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  • 201. Shovsky, A
    et al.
    Varga, I
    Makuška, R
    Claesson, Per M
    YKI – Ytkemiska institutet.
    Adsorption and solution properties of bottle-brush polyelectrolyte complexes: Effect of molecular weight and stoichiometry2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 16, p. 6618-6631Article in journal (Refereed)
    Abstract [en]

    Polyelectrolyte complexes (PECs) self-assembled from bottle-brush polyelectrolytes, having a cationic main chain and uncharged side chains, and linear anionic sodium polystyrenesulfonate (NaPSS) have been investigated with emphasis on (i) the charge density and side chain density of the bottle-brush polyelectrolyte, (ii) the molecular weight of NaPSS, and (iii) the charge stoichiometry of the mixture. Light scattering and electrophoretic mobility data demonstrate that small molecular complexes are formed when the PEO 45 side chain density is sufficiently high to provide steric stabilization and prevent PEC aggregation. The adsorption of PECs on negatively charged silicon oxynitride was investigated using dual polarization interferometry, and the time evolution of the adsorbed amount and thickness was determined. Cationic, uncharged, and negatively charged complexes all adsorb to negatively charged silicon oxynitride, and maximum adsorption is achieved for positively charged complexes containing small amounts of PSS. The adsorbed amount and the kinetics of adsorption are reduced with increasing PSS content, and for any given stoichiometry with increasing PSS molecular weight. These findings are discussed in terms of the PEC structure and the ability of anionic polyelectrolytes to leave the PECs during adsorption.

  • 202. Shovsky, Alexander
    et al.
    Bijelic, Goran
    Imre, Varga
    Makuska, Ricardas
    Claesson, Per M
    YKI – Ytkemiska institutet.
    Adsorption characteristics of stoichiometric and nonstoichiometric molecular polyelectrolyte complexes on silicon oxynitride surfaces2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 3, p. 1044-1050Article in journal (Refereed)
    Abstract [en]

    Adsorption properties of stoichiometric and nonstoichiometric polyelectrolyte complexes (PECs) have been investigated by means of dual polarization interferometry (DPI) and X-ray photoelectron spectroscopy (XPS). Poly(sodium styrenesulfonate) (NaPSS) of molecular weight 4300 g/mol was used as polyanion, and two bottle-brush copolymers possessing different molar ratios of the cationic segment methacryloxyethyltrimethylammonium chloride (METAC) and the nonionic segment poly(ethylene oxide) methyl ether methacrylate (PEO(45)MEMA) were used as polycations. They are referred to as PEO(45)MEMA:METAC-25 and PEO(45)MEMA:METAC-50, where the last digits denote the mol % of charged main-chain segments. The time evolution of the adsorbed amount, thickness, and refractive index of the PEC layers were determined in aqueous solution using DPI. We demonstrate that cationic, uncharged, and negatively charged complexes adsorb to negatively charged silicon oxynitride and that maximum adsorption is achieved when small amounts of PSS are present in the complexes. The surface composition of the adsorbed PEC layers was estimated from XPS measurements that demonstrated very low content of NaPSS. On the basis of these data, the PEC adsorption mechanism is discussed and the competition between PSS and negative surface sites for association with the cationic polyelectrolyte is identified as a key issue.

  • 203. Shovsky, AV
    et al.
    Varga, I
    Makuska, R
    Claesson, PM
    YKI – Ytkemiska institutet.
    Formation and stability of water-soluble, molecular polyelectrolyte complexes: Effects of charge density, mixing ratio, and polyelectrolyte concentration2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 11, p. 6113-6121Article in journal (Refereed)
    Abstract [en]

    The formation of complexes with stoichiometric (1:1) as well as nonstoichiometric (2:1) and (1:2) compositions between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights is reported in this contribution. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion, and a range of copolymers with various molar ratios of the poly(methacryloxyethyltrimethylammonium) chloride, poly(METAC), and the nonionic poly(ethylene oxide) ether methacrylate, poly(PEO45MEMA), were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity, and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration, charge density of the cationic polyelectrolyte, and mixing ratio. The data obtained demonstrate that in the absence of PEO45 side chains the 100% charged polymer (polyMETAC) formed insoluble PECs with PSS that precipitate from solution when exact stoichiometry is achieved. In nonstoichiometric complexes (1:2) and (2:1) large colloidally stable aggregates were formed. The presence of even a relatively small amount of PEO45 side chains (25%) in the cationic copolymer was sufficient for preventing precipitation of the formed stoichiometric and nonstoichiometric complexes. These PECs are sterically stabilized by the PEO45 chains. By further increasing the PEO45 side-chain content (50 and 75%) of the cationic copolymer, small, water-soluble molecular complexes could be formed. The data suggest that PSS molecules and the charged backbone of the cationic brush form a compact core, and with sufficiently high PEO45 chain density (above 25%) molecular complexes are formed that are stable over prolonged times.

