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  • 101. Gilcreest, VP
    et al.
    Carroll, WM
    Rochev, YA
    Blute, I
    YKI – Ytkemiska institutet.
    Dawson, KA
    Gorelov, AV
    Thermoresponsive poly(N-isopropylacrylamide) copolymers: Contact angles and surface energies of polymer films2004Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, s. 10138-10145Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface properties of poly(N-isopropylacrylamide) (PNIPAM) copolymer films were studied by contact angle measurements and optical and atomic force microscopy. We prepared a series of copolymers of N-isopropylacrylamide with N-tert-butylacrylamide (NtBA) in order of increasing hydrophobicity. The measurements of the advancing contact angle of water at 37°C were hampered by the observation of a distinct stick/slip pattern on all polymers in the series with the exception of poly(NtBA) (PNtBA). We attributed this behavior to the film deformation by the vertical component of liquid surface tension leading to the pinning of the moving contact line. This was confirmed by the observation of a ridge formed at the pinned contact line by optical microscopy. However, meaningful contact (without the stick/slip pattern andwith a time-independent advancing contact angle) angles for this thermoresponsive polymer series could be obtained with carefully selected organic liquids. We used the Li and Neumann equation of state to calculate the surface energy and contact angles of water for all polymers in the series of copolymers and van Oss, Chaudhury, and Good (vOCG) acid-base theory for PNtBA. The surface energies of the thermoresponsive polymers were in the range of 38.9 mJ/m2 (PNIPAM) to 31 mJ/m2 (PNtBA) from the equation of state approach. The surface energy of PNtBA calculated using vOCG theory was 29.0 mJ/m2. The calculated contact angle for PNIPAM (74.5 ± 0.2°) is compared with previously reported contact angles obtained for PNIPAM-modified surfaces.

  • 102. Grant, LM
    et al.
    Ederth, T
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Influence of surface hydrophobicity on the layer properties of adsorbed nonionic surfactants2000Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, s. 2285-2291Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of adsorbed octa(oxyethlyene) n-dodecyl ether (C12E8) layers at a series of gold-alkanethiolate surfaces was investigated by atomic force microscopy. The hydrophobicity of the surfaces was systematically varied by changing the relative amounts of chemisorbed thiohexadecane (CH3(CH2)15SH) and thiohexadecanol (CH2OH(CH2)15SH) surface groups. This allowed complete control over the hydrophobicity of the surface. Adsorption was studied on five different thiol-modified gold surfaces prepared from solutions containing 0%, 25%, 50%, 75%, and 100% hexadecane thiol, respectively (henceforth referred to as 0% CH3, 25% CH3, 50% CH3, 75% CH3, and 100% CH3). The following general evolution of the adsorbed layer morphology with increasing surface hydrophobicity was observed: diffuse micellar coverage; dense micellar coverage; bilayer; and finally a monolayer structure at the most hydrophobic surface. The adsorbed layer structure observed at the different surfaces was interpreted in terms of the effective interaction between different parts of the surfactant and the solid surface. On the basis of our adsorption data, we also infer that hydrophobic interactions are the main driving force for adsorption of ethylene oxide segments at partially hydroxylated surfaces (such as silica) and that hydrogen bonding reduces the free energy penalty of displacing water.

  • 103. Griffiths, PC
    et al.
    Cosgrove, T
    Shar, J
    King, SM
    Yu, G-E
    Booth, C
    Malmsten, M
    YKI – Ytkemiska institutet.
    Role of copolymer architecture on adsorption at the solid/liquid interface1998Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, s. 1779-1785Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption of monodisperse block copolymers comprising poly(ethylene oxide)-poly(butylene oxide) onto polystyrene latex from aqueous solution has been investigated by small-angle neutron scattering and photon correlation spectroscopy with particular reference to the role of molecular architecture. It appears that chain architecture is (i) a weak factor in the adsorption behavior when the hydrophobic block is located in the center of the polymer, since the triblock E100B15E100 behaved very similarly to the cyclic c-E200B15, but (ii) a significant factor when the hydrophobic block is located at the end of the copolymer chain, as shown by the more dense and thicker layer formed by E200B15 compared to the triblock E100B15E100. The hydrodynamic thickness of the layer formed by the small diblock E100B15 was approximately half that exhibited by the larger diblock E200B15. Good agreement was observed between depletion and SANS-derived adsorbed amounts. Theoretical predictions and self-consistent mean-field calculations of the adsorption also show excellent qualitative agreement with experiment.

  • 104. Gruner, MS
    et al.
    Szilvay, GR
    Berglin, Mattias
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Lienemann, M
    Laaksonen, P
    Linder, MB
    Self-assembly of class II hydrophobins on polar surfaces2012Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 9, s. 4293-4300Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydrophobins are structural proteins produced by filamentous fungi that are amphiphilic and function through self-assembling into structures such as membranes. They have diverse roles in the growth and development of fungi, for example in adhesion to substrates, for reducing surface tension to allow aerial growth, in forming protective coatings on spores and other structures. Hydrophobin membranes at the air-water interface and on hydrophobic solids are well studied, but understanding how hydrophobins can bind to a polar surface to make it more hydrophobic has remained unresolved. Here we have studied different class II hydrophobins for their ability to bind to polar surfaces that were immersed in buffer solution. We show here that the binding under some conditions results in a significant increase of water contact angle (WCA) on some surfaces. The highest contact angles were obtained on cationic surfaces where the hydrophobin HFBI has an average WCA of 62.6° at pH 9.0, HFBII an average of 69.0° at pH 8.0, and HFBIII had an average WCA of 61.9° at pH 8.0. The binding of the hydrophobins to the positively charged surface was shown to depend on both pH and ionic strength. The results are significant for understanding the mechanism for formation of structures such as the surface of mycelia or fungal spore coatings as well as for possible technical applications. .

  • 105. Hahn Berg, IC
    et al.
    Muller, D
    Arnebrant, T
    Malmsten, M
    YKI – Ytkemiska institutet.
    Ellipsometry and TIRF studies of enzymatic degradation of interfacial proteinaceous layers2001Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, s. 1641-1652Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ellipsometry and total internal reflectance fluorescence spectroscopy (TIRF) have been employed to investigate the layer structure of gelatin adsorbed from aqueous solutions onto silica/glass and methylated silica/glass, as well as the effects of addition of the proteolytic enzymes krillase and trypsin, in relation to temperature, enzyme concentration and enzymatic activity. The results for the hydrophilic substrates show that homogeneous and heterogeneous exchange occurs readily, as does autolysis of trypsin at the interface. At the hydrophobic substrates, the effect of exchange is limited and a residual gelatin fraction is present at the interface throughout. The interfacial behavior of gelatin above and below the helix formation temperature (Thelix) shows that more extended surface layers are formed at both substrates below Thelix . At the hydrophilic substrates, the higher adsorbed layer thickness below Thelix is mainly due to the adsorption of more gelatin than at the higher temperature, whereas, at the hydrophobic substrates, the increase in layer thickness below Thelix is due to a decrease in packing density. Enzyme addition to preadsorbed gelatin at methylated silica results in the transition to a thinner and denser layer, that contains both residual gelatin and proteolytic enzymes (i.e., krillase or trypsin). At hydrophobic surfaces, a faster and more extensive degradation of the gelatin layer is observed with increasing krillase concentration, the effect of which is similar above and below Thelix . The effect of trypsin addition to preadsorbed gelatin is enhanced at TThelix . Finally, the exposure of preadsorbed gelatin to inactivated krillase showed a nearly complete elimination in the effects observed upon addition of intact krillase. This indicated that the enzymatic activity of krillase in its native form plays a major role for the interaction between krillase and preadsorbed gelatin.

  • 106. Halthur, TJ
    et al.
    Björklund, A
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Self-assembly/aggegation behavior, and adsorption of enamel matrix derivate protein to silica surfaces2006Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, s. 2227-2234Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adsorption of the amelogein protein mixture enamel matrix derivate (EMD) to silica surfaces has been studied by in situ ellipsometry and quartz crystal microbalance with dissipation (QCM-D). The protein was found to adsorb as nanospheres in mono- or multilayers, depending on the concentration of “free” nanospheres available in solution. The concentration of free nanospheres is determined by the competitive processes of adsorption and rapid aggregation into microscopic particles, measured by dynamic light scattering (DLS). Multilayers could also be formed by sequential injections of fresh EMD solution. At higher temperature, an up to 6 times thicker gel-like film was formed on the substrate surface, and decreasing the pH lead to disruption of the multilayer/aggregate formation and a decreased amount adsorbed.

