant topographical differences. Finally, the recrystallization of the surface amorphous regions in response to humidity was followed by studying the dissipation response of a well-defined surface region over time, which confirms both that dissipation measurement is a useful measure of surface amorphicity and that significant recrystallization occurs at the surface in response to humidity.

  • 6.
    Badal Tejedor, Maria
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Niklas, Nordgren
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Schuleit, Michael
    Novartis Pharma AG, Switzerland.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Millqvist-Fureby, Anna
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Tablet mechanics depend on nano and micro scale adhesion, lubrication and structure2015In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 486, no 1-2, p. 315-323Article in journal (Refereed)
    Abstract [en]

    Tablets are the most convenient form for drug administration. However, despite the ease of manufacturing problems such as powder adhesion occur during the production process. This study presents surface and structural characterization of tablets formulated with commonly used excipients (microcrystalline cellulose (MCC), lactose, mannitol, magnesium (Mg) stearate) pressed under different compaction conditions. Tablet surface analyses were performed with scanning electron microscopy (SEM), profilometry and atomic force microscopy (AFM). The mechanical properties of the tablets were evaluated with a tablet hardness test. Local adhesion detected by AFM decreased when Mg stearate was present in the formulation. Moreover, the tablet strength of plastically deformable excipients such as MCC was significantly decreased after addition of Mg stearate. Combined these facts indicate that Mg stearate affects the particle-particle bonding and thus elastic recovery. The MCC excipient also displayed the highest hardness which is characteristic for a highly cohesive material. This is discussed in the view of the relatively high adhesion found between MCC and a hydrophilic probe at the nanoscale using AFM. In contrast, the tablet strength of brittle materials like lactose and mannitol is unaffected by Mg stearate. Thus fracture occurs within the excipient particles and not at particle boundaries, creating new surfaces not previously exposed to Mg stearate. Such uncoated surfaces may well promote adhesive interactions with tools during manufacture.

  • 7.
    Badal Tejedor, Maria
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Pazesh, Samaneh
    Uppsala University, Sweden.
    Niklas, Nordgren
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation.
    Schuleit, Micheal
    Novartis Pharma AG, Switzerland.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Alderborn, Göran
    Uppsala University, Sweden.
    Millqvist-Fureby, Anna
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Surface, Process and Formulation.
    Milling induced amorphisation and recrystallization of α-lactose monohydrate2018In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 537, no 1-2, p. 140-147Article in journal (Refereed)
    Abstract [en]

    Preprocessing of pharmaceutical powders is a common procedure to condition the materials for a better manufacturing performance. However, such operations may induce undesired material properties modifications when conditioning particle size through milling, for example. Modification of both surface and bulk material structure will change the material properties, thus affecting the processability of the powder. Hence it is essential to control the material transformations that occur during milling. Topographical and mechanical changes in surface properties can be a preliminary indication of further material transformations. Therefore a surface evaluation of the α-lactose monohydrate after short and prolonged milling times has been performed. Unprocessed α-lactose monohydrate and spray dried lactose were evaluated in parallel to the milled samples as reference examples of the crystalline and amorphous lactose structure. Morphological differences between unprocessed α-lactose, 1 h and 20 h milled lactose and spray dried lactose were detected from SEM and AFM images. Additionally, AFM was used to simultaneously characterize particle surface amorphicity by measuring energy dissipation. Extensive surface amorphicity was detected after 1 h of milling while prolonged milling times showed only a moderate particle surface amorphisation. Bulk material characterization performed with DSC indicated a partial amorphicity for the 1 h milled lactose and a fully amorphous thermal profile for the 20 h milled lactose. The temperature profiles however, were shifted somewhat in the comparison to the amorphous reference, particularly after extended milling, suggesting a different amorphous state compared to the spray-dried material. Water loss during milling was measured with TGA, showing lower water content for the lactose amorphized through milling compared to spray dried amorphous lactose. The combined results suggest a surface-bulk propagation of the amorphicity during milling in combination with a different amorphous structural conformation to that of the amorphous spray dried lactose. The hardened surface may be due to either surface crystallization of lactose or to formation of a low-water glass transition.

  • 8.
    Bergendal, E.
    et al.
    KTH Royal Institute of Technology, Sweden.
    Gutfreund, P.
    Institute Laue-Langevin, France.
    Pilkington, G. A.
    KTH Royal Institute of Technology, Sweden.
    Campbell, R. A.
    Institute Laue-Langevin, France; University of Manchester,UK.
    Müller-Buschbaum, P.
    Technische Universität München, Germany.
    Holt, S. A.
    Australian Nuclear Science and Technology Organisation, Australia.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden.
    Tuneable interfacial surfactant aggregates mimic lyotropic phases and facilitate large scale nanopatterning2021In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 13, no 1, p. 371-379Article in journal (Refereed)
    Abstract [en]

    It is shown that the air-liquid interface can be made to display the same rich curvature phenomena as common lyotropic liquid crystal systems. Through mixing an insoluble, naturally occurring, branched fatty acid, with an unbranched fatty acid of the same length, systematic variation in the packing constraints at the air-water interface could be obtained. The combination of atomic force microscopy and neutron reflectometry is used to demonstrate that the water surface exhibits significant tuneable topography. By systematic variation of the two fatty acid proportions, ordered arrays of monodisperse spherical caps, cylindrical sections, and a mesh phase are all observed, as well as the expected lamellar structure. The tuneable deformability of the air-water interface permits this hitherto unexplored topological diversity, which is analogous to the phase elaboration displayed by amphiphiles in solution. It offers a wealth of novel possibilities for the tailoring of nanostructure

  • 9.
    Bergendal, Erik
    et al.
    KTH Royal Institute of Technology, Sweden.
    Campbell, Rchard
    Institut Laue-Langevin, France; University of Manchester, UK.
    Pilkington, Gerorgia
    KTH Royal Institute of Technology, Sweden.
    Müller-Buschbaum, Peter
    Technische Universität München, Germany.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden.
    3D texturing of the air-water interface by biomimetic self-assembly2020In: Nanoscale Horizons, ISSN 2055-6764, E-ISSN 2055-6756, Vol. 5, no 5, p. 839-846Article in journal (Refereed)
    Abstract [en]

    A simple, insoluble monolayer of fatty acid is shown to induce 3D nanotexturing of the air-water interface. This advance has been achieved through the study of monolayers of a methyl-branched long chain fatty acid, analogous to those found on the surface of hair and wool, directly at the air-water interface. Specular neutron reflectometry combined with AFM probing of deposited monolayers shows pronounced 3D surface domains, which are absent for unbranched analogues and are attributed to hydrocarbon packing constraints. The resulting surface topographies of the water far exceed the height perturbation that can be explained by the presence of capillary waves of a free liquid surface. These have hitherto been considered the only source of perturbation of the flatness of a planar water interface under gravity in the absence of topographical features from the presence of extended, globular or particulate matter. This amounts to a paradigm shift in the study of interfacial films and opens the possibility of 3D texturing of the air-water interface.

  • 10.
    Besharat, Zahra
    et al.
    KTH Royal Institute of Technology, Sweden.
    Wakeham, Deborah
    KTH Royal Institute of Technology, Sweden.
    Johnson, C. Magnus
    KTH Royal Institute of Technology, Sweden.
    Luengo, Gustavo S.
    L’Oréal Research and Innovation, France.
    Greaves, Andrew
    L’Oréal Research and Innovation, France.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Göthelid, Mats
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Mixed monolayers of alkane thiols with polar terminal group on gold: Investigation of structure dependent surface properties2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 484, p. 279-290Article in journal (Refereed)
    Abstract [en]

    Adsorption of thiols with cationic or anionic terminal group on gold has been studied from mixed solutions of 11-Amino-1-undecanethiol (AUT) and 3-Mercaptopropionic acid (MPA) using Quartz Crystal Microbalance with Dissipation (QCM-D), X-ray Photoelectron Spectroscopy (XPS), atomic force microscopy (AFM) and contact angles. The goal is to probe the nature of such layers, and the additivity or otherwise of the pH responsiveness, with a view to evaluate their suitability as smart materials. For each of the two pure (unmixed) cases, ordered molecular monolayers are formed with sulfur binding to gold and the alkane chain pointing out from the surface as expected. Adsorption from the thiol mixtures, however, leads to a more complex behaviour. The surface concentration of thiols from the mixtures, as determined by QCM-D, is considerably lower than for the pure cases and it reaches a minimum at a 3:1 MPA/AUT relative concentration in the solution. The XPS results confirm a reduction in adsorbed amount in mixtures with the lowest overall intensity for the 3:1 ratio. Monolayers formed from mixtures display a wettability which is much lower and less pH sensitive. Collectively these results confirm that for adsorption from mixed systems, the configuration is completely different. Complex formation in the mixed solutions leads to the adsorption of molecules parallel to the surface in an axially in-plane configuration. This parallel layer of thiols is mechanically relatively robust to nano-shaving based on AFM measurements. These results will have a significant impact on the design of biomimetic surface coatings particularly when mixtures of oppositely charged molecules are present on the surface, as is commonly the case in biological, proteinaceous surfaces (e.g. hair and skin).

