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  • 1. Bodvik, Rasmus
    et al.
    Thormann, Esben
    Karlsson, Leif
    Claesson, Per M
    YKI – Ytkemiska institutet.
    Temperature responsive surface layers of modified celluloses2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 10, p. 4260-4268Article in journal (Refereed)
    Abstract [en]

    The temperature-dependent properties of pre-adsorbed layers of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) were investigated on silica and hydrophobized silica surfaces. Three different techniques, quartz crystal microbalance with dissipation monitoring, ellipsometry, and atomic force microscopy imaging, were used, providing complimentary and concise information on the structure, mass and viscoelastic properties of the polymer layer. 10 Adsorption was conducted at 25 °C, followed by a rinsing step. The properties of such pre-adsorbed layers were determined as a function of temperature in the range 25 °C to 50 °C. It was found that the layers became more compact with increasing temperature and that this effect was reversible, when decreasing the temperature. The compaction was more prominent for MC, as shown in the AFM images and in the thickness data derived from the QCM analysis. This is 15 consistent with the fact that the phase transition temperature is lower, in the vicinity of 50 °C, for MC than for HPMC. The water content of the adsorbed layers was found to be high, even at the highest temperature, 50 °C, explored in this investigation.

  • 2.
    Claesson, Per M.
    et al.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Dobryden, Illia
    KTH Royal Institute of Technology, Sweden.
    Li, Gen
    KTH Royal Institute of Technology, Sweden.
    He, Yunjian
    KTH Royal Institute of Technology, Sweden.
    Huang, Hui
    KTH Royal Institute of Technology, Sweden.
    Thorén, Per-Anders
    KTH Royal Institute of Technology, Sweden.
    Haviland, David B.
    From force curves to surface nanomechanical properties2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 35, p. 23642-23657Article in journal (Refereed)
    Abstract [en]

    Surface science, which spans the fields of chemistry, physics, biology and materials science, requires information to be obtained on the local properties and property variations across a surface. This has resulted in the development of different scanning probe methods that allow the measurement of local chemical composition and local electrical and mechanical properties. These techniques have led to rapid advancement in fundamental science with applications in areas such as composite materials, corrosion protection and wear resistance. In this perspective article, we focussed on the branch of scanning probe methods that allows the determination of surface nanomechanical properties. We discussed some different AFM-based modes that were used for these measurements and provided illustrative examples of the type of information that could be obtained. We also discussed some of the difficulties encountered during such studies.

  • 3.
    Claesson, PM
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Kjellin, Mikael
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Rojas, OJ
    Stubenrauch, C
    Short-range interactions between non-ionic surfactant layers2006In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 8, p. 5501-5514Article in journal (Refereed)
    Abstract [en]

    Short-range interactions between surfactant and lipid layers are of great importance in technical applications in complex fluids such as foams, dispersions and emulsions, as well as in the formulation and performance of dispersants, detergents and flocculants. It is also of utmost importance in biological systems where interactions between biomembranes influence a range of processes. The field of short-range interactions has been thoroughly investigated during the past 30 years, following the emergence of a number of techniques to measure interaction forces. Thus, our understanding has increased considerably and it is timely to summarize relevant knowledge accumulated in this area. In this review we focus on the nature of short-range interactions between non-ionic and zwitterionic surfactant and lipid layers exposing their polar groups to the surrounding medium. We discuss the complex interplay of short-range (van der Waals, hydration, steric and other) forces based on recent theoretical and experimental results.

  • 4.
    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.

  • 5.
    Dedinaite, Andra
    et al.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Claesson, Per M.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Synergies in lubrication2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 35, p. 23677-23689Article in journal (Refereed)
    Abstract [en]

    To slide surfaces against each other with application of a minimum force and minimum wear has been important since ancient times, and it remains equally important today. The use of oil-soluble lubricants is widely spread in technology, whereas living organisms have developed water-soluble lubricants to facilitate sliding motions. In this perspective article we focus on water-based lubrication in the boundary lubrication regime, and particularly lubrication synergies. This focus has, of course, found inspiration from the outstanding lubrication properties of synovial joints. It has ignited significant amount of research, mostly aimed at answering the question: Which molecule is the magic biolubricant? Different research groups have advocated different answers, and the debate has been intensive. In this article we argue that the question in itself is inappropriate. The relevant question is rather the following: How do molecules work in synergy to provide superior lubrication?