  • 107. Halthur, TJ
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Immobilization of enamel matrix derivate protein onto polypeptide multilayers. Comparative in situ measurements using ellipsometry, quartz crystal microbalance with dissipation, and dual polarization interferometry2006Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, s. 11065-11071Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The buildup of biodegradable poly(l-glutamic acid) (PGA) and poly(l-lysine) (PLL) multilayers on silica and titanium surfaces and the immobilization of Enamel Matrix Derivate protein (EMD) was followed by utilizing in situ using ellipsometry, Quartz Crystal Microbalance with Dissipation (QCM-D), and Dual Polarization Interferometry (DPI). The use of the relatively new DPI technique validated earlier published ellipsometry measurements of the PLL/PGA polypeptide films. The hydrophobic aggregating EMD protein was successfully immobilized both on top of as well as within the multilayer structures at pH 5.0. DPI measurements further indicated that the immobilization of EMD is influenced by the flow-pattern during adsorption. The formed polypeptide/EMD multilayer films are of interest since it is known that EMD is able to trigger cell response and induce biomineralization. The multilayer films thus have potential to be useful as bioactive and biodegradable coatings for future dental implants.

  • 108. Halthur, TJ
    et al.
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Multilayers of charged polypeptides as studied by in situ ellipsometry and quartz crystal microbalance with dissipation2004Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, s. 1739-1745Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on silica and titanium surfaces, with and without an initial layer of polyethyleneimine (PEI), was investigated and characterized by means of in situ ellipsometry and quartz crystal microbalance with dissipation. A two-regime buildup was found in all systems, where the length of the first slow-growing regime is dependent on the structure of the initial layers. In the second fast-growing regime, the film thickness grows linearly while the mass increases more than linearly (close to exponentially) with the number of deposited layers. The film refractive indices as well as the water contents indicate that the film density changes as the multilayer film builds up. The change in film density was proposed to be due to polypeptides diffusing into the multilayer film as they attach. Furthermore, the use of PEI as the initial layer was found to induce a difference in the thickness increments for PGA and PLL.

  • 109. Halthur, Tobias J
    et al.
    Arnebrant, Thomas
    Macakova, Lubica
    YKI – Ytkemiska institutet.
    Feiler, Adam
    Sequential adsorption of bovine mucin and lactoperoxidase to various substrates studied with quartz crystal microbalance with dissipation2010Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 7, s. 4901-4908Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mucin and lactoperoxidase are both natively present in the human saliva. Mucin provides lubricating and antiadhesive function, while lactoperoxidase has antimicrobial activity. We propose that combined Films of the two proteins can be used as a strategy for surface modification in biomedical applications such as implants or biosensors. In order to design and ultilize mixed protein films, it is necessary to understand the variation in adsorption behavior of the proteins onto different surfaces and how it affects their interaction. The quartz crystal microbalance with dissipation (QCM-D) technique hats been used to extract information of the adsorption properties of bovine mucin (BSM) and lactoperoxidase (LPO) to gold, silica. and hydrophobized silica surfaces. The information has further been used to retrieve information of the viscoelastic properties of the adsorbed film. The adsorption and compaction of BSM were found to vary depending on the nature of the underlying bare surface, adsorbing as at thick highly hydrated film with loops and tails extending out in the bulk on gold and as a thinner film with much lower adsorbed amount on silica; and on hydrophobic surfaces, BSM adsorbs as a flat and much more compact layer. On gold and silica, the highly hydrated BSM film is cross-linked and compacted by the addition of LPO, whereas the compaction is not as pronounced on the already more compact film formed on hydrophobic surfaces. The adsorption of LPO to bare surfaces also varied depending on the type of surface. The adsorption profile of BSM onto LPO-coated surfaces mimicked the adsorption to the underlying surface, implying little interaction between the LPO and BSM. The interaction between the protein layers was interpreted as a combination of electrostatic and hydrophobic interactions, which was in turn influenced by the interaction of the proteins with the different substrates.

  • 110.
    Hansen, PHF
    et al.
    YKI – Ytkemiska institutet.
    Rödner, S
    YKI – Ytkemiska institutet.
    Bergström, L
    YKI – Ytkemiska institutet.
    Structural characterization of dense colloidal films using a modified pair distribution function and Delaunay triangulation2001Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, s. 4867-4875Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Methods for structural characterization of particle films have been developed. Monodisperse silica particles with alkoxy chains grafted on the surface formed dense colloidal films at the air-liquid interface. The positions of the partly immersed particles were determined by light microscopy and image analysis. The average size of the ordered domains could be estimated from the pair distribution function. We were also able to determine the distribution of pores and defects in the colloidal film using Delaunay triangulation. The two methods were used to study the effect of interparticle bond strength on the film structure. We found that the size of the ordered domains decreased exponentially when the bond strength increased, while the pore density increased. The effect of drying on structural changes of the colloidal film was also discussed.

  • 111.
    Hansson, Petra M
    et al.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Hormozan, Y
    Brandner, Birgit D
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Linnros, J
    Claesson, Per M
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Swerin, Agne
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Effect of surface depressions on wetting and interactions between hydrophobic pore array surfaces2012Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 30, s. 11121-11130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surface structure is known to significantly affect the long-range capillary forces between hydrophobic surfaces in aqueous solutions. It is, however, not clear how small depressions in the surface will affect the interaction. To clarify this, we have used the AFM colloidal probe technique to measure interactions between hydrophobic microstructured pore array surfaces and a hydrophobic colloidal probe. The pore array surfaces were designed to display two different pore spacings, 1.4 and 4.0 μm, each with four different pore depths ranging from 0.2 to 12.0 μm. Water contact angles measured on the pore array surfaces are lower than expected from the Cassie-Baxter and Wenzel models and not affected by the pore depth. This suggests that the position of the three-phase contact line, and not the interactions underneath the droplet, determines the contact angle. Confocal Raman microscopy was used to investigate whether water penetrates into the pores. This is of importance for capillary forces where both the movement of the three-phase contact line and the situation at the solid/liquid interface influence the stability of bridging cavities. By analyzing the shape of the force curves, we distinguish whether the cavity between the probe and the surfaces was formed on a flat part of the surface or in close proximity to a pore. The pore depth and pore spacing were both found to statistically influence the distance at which cavities form as surfaces approach each other and the distance at which cavities rupture during retraction.

  • 112.
    Hansson, Petra M
    et al.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Skedung, Lisa
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Claesson, Per M
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Swerin, Agne
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Schoelkopf, Joachim
    Gane, Patrick A C
    Robust hydrophobic surfaces displaying different surface roughness scales while maintaining the same wettability2011Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 13, s. 8153-8159Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A range of surfaces coated with spherical silica particles, covering the size range from nanometer to micrometer, have been produced using Langmuir-Blodgett (LB) deposition. The particles were characterized both in suspension and in the Langmuir trough to optimize the surface preparation procedure. By limiting the particle aggregation and surface layer failures during the preparation steps, well-defined monolayers with a close-packed structure have been obtained for all particle sizes. Thus, this procedure led to structured surfaces with a characteristic variation in the amplitude and spatial roughness parameters. In order to obtain robust surfaces, a sintering protocol and an AFM-based wear test to determine the stability of the deposited surface layer were employed. Hydrophobization of the LB films followed by water contact angle measurements showed, for all tested particle sizes, the same increase in contact angle compared to the contact angle of a flat hydrophobic surface. This indicates nearly hexagonal packing and gives evidence for nearly, complete surface wetting of the surface features.

  • 113.
    Hansson, Petra M
    et al.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Swerin, Agne
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Schoelkopf, Joachim
    Gane, Patrick A C
    Thormann, Esben
    Influence of surface topography on the interactions between nanostructured hydrophobic surfaces2012Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 21, s. 8026-8034Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanostructured particle coated surfaces, with hydrophobized particles arranged in close to hexagonal order and of specific diameters ranging from 30 nm up to 800 nm, were prepared by Langmuir-Blodgett deposition followed by silanization. These surfaces have been used to study interactions between hydrophobic surfaces and a hydrophobic probe using the AFM colloidal probe technique. The different particle coated surfaces exhibit similar water contact angles, independent of particle size, which facilitates studies of how the roughness length scale affects capillary forces (previously often referred to as "hydrophobic interactions") in aqueous solutions. For surfaces with smaller particles (diameter < 200 nm), an increase in roughness length scale is accompanied by a decrease in adhesion force and bubble rupture distance. It is suggested that this is caused by energy barriers that prevent the motion of the three-phase (vapor/liquid/solid) line over the surface features, which counteracts capillary growth. Some of the measured force curves display extremely long-range interaction behavior with rupture distances of several micrometers and capillary growth with an increase in volume during retraction. This is thought to be a consequence of nanobubbles resting on top of the surface features and an influx of air from the crevices between the particles on the surface.