  • 11.
    Besharat, Zahra
    et al.
    KTH Royal Institute of Technology, Sweden.
    Yazdi, Milad Ghadami
    KTH Royal Institute of Technology, Sweden.
    Wakeham, Deborah
    KTH Royal Institute of Technology, Sweden.
    Johnson, Magnus
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Gothelid, Mats
    KTH Royal Institute of Technology, Sweden.
    Gronbeck, Henrik
    Chalmers University of Technology, Sweden.
    Se-C Cleavage of Hexane Selenol at Steps on Au(111)2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 8, p. 2630-2636Article in journal (Refereed)
    Abstract [en]

    Selenols are considered as an alternative to thiols in self-assembled monolayers, but the Se-C bond is one limiting factor for their usefulness. In this study, we address the stability of the Se-C bond by a combined experimental and theoretical investigation of gas phase-deposited hexane selenol (CH3(CH2)(5)SeH) on Au(111) using photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory (DFT). Experimentally, we find that initial adsorption leaves atomic Se on the surface without any carbon left on the surface, whereas further adsorption generates a saturated selenolate layer. The Se 3d component from atomic Se appears at 0.85 eV lower binding energy than the selenolate-related component. DFT calculations show that the most stable structure of selenols on Au(111) is in the form of RSe-Au-SeR complexes adsorbed on the unreconstructed Au(111) surface. This is similar to thiols on Au(111). Calculated Se 3d core-level shifts between elemental Se and selenolate in this structure nicely reproduce the experimentally recorded shifts. Dissociation of RSeH and subsequent formation of RH are found to proceed with high barriers on defect-free Au(111) terraces, with the highest barrier for scissoring R-Se. However, at steps, these barriers are considerably lower, allowing for Se-C bond breaking and hexane desorption, leaving elemental Se at the surface. Hexane is the selenol to selenolate formed by replacing the Se-C bond with a H-C bond by using the hydrogen liberated from transformation.

  • 12.
    Claesson, Per M
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Measuring interactions between surfaces2002In: Handbook of Applied Colloid and Surface Chemistry, Chichester, Weinheim: Wiley , 2002, p. 383-414Chapter in book (Refereed)
  • 13.
    Cooper, Peter K.
    et al.
    University of Newcastle, Australia.
    Li, Hua
    University of Newcastle, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Webber, Grant B.
    University of Newcastle, Australia.
    Atkin, Rob
    University of Newcastle, Australia.
    Tribotronic control of friction in oil-based lubricants with ionic liquid additives2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 34, p. 23657-23662Article in journal (Refereed)
    Abstract [en]

    Atomic force microscopy (AFM) reveals that tribotronic control of friction using an external potential applied to a gold surface is possible for ionic liquid (IL) concentrations as low as 5 mol% in hexadecane. The IL used is trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate, in which both the cation and anion have surfactant-like structures, and is miscible with hexadecane in all proportions. For IL concentrations less than 5 mol% friction does not vary with applied potential, but for 5 mol% and above changing the potential changes the composition of the IL boundary layer from cation-enriched (negative potentials) to anion-enriched (positive potentials). As the lubricities of the cation-rich and anion-rich boundary layers differ, this enables active control of friction in oil-based lubricants.

  • 14.
    Elbourne, Aaron
    et al.
    University of Newcastle, Australia.
    Sweeney, James
    University of Newcastle, Australia.
    Webber, Grant Bruce
    University of Newcastle, Australia.
    Wanless, Erica J.
    University of Newcastle, Australia.
    Warr, Gregory G.
    University of Sydney, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Atkin, Rob
    University of Newcastle, Australia.
    Adsorbed and near-surface structure of ionic liquids determines nanoscale friction2013In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 49, no 60, p. 6797-6799Article in journal (Refereed)
    Abstract [en]

    Surface-adsorbed and near-surface ion layer structure controls nanotribology in the silica-propylammonium nitrate (PAN)-mica system. Atomic Force Microscopy (AFM) imaging and normal force curves reveal that the normal load dictates the number of interfacial ion layers and the lateral layer structure. Shear force measurements show the lubricity of the interface changes with the number, and lateral structure, of the confined ion layer(s).

  • 15.
    Filippov, Andrei
    et al.
    Luleå University of Technology, Sweden.
    Gnezdilov, Oleg I.
    Kazan Federal University, Russia.
    Hjalmarsson, Nicklas
    KTH Royal Institute of Technology, Sweden.
    Antzutkin, Oleg N.
    Luleå University of Technology, Sweden.
    Glavatskih, Sergei B.
    KTH Royal Institute of Technology, Sweden; Ghent University, Belgium.
    Furó, István
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Acceleration of diffusion in ethylammonium nitrate ionic liquid confined between parallel glass plates2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 38, p. 25853-25858Article in journal (Refereed)
    Abstract [en]

    Diffusion of EAN confined between polar glass plates separated by a few micrometers is higher by a factor of ca. 2 as compared to bulk values. Formation of a new phase, different to the bulk, was suggested. © the Owner Societies 2017.

  • 16.
    Gebbie, Matthew A.
    et al.
    Stanford University, USA.
    Smith, Alexander M.
    University of Oxford, UK.
    Dobbs, Howard A.
    University of California, USA.
    Lee, Alpha A.
    Harvard University, USA.
    Warr, Gregory G.
    University of Sydney, Australia.
    Banquy, Xavier
    Universite de Montreal, Canada.
    Valtiner, Markus
    Max Planck Institut fur Eisenforschung GmbH, Germany.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden .
    Israelachvili, Jacob N.
    University of California, USA.
    Perkin, Susan
    University of Oxford, UK.
    Atkin, Rob
    University of Newcastle, Australia.
    Long range electrostatic forces in ionic liquids2017In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 7, p. 1214-1224Article in journal (Refereed)
    Abstract [en]

    Ionic liquids are pure salts that are liquid under ambient conditions. As liquids composed solely of ions, the scientific consensus has been that ionic liquids have exceedingly high ionic strengths and thus very short Debye screening lengths. However, several recent experiments from laboratories around the world have reported data for the approach of two surfaces separated by ionic liquids which revealed remarkable long range forces that appear to be electrostatic in origin. Evidence has accumulated demonstrating long range surface forces for several different combinations of ionic liquids and electrically charged surfaces, as well as for concentrated mixtures of inorganic salts in solvent. The original interpretation of these forces, that ionic liquids could be envisioned as “dilute electrolytes,” was controversial, and the origin of long range forces in ionic liquids remains the subject of discussion. Here we seek to collate and examine the evidence for long range surface forces in ionic liquids, identify key outstanding questions, and explore possible mechanisms underlying the origin of these long range forces. Long range surface forces in ionic liquids and other highly concentrated electrolytes hold diverse implications from designing ionic liquids for energy storage applications to rationalizing electrostatic correlations in biological self-assembly.