  • 6.
    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.

  • 7.
    Fock, Jeppe
    et al.
    DTU Technical University of Denmark, Denmark .
    Jonasson, Christian
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Hansen, Mikkel F.
    DTU Technical University of Denmark, Denmark .
    Characterization of fine particles using optomagnetic measurements2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 13, p. 8802-8814Article in journal (Refereed)
    Abstract [en]

    The remanent magnetic moment and the hydrodynamic size are important parameters for the synthesis and applications of magnetic nanoparticles (MNPs). We present the theoretical basis for the determination of the remanent magnetic moment and the hydrodynamic size of MNPs with a narrow size distribution using optomagnetic measurements. In these, the 2nd harmonic variation of the intensity of light transmitted through an MNP suspension is measured as a function of an applied axial oscillating magnetic field. We first show how the measurements of the optomagnetic signal magnitude at a low frequency vs. magnetic field amplitude can be used to determine the MNP moment. Subsequently, we use linear response theory to describe the dynamic non-equilibrium response of the MNP suspension at low magnetic field amplitudes and derive a link between optomagnetic measurements and magnetic AC susceptibility measurements. We demonstrate the presented methodology on two samples of commercially available multi-core MNPs. The results compare well with those obtained by dynamic light scattering, AC susceptibility and vibrating sample magnetometry measurements on the same samples when the different weighting of the particle size in the techniques is taken into account. The optomagnetic technique is simple, fast and does not require prior knowledge of the concentration of MNPs and it thus has the potential to be used as a routine tool for quality control of MNPs.

  • 8.
    Fortes Brollo, Maria Eugenia
    et al.
    CSIC Institute of Material Science of Madrid, Spain.
    Hernández Flores, Patricia
    CSIC Centro Nacional de Biotecnología, Spain.
    Gutiérrez, Lucía
    INA Instituto Universitario de Nanociencia de Aragón, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Barber, Domingo Francisco
    CSIC Centro Nacional de Biotecnología, Spain.
    Morales, María Del Puerto
    CSIC Institute of Material Science of Madrid, Spain.
    Magnetic properties of nanoparticles as a function of their spatial distribution on liposomes and cells2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 26, p. 17829-17838Article in journal (Refereed)
    Abstract [en]

    The aggregation processes of magnetic nanoparticles in biosystems are analysed by comparing the magnetic properties of three systems with different spatial distributions of the nanoparticles. The first one is iron oxide nanoparticles (NPs) of 14 nm synthesized by coprecipitation with two coatings, (3-aminopropyl)trimethoxysilane (APS) and dimercaptosuccinic acid (DMSA). The second one is liposomes with encapsulated nanoparticles, which have different configurations depending on the NP coating (NPs attached to the liposome surface or encapsulated in its aqueous volume). The last system consists of two cell lines (Pan02 and Jurkat) incubated with the NPs. Dynamic magnetic behaviour (AC) was analysed in liquid samples, maintaining their colloidal properties, while quasi-static (DC) magnetic measurements were performed on lyophilised samples. AC measurements provide a direct method for determining the effect of the environment on the magnetization relaxation of nanoparticles. Thus, the imaginary (χ'') component shifts to lower frequencies as the aggregation state increases from free nanoparticles to those attached or embedded into liposomes in cell culture media and more pronounced when internalized by the cells. DC magnetization curves show no degradation of the NPs after interaction with biosystems in the analysed timescale. However, the blocking temperature is shifted to higher temperatures for the nanoparticles in contact with the cells, regardless of the location, the incubation time, the cell line and the nanoparticle coating, supporting AC susceptibility data. These results indicate that the simple fact of being in contact with the cells makes the nanoparticles aggregate in a non-controlled way, which is not the same kind of aggregation caused by the contact with the cell medium nor inside liposomes.

  • 9.
    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.