  • 114. Hayward, RC
    et al.
    Alberius, PCA
    YKI – Ytkemiska institutet.
    Kramer, EJ
    Chmelka, BF
    Thin films of bicontinuous cubic mesostructured silica templated by a nonionic surfactant2004Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, s. 5998-6004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin films of bicontinuous cubic mesostructured silica were formed using the nonionic poly(oxyethylene)- alkyl ether surfactant Brij-56 as a structure-directing agent. The synthesis conditions were chosen such that the estimated volume fraction of surfactant in the silica/surfactant films corresponded approximately to the composition at which the bicontinuous cubic phase occurs in the water/surfactant phase diagram. Small-angle X-ray scattering and transmission electron microscopy measurements reveal that the cubic phase corresponds to the Iad double-gyroid structure, with some distortion due to anisotropic film shrinkage. The cubic structure grows as faceted domains that are well-oriented with respect to the substrate and often occur in coexistence with a lamellar phase. By adjusting the temperature at which the films are aged, it is possible to create films with 2D hexagonal, cubic, or lamellar structures at a single composition. microscopy and X-ray diffraction showed that well ordered internal 2D hexagonal mesostructures could be prepared using both nonionic block copolymers and cationic surfactants as the templating molecules. Disordered cubic and well ordered lamellar, onion like, particles were prepared from the block copolymer templates. Nitrogen sorption data and mercury porosimetry show that pore size distribution of the mesoporous particles is very narrow with pore sizes varying from 2.5 to 8.5 nm as a function of templating amphiphiles. We have shown that the mesoscopic pores are accessible after calcination and can be filled with relatively large molecules; the particles adsorbed more than 20% (by weight) of the cationic dye Janus Green B from aqueous solutions.

  • 115. Hedberg, YS
    et al.
    Killian, MS
    Blomberg, Eva
    YKI – Ytkemiska institutet.
    Virtanen, S
    Schmuki, P
    Odnevall Wallinder, I
    Interaction of bovine serum albumin and lysozyme with stainless steel studied by time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy2012Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 47, s. 16306-16317Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An in-depth mechanistic understanding of the interaction between stainless steel surfaces and proteins is essential from a corrosion and protein-induced metal release perspective when stainless steel is used in surgical implants and in food applications. The interaction between lysozyme (LSZ) from chicken egg white and bovine serum albumin (BSA) and AISI 316L stainless steel surfaces was studied ex situ by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) after different adsorption time periods (0.5, 24, and 168 h). The effect of XPS measurements, storage (aging), sodium dodecyl sulfate (SDS), and elevated temperature (up to 200 °C) on the protein layers, as well as changes in surface oxide composition, were investigated. Both BSA and LSZ adsorption induced an enrichment of chromium in the oxide layer. BSA induced significant changes to the entire oxide, while LSZ only induced a depletion of iron at the utmost layer. SDS was not able to remove preadsorbed proteins completely, despite its high concentration and relatively long treatment time (up to 36.5 h), but induced partial denaturation of the protein coatings. High-temperature treatment (200 °C) and XPS exposure (X-ray irradiation and/or photoelectron emission) induced significant denaturation of both proteins. The heating treatment up to 200 °C removed some proteins, far from all. Amino acid fragment intensities determined from ToF-SIMS are discussed in terms of significant differences with adsorption time, between the proteins, and between freshly adsorbed and aged samples. Stainless steel-protein interactions were shown to be strong and protein-dependent. The findings assist in the understanding of previous studies of metal release and surface changes upon exposure to similar protein solutions.

  • 116.
    Hellsing, Maja
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Rennie, Adrian
    Uppsala University, Sweden.
    Rodal, Michael
    Biolin Scientific AB, Sweden.
    Höök, Fredrik
    Chalmers University of Technology, Sweden.
    Charged polystyrene nanoparticles near a SiO2/water interface2019Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, nr 1, s. 222-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quartz crystal microbalance with dissipation (QCM-D) monitoring is traditionally used to investigate adsorption processes at liquid-solid interfaces but has also been applied increasingly to characterize the viscoelastic properties of complex liquids. Here, we contribute new insights to the latter field by using QCM-D to investigate the structure near an interface and high-frequency viscoelastic properties of charge stabilized polystyrene particles (radius 37 nm) dispersed in pure water. The study reveals changes with increasing ionic-strength from the crystalline order at low salt concentration to that with a less-structured particle distribution at high ionic strength. Replacing pure water with an aqueous particle dispersion is due to an increased mass load expected to give rise to a decrease in frequency, f. In the present work increases in both f and dissipation, D, were observed on exchanging pure water for the particle dispersion at low ionic strength. However, the QCM-D data are still well-represented by a viscoelastic Voigt model, with the viscosity increasing from 1.0 to 1.3 mPa s as the particle volume fraction changed from 0.005 to 0.07. This increase is higher than predicted for dilute dispersions according to Einstein’s equation for the viscosity of non-interacting hard spheres particles in liquids but can be explained by the charge repulsion between the particles giving rise to a higher effective volume fraction. It is also concluded that the polystyrene particles did not adhere to the solid surface but rather were separated by a layer of pure dispersion medium. The QCM-D response was successfully represented using a viscoelastic Kelvin-Voigt model, from which it was concluded that the thickness of the Newtonian dispersion medium layer was of the order of the particle-particle bulk separation, in the range 50 to 250 nm and was observed to decrease with both particle concentration and with addition of salt. Similar anomalous frequency and dissipation responses have been seen previously for colloidal systems containing weakly adherent colloidal particles and bacteria and in these cases interpreted in terms of coupled resonators. We here demonstrate that surface attachment is not required for such phenomena to occur, but that a viscoelastic liquid separated from the oscillating surface by a thin Newtonian layer can give rise to very similar responses.

  • 117.
    Heydari, Golrokh
    et al.
    KTH Royal Institute of Technology, Sweden.
    Tyrode, Erik
    KTH Royal Institute of Technology, Sweden.
    Visnevskij, Ceslav
    Vilnius University, Lithuania.
    Makuska, Ricardas
    Vilnius University, Lithuania.
    Claesson, Per M.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Temperature-dependent deicing properties of electrostatically anchored branched brush layers of poly(ethylene oxide)2016Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 17, s. 4194-4202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The hydration water of hydrophilic polymers freezes at subzero temperatures. The adsorption of such polymers will result in a hydrophilic surface layer that strongly binds water. Provided this interfacial hydration water remains liquidlike at subzero temperatures, its presence could possibly reduce ice adhesion, in particular, if the liquidlike layer is thicker than or comparable to the surface roughness. To explore this idea, a diblock copolymer, having one branched bottle-brush block of poly(ethylene oxide) and one linear cationic block, was electrostatically anchored on flat silica surfaces. The shear ice adhesion strength on such polymer-coated surfaces was investigated down to -25 °C using a homebuilt device. In addition, the temperature dependence of the ice adhesion on surfaces coated with only the cationic block, only the branched bottle-brush block, and with linear poly(ethylene oxide) was investigated. Significant ice adhesion reduction, in particular, at temperatures above -15 °C, was observed on silica surfaces coated with the electrostatically anchored diblock copolymer. Differential scanning calorimetry measurements on bulk polymer solutions demonstrate different thermal transitions of water interacting with branched and linear poly(ethylene oxide) (with hydration water melting points of about -18 and -10 °C, respectively). This difference is consistent with the low shear ice adhesion strength measured on surfaces carrying branched bottle-brush structured poly(ethylene oxide) at -10 °C, whereas no significant adhesion reduction was obtained with linear poly(ethylene oxide) at this temperature. We propose a lubrication effect of the hydration water bound to the branched bottle-brush structured poly(ethylene oxide), which, in the bulk, does not freeze until -18 °C.

  • 118.
    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, Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Electro-Responsive Surface Composition and Kinetics of an Ionic Liquid in a Polar Oil.2019Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, nr 48, s. 15692-15700Artikel i tidskrift (Refereegranskat)
    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.