  • 17.
    Hammond, Oliver
    et al.
    Stockholm University, Sweden; Aarhus University, Denmark.
    Bousrez, Guillaume
    Stockholm University, Sweden; Aarhus University, Denmark.
    Mehler, Filip
    KTH Royal Institute of Technology, Sweden.
    Li, Sichao
    KTH Royal Institute of Technology, Sweden.
    Shimpi, Manishkumar
    Stockholm University, Sweden; Luleå University of Technology, Sweden.
    Doutch, James
    Rutherford Appleton Laboratory, UK.
    Cavalcanti, Leide
    Rutherford Appleton Laboratory, UK.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia; Ghent University, Belgium.
    Antzutkin, Oleg
    Luleå University of Technology, Sweden.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia; École Centrale de Lyon, France.
    Mudring, A. -V
    Stockholm University, Sweden; Aarhus University, Denmark.
    Molecular Architecture Effects on Bulk Nanostructure in Bis(Orthoborate) Ionic Liquids2023In: Small, ISSN 1613-6810, E-ISSN 1613-6829Article in journal (Refereed)
    Abstract [en]

    A series of 19 ionic liquids (ILs) based on phosphonium and imidazolium cations of varying alkyl-chain lengths with the orthoborate anions bis(oxalato)borate [BOB]−, bis(mandelato)borate, [BMB]− and bis(salicylato)borate, [BScB]−, are synthesized and studied using small-angle neutron scattering (SANS). All measured systems display nanostructuring, with 1-methyl-3-n-alkyl imidazolium-orthoborates forming clearly bicontinuous L3 spongelike phases when the alkyl chains are longer than C6 (hexyl). L3 phases are fitted using the Teubner and Strey model, and diffusely-nanostructured systems are primarily fitted using the Ornstein-Zernicke correlation length model. Strongly-nanostructured systems have a strong dependence on the cation, with molecular architecture variation explored to determine the driving forces for self-assembly. The ability to form well-defined complex phases is effectively extinguished in several ways: methylation of the most acidic imidazolium ring proton, replacing the imidazolium 3-methyl group with a longer hydrocarbon chain, substitution of [BOB]− by [BMB]−, or exchanging the imidazolium for phosphonium systems, irrespective of phosphonium architecture. The results suggest there is only a small window of opportunity, in terms of molecular amphiphilicity and cation:anion volume matching, for the formation of stable extensive bicontinuous domains in pure bulk orthoborate-based ILs. Particularly important for self-assembly processes appear to be the ability to form H-bonding networks, which offer additional versatility in imidazolium systems. © 2023 The Authors.

  • 18.
    Harris, Kathryn L
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Collier, Elizabeth S
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Skedung, Lisa
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden.
    A Sticky Situation or Rough Going?: Influencing Haptic Perception of Wood Coatings Through Frictional and Topographical Design2021In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 69, no 3, article id 113Article in journal (Refereed)
    Abstract [en]

    Improving the tactile aesthetics of products that can be described as touch intensive is an increasing priority within many sectors, including the furniture industry. Understanding which physical characteristics contribute to the haptic experience of a surface, and how, is therefore highly topical. It has earlier been shown that both friction and topography affect tactile perception. Thus, two series of stimuli have been produced using standard coating techniques, with systematic variation in (physical) friction and roughness properties. This was achieved through appropriate selection of matting agents and resins. The stimuli sets were then evaluated perceptually to determine the extent to which discrimination between pairs of surfaces followed the systematic materials variation. In addition to investigating the role of the physical properties in discrimination of the surfaces, their influence on perceived pleasantness and naturalness was also studied. The results indicate that changes in tactile perception can be understood in terms of friction and roughness, and that varying the matting agents (topography) and resins (material properties) in the coatings provide the controlling factors for furniture applications. Perceived pleasantness is associated with low friction and smoother topography, whilst perceived naturalness is found to be described by an interaction between tactile friction and the average maximum peak height of the surface features. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

  • 19.
    Hedberg, Yolanda S.
    et al.
    KTH Royal Institute of Technology, Sweden; Karolinska Institute, Sweden.
    Pettersson, Maria
    Uppsala University, Sweden.
    Pradhan, Sulena
    KTH Royal Institute of Technology, Sweden.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Persson, Cecilia
    Uppsala University, Sweden.
    Can Cobalt(II) and Chromium(III) ions released from joint prostheses influence the friction coefficient?2015In: ACS Biomaterial Science and Engineering, E-ISSN 2373-9878, Vol. 1, no 8, p. 617-620Article in journal (Refereed)
    Abstract [en]

    Cobalt chromium molybdenum alloys (CoCrMo) are commonly used as articulating components in joint prostheses. In this tribocorrosive environment, wear debris and metal ionic species are released and interact with proteins, possibly resulting in protein aggregation. This study aimed to investigate whether this could have an effect on the friction coefficient in a typical material couple, namely CoCrMo-on-polyethylene. It was confirmed that both Co(II) and Cr(III) ions, and their combination, at concentrations relevant for the metal release situation, resulted in protein aggregation and its concomitant precipitation, which increased the friction coefficient. Future studies should identify the clinical importance of these findings.

  • 20.
    Hjalmarsson, N.
    et al.
    KTH Royal Institute of Technology, Sweden.
    Atkin, R.
    The University of Newcastle, Australia.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Switchable long-range double layer force observed in a protic ionic liquid2017In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 3, p. 647-650Article in journal (Refereed)
    Abstract [en]

    A repulsive double layer force has been measured for ethylammonium nitrate (EAN) at 373 K and 393 K, which is absent at lower temperatures. This temperature-tuneable change in behaviour is the opposite of recent observations which challenge traditional views of ionicity. This finding thus widens the debate about the very nature of ionic liquids.

  • 21.
    Hjalmarsson, Nicklas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Atkin, Rob
    University of Newcastle, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Effect of Lithium ions on rheology and interfacial forces in Ethylammonium Nitrate and Ethanolammonium Nitrate2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 47, p. 26960-26967Article in journal (Refereed)
    Abstract [en]

    The effect of added Li+ to two ionic liquids (ILs), ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), has been investigated using rheology and colloidal probe atomic force microscopy (AFM). Rheology data revealed a complex viscosity dependence that can be ascribed to the different bulk nanostructures. AFM force curves revealed steps for the neat ILs, analogous to those in previous studies. The addition of Li+ broadened the steps, which is likely an effect of ion clusters formed. Friction measurements corroborate this data and also showed that the structure of EtAN is much more prone to change as Li+ is added. These results demonstrate the complex behavior of ILs on interfaces and the effect of perturbing such interactions. (Graph Presented).

  • 22.
    Hjalmarsson, Nicklas
    et al.
    KTH The Royal Institute of Technology, Sweden.
    Atkin, Rob
    University of Newcastle, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Is the boundary layer of an ionic liquid equally lubricating at higher temperature?2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 13, p. 9232-9239Article in journal (Refereed)
    Abstract [en]

    Atomic force microscopy has been used to study the effect of temperature on normal forces and friction for the room temperature ionic liquid (IL) ethylammonium nitrate (EAN), confined between mica and a silica colloid probe at 25 °C, 50 °C, and 80 °C. Force curves revealed a strong fluid dynamic influence at room temperature, which was greatly reduced at elevated temperatures due to the reduced liquid viscosity. A fluid dynamic analysis reveals that bulk viscosity is manifested at large separation but that EAN displays a nonzero slip, indicating a region of different viscosity near the surface. At high temperatures, the reduction in fluid dynamic force reveals step-like force curves, similar to those found at room temperature using much lower scan rates. The ionic liquid boundary layer remains adsorbed to the solid surface even at high temperature, which provides a mechanism for lubrication when fluid dynamic lubrication is strongly reduced. The friction data reveals a decrease in absolute friction force with increasing temperature, which is associated with increased thermal motion and reduced viscosity of the near surface layers but, consistent with the normal force data, boundary layer lubrication was unaffected. The implications for ILs as lubricants are discussed in terms of the behaviour of this well characterised system.