  • 204.
    Sierra, ML
    et al.
    YKI – Ytkemiska institutet.
    Svensson, M
    YKI – Ytkemiska institutet.
    Mixed micelles containing alkylglycosides: Effect of the chain length and the polar head group1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 2301-2306Article in journal (Refereed)
    Abstract [en]

    The mixing behavior of binary mixtures of the pure alkylglycosides: -decylglucoside (-C10G), -dodecylglucoside (-C12G), -decylmaltoside (-C10M), and dodecylmaltoside (C12M) in combination with different common surfactants has been studied. First, the effect of the nonionic polar headgroup and chain length of the glycosidic surfactants in the mixed micellization with sodium dodecyl sulfate (SDS) was investigated. Further on, to analyze the effect of the ionic headgroup on the micellization of the glycosidic surfactant, -C10G was mixed with different surfactants: dodecyltrimethylammonium bromide (DTAB), dodecylheptaethylene glycol ether (C12E7), and -C10M. All the mixed systems under study adapt reasonably well to the model developed by Rubingh, with negative values for the interaction parameter, m, indicating a favorable interaction between the mixed surfactants. In the mixtures with SDS and the glycosides, the interactions become stronger when the hydrocarbon chain length of the surfactant is shorter and the hydrophilic headgroup is larger, i.e., when the surfactants become more hydrophilic. The -C10G mixes favorably with the other surfactants, the interaction becoming stronger in the order C12E7, -C10M, SDS, DTAB. The strong interaction in micellization with DTAB is explained by assuming an anionic character in the -C10G molecule, as shown by electroosmosis measurements. Finally, the favorable interaction with -C10M is explained by considering the packing between the headgroups of both nonionic surfactants.

  • 205.
    Silvander, M
    et al.
    YKI – Ytkemiska institutet.
    Hansson, P
    Edwards, K
    Liposomal surface potential and bilayer packing as affected by PEG-lipid inclusion2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 3696-3702Article in journal (Refereed)
    Abstract [en]

    The surface potentials and the packing properties of phospholipid liposomes containing anionic lipids with covalently attached poly(ethylene glycol) polymers (PEG(2000)-PE) were investigated. The negative surface potential induced by the PEG-lipid in EPC/cholesterol and SPC/cholesterol liposomes was determined by means of titration of the fluorescent probe 4-heptadecyl-7-hydroxycoumarin (HC). The shift in the apparent pK of the probe corresponds to an induced potential of -13 mV for 5 mol % PEG-lipid in the phospholipid/cholesterol (ionic strength = 150 mM). For EPC liposomes without cholesterol, 5 mol % PEG-lipid did not cause any detectable shift in the pK of the probe. This indicates that the EPC liposome surface in fact carries a net negative charge. The above results were supported by determinations of the potential. The packing order of the outer and inner parts of the phospholipid/cholesterol bilayer membranes was investigated by fluorescence depolarization anisotropy of the probes HC and 1,6-diphenyl-1,3,5-hexatriene (DPH). The PEG-lipid inclusion caused an increase in the anisotropy of HC, located at the water/hydrocarbon interface. In addition, a small increase in anisotropy was observed for DPH upon PEG-lipid inclusion. Since DPH is situated in the hydrocarbon region, these data together with the HC data indicate that the PEG-lipids impose restrictions on the molecular motion in the outer as well as the inner parts of the hydrocarbon region.

  • 206.
    Sjöberg, M
    et al.
    YKI – Ytkemiska institutet.
    Henriksson, U
    Wärnheim, T
    YKI – Ytkemiska institutet.
    2H Nuclear magnetic relaxation of 1.1-2H hexadecyltrimethylammonium bromide in micellar solutions of nonaqueous polar solvents and their mixtures with water1990In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 6, p. 1205-1211Article in journal (Refereed)
    Abstract [en]

    The 2H spin-lattice and spin-spin nuclear magnetic relaxtion rates were measured at different frequencies for α-deuterated hexadecyltrimethylammonium bromide in micellar solutions of nonaqueous and mixed solvent systems. Three nonaqueous polar solvents, viz., formamide, ethylene glycol, and N-methylformamide, and their mixtures with water were used. The two-step model for magnetic relaxation of surfactant aggregates was fitted to the frequency-dependent relaxation rates for the surfactant, yielding a local order parameter and correlation times for a fast local motion and for a slow aggregate motion. The measurements show that the surfactant aggregates in formamide, ethylene glycol, and their mixtures with water. No aggregation occurs in N-methylformamide at water contents lower than 50 wt%. Approximate aggregate radii, obtained from the slow correlation times, show that the aggregates formed in formamide and in ethylene glycol are smaller than in water. The local order parameter, obtained from the relaxation measurements as well as from the quadrupolar splittings in the hexagonal phases, increases with increasing water content both in the formamide and in the ethylene glycol systems.