  • 119. Horvath, A. T.
    et al.
    Horvath, A. E.
    Lindström, Tom
    RISE., STFI-Packforsk.
    Wågberg, L.
    Adsorption of highly charged polyelectrolytes onto an oppositely charged porous substrate2008Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 15, s. 7857-7866Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption behavior of highly charged cationic polyelectrolytes onto porous substrates is electrostatic in nature and has been shown to be highly dependent on the poly electrolyte properties. Copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) were synthesized to have a range of macromolecular properties (i.e., charge density and molecular mass). Traditional titration methods have been complemented by fluorescence labeling techniques that were developed to directly observe the extent that fluorescently labeled poly(AM-co-DADMAC) adsorbs into the pore structure of a cellulosic substrate. Although contributing to the electrostatic driving force, the charge density acts to limit adsorption to the outermost surface under electrolyte-free conditions. However, adsorption into the pores can occur if both the molecular mass and charge density of poly(AM-co-DADMAC) are sufficiently low. Adsorption initially increases as the electrolyte concentration is increased. However, the electrostatic persistence length of poly(AM-co-DADMAC) restricts the polyelectrolyte from entering the pores. Therefore, changes in the adsorption behavior at moderate electrolyte concentrations have been attributed to swelling of the polyelectrolyte layer at the fiber exterior. The adsorption behavior changes again at high electrolyte concentrations such that poly(AMco-DADMAC) could adsorb into the pore structure. This occurred when the electrolyte concentration was sufficient to screen the electrostatic persistence length of poly(AM-co-DADMAC), provided that the entropie driving force for adsorption still existed. It is suggested that adsorption into the pore structure is a kinetic process that is governed by localized electrostatic interactions between poly(AM-co-DADMAC) and the charges located within the pores.

  • 120. Horvath, A. T.
    et al.
    Horvath, A. E.
    Lindström, Tom
    RISE., STFI-Packforsk.
    Wågberg, L.
    Adsorption of low charge density polyelectrolytes to an oppositely charged porous substrate2008Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 13, s. 6585-6594Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption behavior of a low charge density cationic polyelectrolyte to cellulosic fibers has been studied. Cationic dextran served as a model polyelectrolyte, as it can be prepared over a range in molecular mass and charge density. The adsorption behavior of the cationic dextran was measured in electrolyte-free conditions using polyelectrolyte titration techniques. By fluorescent labeling the cationic dextran, the extent to which adsorption occurs inside the porous structure was further determined by fluorescent confocal laser scanning microscopy. Cationic dextran having a sufficiently low charge density adsorbed into the pores, although the extent the cationic dextran adsorbed was governed by the molecular mass. The adsorption behavior of the cationic dextran was also studied in various electrolyte concentrations. The adsorbed mass monotonically decreased with increasing electrolyte, as the electrostatic interaction with the substrate was more effectively screened. This behavior also suggests that the interactions between adsorbed polyelectrolyte chains, i.e. lateral correlation effects, are negligible for low charge density polyelectrolytes. Finally, the effect of having a preadsorbed layer of cationic dextran on the adsorption behavior was determined in electrolytefree conditions using fluorescent double staining techniques. The preadsorbed cationic dextran had almost no effect on the adsorption of low molecular mass fractions. Low molecular mass fractions directly adsorbed into the pore structure, as opposed to adsorbing to a free surface and diffusing into the pores. It was also shown that cationic dextran can be selectively adsorbed to different locations, such that the surface of a porous substrate can be treated uniquely from the bulk.

  • 121. Horvath, A. T.
    et al.
    Horvath, A. E.
    Lindström, Tom
    RISE., STFI-Packforsk.
    Wågberg, L.
    Diffusion of cationic polyelectrolytes into cellulosic fibers2008Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 19, s. 10797-10806Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The penetration of cationic polyelectrolytes into anionic cellulosic fibers was evaluated with fluorescent imaging techniques in order to clarify the mechanism and time scales for the diffusion process. The bulk charge of the cellulosic fibers indirectly creates a driving force for diffusion into the porous fiber wall, which is entropic in nature due to a release of counterions as the polyelectrolyte adsorbs. The individual bulk charges in the fiber cell wall also interact with the diffusing polyelectrolyte, such that the polyelectrolyte diffuses to the first available charge and consequently adsorbs and remains fixed. Thus, subsequent polyelectrolyte chains must first diffuse through the adsorbed polyelectrolyte layer before adsorbing to the next available bulk charges. This behavior differs from earlier suggested diffusion mechanisms, by which polyelectrolytes were assumed to first adsorb to the outermost surface and then reptate into the pore structure. The time scales for polyelectrolyte diffusion were highly dependent on the flexibility of the chain, which was estimated from calculations of the persistence length. The persistence length ultimately depended on the charge density and electrolyte concentration. The charge density of the polyelectrolyte had a greater influence on the time scales for diffusion. High charge density polyelectrolytes were observed to diffuse on a time scale of months, whereas the diffusion of low charge density polyelectrolytes was measured on the order of hours. An influence of the chain length, that is, steric interactions due the persistence length of the polyelectrolyte and to the tortuosity of the porous structure of the fiber wall, could only be noted for low charge density polyelectrolytes. Increasing the electrolyte concentration increased the chain flexibility by screening the electrostatic contribution to the persistence length, in turn inducing a faster diffusion process. However, a significant change in the diffusion behavior was observed at high electrolyte concentrations, at which the interaction between the polyelectrolyte charges and the fiber charges was almost completely screened.

  • 122. Imae, T
    et al.
    Kato, M
    Rutland, MW
    YKI – Ytkemiska institutet.
    Forces between two glass surfaces with adsorbed hexadecyltrimethylammonium salicylate2000Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, s. 1937-1942Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Forces have been measured for hexadecyltrimethylammonium salicylate (C16TASal) layers on glass beads. During the inward process, hydrophobic attraction occurred at lower adsorption of C16TASal and electrostatic repulsion interactions happened at higher adsorption. While the jump-in phenomenon was observed for solutions of concentrations below the critical micelle concentration (cmc = 0.15 mM), the step-in phenomenon was characteristic for solutions at the cmc and above the cmc, suggesting the push-out of adsorbed C16TASal layers and/or inserted micelles. The remarkable pull-off phenomenon on the outward process occurred for all solutions, indicating a strong interaction between C16TASal molecules. For aqueous 0.15 mM C16TASal solutions of various NaSal concentrations, on the inward process, the electrostatic repulsive interaction decreased with adding NaSal. This is due to the electrostatic shielding by salt excess. The height of the force wall on the inward process reached a maximum at 0.01 M NaSal, but the interlocking between molecules on two surfaces during the outward process was minimized at 0.1 M NaSal. These tendencies, which are different from that of the electrostatic repulsion interaction, imply the strong cohesion between adsorbed C16TASal layers.

  • 123. Joabsson, F
    et al.
    Thuresson, K
    Blomberg, E
    YKI – Ytkemiska institutet.
    Interfacial interaction between sodium dodecyl sulfate and hydrophobically modified ethyl(hydroxyethyl)cellulose. A surface force study2001Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, s. 1506-1510Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of addition of sodium dodecyl sulfate (SDS) to a layer of hydrophobically modified ethyl(hydroxyethyl)cellulose (HM-EHEC) preadsorbed on hydrophobized mica has been studied with an interferometric surface force apparatus (SFA). The force between the surfaces was always repulsive on both compression and separation. The range of this force, which is 1500 Å for the HM-EHEC layers, undergoes a non-monotonic change on addition of SDS. Initially, at low SDS concentrations the layer expand, while at higher surfactant concentrations a contraction of the adsorbed layer is observed. At 1.5 mM SDS the range of the force is at maximum, while at 6 mM SDS the layer is significantly thinner than before addition of SDS. The results are discussed in terms of polymer-surfactant interfacial association and competitive adsorption. The data obtained by surface force measurements agree qualitatively with ellipsometry findings on the same system

  • 124. Johansson, Erik
    et al.
    Blomberg, Eva
    YKI – Ytkemiska institutet.
    Lingström, Rikard
    Wågberg, Lars
    Adhesive interaction between polyelectrolyte multilayers of polyallylamine hydrochloride and polyacrylic acid studied using atomic force microscopy and surface force apparatus2009Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, nr 5, s. 2887-2894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, the adhesion between substrates treated with identical polyelectrolyte multilayers (PEM) from polyallylamine hydrochloride (PAR) and poly(acrylic acid) (PAA) was studied using atomic force microscopy (AFM) and the Surface force apparatus (SFA). The AFM measurements, conducted under wet conditions for PEMs formed at pH 7.5, showed a higher adhesion (pull-off force) when PAH was adsorbed in the outermost layers. There was also a difference depending on the Molecular mass of the polymers, demonstrating a greater adhesion for the low molecular mass combination of polyelectrolytes. Furthermore, die time in contact showed to be of importance, with increasing pull-off forces with contact time at maximum load. The SFA measurements were conducted under dry conditions, at 100% RH, and under wet conditions for PEMs adsorbed at pH 7.5/3.5. The SFA adhesion measurements showed that under dry conditions, the adhesive forces between two high energetic mica substrates were lowered when they were covered by PEMs before the measurements. The thickness of the adsorbed layers was also measured using SFA. This showed that there was a significant swelling when the dry layers were exposed to 100% RH or to wet conditions. The swelling was higher, indicating a less rigid layer, when PAH was adsorbed in the outermost layer than when the PEM was capped with PAA.