  • 23.
    Hjalmarsson, Nicklas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Bergendal, Erik
    KTH Royal Institute of Technology, Sweden.
    Wang, Yong-Lei
    KTH Royal Institute of Technology, Sweden.
    Munavirov, Bulat
    KTH Royal Institute of Technology, Sweden.
    Wallinder, Daniel
    Attana AB, Sweden .
    Glavatskih, Sergei
    Ghent University, Belgium; KTH Royal Institute of Technology, Sweden.
    Aastrup, Teodor
    Attana AB, Sweden .
    Atkin, Rob
    University of Western Australia, Australia.
    Furó, István
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Electro-Responsive Surface Composition and Kinetics of an Ionic Liquid in a Polar Oil.2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 48, p. 15692-15700Article in journal (Refereed)
    Abstract [en]

    The quartz crystal microbalance (QCM) has been used to study how the interfacial layer of an ionic liquid dissolved in a polar oil at low weight percentages responds to changes in applied potential. The changes in surface composition at the QCM gold surface depend on both the magnitude and sign of the applied potential. The time-resolved response indicates that the relaxation kinetics are limited by the diffusion of ions in the interfacial region and not in the bulk, since there is no concentration dependence. The measured mass changes cannot be explained only in terms of simple ion exchange; the relative molecular volumes of the ions and the density changes in response to ion exclusion must be considered. The relaxation behavior of the potential between the electrodes upon disconnecting the applied potential is more complex than that observed for pure ionic liquids, but a measure of the surface charge can be extracted from the exponential decay when the rapid initial potential drop is accounted for. The adsorbed film at the gold surface consists predominantly of ionic liquid despite the low concentration, which is unsurprising given the surtactant-like structures of (some of) the ionic liquid ions. Changes in response to potential correspond to changes in the relative numbers of cations and anions, rather than a change in the oil composition. No evidence for an electric field induced change in viscosity is observed. This work shows conclusively that electric potentials can be used to control the surface composition, even in an oil-based system, and paves the way for other ion solvent studies.

  • 24.
    Hjalmarsson, Nicklas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Wallinder, Daniel
    Attana AB, Sweden.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; Ghent University, Belgium.
    Atkin, Rob
    University of Newcastle, Australia.
    Aastrup, Teodor
    Attana AB, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Weighing the surface charge of an ionic liquid2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 38, p. 16039-16045Article in journal (Refereed)
    Abstract [en]

    Electrochemical quartz crystal microbalance has been used to measure changes in the composition of the capacitive electrical double layer for 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, an ionic liquid, in contact with a gold electrode surface as a function of potential. The mass difference between the cation and anion means that the technique can effectively "weigh" the surface charge accurately with high temporal resolution. This reveals quantitatively how changing the potential alters the ratio of cations and anions associated with the electrode surface, and thus the charge per unit area, as well as the kinetics associated with these interfacial processes. The measurements reveal that it is diffusion of co-ions into the interfacial region rather than expulsion of counterions that controls the relaxation. The measured potential dependent double layer capacitance experimentally validates recent theoretical predictions for counterion overscreening (low potentials) and crowding (high potentials) at electrode surfaces. This new capacity to quantitatively measure ion composition is critical for ionic liquid applications ranging from batteries, capacitors and electrodeposition through to boundary layer structure in tribology, and more broadly provides new insight into interfacial processes in concentrated electrolyte solutions.

  • 25.
    Jin, Ruting
    et al.
    University of Massachusetts, USA.
    Skedung, Lisa
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Cazeneuve, Colette
    L'Oreal, France.
    Chang, Jeanne C.
    L'Oreal, USA.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Ruths, Marina
    University of Massachusetts, USA.
    Luengo, Gustavo S.
    L'Oreal, France.
    Bioinspired Self-Assembled 3D Patterned Polymer Textures as Skin Coatings Models: Tribology and Tactile Behavior2020In: Biotribology, ISSN 2352-5738, Vol. 24, article id 100151Article in journal (Refereed)
    Abstract [en]

    It is well known that during evolution, specific surface patterns emerged (e.g., on lotus leaves and butterfly wings) endowed with many remarkable surface properties (superhydrophobicity, vibrant structural color, delicate textures, etc.). In order to obtain these natural effects in cosmetics, we look for ways to transfer topographic patterns in coatings and treatments. Textured polymer surfaces were studied to explore their friction properties on the microscale and possible correlations with human tactile friction on the macroscale. We have chosen self-assembling block and random copolymers as model systems to prepare reliable biomimetic films with different micrometer and nanometer scale randomly patterned and randomly rough surfaces. The surface texture of the films was characterized by atomic force microscopy (AFM), and their tribological (friction) properties were studied with a surface forces apparatus (SFA) at a low sliding speed of 3 μm/s and at a speed of 10 cm/s relevant to realistic applications. The results are evaluated in terms of polymer segment mobility, interpenetration, entanglement and relaxation at interfaces, surface texture as described by roughness parameters, and interlocking of asperities. A stiction spike (static friction) was commonly found for the randomly patterned glassy polymer films. Random roughness patterns made from semi-crystalline polymers above their Tg gave high friction at low speed, but their friction coefficients were reduced at high speed due to less time for local entanglement and relaxations. The friction response of one of them was also affected differently by humidity than that of glassy polymer films. Tactile friction measurements with a human finger sliding against the polymer films revealed that the textures also provided differences at the macroscale, although the dynamic changes possibly due to lipid transfer, occlusion of moisture and/or damage of the films makes it difficult to draw robust conclusions. Finally, as an example, it is shown that these textures can be transferred to a soft elastomeric skin mimic substrate. This study introduces the concept of surface patterning by self-assembly to deliver tactile sensorial properties in coatings.

  • 26.
    Li, H.
    et al.
    University of Western Australia, Australia.
    Choi, Y. S.
    University of Western Australia, Australia.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden.
    Atkin, R.
    University of Western Australia, Australia.
    Nanotribology of hydrogels with similar stiffness but different polymer and crosslinker concentrations2020In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 563, p. 347-353Article in journal (Refereed)
    Abstract [en]

    Hypothesis: The stiffness has been found to regulate hydrogel performances and applications. However, the key interfacial properties of hydrogels, like friction and adhesion are not controlled by the stiffness, but are altered by the structure and composition of hydrogels, like polymer volume fraction and crosslinking degree. Experiments: Colloidal probe atomic force microscopy has been use to investigate the relationship between tribological properties (friction and adhesion) and composition of hydrogels with similar stiffness, but different polymer volume fractions and crosslinking degrees. Findings: The interfacial normal and lateral (friction) forces of hydrogels are not directly correlated to the stiffness, but altered by the hydrogel structure and composition. For normal force measurements, the adhesion increases with polymer volume fraction but decreases with crosslinking degree. For lateral force measurements, friction increases with polymer volume fraction, but decreases with crosslinking degree. In the low normal force regime, friction is mainly adhesion-controlled and increases significantly with the adhesion and polymer volume fraction. In the high normal force regime, friction is predominantly load-controlled and shows slow increase with normal force. 

  • 27.
    Li, Hua
    et al.
    The University of Newcastle, Australia.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Watanabe, Masayoshi
    Yokohama National University, Japan.
    Atkin, Rob
    The University of Newcastle, Australia.
    Boundary layer friction of solvate ionic liquids as a function of potential2017In: Faraday discussions, ISSN 1359-6640, E-ISSN 1364-5498, Vol. 199, p. 311-322Article in journal (Refereed)
    Abstract [en]

    Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li+ cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI- anion rich boundary layer at positive potentials is more lubricating than the Li+ cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li+ cations for both surfaces at negative potentials. However, at Au(111), the TFSI- rich boundary layer is less lubricating than the Li+ rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO3 - rich boundary layer. © The Royal Society of Chemistry.

  • 28.
    Li, Hua
    et al.
    University of Newcastle, Australia.
    Somers, Anthony E.
    Deakin University, Australia.
    Howlett, Patrick C.
    Deakin University, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Forsyth, Maria
    Deakin University, Australia.
    Atkin, Rob
    University of Newcastle, Australia.
    Addition of low concentrations of an ionic liquid to a base oil reduces friction over multiple length scales: A combined nano- and macrotribology investigation2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 9, p. 6541-6547Article in journal (Refereed)
    Abstract [en]

    The efficacy of ionic liquids (ILs) as lubricant additives to a model base oil has been probed at the nanoscale and macroscale as a function of IL concentration using the same materials. Silica surfaces lubricated with mixtures of the IL trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate and hexadecane are probed using atomic force microscopy (AFM) (nanoscale) and ball-on-disc tribometer (macroscale). At both length scales the pure IL is a much more effective lubricant than hexadecane. At the nanoscale, 2.0 mol% IL (and above) in hexadecane lubricates the silica as well as the pure IL due to the formation of a robust IL boundary layer that separates the sliding surfaces. At the macroscale the lubrication is highly load dependent; at low loads all the mixtures lubricate as effectively as the pure IL, whereas at higher loads rather high concentrations are required to provide IL like lubrication. Wear is also pronounced at high loads, for all cases except the pure IL, and a tribofilm is formed. Together, the nano- and macroscales results reveal that the IL is an effective lubricant additive - it reduces friction - in both the boundary regime at the nanoscale and mixed regime at the macroscale.