  • 207.
    Sjöberg, M
    et al.
    YKI – Ytkemiska institutet.
    Jansson, M
    YKI – Ytkemiska institutet.
    Henriksson, U
    A comparison of the counterion binding to ionic micelles in aqueous and nonaqueous systems1992In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 8, p. 409-413Article in journal (Refereed)
    Abstract [en]

    The counterion binding to hexadecyltrimethylammonium fluoride (C16TAF) micelles in three different solvents; water, formamide and ethylene glycol, has been studied both experimentally and theoretically. Self-diffusion measurements by NMR spectroscopy was used as the experimental technique, and the counterion binding was determined for surfactant concentrations up to 20 wt%. The degree of counterion binding was found to be very different in the three solvents; high in water and ethylene glycol but much lower in formamide, with an increase with concentration in the latter system. The Poisson-Boltzman equation was used to calculate how the aggregation number and the dielectrical constant of the solvent affect the counterion binding. A comparison between experimental and calculated values of degrees of counterion binding indicates that the micelles are significally smaller in the non-aqueous systems. The concentration dependence of the counterion binding in formamide was explained as aggregate growth with increasing surfactant concentration.

  • 208. Sjöberg, M
    et al.
    Silveston, R
    Kronberg, B
    YKI – Ytkemiska institutet.
    A thermodynamic study of the solvophobic effect in formamide solutions of nonpolar molecules1993In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 9, p. 973-979Article in journal (Refereed)
    Abstract [en]

    The thermodynamics associated with the solvophobic effect in solutions of nonpolar molecules in formamide were esamined using high performance liquid chromatography (HPLC). The transfer of a serie of alkylbenzenes from forma mide to hydrocarbon environ ment was studied in the temperature range S80 °C in order to obtain the molar free energy, entropy, and enthalpy of transfer. The HPLC system consisted of poly(dimethylsilosane), PDMS, coated glass beads as the stationary phase and formamide as the mobile phase. The free energy and the enthalpy of transfer were found to be negative, while the entropy of transfer was positive. In general, the thermodynamic transfer quantities for formamide are both smaller in magnitude and les s tempe rature depe n de nt than those previou sly dete rm ined with water as the mobile phase. The relatively small ZxCp of transfer in the case of formamide indicates that there is negligible structuring of the formamide molecules around the nonpolar molecules, in contrast to the water case. The positive entropy of transfer in the case of formamide is attributed to comples formation between the alkylbenzenes and formamide. The driving force for the solvophobic effect seems to arise from the same source as the hydrophobic effect, namely the large cohesive energy of the solvent. This interpretation was used to explain differences in surfactant aggregation in formamide and water.

  • 209. Sonesson, AW
    et al.
    Brismar, H
    Callisen, TH
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Mobility of Thermomyces lanuginosus lipase on a trimyristin substrate surface2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 5, p. 2706-2713Article in journal (Refereed)
    Abstract [en]

    We have studied the mobility of active and inactive Thermomyces lanuginosus lipase (TLL) on a spin-coated trimyristin substrate surface using fluorescence recovery after photobleaching (FRAP) in a confocal microscopy setup. By photobleaching a circular spot of fluorescently labeled TLL adsorbed on a smooth trimyristin surface, both the diffusion coefficient D and the mobile fraction f could be quantified. FRAP was performed on surfaces with different surface density of lipase and as a function of time after adsorption. The data showed that the mobility of TLL was significantly higher on the trimyristin substrate surfaces compared to our previous studies on hydrophobic model surfaces. For both lipase variants, the diffusion decreased to similar rates at high relative surface density of lipase, suggesting that crowding effects are dominant with higher adsorbed amount of lipase. However, the diffusion coefficient at extrapolated infinite surface dilution, D0 , was higher for the active TLL compared to the inactive (D0 = 17.9 x10-11 cm2/s vs D0 = 4.1 x10-11 cm2/s, data for the first time interval after adsorption). Moreover, the diffusion decreased with time after adsorption, most evident for the active TLL. We explain the results by product inhibition, i.e., that the accumulation of negatively charged fatty acid products decreased the diffusion rate of active lipases with time. This was supported by sequential adsorption experiments, where the adsorbed amount under flow conditions was studied as a function of time after adsorption. A second injection of lipase led to a significantly lower increase in adsorbed amount when the trimyristin surface was pretreated with active TLL compared to pretreatment of inactive TLL.