  • 10. Johnson, M
    et al.
    Tyrod, E
    YKI – Ytkemiska institutet.
    Study of the adsorption of sodium dodecyl sulphate (SDS) at the air/water interface: Targeting the sulphate headgroup using vibrational sum frequency spectroscopy2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, p. 2635-2640Article in journal (Refereed)
    Abstract [en]

    The surface sensitive technique vibrational sum frequency spectroscopy (VSFS), has been used to study the adsorption behaviour of SDS to the liquid/vapour interface of aqueous solutions, specifically targeting the sulfate headgroup stretches. In the spectral region extending from 980 to 1850 cm(-1), only the vibrations due to the SO3 group were detectable. The fitted amplitudes for the symmetric SO3 stretch observed at 1070 cm(-1) for the polarization combinations ssp and ppp, were seen to follow the adsorption isotherm calculated from surface tension measurements. The orientation of the sulfate headgroup in the concentration range spanning from 1.0 mM to above the critical micellar concentration ( c. m. c.) was observed to remain constant within experimental error, with the pseudo-C-3 axis close to the surface normal. Furthermore, the effect of increasing amounts of sodium chloride at SDS concentrations above c. m. c. was also studied, showing an increase of approximately 12% in the fitted amplitude for the symmetric SO3 stretch when increasing the ionic strength from 0 to 300 mM NaCl. Interestingly, the orientation of the SDS headgroup was also observed to remain constant within this concentration range and identical to the case without NaCl

  • 11.
    Langer, Sarka
    Organisk kemi (Kmo).
    Rate coefficients and Arrhenius parameters for the reaction of the NO3 radical with acetaldehyde and acetaldehyde-1d2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 9, p. 1631-1637Article in journal (Other academic)
  • 12.
    Langer, Sarka
    Organisk kemi (Kmo).
    Reactions of acrolein, crotonaldehyde and pivalaldehyde with Cl atoms; Structure activity relationship and comparison with OH and NO3 reactions2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 6, p. 986-992Article in journal (Other academic)
  • 13.
    Langer, Sarka
    Organisk kemi (Kmo).
    Techniques for quantifying gaseous HOCI using atmospheric pressure ionization mass spectrometry1999In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 1, no 24, p. 5615-5621Article in journal (Other academic)
  • 14.
    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.

  • 15.
    Liljeblad, J F D
    et al.
    KTH Royal Institute of Technology, Sweden.
    Tyrode, E
    L’Oréal, France.
    Thormann, E
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. KTH Royal Institute of Technology, Sweden.
    Dublanchet, A-C
    L’Oréal, France.
    Luengo, G
    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.
    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.

  • 16.
    Lindh, Erik L.
    et al.
    RISE - Research Institutes of Sweden, Bioeconomy. RISE, Innventia. KTH Royal Institute of Technology, Sweden .
    Terenzi, Camilla
    KTH Royal Institute of Technology, Sweden .
    Salmen, Lennart
    RISE - Research Institutes of Sweden, Bioeconomy. RISE, Innventia. KTH Royal Institute of Technology, Sweden .
    Furo, Istvan
    KTH Royal Institute of Technology, Sweden .
    Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, p. 4360-4369Article in journal (Refereed)
    Abstract [en]

    The organization of water molecules adsorbed onto cellulose and the supramolecular hydrated structure of microfibril aggregates represents, still today, one of the open and complex questions in the physical chemistry of natural polymers. Here, we investigate by 2H MAS NMR the mobility of water molecules in carefully 2H-exchanged, and thereafter re-dried, microcrystalline cellulose. By subtracting the spectral contribution of deuteroxyls from the spectrum of hydrated cellulose, we demonstrate the existence of two distinct 2H2O spectral populations associated with mobile and immobile water environments, between which the water molecules do not exchange at the NMR observation time scale. We conclude that those two water phases are located at differently-accessible adsorption sites, here assigned to the cellulose surfaces between and within the microfibril aggregates, respectively. The superior performance of 2H MAS NMR encourages further applications of the same method to other complex systems that expose heterogeneous hygroscopic surfaces, like wood cell walls.