  • 29.
    Li, Hua
    et al.
    University of Newcastle, Australia.
    Somers, Anthony E.
    Deakin University, Australia.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Howlett, Patrick C.
    Deakin University, Australia.
    Atkin, Rob
    University of Newcastle, Australia.
    Combined nano- and macrotribology studies of titania lubrication using the oil-ionic liquid mixtures2016In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 4, no 9, p. 5005-5012Article in journal (Refereed)
    Abstract [en]

    The lubrication of titania surfaces using a series of ionic liquid (IL)-hexadecane mixtures has been probed using nanoscale atomic force microscopy (AFM) and macroscale ball-on-disk tribometer measurements. The IL investigated is trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate, which is miscible with hexadecane in all proportions. At both length scales, the pure IL is a much more effective lubricant than pure hexadecane. At low loads, which are comparable to common industrial applications, the pure IL reduces the friction by 80% compared to pure hexadecane; while the IL-hexadecane mixtures lubricate the titania surface as effectively as the pure IL and wear decreases with increasing IL concentration. At high test loads the adsorbed ion boundary layer is displaced leading to surface contact and high friction, and wear is pronounced for all IL concentrations. Nonetheless, the IL performs better than a traditional zinc-dialkyl-dithophosphate (ZDDP) antiwear additive at the same concentration.

  • 30.
    Li, Sichao
    et al.
    KTH Royal Institute of Technology, Sweden.
    Pilkington, Georgia A.
    KTH Royal Institute of Technology, Sweden.
    Mehler, Filip
    KTH Royal Institute of Technology, Sweden.
    Hammond, Oliver S.
    Stockholm University, Sweden; Aarhus University, Denmark.
    Boudier, Anthony
    Stockholm University, Sweden.
    Vorobiev, Alexei
    Uppsala University, Sweden.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia; Ghent University, Belgium; .
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia; École Centrale de Lyon, France.
    Tuneable interphase transitions in ionic liquid/carrier systems via voltage control2023In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 652, p. 1240-1249Article in journal (Refereed)
    Abstract [en]

    The structure and interaction of ionic liquids (ILs) influence their interfacial composition, and their arrangement (i.e., electric double-layer (EDL) structure), can be controlled by an electric field. Here, we employed a quartz crystal microbalance (QCM) to study the electrical response of two non-halogenated phosphonium orthoborate ILs, dissolved in a polar solvent at the interface. The response is influenced by the applied voltage, the structure of the ions, and the solvent polarizability. One IL showed anomalous electro-responsivity, suggesting a self-assembly bilayer structure of the IL cation at the gold interface, which transitions to a typical EDL structure at higher positive potential. Neutron reflectivity (NR) confirmed this interfacial structuring and compositional changes at the electrified gold surface. A cation-dominated self-assembly structure is observed for negative and neutral voltages, which abruptly transitions to an anion-rich interfacial layer at positive voltages. An interphase transition explains the electro-responsive behaviour of self-assembling IL/carrier systems, pertinent for ILs in advanced tribological and electrochemical contexts.

  • 31. Liljebad, Jonathan FD
    et al.
    Bulone, Vincent
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Johnson, C Magnus
    Supported phospholipid monolayers. The molecular structure investigated by vibrational sum frequency spectroscopy2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 21, p. 10617-10629Article in journal (Refereed)
    Abstract [en]

    The molecular structure, packing properties, and hydrating water of Langmuir-Blodgett monolayers of the phospholipids 1, 2-distearoyl-sn-glyercophosphatidylcholine (DSPC, 18:0 PC), its deuterated analogue (18:0 PC-d83), and 1, 2-distearoyl-sn-glyerco-phosphatidylserine (DSPC, 18:0 PS) deposited on planar calcium fluoride (CaF2) substrates have been investigated using the surface-specific nonlinear optical technique vibrational sum frequency spectroscopy (VSFS). Compression isotherms were recorded before the deposition of the monolayers at a surface pressure of 35 mN/m, mimicking the conditions of biological cell membranes. The CH and CD stretch regions, the water region, and the lower wavenumber region, containing phosphate, ester, carboxylate, and amine signals, thus partly covering the fingerprint region, were probed to obtain a complete map of the molecules. The data indicate that all deposited monolayers formed a well-ordered and stable film, and probing the water region revealed significant differences in hydration for the different headgroups. In addition, the tilt angle of the aliphatic chains relative to the surface normal was estimated to be approximately 4 degrees to 10 degrees based on orientational analysis using the antisymmetric methyl stretching vibration. Orientational analysis of the ester C=O groups was also performed, and the result was consistent with the estimated tilt angle of the aliphatic chains.

  • 32. Liljeblad, Jonathan FD
    et al.
    Bulone, Vincent
    Tyrode, Eric
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Johnson, C Magnus
    Phospholipid monolayers probed by vibrational sum frequency spectroscopy: Instability of unsaturated phospholipids2010In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, no 10, p. L50-Article in journal (Refereed)
    Abstract [en]

    The surface specific technique vibrational sum frequency spectroscopy has been applied to in situ studies of the degradation of Langmuir monolayers of 1, 2-diacyl-phosphocholines with various degrees of unsaturation in the aliphatic chains. To monitor the degradation of the phospholipids, the time-dependent change of the monolayer area at constant surface pressure and the sum frequency intensity of the vinyl CH stretch at the carbon-carbon double bonds were measured. The data show a rapid degradation of monolayers of phospholipids carrying unsaturated aliphatic chains compared to the stable lipids carrying fully saturated chains when exposed to the ambient laboratory air. In addition, the degradation of the phospholipids can be inhibited by purging the ambient air with nitrogen. This instability may be attributed to spontaneous degradation by oxidation mediated by various reactive species in the air. To further elucidate the process of lipid oxidation in biological membranes artificial Langmuir monolayers probed by a surface specific spectroscopic technique as in this study can serve as a model system for studying the degradation/oxidation of cell membrane constituents.

  • 33.
    Liljeblad, Jonathan F.D.
    et al.
    KTH Royal Institute of Technology, Sweden.
    Tyrode, Eric C.
    L’Oréal, France.
    Thormann, Esben
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Dublanchet, Anne Claude
    L’Oréal, France.
    Luengo, Gustavo S.
    L’Oréal, France.
    Johnson, Magnus C.
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Self-assembly of long chain fatty acids: Effect of a methyl branch2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 33, p. 17869-17882Article in journal (Refereed)
    Abstract [en]

    The morphology and molecular conformation of Langmuir-Blodgett deposited and floating monolayers of a selection of straight chain (eicosanoic acid, EA), iso (19-methyl eicosanoic acid, 19-MEA), and anteiso (18-methyl eicosanoic acid, 18-MEA) fatty acids have been investigated by Vibrational Sum Frequency Spectroscopy (VSFS), AFM imaging, and the Langmuir trough. While the straight chain fatty acid forms smooth, featureless monolayers, all the branched chain fatty acids display 10-50 nm sized domains (larger for 19-MEA than the 18-MEA) with a homogeneous size distribution. A model is suggested to explain the domain formation and size in terms of the branched fatty acid packing properties and the formation of hemispherical caps at the liquid-air interface. No difference between the chiral (S) form and the racemic mixture of the 18-MEA is observed with any of the utilized techniques. The aliphatic chains of the straight chain fatty acids appear to be oriented perpendicular to the sample surface, based on an orientational analysis of VSFS data and the odd/even effect. In addition, the selection of the subphase (neat water or CdCl2 containing water buffered to pH 6.0) used for the LB-deposition has a profound influence on the monolayer morphology, packing density, compressibility, and conformational order. Finally, the orientation of the 19-MEA dimethyl moiety is estimated, and a strategy for performing an orientational analysis to determine the complete molecular orientation of the aliphatic chains of 19-MEA and 18-MEA is outlined and discussed.