  • 210. Sonesson, AW
    et al.
    Callisen, TH
    Brismar, H
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Lipase surface diffusion studied by fluoroscence recovery after photobleaching2005In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, p. 11949-11956Article in journal (Refereed)
    Abstract [en]

    A Fluorescence Recovery after Photobleaching (FRAP) method to study protein diffusion on solid surfaces was developed using confocal microscopy. By photobleaching a rectangular area of the sample, fluorescence recovery could be analyzed as one-dimensional diffusion, leading to s simplified mathematical expressions for fitting the data. The method was tested by measuring bovine serum albumin (BSA) diffusion on glass, which led to a diffusion coefficient in good correspondence to earlier reports. Furthermore, the method was used to analyze the diffusion of a variant of Thermomyces lanuginosa lipase (TLL) on hydrophilic silica and silica methylated with dichlorodimethylsilane (DDS) or octadecyltrichlorosilane (OTS). Using ellipsometry data of TLL adsorption, fluorescence intensity could be calibrated to surface density of lipase, enabling measurements of the diffusion coefficient at different surface densities. The average diffusion coefficient was calculated in two time intervals after adsorption. Mobile fraction and diffusion coefficient was lowest on the OTS-surface, when extrapolated to infinite surface dilution. Moreover, the diffusion rate decreased with time on the hydrophobic surfaces. Our observations can be explained by the surface dependence on the distribution of orientations and conformations of adsorbed TLL, where the transition from the closed to the catalytically active open and more hydrophobic structure is important

  • 211. Sonesson, AW
    et al.
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Brismar, H
    Callisen, TH
    Adsorption and mobility of a lipase at a hydrophobic surface in the presence of surfactants2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, p. 5810-5817Article in journal (Refereed)
    Abstract [en]

    With the aim of being able to manipulate the processes involved in interfacial catalysis, we have studied the effects of a mixture of nonionic/anionic surfactants, C12E6/LAS (1:2 mol %), on the adsorption and surface mobility of a lipase obtained from Thermomyces lanuginosus (TLL). Surface plasmon resonance (SPR) and ellipsometry were used to analyze the competitive adsorption process between surfactants and TLL onto hydrophobic model surfaces intended to mimic an oily substrate for the lipase. We obtained the surface diffusion coefficient of a fluorescently labeled TLL variant on silica silanized with octadecyltrichlorosilane (OTS) by fluorescence recovery after photobleaching (FRAP) on a confocal laser scanning microscope. By means of ellipsometry we calibrated the fluorescence intensity with the surface density of the lipase. The TLL diffusion was measured at different surface densities of the enzyme and at two time intervals after coadsorption with different concentrations of C12E6/LAS. The surfactant concentrations were chosen to represent concentrations below the critical micelle concentration (CMC), in the CMC region, and above the CMC. The apparent TLL surface diffusion was extrapolated to infinite surface dilution, D0. We found that the presence of surfactants strongly modulated the surface mobility of TLL: with D0 = 0.8 x 10-11 cm2/s without surfactants and D0 = 13.1 x 10-11 cm2/s with surfactants above the CMC. The increase in lipase mobility on passing the CMC was also accompanied by a 2-fold increase in the mobile fraction of TLL. SPR analysis revealed that surface bound TLL was displaced by C12E6/LAS in a concentration-dependent manner, suggesting that the observed increase in surface mobility imparts bulk-mediated diffusion and so-called rebinding of TLL to the surface. Our combined results on lipase/surfactant competitive adsorption and lipase surface mobility show how surfactants may play an important role in regulating interfacial catalysis from physiological digestion to technical applications such as detergency.

  • 212. Sonesson, AW
    et al.
    Elofsson, UM
    YKI – Ytkemiska institutet.
    Callisen, TH
    Brismar, H
    Tracking single lipase molecules on a trimyristin substrate surface using quantum dots2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 16, p. 8352-8356Article in journal (Refereed)
    Abstract [en]

    : The mobility of single lipase molecules has been analyzed using single molecule tracking on a trimyristin substrate surface. This was achieved by conjugating lipases to quantum dots and imaging on spin-coated trimyristin surfaces by means of confocal laser scanning microscopy. Image series of single lipase molecules were collected, and the diffusion coefficient was quantified by analyzing the mean square displacement of the calculated trajectories. During no-flow conditions, the lipase diffusion coefficient was (8.0 +/- 5.0) x 10(-10) cm(2)/s. The trajectories had a "bead on a string" appearance, with the lipase molecule restricted in certain regions of the surface and then migrating to another region where the restricted diffusion continued. This gave rise to clusters in the trajectories. When a flow was applied to the system, the total distance and average step length between the clusters increased, but the restricted diffusion in the cluster regions was unaffected. This can be explained by the lipase operating in two different modes on the surface. In the cluster regions, the lipase is likely oriented with the active site toward the surface and hydrolyzes the substrate. Between these regions, a diffusion process is proposed where the lipase is in contact with the surface but affected by the external flow