  • 17. Oliynyk, V
    et al.
    Mille, Christian B
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Ng, JBS
    Von Ballmoos, C
    Corkery, Robert W
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Bergstrom, L
    Selective and ATP-driven transport of ions across supported membranes into nanoporous carriers using gramicidin A and ATP synthase2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 8, p. 2733-2740Article in journal (Refereed)
    Abstract [en]

    We report a robust and versatile membrane protein based system for selective uptake and release of ions from nanoporous particles sealed with ion-tight lipid bilayers of various compositions that is driven by the addition of ATP or a chemical potential gradient. We have successfully incorporated both a passive ion channel-type peptide (gramicidin A) and a more complex primary sodium ion transporter (ATP synthase) into the supported lipid bilayers on solid nanoporous silica particles. Protein-mediated controlled release/uptake of sodium ions across the ion-tight lipid bilayer seal from or into the nanoporous silica carrier was imaged in real time using a confocal laser scanning microscope and the intensity changes were quantified. ATP-driven transport of sodium ions across the supported lipid bilayer against a chemical gradient was demonstrated. The possibility of designing durable carriers with tight lipid membranes, containing membrane proteins for selective ion uptake and release, offers new possibilities for functional studies of single or cascading membrane protein systems and could also be used as biomimetic microreactors for controlled synthesis of inorganic multicomponent materials.

  • 18. Pilkington, Georgia A
    et al.
    Thormann, Esben
    Claesson, Per M
    YKI – Ytkemiska institutet.
    Fuge, Gareth M
    Fox, Oliver JL
    Ashfold, Michael NR
    Amontonian frictional behaviour of nanostructured surfaces2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 20, p. 9318-9326Article in journal (Refereed)
    Abstract [en]

    With nanotextured surfaces and interfaces increasingly being encountered in technological and biomedical applications, there is a need for a better understanding of frictional properties involving such surfaces. Here we report friction measurements of several nanostructured surfaces using an Atomic Force Microscope (AFM). These nanostructured surfaces provide well defined model systems on which we have tested the applicability of Amontons' laws of friction. Our results show that Amontonian behaviour is observed with each of the surfaces studied. However, no correlation has been found between measured friction and various surface roughness parameters such as average surface roughness (R-a) and root mean squared (rms) roughness. Instead, we propose that the friction coefficient may be decomposed into two contributions, i.e., mu = mu(0) + mu(g), with the intrinsic friction coefficient mu(0) accounting for the chemical nature of the surfaces and the geometric friction coefficient mu(g) for the presence of nanotextures. We have found a possible correlation between mu(g) and the average local slope of the surface nanotextures.

  • 19.
    Rutland, Mark
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Effect of ion structure on nanoscale friction in protic ionic liquids2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 31, p. 16651-16658Article in journal (Refereed)
  • 20.
    Rutland, Mark
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Ionic liquid lubrication: Influence of ion structure, surface potential and sliding velocity2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 35, p. 14616-14623Article in journal (Refereed)
  • 21.
    Skoglund, Sara
    et al.
    KTH Royal Institute of Technology, Sweden.
    Blomberg, Eva
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry, Materials and Surfaces. KTH Royal Institute of Technology, Sweden.
    Wallinder, Inger O.
    KTH Royal Institute of Technology, Sweden.
    Grillo, Isabelle
    Institut Laue Langevin, France.
    Pedersen, Jan S.
    Aarhus University, Denmark.
    Bergström, L Magnus
    KTH Royal Institute of Technology, Sweden.
    A novel explanation for the enhanced colloidal stability of silver nanoparticles in the presence of an oppositely charged surfactant2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 41, p. 28037-28043Article in journal (Refereed)
    Abstract [en]

    The structural behavior in aqueous mixtures of negatively charged silver nanoparticles (Ag NPs) together with the cationic surfactants cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium chloride (DTAC), respectively, has been investigated using SANS and SAXS. From our SANS data analysis we are able to conclude that the surfactants self-assemble into micellar clusters surrounding the Ag NPs. We are able to quantify our results by means of fitting experimental SANS data with a model based on cluster formation of micelles with very good agreement. Based on our experimental results, we propose a novel mechanism for the stabilization of negatively charged Ag NPs in a solution of positively charged surfactants in which cluster formation of micelles in the vicinity of the particles prevents the particles from aggregating. Complementary SAXS and DLS measurements further support this novel way of explaining stabilization of small hydrophilic nanoparticles in surfactant-containing solutions.