  • 125. Kadi, M
    et al.
    Hansson, P
    Almgren, M
    Bergström, M
    YKI – Ytkemiska institutet.
    Garamus, VM
    Mixed micelles of fluorocarbon and hydrocarbon surfactants. A small angle neutron scattering study2004Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, s. 3933-3939Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mixtures of the partly fluorinated cationic surfactant HFDePC (N-(1, 1,2,2-tetrahydroperfluorodecanyl)pyridinium chloride and deuterated headgroup) with C(16)TAC, hexadecyl-trimethylammonium chloride, have been investigated using small angle neutron scattering with contrast matching. Earlier results from this system suggested that a demixing occurred, into two coexisting populations of micelles, hydrocarbon-rich and fluorocarbon-rich, respectively. The present results could be explained by one type of mixed micelles with an inhomogeneous distribution of fluorinated and hydrogenated surfactants within the micelles although a demixing cannot be definitely excluded.

  • 126. Kaufman, ED
    et al.
    Belyea, J
    Johnson, MC
    Nicholson, ZM
    Ricks, JL
    Blomberg, E
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Probing protein adsorption onto mercaptoundecanoic acid stabilized gold nanoparticles and surfaces by quartz crystal microbalance and -Potential measurements2007Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, s. 6053-6062Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption characteristics of three proteins [bovine serum albumin (BSA), myoglobin (Mb), and cytochrome c (CytC)] onto self-assembled monolayers of mercaptoundecanoic acid (MUA) on both gold nanoparticles (AuNP) and gold surfaces (Au) are described. The combination of quartz crystal microbalance measurements with dissipation (QCM-D) and pH titrations of the -potential provide information on layer structure, surface coverage, and potential. All three proteins formed adsorption layers consisting of an irreversibly adsorbed fraction and a reversibly adsorbed fraction. BSA showed the highest affinity for the MUA/Au, forming an irreversibly adsorbed rigid monolayer with a side-down orientation and packing close to that expected in the jamming limit. In addition, BSA showed a large change in the adsorbed mass due to reversibly bound protein. The data indicate that the irreversibly adsorbed fraction of CytC is a monolayer structure, whereas the irreversibly adsorbed Mb is present in form of a bilayer. The observation of stable BSA complexes on MUA/AuNPs at the isoelectric point by ?-potential measurements demonstrates that BSA can sterically stabilize MUA/AuNP. On the other hand, MUA/AuNP coated with either Mb or CytC formed a reversible flocculated state at the isoelectric point. The colloidal stability differences may be correlated with weaker binding in the reversibly bound overlayer in the case of Mb and CytC as compared to BSA.

  • 127. Kjellin, URM
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Surface properties of tetra(ethylene oxide)dodecyl amide compared with poly(ethylene oxide) surfactants. 2. Effect of the headgroup on surface forces2002Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, s. 6754-6763Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface interaction forces between layers of tetra(ethylene oxide) n-dodecyl amide, TEDAd, were compared with those of C12E5, C12E4, C10E5, and C10E4. It was found that adsorbed layers of TEDAd on a hydrophobic surface are thinner and less diffuse than layers of C12E5. As the number of EO-groups decreases, the short-range repulsion commences at shorter distances and at the same time the compressibility decreases. These results can be qualitatively explained with model mean-field lattice calculations, except the fact that a higher attractive force was found between layers of TEDAd, whereas no adhesion was found in case of the alcohol ethoxylates. The reason for this is proposed to be a smaller steric/protrusion force in case of TEDAd caused by intralayer interactions between the amide groups inside the adsorbed layer. The force required to squeeze out the surfactant layers from the contact zone increased with concentration and at the same time the adhesion decreased. Above the cmc, no adhesion was found between the surfaces, and an outward jump from hydrophobic surface contact occurred on the repulsive side of the force curve as the compressive force was decreased. The force when this occurred was found to be highest for the largest hydrophilic headgroups, indicating that the surface pressure outside the contact region, and the pressure from surfactants remaining between the surfaces, was largest for these surfactants. In contrast to the ethoxylated surfactants, sugar surfactant layers are less compressible, shows considerably larger adhesion and are not possible to squeeze out at the compressive forces used in this study.

  • 128. Kjellin, URM
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Linse, P
    Surface properties of tetra(ethylene oxide)dodecyl amide compared with poly(ethylene oxide) surfactants. 1. Effect of the headgroup on adsorption2002Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, s. 6745-6753Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surfactant tetra(ethylene oxide) n-dodecyl amide (TEDAd) was compared with the poly(ethylene oxide) n-alkyl ethers C12E5, C10E5, and C12E4. The adsorption to hydrophobic liquid-vapor and solid-liquid interfaces, as well as the wetting behavior on a hydrophobic surface was investigated. The amide group is more hydrophilic than the ethylene oxide group, raising the cloud-point and critical micelle concentration (cmc). The incorporation of an amide group decreases the adsorbed amount at a fixed surfactant concentration. For all studied surfactants, the adsorbed amount was significantly lower on the solid-liquid interface than on the liquid-vapor interface at a fixed concentration below the cmc, but the maximum adsorbed amount was only slightly lower on the solid-liquid interface. The surface pressure vs. area/molecule isotherms reveal attractive interactions between the amide groups in the adsorbed layer, which reduces the surface pressure at a fixed area/molecule. The advancing contact angles were only dependent on the surface tension at the liquid-vapor interface for C12E5 and TEDAd. The calculated adsorbed amount from the advancing contact angle agreed with the adsorbed amount on the liquid-vapor interface, while the adsorbed amount calculated from the receding contact angle was closer to the equilibrium value obtained with ellipsometry on the solid-liquid interface. The experimental results are supported by mean-field lattice model calculations and due to the unfavorable interaction between the hydrocarbon region and the amide group in the adsorbed layer, the boundary between the hydrophobic and hydrophilic regions in the adsorbed layer becomes better defined in the presence of an amide group. This might be one of the explanations for the differences found in surface force measurements, and this will be described in part two of this investigation.

  • 129. Kjellin, URM
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Vulfson, EN
    Studies of N-dodecyllactobionamide, maltose 6'-O-dodecanoate and octyl-ß-glucoside with surface tension, surface force, and wetting techniques2001Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, s. 1941-1949Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three different types of sugar surfactants, octyl--glucoside, maltose 6'-O-dodecanoate, and N-dodecyllactobionamide have been investigated to examine the effect of the structure of the sugar headgroup on the adsorption to liquid/vapor and solid/liquid interfaces using a number of techniques (surface tension, surface force apparatus, MASIF, and wetting). It was found that all the surfactants form monolayers when adsorbed to a hydrophobic interface at high concentrations. Increased headgroup flexibility leads to the adsorption of higher amounts on both the liquid/vapor and solid/liquid interfaces, resulting in a higher van der Waals attraction between two such monolayers. Increased hydrogen bonding within layers of more flexible surfactants is suggested to explain this difference. The most flexible surfactant, N-dodecyllactobionamide, is the least efficient wetting agent with the highest SL. The behavior of the receding contact angles indicates the importance of intralayer hydrogen bonds between larger and more flexible sugar headgroups.

  • 130. Kondo, M
    et al.
    Shinozaki, K
    Bergström, L
    YKI – Ytkemiska institutet.
    Mizutani, N
    Preparation of colloidal monolayers of alkoxylated silica particles at the air-liquid interface1995Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, s. 394-397Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new concept of the formation of the monolayer of colloidal particles on the air-liquid interface based on a new simple model to consider the relation between the interparticle forces and the monolayer structures was proposed. Colloidal monolayers were formed by spreading monodisperse silica particles coated with alkyl chains of different length at the air-benzene interface and picking up the floating clusters or ordered domains with a mica substrate. Polycrystalline, two-dimensional monolayers was formed when the particles was coated with dodecane chains while coating with short alkane chains (butane, octane and decane) resulted in inhomogeneous, porous films. The difference in monolayer structure could be related to the interparticle forces and it was concluded that the formation of ordered colloidal monolayer required that the interparticle attraction is sufficiently weak allowing the formation of ordered domains which can deform during drying.