  • 213. Stiernstedt, J
    et al.
    Fröberg, JC
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Rutland, MW
    Forces between silica surfaces with adsorbed cationic surfactants: Influence of salt and added nonionic surfactants2005In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, p. 1875-1883Article in journal (Refereed)
    Abstract [en]

    Forces have been measured between silica surfaces with adsorbed surfactants by means of a bimorph surface force apparatus. The surfactants used are the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the nonionic surfactant hexakis(ethylene glycol) mono-n-tetradecyl ether (C14E6) as well as mixtures of these two surfactants. The measurements were made at elevated pH, and the effect of salt was studied. At high pH the glass surface is highly charged, which increases the adsorption of TTAB. Despite the low adsorption generally seen for nonionic surfactants on silica at high pH, addition of C14E6 has a considerable effect on the surface forces between two glass surfaces in a TTAB solution. The barrier force is hardly affected, but the adhesion is reduced remarkably. Also, addition of salt decreases the adhesion, but increases the barrier force. In the presence of salt, addition of C14E6 also increases the thickness of the adsorbed layer. The force barrier height is also shown to be related to literature values for surface pressure data in these systems

  • 214. Stokes, JR
    et al.
    Macakova, L
    YKI – Ytkemiska institutet.
    Chojnicka-Paszun, A
    De Kruif, CG
    De Jongh, HHJ
    Lubrication, adsorption, and rheology of aqueous polysaccharide solutions2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 7, p. 3474-3484Article in journal (Refereed)
    Abstract [en]

    Aqueous lubrication is currently at the forefront of tribological research due to the desire to learn and potentially mimic how nature lubricates biotribological contacts. We focus here on understanding the lubrication properties of naturally occurring polysaccharides in aqueous solution using a combination of tribology, adsorption, and rheology. The polysaccharides include pectin, xanthan gum, gellan, and locus bean gum that are all widely used in food and nonfood applications. They form rheologically complex fluids in aqueous solution that are both shear thinning and elastic, and their normal stress differences at high shear rates are found to be characteristic of semiflexible/rigid molecules. Lubrication is studied using a ball-on-disk tribometer with hydrophobic elastomer surfaces, mimicking biotribological contacts, and the friction coefficient is measured as a function of speed across the boundary, mixed, and hydrodynamic lubrication regimes. The hydrodynamic regime, where the friction coefficient increases with increasing lubricant entrainment speed, is found to depend on the viscosity of the polysaccharide solutions at shear rates of around 10 4 s -1. The boundary regime, which occurs at the lowest entrainment speeds, depends on the adsorption of polymer to the substrate. In this regime, the friction coefficient for a rough substrate (400 nm rms roughness) is dependent on the dry mass of polymer adsorbed to the surface (obtained from surface plasmon resonance), while for a smooth substrate (10 nm rms roughness) the friction coefficient is strongly dependent on the hydrated wet mass of adsorbed polymer (obtained from quartz crystal microbalance, QCM-D). The mixed regime is dependent on both the adsorbed film properties and lubricant's viscosity at high shear rates. In addition, the entrainment speed where the friction coefficient is a minimum, which corresponds to the transition between the hydrodynamic and mixed regime, correlates linearly with the ratio of the wet mass and viscosity at ∼10 4 s -1 for the smooth surface. These findings are independent of the different polysaccharides used in the study and their different viscoelastic flow properties.

  • 215. Stubenrauch, C
    et al.
    Langevin, D
    Exerowa, D
    Manev, E
    Claesson, PM
    YKI – Ytkemiska institutet.
    Boinovich, LB
    Comment on “Hydrophobic forces in the foam films stabilized by sodium dodecyl sulfate: Effect of electrolyte” and subsequent criticism2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 24, p. 12457-12460Article in journal (Refereed)
  • 216. Stubenrauch, C
    et al.
    Rojas, OJ
    Schlarmann, J
    Claesson, PM
    YKI – Ytkemiska institutet.
    Interactions between non-polar surfaces coated with the non-ionic surfactant hexaoxyethylene dodecylether C12E6 and the origin of surface charges at the air/water interface2004In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, p. 4977-4988Article in journal (Refereed)
    Abstract [en]

    The interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 were investigated using two techniques and three different types of surfaces. As nonpolar surfaces, the air/water interface, silanated negatively charged glass, and thiolated uncharged gold surfaces were chosen. The interactions between the air/water interfaces were measured with a thin film pressure balance in terms of disjoining pressure as a function of film thickness. The interactions between the solid/liquid interfaces were determined using a bimorph surface force apparatus. The influence of the nature of the surface on the interaction forces was investigated at surfactant concentrations below and above the cmc. The adsorption of the nonionic surfactant on the uncharged thiolated surface does not, as expected, lead to any buildup of a surface charge. On the other hand, adsorption of C12E6 on the charged silanated glass and the charged air/water interface results in a lowering of the surface charge density. The reduction of the surface charge density on the silanated glass surfaces is rationalized by changes in the dielectric permittivity around the charged silanol groups. The reason for the surface charge observed at the air/water interface as well as its decrease with increasing surfactant concentration is discussed and a new mechanism for generation of OH- ions at this particular interface is proposed.