  • 22.
    Swerin, Agne
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Claesson, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 41, p. 17893-17902Article in journal (Refereed)
  • 23. Thormann, Esben
    et al.
    Claesson, Per M
    YKI – Ytkemiska institutet.
    Mouritsen, Ole G
    Tuning structural forces between silica surfaces by temperature-induced micellization of responsive block copolymers2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 36, p. 10730-10735Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to demonstrate a method to control interactions between two surfaces by the use of a responsive solution. This was done by performing AFM-based force measurements between two silica surfaces immersed in an aqueous solution of thermo-responsive Pluronics P85 block copolymers. For this system we demonstrate that one can switch between a situation where no long-range forces are acting between the surfaces to a situation where a long-range structural force, oscillating between attractive and repulsive force regimes, is controlling the surface interaction. This shift in behavior is caused by a long-range order introduced by temperature-induced micellization of the block copolymers and is thus simply achieved by changing the temperature from below to above the micellization temperature. We propose that the use of micelle-forming responsive block copolymers is a general method for reversibly controlling surface interactions by a temperature switch. Since the force control is achieved by changes occurring in bulk solution, the nature of the surfaces is expected to play only a relative minor role.

  • 24.
    Tiberg, F
    et al.
    YKI – Ytkemiska institutet.
    Zhmud, B
    YKI – Ytkemiska institutet.
    Hallstensson, K
    YKI – Ytkemiska institutet.
    von Bahr, M
    Capillary rise of surfactant solutions2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, p. 5189-5196Article in journal (Refereed)
    Abstract [en]

    The capillary flow of surfactant solutions in hydrophobic and hydrophilic capillaries has been studied. The results obtained are discussed in the light of surface tension relaxation and adsorption phenomena. Modes of surfactant transport and effects of surfactant adsorption, aggregation, and monomer–micelle interconversion on the capillary rise dynamics are further analyzed in the framework of a theoretical model. This provides a self-consistent and quantitatively correct picture of the experimental results. In the case of hydrophobic capillaries, two limiting types of dynamic behavior are adsorption-controlled rise and diffusion-controlled rise. In some cases, slow relaxation of adsorbed layers at the liquid/solid interface can cause a drift of the rise height over a long time under quasi-equilibrium conditions. A slow relaxation, as compared to the capillary rise rate, of the liquid/vapor interface may also produce a maximum in the rise s. time curve. This behavior was, for instance, seen for a surfactant solution penetrating into a hydrophilic capillary.

  • 25. Valle-Delgado, JJ
    et al.
    Molina-Bolivar, JA
    Galisteo-González, F
    Gálvez-Ruiz, MJ
    Feiler, A
    Rutland, MW
    YKI – Ytkemiska institutet.
    Interactions between bovine serum albumin layers adsorbed on different substrates measured with an atomic force microscope2004In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, p. 1482-1486Article in journal (Refereed)
    Abstract [en]

    By the aid of an atomic force microscope (AFM) and the colloid probe technique, the interaction forces between bovine serum albumin (BSA) layers adsorbed on different substrates (silica and polystyrene) have been measured directly as a function of pH and salt concentration. Electrostatic and steric forces dominate the interactions at low salt concentrations. At high salt concentrations, when electrostatic interactions are screened, a very strange behaviour is found as a function of pH. The behaviour around the i.e.p. of the protein is also very striking: the interaction is attractive at low salt concentration, but it is repulsive at high salt concentration. These results could be explained if the presence of hydration forces is assumed. Theoretical predictions including a hydration term in the DLVO theory fit the experimental results satisfactorily.