  • 131. Kull, T
    et al.
    Nylander, T
    Tiberg, F
    YKI – Ytkemiska institutet.
    Wahlgren, NM
    Effect of surface properties and added electrolyte on the structure of β-casein layers adsorbed at the solid/aqueous interface1997Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, s. 5141-5147Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption of -casein at hydrophobic and hydrophilic silica surfaces has been studied by time-resolved ellipsometry. Marked differences in, e.g., adsorption kinetics and plateau adsorption coverage, were observed on the two types of surfaces. The miscellaneous adsorption mechanisms at the two surfaces resulted in different structures of the adsorbed layers as evident from the thicknesses and protein densities measured on the two substrates as well as the effect on the adsorbed layer properties of a subsequently added specific proteolytic enzyme, endoproteinase Asp-N. At the hydrophobic surface, the adsorption is fast and the surface is saturated within a relatively short period. The addition of endoproteinase Asp-N reduces the surface excess and the thickness by 24 and 45%, respectively. This corresponds to cleavage at amino acid residues 43 and/or 47 in the hydrophilic portion of the protein. Adsorption from solutions containing added electrolyte leads to significant increase of the surface excess. However, no significant change was observed in the ellipsometric layer thickness. At constant ionic strength, the surface excess increased in the order NaCl < MgCl2 < CaCl2. From the experimental evidence, it was concluded that the adsorbed layer structure at the hydrophobic surface can be described as a monolayer with an inner dense region comprising the relatively large hydrophobic portions of the protein molecules and an outer region of the highly charged N-terminal portions protruding into the aqueous phase. The adsorption kinetics at the hydrophilic silica surface, although initially the same as on the hydrophobic surface, was found to be much slower and plateau surface excess values were not reached even after 2 h of adsorption. This suggests that substantial rearrangements of the protein molecules take place within the adsorbed layer during the adsorption process. Although the maximum surface excess at the hydrophilic surface of 4.3 mg m-2 is higher than the value of 2.8 mg m-2 measured at the hydrophobic surface, the thickness is slightly smaller, i.e., 60 Å and 66 Å, respectively. Hence, the protein adopt a more compact structure at the hydrophilic surface, at least in the inner part of the adsorbed layer. The different structure at the hydrophilic surface was confirmed by the larger reduction of the surface excess and layer thickness associated with the addition of endoproteinase Asp-N, leaving a very thin compact layer at the surface.

  • 132.
    Kumpulainen, AJ
    et al.
    YKI – Ytkemiska institutet.
    Persson, CM
    YKI – Ytkemiska institutet.
    Eriksson, JC
    YKI – Ytkemiska institutet.
    Tyrod, EC
    YKI – Ytkemiska institutet.
    Johnson, CM
    Soluble monolayers of n-decyl glucopyranoside and n-decyl maltopyranoside. Phase changes in the gaseous to the liquid-expanded range2005Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, s. 305-315Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To examine the transition from the gaseous to the liquid-expanded monolayer state, surface tension data were recorded for n-decyl beta-D-glucopyranoside (Glu) and n-decyl beta-D-maltopyranoside (Mal) solutions at low concentrations and at different temperatures. Comparisons were also made with n-decyl beta-D-thiomaltopyranoside (S-Mal) solutions at room temperature. The transitions observed occur at very low concentrations and surface pressures, about 0.5% of the critical micelle concentration (cmc) and between 0.8 and 1 mN/m for Glu and Mal at 22 degreesC. For S-Mal the transition is recorded for a concentration of 0.5% of the cmc as well, but the surface pressure is lower, about 0.4 mN/m. The gradual change in molecular area about the transition is from about 500 to 200 Angstrom(2) and 400 to 150 Angstrom(2) for Mal and Glu, respectively, and from about 800 to 250 Angstrom(2) for S-Mal. The comparatively large molecular areas after the transitions are incompatible with the notion that a coherent hydrocarbon film would cover the entire surface already at this stage. Standard surface thermodynamics was applied to elucidate the nature of these transitions in combination with two model concepts: The formation of an infinite network of surfactant molecules and, second, the formation of surface micelles. Hard-disk simulation results were employed to quantify the additional surface pressure after the transition attributed to the formation of surface micelles. In conclusion the formation of surface micelles is plausible as the hard-disk model is capable of accounting for the additional surface pressure increase with acceptable accuracy. Further, vibrational sum frequency spectroscopy was used to investigate the transition for Mal. Using the distinct feature of the non-hydrogen-bonded OH ("free OH") at 3700 cm(-1) for probing the surface water state, it could be determined that the surface holds a sizable fraction of unperturbed surface water even after the transition from the Henry range. The decrease in the free OH signal was found to correlate with the increase in surface density of surface micelles.

  • 133. Larson, I
    et al.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Qualitative adsorption measurements with an atomic force microscope1998Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, s. 5676-5679Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple method for the qualitative measurement of adsorption of solution species onto silicon nitride atomic force microscope cantilevers is presented. In this method, the change in resonant frequency of the cantilever, resulting from the added mass of the adsorbate, is measured as a function of time during the adsorption process. Results from the adsorption of copper(II) species and CTAB from aqueous solutions are presented. Cu(II) was seen to attain maximum coverage in a matter of minutes, while the adsorption of CTAB was beyond the resolution of the technique. Force measurements taken between the cantilever tip and a glass substrate during the adsorption process provide evidence that the change in cantilever frequency is a result of the adsorbate mass and is not just the result of any small viscosity differences.

  • 134. Le Berre, F
    et al.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Interfacial properties of a model polyampholyte studied by surface force measurements, ESCA, and ellipsometry2001Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, s. 699-704Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption of a model polyampholyte, i.e. [acryl amide]-[sodium 2-(acrylamido)-2-methylpropanesulfonate]-[2-(methacryloyloxy)-ethyltrimethyl-ammmonium chloride] ([AM]-[NaAMPS]-[MADQUAT]) at mica and silica surfaces was investigated by surface force measurements, electron spectroscopy for chemical analysis (ESCA), and ellipsometry. It was found that the adsorption isotherm of this polyampholyte on mica was of the high affinity type, yielding an adsorbed amount at saturation of 5.5 ± 0.5 mg/m2. From ellipsometry studies with silica, it was found that the adsorption was relatively fast, reaching saturation after about 1000 s on adsorption from a 20 ppm solution. From both ellipsometry and ESCA it was found that the effect of electrolyte on the adsorbed amount of pre-adsorbed polyampholyte is relatively minor at concentrations up to 10 mM. At higher electrolyte concentrations, however, some desorption of the polyampholyte occurs. Surface force measurements showed that the extension of the polymer layer normal to the mica surface was small compared to the radius of gyration of the polymer in bulk. Upon addition of electrolyte the adsorbed layer was found to contract.

  • 135. Liu, X
    et al.
    Dedinaite, Andra
    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.
    Thormann, E
    Visnevskij, C
    Makuska, R
    Electrostatically anchored branched brush layers2012Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 44, s. 15537-15547Artikel i tidskrift (Refereegranskat)
    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.

  • 136. Lundgren, SM
    et al.
    Persson, K
    YKI – Ytkemiska institutet.
    Mueller, G
    Kronberg, B
    YKI – Ytkemiska institutet.
    Clarke, J
    Chtaib, M
    Unsaturated fatty acids in alkane solutions: Adsorption to steel surfaces2007Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, s. 10598-10602Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption of the unsaturated fatty acids oleic, linoleic, and linolenic acid on steel surfaces has been investigated by means of a quartz crystal microbalance (QCM). Two different solvents were used, n-hexadecane and its highly branched isomer, viz., 2,2,4,4,6,8,8-heptamethylnonane. The area occupied per molecule of oleic acid at 1 wt % corresponds to what is needed for adsorption parallel to the surface. At the same concentration, the adsorbed amount of linoleic acid and linolenic acid indicates that they adsorb in multilayers. The chemisorbed amount estimated from static secondary ion mass spectroscopy (SIMS) measurements was found to be similar for the three unsaturated fatty acids. In the case of linolenic acid, it was found that the presence of water significantly alters the adsorption, most likely because of the precipitation of fatty acid/water aggregates. Furthermore, static SIMS results indicate that the amount of water used here inhibits the chemisorption of linolenic acid.