  • 34.
    Liu, Xiaoyan
    et al.
    KTH Royal Institute of Technology, Sweden.
    Thormann, Esben
    KTH Royal Institute of Technology, Sweden.
    Dedinaite, Andra A.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut. KTH Royal Institute of Technology, Sweden.
    Visnevskij, Ceslav
    Vilnius University, Lithuania.
    Makuska, Ricardas
    Vilnius University, Lithuania.
    Claesson, Per Martin
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Low friction and high load bearing capacity layers formed by cationic-block-non-ionic bottle-brush copolymers in aqueous media2013In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 9, no 22, p. 5361-5371Article in journal (Refereed)
    Abstract [en]

    Efficient lubricants should be able to build surface layers that result in low friction and high load bearing capacity. In this work we show how this can be achieved in aqueous media by means of adsorption of a diblock copolymer consisting of a cationic anchor block without side chains and an uncharged and hydrophilic bottle-brush block that protrudes into solution. Surface and friction forces were measured between negatively charged silica surfaces coated with adsorbed layers of the cationic diblock copolymer, utilizing the atomic force microscope colloidal probe technique. The interactions between the surfaces coated with this copolymer in water are purely repulsive, due to a combination of steric and electrostatic double-layer forces, and no hysteresis is observed between forces measured on approach and separation. Friction forces between the diblock copolymer layers are characterized by a low friction coefficient, μ ≈ 0.03-0.04. The layers remain intact under high load and shear due to the strong electrostatic anchoring, and no destruction of the layer was noted even under the highest pressure employed (about 50 MPa). Addition of NaCl to a concentration of 155 mM weakens the anchoring of the copolymer to the substrate surface, and as a result the friction force increases.

  • 35.
    Liu, Xiaoyuan
    et al.
    KTH Royal Institute of Technology, Sweden.
    Dedinaite, Andra
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Thormann, Esben
    KTH Royal Institute of Technology, Sweden.
    Visnevskij, Ceslav
    Vilnius University, Lithuania.
    Makuska, Ricardas
    Vilnius University, Lithuania.
    Claesson, Per Martin
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Electrostatically anchored branched brush layers2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 44, p. 15537-15547Article in journal (Refereed)
    Abstract [en]

    A novel type of block copolymer has been synthesized. It consists of a linear cationic block and an uncharged bottle-brush block. The nonionic bottle-brush block contains 45 units long poly(ethylene oxide) side chains. This polymer was synthesized with the intention of creating branched brush layers firmly physisorbed to negatively charged surfaces via the cationic block, mimicking the architecture (but not the chemistry) of bottle-brush molecules suggested to be present on the cartilage surface, and contributing to the efficient lubrication of synovial joints. The adsorption properties of the diblock copolymer as well as of the two blocks separately were studied on silica surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry. The adsorption kinetics data highlight that the diblock copolymers initially adsorb preferentially parallel to the surface with both the cationic block and the uncharged bottle-brush block in contact with the surface. However, as the adsorption proceeds, a structural change occurs within the layer, and the PEO bottle-brush block extends toward solution, forming a surface-anchored branched brush layer. As the adsorption plateau is reached, the diblock copolymer layer is 46-48 nm thick, and the water content in the layer is above 90 wt %. The combination of strong electrostatic anchoring and highly hydrated branched brush structures provide strong steric repulsion, low friction forces, and high load bearing capacity. The strong electrostatic anchoring also provides high stability of preadsorbed layers under different ionic strength conditions.

  • 36. Lundin, Maria
    et al.
    Elofsson, Ulla
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Blomberg, Eva
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Adsorption of lysozyme, beta-casein and their layer-by-layer formation on hydrophilic surfaces: Effect of ionic strength2010In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 77, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    The adsorbed amount and layer structure of lysozyme, _x0002_-casein and mixed layers of the two proteins were studied on hydrophilic silica and quartz surfaces using the following techniques: ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D) and total internal reflection fluorescence (TIRF). Particular emphasis was put on the effect of solution ionic strength on the layer formation. Both lysozyme and _x0002_-casein showed a higher affinity for the silica surface when adsorbed from a solution of low ionic strength even though _x0002_-casein and silica are negatively charged at the pH used. No _x0002_-casein remained adsorbed after rinsing with a 150mMbuffer solution. The adsorbed amount of lysozyme on silica exceeded a monolayer coverage irrespective of the solution conditions and displayed a rigid structure. _x0002_-Casein forms more than a single layer on pre-adsorbed lysozyme; an inner flat layer and an outer layer with an extended structure, which largely desorbs on rinsing. The build-up through sequential adsorption of lysozyme and _x0002_-casein is favoured at intermediate and high ionic strength. The total adsorbed amount increased slightly with each deposition cycle and the mixed lysozyme/_x0002_-casein layers contain higher amounts of protein compared to those of pure lysozyme or _x0002_-casein. Sequential adsorption gives rise to a proteinaceous layer consisting of both lysozyme and _x0002_-casein. The protein layers are probably highly interpenetrated with no clear separation between them.

  • 37. Mizuno, Hiroyasu
    et al.
    Luengo, Gustavo S
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Interactions between crossed hair fibers at the nanoscale2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 24, p. 18909-18915Article in journal (Refereed)
    Abstract [en]

    The atomic force microscope fiber probe is used to directly measure the forces and friction between two human hairs under various conditions. It is shown that the forces between the hair fibers in solution can be well explained by a DLVO interaction and that cationic surfactant modifies the interactions in a manner entirely consistent with current views of adsorption behavior. A Coulombic attraction occurs between the crossed hair fibers in air due to the heterogeneity of the surface, and at shorter separations a clear dispersion interaction is observed. Exposure of the hair to a bleaching solution leads to the removal of the adhesion and solely a double-layer interaction. Two crossed hair fibers obey Amontons' classic law of friction, with a linear relation between applied load and frictional force, allowing the determination of a friction coefficient; positively charged surfactant adsorption is shown to reduce the friction coefficient between the fibers in a manner consistent with boundary lubrication by a palisade layer.

  • 38.
    Munavirov, Bulat
    et al.
    KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia.
    Black, Jeffrey
    Shah, Faiz
    Luleå University of Technology, Sweden.
    Leckner, Johan
    Axel Christiernsson International AB, Sweden.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia.
    Harper, Jason
    University of New South Wales, Australia.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia; Ghent University, Belgium.
    The effect of anion architecture on the lubrication chemistry of phosphonium orthoborate ionic liquids2021In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, no 1, article id 24021Article in journal (Refereed)
    Abstract [en]

    Phosphonium ionic liquids with orthoborate anions have been studied in terms of their interfacial film formation, both physisorbed and sacrificial from chemical breakdown, in sheared contacts of varying harshness. The halogen-free anion architecture was varied through (i) the heteronuclear ring size, (ii) the hybridisation of the constituent atoms, and (iii) the addition of aryl functionalities. Time of Flight-Secondary Ion Mass Spectrometry analysis revealed the extent of sacrificial tribofilm formation allowing the relative stability of the ionic liquids under tribological conditions to be determined and their breakdown mechanisms to be compared to simple thermal decomposition. Overall, ionic liquids outperformed reference oils as lubricants; in some cases, sacrificial films were formed (with anion breakdown a necessary precursor to phosphonium cation decomposition) while in other cases, a protective, self-assembly lubricant layer or hybrid film was formed. The salicylate-based anion was the most chemically stable and decomposed only slightly even under the harshest conditions. It was further found that surface topography influenced the degree of breakdown through enhanced material transport and replenishment. This work thus unveils the relationship between ionic liquid composition and structure, and the ensuing inter- and intra-molecular interactions and chemical stability, and demonstrates the intrinsic tuneability of an ionic liquid lubrication technology. © 2021, The Author(s).