  • 217. Stålgren, JJR
    et al.
    Boschkova, K
    YKI – Ytkemiska institutet.
    Ericsson, J-C
    Frank, CW
    Knoll, W
    Satija, S
    Enrichment of deuterium oxide at hydrophilic interfaces in aqueous solutions2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 24, p. 11943-11946Article in journal (Refereed)
    Abstract [en]

    The structure of water at aqueous interfaces is of the utmost importance in biology, chemistry, and geology. We use neutron reflectivity and quartz crystal microbalance to probe an interface between hydrophilic quartz and bulk liquid solutions of H2O/D2O mixtures. We find that near the interface the neutron scattering length density is larger than in the bulk solution and there is an excess adsorbed mass. We interpret this as showing that there is a region adjacent to the quartz that is enriched in D2O and extends 5-10 nm into the solution. This suggests caution when interpreting results where D2O is substituted for H2O in aqueous interfacial chemistry.

  • 218.
    Svensson, B
    et al.
    YKI – Ytkemiska institutet.
    Olsson, U
    Alexandridis, P
    Self-assembly of block copolymers in selective solvents: Influence of relative block size on phase behavior2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 6839-6846Article in journal (Refereed)
    Abstract [en]

    Two isothermal (25° C) phase diagrams with the block copolymer (EO)43(PO)16(EO)43 and the block copolymer (EO)5(PO)68(EO)5, respectively, in water and p-xylene are presented (EO is ethylene oxide and PO is propylene oxide). The copolymers have approximately the same molecular weight, albeit are unbalanced in PEO/PPO block ratio. The amounts and relative proportions of the solvents can modulate the resulting microstructures, although the phase sequence observed depends on the relative PEO/PPO block ratio. The copolymer rich in EO forms predominantly normal (oil-in-water) structures while the copolymer rich in PO forms predominantly reverse (water-in-oil) structures.

  • 219.
    Sörensen, MH
    et al.
    YKI – Ytkemiska institutet.
    Valle-Delgado, JV
    Corkery, RW
    YKI – Ytkemiska institutet.
    Rutland, MW
    YKI – Ytkemiska institutet.
    Alberius, PC
    YKI – Ytkemiska institutet.
    AFM-porosimetry: Density and pore volume measurements of particulate materials2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 13, p. 7024-7030Article in journal (Refereed)
    Abstract [en]

    We introduced the novel technique of AFM-porosimetry and applied it to measure the total pore volume of porous particles with a spherical geometry. The methodology is based on using an atomic force microscope as a balance to measure masses of individual particles. Several particles within the same batch were measured, and by plotting particle mass versus particle volume, the bulk density of the sample can be extracted from the slope of the linear fit. The pore volume is then calculated from the densities of the bulk and matrix materials, respectively. In contrast to nitrogen sorption and mercury porosimetry, this method is capable of measuring the total pore volume regardless of pore size distribution and pore connectivity. In this study, three porous samples were investigated by AFM-porosimetry: one ordered mesoporous sample and two disordered foam structures. All samples were based on a matrix of amorphous silica templated by a block copolymer, Pluronic F127, swollen to various degrees with poly(propylene glycol). In addition, the density of silica spheres without a template was measured by two independent techniques: AFM and the Archimedes principle.

  • 220. Tchaliovska, S
    et al.
    Herder, P
    Pugh, R
    YKI – Ytkemiska institutet.
    Stenius, P
    YKI – Ytkemiska institutet.
    Eriksson, JC
    Studies of the contact interaction between an air bubble and a MICA surface submerged in dodecylammonium chloride solution1990In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 6, p. 1535-1543Article in journal (Refereed)
  • 221. Tilton, RD
    et al.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Effect of anionic surfactant on interactions between lysozyme layers adsorbed on mica1993In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 9, p. 2102-2108Article in journal (Refereed)
    Abstract [en]

    Protein-surfactant interactions play a key role in competitive adsorption and desorption of adsorbed proteins by surfactants. The influence of nonmicellar solutions of an anionic surfactant, sodium dodecane-sulfonate, on the interaction forces between preadsorbed layers of Iysozyme on mica were investigated using the surface force apparatus. In the absence of surfactant, Iysozyme adsorbs irreversibly and neutralizes the negative mica surface charge. The force profile indicates that the adsorbed layer is heterogeneous and deformable, consisting of protein monomers and loosely associated dimers. An adhesion force is established upon contact of the adsorbed layers. Surfactant binding increases the interfacial charge and eliminates the adhesion force between opposing surfaces. Large-scale desorption or conforma-tional change in response to surfactant binding is not observed, although partial desorption of the outer members of adsorbed dimers is induced at the highest surfactant concentration investigated.