  • 137. Lundin, M
    et al.
    Macakova, L
    YKI – Ytkemiska institutet.
    Dedinaite, A
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Interactions between chitosan and SDS at a low charged silica substrate compared to interactions in the bulk. The effect of ionic strength2008Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 8, s. 3814-3827Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of ionic strength on association between the cationic polysaccharide chitosan and the anionic surfactant sodium dodecyl sulfate, SDS, has been studied in bulk solution and at the solid/liquid interface. Bulk association was probed by turbidity, electrophoretic mobility, and surface tension measurements. The critical aggregation concentration, cac, and the saturation binding of surfactants were estimated from surface tension data. The number of associated SDS molecules per chitosan segment exceeded one at both salt concentrations. As a result, a net charge reversal of the polymer-surfactant complexes was observed, between 1.0 and 1.5 mM SDS, independent of ionic strength. Phase separation occurs in the SDS concentration region where low charge density complexes form, whereas at high surfactant concentrations (up to several multiples of cmc SDS) soluble aggregates are formed. Ellipsometry and QCM-D were employed to follow adsorption of chitosan onto low-charged silica substrates, and the interactions between SDS and preadsorbed chitosan layers. A thin (0.5 nm) and rigid chitosan layer was formed when adsorbed from a 0.1 mM NaNO3 solution, whereas thicker (2 nm) chitosan layers with higher dissipation/unit mass were formed from solutions at and above 30 mM NaNO3. The fraction of solvent in the chitosan layers was high independent of the layer thickness and rigidity and ionic strength. In 30 mM NaNO3 solution, addition of SDS induced a collapse at low concentrations, while at higher SDS concentrations the viscoelastic character of the layer was recovered. Maximum adsorbed mass (chitosan + SDS) was reached at 0.8 times the cmc of SDS, after which surfactant-induced polymer desorption occurred. In 0.1 mM NaNO3, the initial collapse was negligible and further addition of surfactant lead to the formation of a nonrigid, viscoelastic polymer layer until desorption began above a surfactant concentration of 0.4 times the cmc of SDS

  • 138. Lundin, Maria
    et al.
    Blomberg, Eva
    YKI – Ytkemiska institutet.
    Tilton, Robert D
    Polymer dynamics in layer-by-layer assemblies of Chitosan and Heparin2010Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 5, s. 3242-3251Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The layer-by-layer deposition method has been used to build a multilayer thin film with two polysaccharides, chitosan CH(weak polycation) and heparin HEP (strong polyanion), on planar quartz surfaces. The film structure and dynamics in aqueous solution were studied with fluorescence resonance energy transfer (FRET) and total internal reflection fluorescence (TIRF). Particular emphasis was placed on the effect of deposition conditions, i.e., pH and salt concentration, on the out-of-plane (vertical) diffusion of fluorescence labeled chitosan in the chitosan/heparin (CH/HEP) film. FRET analysis showed that CH molecules diffused within the film with a diffusion coefficient that was not significantly sensitive to the deposition pH and solution ionic strength. A pH-sensitive label bound to CH embedded within the CH/HEP film was sensitive to the charge of the outermost polymer layer even when buried under 14 alternate layers of CH and HEP. A consideration of the results obtained with both fluorescence techniques showed that the structure of the CH/HEP thin film was highly interpenetrated without clear boundaries between each layer. These results are consistent with the hypothesis that the previously observed exponential-like film growth of CH and HEP in terms of layer thickness and deposited amount versus deposition cycle can be attributed to out-of-plane diffusion of CH molecules in the multilayer.

  • 139.
    Lundin, Maria
    et al.
    YKI – Ytkemiska institutet.
    Solaqa, Faten
    Thormann, Esben
    Macakova, Lubica
    YKI – Ytkemiska institutet.
    Blomberg, Eva
    YKI – Ytkemiska institutet.
    Layer-by-layer assemblies of chitosan and heparin: effect of ionic strength and pH2011Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 12, s. 7537-7548Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The growth of polysaccharide multilayers consisting of positively charged chitosan (CH) and negatively charged heparin (HEP) was monitored in situ by employing a quartz crystal microbalance (QCM-D) and dual-polarization interferometry (DPI). The main focus was on how the physicochemical properties of the solution affect the growth and structure of the resulting multilayer film These results showed that when increasing the ionic strength of the polysaccharide solutions at a fixed pH, both the "dry" (optical) (DPI) mass and wet (QCM) mass of the adsorbed multilayer film increased. The same effect was found when increasing the pH while keeping the ionic strength constant. Furthermore, the growth of multilayers showed an exponential-like behavior independent of the solution conditions that were used in this study. It was also established that chitosan was the predominant species present in the chitosan heparin multilayer film. We discuss the viscoelastic properties of the adsorbed layers and their variation during the multilayer buildup. Interestingly and contrary to common interpretation of the QCM-D results, we found that under one particular solution condition (pH 4.2 and 30 mM NaCl) the increase in the dissipation of oscillation energy from the adsorbed layer was a consequence of layer stiffening rather than indicating a more hydrated and viscous film. On the basis of the widely used Voigt viscoelastic model for an adsorbed layer, we show that it is the film viscosity and shear that define the layer viscoelasticity (structure) of the film and not the absolute value of energy dissipation, which in fact can be very misleading.

  • 140.
    Löwenhielm, Peter
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Medicinteknik.
    Templating gold surfaces with function: A self-assembled dendritic monolayer methodology based on monodisperse polyester scaffolds2013Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, nr 1, s. 456-465Artikel i tidskrift (Refereegranskat)
  • 141.
    Macakova, L
    et al.
    YKI – Ytkemiska institutet.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Effect of adsorbed layer surface roughness on the QCM-D response: Focus on trapped water2007Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, s. 12436-12444Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of surface roughness on the quartz crystal microbalance with dissipation monitoring (QCM-D) response was investigated with emphasis on determining the amount of trapped water. Surfaces with different nanoroughnesses were prepared on silica by self-assembly of cationic surfactants with different packing parameters. We used surfactants with quaternary ammonium bromide headgroups: the double-chained didodecyltrimethylammonium bromide (C12)2- DAB (DDAB), the single-chained hexadecyltrimethylammonium bromide C16TAB (CTAB), and dodecyltrimethylammonium bromide C12TAB (DTAB). The amount of trapped water was obtained from the difference between the mass sensed by QCM-D and the adsorbed amount detected by optical reflectometry. The amount of water, which is sensed by QCM-D, was found to increase with the nanoroughness of the adsorbed layer. The water sensed by QCM-D cannot be assigned primarily to hydration water, because it differs substantially for adsorbed surfactant layers with similar headgroups but with different nanoscale topographies.

  • 142.
    Macakova, L
    et al.
    YKI – Ytkemiska institutet.
    Nordstierna, L
    Karlsson, G
    Blomberg, E
    YKI – Ytkemiska institutet.
    Furó, I
    Lack of association between a cationic protein and a cationic fluorosurfactant2007Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, nr 2, s. 771-775Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface tension, 19F and 1H NMR spectroscopy, and cryotransmission electron microscopy are used to characterize the state of association in aqueous solutions of a fluorosurfactant CF3(CF2)nSO2NH(CH2)3-4N(CH3)3 +I- (n ) 8, 6) with and without lysozyme added. In the absence of lysozyme, we find monomers, small aggregates, and large vesicles to coexist, with the individual fluorosurfactant molecules exchanging slowly (>1 ms) among those states. When both lysozyme and fluorosurfactant are present in the solution, they have no measurable influence on the physical state of the other. In contrast, a hydrogenated cationic surfactant with the same headgroup, hexadecyltrimethylammonium bromide, is shown to associate to lysozyme.

  • 143. Malmsten, A
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Temperature-dependent adsorption and surface forces in aqueous ethyl(hydroxyethyl)cellulose solutions1991Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 7, s. 988-994Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Forces between hydrophobized mica surfaces across an aqueous solution of ethyl(hydroxyethyl)cellulose (EHEC) have been studied, inter alia, as a function of surface separation and temperature. EHEC adsorbs strongly to hydrophobic surfaces in a rather flat conformation. The force is reversible on approach and separation up to a temperature of about 40°C. As the temperature was increased from 20°C to 37°C, which is slightly above the cloud point (CP=35°C), the adsorbed amount increased by a factor of three. The force remained monotonically repulsive, despite the fact that the temperature was higher than CP. On increasing the temperature further, the adsorbed amount, as well as the thickness of the adsorbed layer (at a high compressional force), remains essentially unchanged. However, due to the decreased solvency, there is a contraction of the outer part of the adsorbed layer. The force was essentially repulsive at 41°C, with only a very weak attraction observed on separating the surfaces. At 52°C, a weak attraction was observed on both approach and separation, as would be expected in a significantly worse than q-solvent. As the temperature was decreased again, the adsorbed amount as well as the compressed adsorbed layer thickness decreased. The adsorbed amount was the same (within experimental uncertainty) after heating as before. However, the force curve was shifted outwards after heating as compared to the situation before heating. Hence, the temperature dependence of the adsorption, in the absence of constraints on the adsorbed amount, is not completely reversible, at least over the incubation time used (12 h).