  • 39.
    Naranjo, Teresa
    et al.
    IMDEA Nanociencia, Spain.
    Álvarez-Asencio, Ruben
    RISE Research Institutes of Sweden, Bioeconomy and Health, Chemical Process and Pharmaceutical Development.
    Pedraz, Patricia
    IMDEA Nanociencia, Spain.
    Nieto-Ortega, Belen
    IMDEA Nanociencia, Spain.
    Silva, Sara
    IMDEA Nanociencia, Spain.
    Burzurí, Enrique
    IMDEA Nanociencia, Spain.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden.
    Pérez, Emilio
    IMDEA Nanociencia, Spain.
    Hydrogen-bonded host–guest systems are stable in ionic liquids2020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, article id 15414Article in journal (Refereed)
    Abstract [en]

    We show that H-bonded host–guest systems associate in ionic liquids (ILs), pure salts with melting point below room temperature, in which dipole–dipole electrostatic interactions should be negligible in comparison with dipole-charge interactions. Binding constants (Ka) obtained from titrations of four H-bonded host–guest systems in two organic solvents and two ionic liquids yield smaller yet comparable Ka values in ionic liquids than in organic solvents. We also detect the association event using force spectroscopy, which confirms that the binding is not solely due to (de)solvation processes. Our results indicate that classic H-bonded host–guest supramolecular chemistry takes place in ILs. This implies that strong H-bonds are only moderately affected by surroundings composed entirely of charges, which can be interpreted as an indication that the balance of Coulombic to covalent forces in strong H-bonds is not tipped towards the former. © 2020, The Author(s).

  • 40.
    Niklas, Nordgren
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Stiernstedt, Johanna
    Brumer, Harry
    Wågberg, Lars
    Gray, Derek G
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    CELL 109-Interactions of cellulose surfaces: Friction, adhesion and polysaccharide adsorption2007In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 233, p. 838-838Article in journal (Refereed)
  • 41.
    Nyström, Lina
    et al.
    Uppsala University, Sweden.
    Nordström, Randi
    Uppsala University, Sweden.
    Bramhill, Jane
    University of Manchester, UK.
    Saunders, Brian R.
    University of Manchester, UK.
    Álvarez-Asencio, Rubén
    KTH Royal Institute of Technology, Sweden; IMDEA Nanoscience, Spain.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Malmsten, Martin
    Uppsala University, Sweden.
    Factors affecting peptide interactions with surface-bound microgels2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 2, p. 669-678Article in journal (Refereed)
    Abstract [en]

    Effects of electrostatics and peptide size on peptide interactions with surface-bound microgels were investigated with ellipsometry, confocal microscopy, and atomic force microscopy (AFM). Results show that binding of cationic poly-l-lysine (pLys) to anionic, covalently immobilized, poly(ethyl acrylate-co-methacrylic acid) microgels increased with increasing peptide net charge and microgel charge density. Furthermore, peptide release was facilitated by decreasing either microgel or peptide charge density. Analogously, increasing ionic strength facilitated peptide release for short peptides. As a result of peptide binding, the surface-bound microgels displayed pronounced deswelling and increased mechanical rigidity, the latter quantified by quantitative nanomechanical mapping. While short pLys was found to penetrate the entire microgel network and to result in almost complete charge neutralization, larger peptides were partially excluded from the microgel network, forming an outer peptide layer on the microgels. As a result of this difference, microgel flattening was more influenced by the lower Mw peptide than the higher. Peptide-induced deswelling was found to be lower for higher Mw pLys, the latter effect not observed for the corresponding microgels in the dispersed state. While the effects of electrostatics on peptide loading and release were similar to those observed for dispersed microgels, there were thus considerable effects of the underlying surface on peptide-induced microgel deswelling, which need to be considered in the design of surface-bound microgels as carriers of peptide loads, for example, in drug delivery or in functionalized biomaterials.

  • 42.
    Nyström, Lina
    et al.
    Uppsala University, Sweden.
    Álvarez-Asencio, Rubén
    KTH Royal Institute of Technology, Sweden; IMDEA Nanoscience, Spain.
    Frenning, Göran
    Uppsala University, Sweden.
    Saunders, Brian R.
    University of Manchester, UK.
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Malmsten, Martin
    Uppsala University, Sweden.
    Electrostatic swelling transitions in surface-bound microgels2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 40, p. 27129-27139Article in journal (Refereed)
    Abstract [en]

    Herein, electrostatic swelling transitions of poly(ethyl acrylate-co-methacrylic acid) microgels covalently bound to silica surfaces are investigated. Confined at a solid surface, microgel swelling is anisotropically hindered and the structure is flattened to an extent dictated by pH and microgel composition. Microgel deformation under applied load is also shown to depend on microgel charge density, with the highest deformation observed at intermediate charge densities. Two modes of microgel deformation under load were observed, one elastic and one viscoelastic, related to polymer strand deformation and displacement of trapped water, respectively. Results on polymer strand dynamics reveal that the microgels are highly dynamic, as the number of strand-tip interaction points increases 4-fold during a 10 s contact time. Furthermore, finite element modeling captures these effects qualitatively and shows that stress propagation in the microgel network decays locally at the rim of contact with a solid interface or close to the tip probe. Taken together, the results demonstrate a delicate interplay between the surface and microgel which determines the structure and nanomechanical properties of the latter and needs to be controlled in applications of systems such as pH-responsive surface coatings in biomaterials.

  • 43.
    Pilkington, Georgia A.
    et al.
    KTH Royal Institute of Technology, Sweden.
    Harris, Kathryn L
    KTH Royal Institute of Technology, Sweden.
    Bergendal, Erik
    KTH Royal Institute of Technology, Sweden.
    Reddy, Akepati Bhaskar
    KTH Royal Institute of Technology, Sweden.
    Palsson, Gunnar K.
    Uppsala University, Sweden.
    Vorobiev, Alexei
    Uppsala University, Sweden.
    Antzutkin, Oleg N.
    Luleå University of Technology, Sweden.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden ; Ghent University, Belgium.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 19, article id 193806Article in journal (Refereed)
    Abstract [en]

    Using neutron reflectivity, the electro-responsive structuring of the non-halogenated ionic liquid (IL) trihexyl(tetradecyl)phosphonium-bis(mandelato)borate, [P6,6,6,14][BMB], has been studied at a gold electrode surface in a polar solvent. For a 20% w/w IL mixture, contrast matched to the gold surface, distinct Kiessig fringes were observed for all potentials studied, indicative of a boundary layer of different composition to that of the bulk IL-solvent mixture. With applied potential, the amplitudes of the fringes from the gold-boundary layer interface varied systematically. These changes are attributable to the differing ratios of cations and anions in the boundary layer, leading to a greater or diminished contrast with the gold electrode, depending on the individual ion scattering length densities. Such electro-responsive changes were also evident in the reflectivities measured for the pure IL and a less concentrated (5% w/w) IL-solvent mixture at the same applied potentials, but gave rise to less pronounced changes. These measurements, therefore, demonstrate the enhanced sensitivity achieved by contrast matching the bulk solution and that the structure of the IL boundary layers formed in mixtures is strongly influenced by the bulk concentration. Together these results represent an important step in characterising IL boundary layers in IL-solvent mixtures and provide clear evidence of electro-responsive structuring of IL ions in their solutions with applied potential.

  • 44.
    Pilkington, Georgia A.
    et al.
    KTH Royal Institute of Technology, Sweden .
    Oleshkevych, Anna
    KTH Royal Institute of Technology, Sweden .
    Pedraz, Patricia
    KTH Royal Institute of Technology, Sweden .
    Watanabe, Seiya
    KTH Royal Institute of Technology, Sweden .
    Radiom, Milad
    KTH Royal Institute of Technology, Sweden .
    Reddy, Akepati Bhaskar
    KTH Royal Institute of Technology, Sweden .
    Vorobiev, Alexei
    Uppsala University, Sweden .
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; Ghent University, Belgium .
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden .
    Electroresponsive structuring and friction of a non-halogenated ionic liquid in a polar solvent: effect of concentration2020In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, no 34, p. 19162-19171Article in journal (Refereed)
    Abstract [en]

    Neutron reflectivity (NR) measurements have been employed to study the interfacial structuring and composition of electroresponsive boundary layers formed by an ionic liquid (IL) lubricant at an electrified gold interface when dispersed in a polar solvent. The results reveal that both the composition and extent of the IL boundary layers intricately depend on the bulk IL concentration and the applied surface potential. At the lowest concentration (5% weight/weight), a preferential adsorption of the IL cation at the gold electrode is observed, which hinders the ability to electro-induce changes in the boundary layers. In contrast, at higher IL bulk concentrations (10 and 20% weight/weight), the NR results reveal a significantly larger concentration of the IL ions at the gold interface that exhibit significantly greater electroresponsivity, with clear changes in the layer composition and layer thickness observed for different potentials. In complementary at. force microscopy (AFM) measurements on an electrified gold surface, such IL boundary layers are demonstrated to provide excellent friction reduction and electroactive friction (known as tribotronics). In agreement with the NR results obtained, clear concentration effects are also observed Together such results provide valuable mol. insight into the electroactive structuring of ILs in solvent mixtures, as well as provide mechanistic understanding of their tribotronic behaviors.