  • 222. Tyrode, E
    et al.
    Niga, P
    Johnson, M
    Rutland, MW
    YKI – Ytkemiska institutet.
    Molecular structure upon compression and stability toward oxidation of langmuir films of unsaturated fatty acids: A vibrational sum frequency spectroscopy study2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 17, p. 14024-14031Article in journal (Refereed)
    Abstract [en]

    Vibrational sum frequency spectroscopy (VSFS) has been used to determine the stability toward oxidation in air of a series of unsaturated fatty acids, measuring as a function of time the changes in the chemical structure and conformational order of films spread on a Langmuir trough. The fatty acids studied consisted of a 20-carbon backbone with increasing numbers of cis double bonds in the chain: 11c-eicosenoic acid (20:1 EA, omega-9), 11c,14c- eicosadienoic acid (20:2 EA, omega-6), and 11c,14c,17c-eicosatrienoic acid (20:3 EA, omega-3). Measurements at constant surface pressure show that double bonds are lost from the surface region and that drops in intensity of the vinyl CH stretch are detectable within a few minutes of spreading the monolayer. The results are consistent with the fatty acid peroxidation free radical mechanism. The sum frequency spectra also reveal that what remains on the surface is conformationally more disordered with a larger number of gauche defects. The oxidation kinetics are found to be strongly dependent on the packing density of the monolayer, being more stable at higher pressures. Oxidation can be avoided by purging the system in an inert atmosphere. Finally, the molecular structure upon compression was tracked in unoxidized monolayers. The results suggest that the packing and orientation of the double bond sections of all three unsaturated fatty acids show remarkable similarities, with the direction of the double bonds approximately parallel to each other irrespective of the number of unsaturations in the chain, with the 20:3EAprobably forming "iron- angle" structures. The possibility of unsaturated chains in a "hairpin" configuration is discarded for area per molecules smaller than ∼50 Å 2, which corresponds to the lowest surface pressure measured with VSFS.

  • 223. Ulcinas, Arturas
    et al.
    Valdre, Giovanni
    Snitka, Valentinas
    Miles, Mervyn J
    Claesson, Per M
    YKI – Ytkemiska institutet.
    Antognozzi, Massimo
    Shear response of nanoconfined water on muscovite mica: Role of cations2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 17, p. 10351-10355Article in journal (Refereed)
    Abstract [en]

    By monitoring the thermal noise of a vertically oriented micromechanical force sensor, we detect the viscoelastic response to shear for water in a subnanometer confinement. Measurements in pure water as well as under acidic and high-ionic-strength conditions relate this response to the effect of surface-adsorbed cations, which, because of their hydration, act as pinning centers restricting the mobility of the confined water molecules.

  • 224. Valle-Delgado, JJ
    et al.
    Molina-Bolivar, JA
    Galisteo-González, F
    Gálvez-Ruiz, MJ
    Feiler, A
    Rutland, MW
    YKI – Ytkemiska institutet.
    Adhesion forces between protein layers studied by means of atomic force microscopy2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, p. 5108-5114Article in journal (Refereed)
    Abstract [en]

    Adhesion forces between different protein layers adsorbed on different substrates in aqueous media have been measured by means of an atomic force microscope using the colloid probe technique. The effects of the loading force, the salt concentration and pH of the medium, and the electrolyte type on the strength, the pull-off distance, and the separation energy of such adhesion forces have been analyzed in depth. Two very different proteins (bovine serum albumin and apoferritin) and two dissimilar substrates (silica and polystyrene) were used in the experiments. The results clearly point out a very important contribution of the electrostatic interactions in the adhesion between protein layers

  • 225. Valle-Delgado, JJ
    et al.
    Molina-Bolivar, JA
    Galisteo-González, F
    Gálvez-Ruiz, MJ
    Feiler, A
    Rutland, MW
    YKI – Ytkemiska institutet.
    Existence of hydration forces in the interaction between apoferritin molecules adsorbed on silica surfaces2005In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, p. 9544-9554Article in journal (Refereed)
    Abstract [en]

    The atomic force microscope, together with the colloid probe technique, has become a very useful instrument to measure interaction forces between two surfaces. Its potential has been exploited in this work to study the interaction between protein (apoferritin) layers adsorbed on silica surfaces and to analyze the effect of the medium conditions (pH, salt concentration, salt type) on such interactions. It has been observed that the interaction at low salt concentrations is dominated by electrical double layer (at large distances) and steric forces (at short distances), the latter being due to compression of the protein layers. The DLVO theory fits these experimental data quite well. However, a non-DLVO repulsive interaction, prior to contact of the protein layers, is observed at high salt concentration above the isoelectric point of the protein. This behavior could be explained if the presence of hydration forces in the system is assumed. The inclusion of a hydration term in the DLVO theory (extended DLVO theory) gives rise to a better agreement between the theoretical fits and the experimental results. These results seem to suggest that the hydration forces play a very important role in the stability of the proteins in the physiological media