  • 26. Wakeham, D
    et al.
    Niga, P
    Ridings, C
    Andersson, G
    Nelson, A
    Warr, GG
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Surface structure of a "non-amphiphilic" protic ionic liquid2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 15, p. 5106-5114Article in journal (Refereed)
    Abstract [en]

    The nanostructure of the ethanolammonium nitrate (EtAN)-air surface has been investigated using X-ray reflectometry (XRR), vibrational sum frequency spectroscopy (VSFS) and neutral impact collision ion scattering spectroscopy (NICISS). The XRR data decays more rapidly than expected for a perfectly sharp interface, indicating a diffuse electron (scattering length) density profile. Modelling of the XRR data using three different fitting routines produced consistent interfacial profiles that suggest the formation of interfacial EtAN clusters. Consistent with this, VSFS reveals that the EtAN surface is predominantly covered by -CH 2- moieties, with the -NH 3 + and -OH groups of the cation buried slightly deeper in the interface. The elemental profiles determined using NICISS also show enrichment of carbon relative to nitrogen and oxygen in the outermost surface layer, which is consistent with the surface cation orientation deduced from VSFS, and with the presence of EtAN aggregates at the liquid surface.

  • 27.
    Wang, Xuying
    et al.
    KTH Royal Institute of Technology, Sweden.
    Herting, Gunilla
    KTH Royal Institute of Technology, Sweden.
    Odnevall Wallinder, Inger
    KTH Royal Institute of Technology, Sweden.
    Blomberg, Eva
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science. KTH Royal Institute of Technology, Sweden.
    Adsorption of bovine serum albumin on silver surfaces enhances the release of silver at pH neutral conditions2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 28, p. 18524-18534Article in journal (Refereed)
    Abstract [en]

    Metallic biomaterials are widely used to replace and/or restore the function of damaged bodily parts. The use of silver as antibacterial coatings onto implants has recently gained large interest in medical applications. The extent of silver that can be released into different biological fluids from such coatings is, except for the surface characteristics of the coating, governed by parameters such as protein characteristics, adsorbed layer properties, formation of silver-protein complexes as well as concentrations of proteins in the solution. This study aims to relate the structure of adsorbed net negatively charged bovine serum albumin (BSA), which is the most abundant protein in serum, to the release of silver from metallic silver surfaces in order to elucidate if the net charge of the protein has any effect of the silver release. Simultaneous adsorption measurements were performed in real time on the very same surface using combined ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements to provide a more comprehensive understanding on adsorption kinetics and layer structures. The amount of released silver into solution was measured by means of graphite furnace atomic absorption spectroscopy (GF-AAS). The structure of the adsorbed BSA layer largely influenced the amount of released silver, an enhancement that increased with BSA concentration. These observations are in complete contrast to the effect of net positively charged lysozyme (LSZ) adsorbed on silver, previously studied by the authors, for which a complete surface coverage suppressed the possibility for silver release. The underlying mechanisms behind the enhanced release of silver in the presence of BSA were mainly attributed to surface complexation between BSA and silver followed by an enhanced exchange rate of these surface complexes with BSA molecules in the solution, which in turn increase the amount of released silver in solution.

  • 28. Werzer, O
    et al.
    Cranston, ED
    Warr, GG
    Atkin, R
    Rutland, Mark W.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Ionic liquid nanotribology: Mica-silica interactions in ethylammonium nitrate2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 15, p. 5147-5152Article in journal (Refereed)
    Abstract [en]

    Colloid probe atomic force microscopy has been used to study the nanotribological properties of the silica-ethylammonium nitrate (EAN)-mica system. Normal force curve measurements reveal a series of steps at separations that are consistent with the size of an EAN ion pair (0.5 nm) due to displacement of structured solvent layers as the two surfaces are brought together. At closest separations, two steps are measured with widths of 0.3 nm and 0.1 nm, which are too small to be due to an ion pair layer. The 0.3 nm step is attributed to a partial displacement of a silica-bound cation-rich layer, with residual cations being removed in the subsequent 0.1 nm step. Lateral force measurements reveal that the frictional response is dependent on the number of ion pair layers between the surfaces. At low forces, when there is more than a single layer of EAN between silica and mica, the lateral force increases relatively steeply with applied load, and is independent of the sliding speed. At intermediate forces, a single layer of cations in an intercalated bilayer structure is present between the surfaces. The friction coefficient (μ) increases logarithmically with sliding speed consistent with an activated, discontinuous sliding process. At high force, μ is small and once again, independent of sliding velocity. The adsorbed cation layer is bound primarily to mica and compressed by the high normal force. This robust layering with a well-defined sliding plane permits the colloid probe to slide easily over the mica surface.

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