  • 45.
    Pilkington, Georgia
    et al.
    KTH Royal Institute of Technology, Sweden.
    Welbourn, Rebecca
    ISIS Facility, UK.
    Oleshkevych, Anna
    KTH Royal Institute of Technology, Sweden.
    Watanabe, Seiya
    KTH Royal Institute of Technology, Sweden.
    Pedraz, Patricia
    KTH Royal Institute of Technology, Sweden.
    Radiom, Milad
    KTH Royal Institute of Technology, Sweden.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; Ghent University, Belgium.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden.
    Effect of water on the electroresponsive structuring and friction in dilute and concentrated ionic liquid lubricant mixtures2020In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, no 48, p. 28191-28201Article in journal (Refereed)
    Abstract [en]

    The effect of water on the electroactive structuring of a tribologically relevant ionic liquid (IL) when dispersed in a polar solvent has been investigated at a gold electrode interface using neutron reflectivity (NR). For all solutions studied, the addition of small amounts of water led to clear changes in electroactive structuring of the IL at the electrode interface, which was largely determined by the bulk IL concentration. At a dilute IL concentration, the presence of water gave rise to a swollen interfacial structuring, which exhibited a greater degree of electroresponsivity with applied potential compared to an equivalent dry solution. Conversely, for a concentrated IL solution, the presence of water led to an overall thinning of the interfacial region and a crowding-like structuring, within which the composition of the inner layer IL layers varied systematically with applied potential. Complementary nanotribotronic atomic force microscopy (AFM) measurements performed for the same IL concentration, in dry and ambient conditions, show that the presence of water reduces the lubricity of the IL boundary layers. However, consistent with the observed changes in the IL layers observed by NR, reversible and systematic control of the friction coefficient with applied potential was still achievable. Combined, these measurements provide valuable insight into the implications of water on the interfacial properties of ILs at electrified interfaces, which inevitably will determine their applicability in tribotronic and electrochemical contexts.

  • 46.
    Plunkett, Mark A
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Rutland, Mark W.
    Dynamic adhesion of grafted polymer surfaces as studied by surface force measurements2005In: Atomic Force Microscopy in Adhesion Studies / [ed] J. Drelich, Kash L. Mittal, CRC Press, 2005, p. 173-186Chapter in book (Refereed)
  • 47.
    Reddy, Akepati
    et al.
    KTH Royal Institute of Technology, Sweden.
    Munavirov, Bulat
    KTH Royal Institute of Technology, Sweden.
    Pilkington, Georgia
    KTH Royal Institute of Technology, Sweden.
    Calderon Salmeron, Gabriel
    KTH Royal Institute of Technology, Sweden.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; Ghent University, Belgium; University of New South Wales, Australia .
    Micro- To Nano- To from Surface to Bulk: Influence of Halogen-Free Ionic Liquid Architecture and Dissociation on Green Oil Lubricity2021In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 9, no 40, p. 13606-13617Article in journal (Refereed)
    Abstract [en]

    Four nonhalogenated ionic liquids (ILs) based on the same phosphonium cation are investigated in terms of the anion suitability for enhancing the lubricity of a biodegradable oil. For all test conditions, typical for industrial machine components, the lubrication is shown to be governed by nonsacrificial films formed by the physisorption of ionic species on the tribo-surfaces. The anionic structure appears to have an important role in the formation of friction modifying films. The orthoborate ILs exhibit the formation of robust ionic boundary films, resulting in reduced friction and better wear protection. On the contrary, the surface adsorption of phosphinate and phosphate ILs appears to antagonistically disrupt the intrinsic lubrication properties of the biodegradable oil, resulting in high friction and wear. Through additional investigations, it is postulated that the higher dissociation of orthoborate ILs in the biodegradable oil allows the formation of hierarchical and electrostatically overscreened layer structures with long-range order, whereas the ILs with phosphate and phosphinate anions exhibit low dissociation in biodegradable oil, possibly due to the ion pairs being surrounded by a hydrocarbon halo, which presumably results in weak adsorption to form a mixed interfacial layer with no long-range order. © 2021 The Authors. 

  • 48.
    Rohlmann, Patrick
    et al.
    KTH Royal Institute of Technology, Sweden.
    Watanabe, Seiya
    KTH Royal Institute of Technology, Sweden; Tokyo University of Science, Japan.
    Shimpi, Manishkumar
    Luleå University of Technology, Sweden.
    Leckner, Johan
    Axel Christiernsson International AB, Sweden.
    Rutland, Mark W.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design. KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia.
    Harper, Jason
    University of New South Wales, Australia.
    Glavatskih, Sergei
    KTH Royal Institute of Technology, Sweden; University of New South Wales, Australia; Ghent University, Belgium.
    Boundary lubricity of phosphonium bisoxalatoborate ionic liquids2021In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 161, article id 107075Article in journal (Refereed)
    Abstract [en]

    The lubricating performance of trihexyl(tetradecyl)phosphonium bisoxalatoorthoborate (P-BOB) ionic liquid is analysed at 80 °C and 140 °C, and compared to an ionic liquid containing a partially hydrated version of the anion. The reduction of the anions produces oxalate complexes that contribute synergistically to lower friction. The role of oxalate in enhancing lubricity was indicated by the fact that the partially hydrated anion is a precursor orthoborate anion complexed with oxalic acid. It consequently showed the lowest friction at 80 °C. Upon heating, the precursor was converted into [BOB]− and displayed the same friction at 140 °C as the fully synthesised species. The mechanisms of the breakdown of the [BOB]− anion and formation of the tribofilm are elucidated. © 2021 The Authors

  • 49.
    Rutland, Mark W.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials. KTH Royal Institute of Technology, Sweden.
    Chemical physics of electroactive materials: Concluding remarks2017In: Faraday discussions, ISSN 1359-6640, E-ISSN 1364-5498, Vol. 199, p. 615-630Article in journal (Refereed)
    Abstract [en]

    It is an honour to be charged with providing the concluding remarks for a Faraday Discussion. As many have remarked before, it is nonetheless a prodigious task, and what follows is necessarily a personal, and probably perverse, view of a watershed event in the Chemical Physics of Electroactive materials. The spirit of the conference was captured in a single sentence during the meeting itself. "It is the nexus between rheology, electrochemistry, colloid science and energy storage". The current scientific climate is increasingly dominated by a limited number of global challenges, and there is thus a tendency for research to resemble a football match played by 6 year olds, where everyone on the field chases the (funding) ball instead of playing to their "discipline". It is thus reassuring to see how the application of rigorous chemical physics is leading to ingenious new solutions for both energy storage and harvesting, via, for example, nanoactuation, electrowetting, ionic materials and nanoplasmonics. In fact, the same language of chemical physics allows seamless transition between applications as diverse as mechano-electric energy generation, active moisture transport and plasmonic shutters-even the origins of life were addressed in the context of electro-autocatalysis!.

  • 50.
    Rutland, Mark W.
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Tyrrell, J W G
    Analysis of atomic force microscopy data for deformable materials2005In: Atomic Force Microscopy in Adhesion Studies / [ed] J. Drelich, Kash L. Mittal, Leiden-Boston: VSP , 2005, p. 155-171Chapter in book (Refereed)
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