  • 144.
    Malmsten, M
    et al.
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Siegel, G
    Forces between proteoheparan sulfate layers adsorbed at hydrophobic surfaces1994Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 10, s. 1274-1280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The forces between proteoheparan sulphate layers adsorbed at hydrophobic surfaces were investigated by direct surface force measurements. In 0.2 mg/ml proteoheparan sulphate and 0.1 mM NaCl, the forces were monotonically repulsive, with one distant regime having a decay length of about 180 Å, and one steeply repulsive proximal part at distances smaller than about 100 Å. Only small effects were observed on dilution with 0.1 mM NaCl, indicating ”irreversible” adsorption. The decay length of the distant force component was 280 Å after dilution, whereas the proximal repulsive component remained unchanged. Furthermore, after dilution, a weak adhesion (F/R = 200 mN/m) was observed. At addition of CaCl2, the decay length of the distant repulsion decreased from 280 Å in 0.1 mM NaCl to 86 Å and 77 Å in 1.25 and 2.5 mM CaCl2, respectively. The deacay-lenghts in CaCl2 solutions are significantly larger than the expected Debye-lengths, demonstrating the predominance of steric forces. Furthermore, on addition of CaCl2 the magnitude of the adhesion increased from 200 mN/m to 1000 mN/m, and the proximal repulsion was observed at slightly smaller distances. It was found that both steric and electrostatic forces contribute to the interactions between proteoheparan sulphate layers

  • 145.
    Malmsten, M
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Pezron, E
    Pezron, I
    Temperature dependent forces between hydrophobic surfaces coated with ethyl(hydroxyethyl)cellulose1990Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 6, s. 1572-1578Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The forces acting between hydrophobic surfaces coated with a layer of noniomic polymer, ethyl-(hydroxyethyl)cellulose (EHEC), were studied inter alia as a function of surface separation and temperature. EHEC adsorbs strongly at hydrophobic surfaces, and the force measurements were performed with a constant adsorbed amount. The force vs distance curves were reversible; i.e., the same forces were measured on approach and separation. The surface interaction is very sensitive to temperature. At room temperature, the forces are purely repulsive. At 44°C (5°C above the cloud point), the force curve remains monotonically repulsive but less long-range. Hence, the EHEC layer contracts due to the poor solvency at this temperature. The fact that no attraction is observed despite that the temperature is above the cloud point is rationalized by considering that the most hydrophilic segements are oriented toward the bulk solution. Consequenyly, the local χ-parameter for the stabilizing moieties is, for this chemically hetereogeneous polymer, different from the average χ-parameter. However, an elastic repulsion, due to the loss of conformational entropy, als contributes significantly to the repulsive force at this temperature. At an even higher temperature (55°C), a strong, but rather short-range, attractive force was observed. The temperature dependence of the force curves was found to be completely reversible at the incubation times used (approximately 15 h).

  • 146. Manev, ED
    et al.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Diffuse layer electrostatic potential and stability of thin aqueous films containing a nonionic surfactant1991Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 7, s. 2253-2260Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption of a hydrolyzable surfactant, dodecylammonium chloride, and interactions between layers thereof, has been studied at a surfactant concentration of 10-4 M as a function of pH using the surface force apparatus. At low pH the surfaces undergo charge reversal as dodecylammonium ions adsorb to form a sparse monolayer. At pH 8-9, adsorption of neutral dodecylamine molecules becomes important, rendering the monolayer more compact with a thickness close to the length of an extended molecule. A hydrophobic attraction is observed between the surfactant monolayers. At pH 9.5-10.3, a bilayer forms on each surface. The double layer force decreases gradually with incrasing pH and disappears at pH 10.3. At this and slightly higher pH values a multilayer gradually builds up on the surface. At pH values around 12 the multilayer buildup is prevented by a recharging of the adsorbed layer. Both the adsorption behavior and the interactions between the layers are reversible with respect to changes in the pH. The structure of the adsorbed surfactant layer on mica is compared to that on other surfaces.

  • 147. Matsson, MK
    et al.
    Kronberg, B
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Adsorption of alkyl polyglucosides on the solid/water interface: Equilibrium effects of alkyl chain length and head group polymerization2004Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, s. 4051-4058Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The equilibrium adsorption behavior of two n-alkyl-b-D-glucosides (octyl, C8G1 and decyl, C10G1) and four n-alkyl-β-D-maltosides (octyl, C8G2, decyl, C10G2, dodecyl, C12G2 and tetradecyl, C14G2) from aqueous solution on a titania surface, as measured by ellipsometry, has been investigated. The main focus has been on the effect of changes in the alkyl chain length and head group polymerization, but a comparison with their adsorption on the silica/water and air/water interface is also presented. Some comparison with the corresponding adsorption of ethylene oxide surfactants, in particular C10E6 and C12E6 is given as well. For all alkyl polyglucosides, the maximum adsorbed amount on titania is reached slightly below cmc where it levels off to a plateau and the amount adsorbed corresponds roughly to a bilayer. However, there is no evidence that this is the actual conformation of the surfactant assemblies on the surface, but the surfactants could also be arranged in a micellar network. On hydrophilic silica, the adsorbed amount is a magnitude lower than on titania, corresponding roughly to a layer of surfactants lying flat on the surface. A change in the alkyl chain length does not result in any change in the plateau molar adsorbed amount at equilibrium, however the isotherm slope for the alkyl maltosides increases with increasing chain length. Head group polymerization on the other hand affects the adsorbed amount. The alkyl glucosides start adsorbing at lower bulk concentrations than the maltosides and equilibrate at higher adsorbed amounts above cmc. When compared with the ethylene oxide surfactants, it is confirmed that the EO-surfactants hardly adsorb on titania, since the measured changes in the ellipsometric angles are within the noise level. They do, however, adsorb strongly on silica

  • 148. Matsson, MK
    et al.
    Kronberg, B
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Enhanced adsorption of alkyl glucosides on the silica/water interface by addition of amine oxides2005Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, s. 2766-2772Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of adding a small amount of dodecyl dimethyl amine oxide (DDAO) on adsorption on silica from an aqueous solution of dodecyl maltoside (C12G2) has been investigated. The C12G2 itself does not adsorb significantly on silica at any concentration. DDAO on the other hand readily adsorbs in a bilayer-like structure at concentrations approaching cmc, but the adsorbed amount at the concentrations it has been applied in these mixtures is small. In contrast, by combining the two surfactants significant adsorption is observed at concentrations where the adsorption of the pure DDAO, as well as pure C12G2, is very low. We thus see a strong enhancement of the adsorption from the mixed system. The adsorption is suggested to be a two-step process, where individual DDAO molecules first adsorb to the silica surface through electrostatic interactions, and then C12G2 adsorbs at the hydrophobic sites the DDAO tails constitute through hydrophobic bonding. A minimum concentration of DDAO is required to induce adsorption from a solution with constant C12G2 concentration. This concentration is lower for C12G2 solutions below and equal to cmc than above cmc. In addition, the total adsorbed amount shows a maximum around cmc of the mixture for a solution with low DDAO contents. Both these effects are explained by incorporation of DDAO in the C12G2 micelles above cmc, which leads to a desorption of DDAO from the surface.

  • 149. Mays, H
    et al.
    Almgren, M
    Dedinaite, A
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Spontaneous formation of reverse vesicles with soybean phosphatidyl ethanolamine in mixture with triglyceride and some water1999Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, s. 8072-8079Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mixing the phospholipid soybean phosphatidyl ethanolamine (PE) with the triglyceride triolein and a trace amount of water leads to a spontaneous formation of isotropic aggregates. Evidence for the existence of such aggregates in pseudo-three-component systems is presented here for the first time. Dynamic light scattering and cryogenic temperature transmission electron microscopy reveal polydisperse spherical particles with radii in the range of 250-840 nm and a mean radius of the order 600 nm. From the results of both depolarized light scattering and time-resolved electro-optical birefringence (Kerr effect) the presence of aggregates with an optical anisotropy (rodlike or wormlike reverse micelles as well as particles with lamellar structure) can be excluded. The remaining possibilities are reverse vesicles and a dispersed cubic bicontinuous phase, where our results favor reverse vesicles. A necessary condition for the formation of reverse vesicles is a saturation of the PE-triolein mixture with water; at lower water content the particles are significantly smaller.

  • 150. Meurk, A
    et al.
    Luckham, PF
    Bergström, L
    YKI – Ytkemiska institutet.
    Direct measurement of repulsive and attractive van der Waals forces between inorganic materials1997Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, s. 3896-3899Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The repulsive and attractive interactions between silicon nitride and silica across diiodomethane and 1-bromonaphtalene were measured using an atomic force microscope (AFM). By combining measuremnets of asymmetric (silicon nitride versus silica) and symmetric (silicon nitride versus silicon nitride) material combinations in these solvents, a thorough analysis of the nature of the observed force curves was enabled. The sign, magnitude and separation distance scaling of the interactions could be well described with a van der Waals interaction between a flat surface and a sphere using calculated Hamaker constants from Lifshitz theory.

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