  • 226. Van Alstine, JM
    et al.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Poly(ethylene glycol) amphiphiles: Surface behavior of biotechnical significance1997In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, p. 4044-4053Article in journal (Refereed)
    Abstract [en]

    The interfacial behavior of surface localized, poly(ethylene glycol) (1PEG) esterified fatty acid amphiphiles was comparatively studied at microparticle surfaces via phase partition, and at flat surfaces via in situ null ellipsometry. Ellipsometry was performed on methylsilane (MeSi), phosphatidic acid (PA) and phosphatidylcholine (PC) coated silica slides, while human erythrocyte and PC liposomes were subjected to partition in aqueous PEG, dextran two-phase systems. Analogous results from both methods suggest that PEG-amphiphile adsorption can be relatively independent of the underlying surface. Ellipsometry indicated that members of a series of PEG-fatty acid esters of type Ci:j-EO151 (16≤i≤18, 0≤j≤2) adsorb similarly at MeSi-, PC-, and PA-coated surfaces, reaching a plateau (≈0.1 PEG chains * nm-2) independent of micelle formation. When normalized for acyl tail hydrophobicity, PEG-amphiphile adsorption is relatively non-cooperative and independent of acyl tail; saturation being largely determined by repulsive PEG inter-chain interactions. At saturation EO151-ester layers were 10-15 nm thick, suggesting close packed PEG molecules unfolded normal to the target surface. Ellipsometry also indicated the average PEG concentration in the layer was ≈0.07 g * cm-3, and greater than in the PEG-enriched phase of >many two-phase systems. This suggests the partition of PEG-coated colloids reflects interfacial free energy differences between solution- and surface-localized, polymer-enriched phases. PEG-ester adsorption (mg * m-2) isotherms determined on flat slides via ellipsometry correlate directly with those reflected by the partition of analogous microparticles. These results help explain previous observations that changes in partition induced by surface localized PEG, mirror the effects of such localization on the physiological behavior of bio-active colloids.

  • 227. Vangeyte, P
    et al.
    Leyh, B
    Rojas, OJ
    Claesson, PM
    YKI – Ytkemiska institutet.
    Heinrich, M
    Auvray, L
    Adsorption pf poly(ethylene oxide)-b-poly(e-caprolactone) copolymers at the silica-water interface.2005In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, p. 2930-2940Article in journal (Refereed)
    Abstract [en]

    The adsorption of amphiphilic poly(ethylene xide)-b-poly(-caprolactone) and poly(ethylene oxide)-b-poly(-methyl--caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of Mn = 5000 and a hydrophobic polyester block of poly(-caprolactone) (PCL) or poly(-methyl--caprolactone) (PMCL) of Mn in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.

  • 228. Varga, I
    et al.
    Mezaros, R
    Makuska, R
    Claesson, PM
    YKI – Ytkemiska institutet.
    Gilanyi, T
    Effect of graft density on the nonionic bottle brush polymer/surfactant interaction2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 19, p. 11383–11389-Article in journal (Refereed)
    Abstract [en]

    The effect of graft density on the interaction of nonionic bottle brush polymers with an anionic surfactant (sodium dodecyl sulfate) was investigated. The graft density of 45 units long poly(ethylene oxide) (PEO) side chains was varied in a wide range (30, 50, 75, 90, and 100%) on a methacrylate type polymer backbone. The surfactant binding isotherms were determined by the potentiometric method in the presence of 0.1 M sodium bromide. It was found that due to the grafting of the PEO chains to a polymer backbone the surfactant binding becomes significantly suppressed. The amount of bound surfactant at the critical micelle concentration (cmc) decreases almost 2 orders of magnitude compared to the binding on a linear PEO having a similar molecular weight. The binding of the surfactant was found to occur in cooperative fashion, though the critical aggregation concentration (cac) of the binding was found surprisingly small. This result was interpreted in terms of the surfactant aggregation numbers that were found much smaller in the case of the bottle brush polymers than in the case of linear PEOs due to the steric crowding of the grafted PEO chains. To confirm the results of the binding isotherm measurements, steady-state fluorescence probe (pyrene) measurements as well as static and dynamic light scattering measurements were performed.

  • 229. Vargas-Florencia, D
    et al.
    Furó, I
    Corkery, RW
    YKI – Ytkemiska institutet.
    Pore morphology and interconnectivity in a mesoporous/macroporous polyhedral silica foam material2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 9, p. 4827-4832Article in journal (Refereed)
    Abstract [en]

    The pore system of a highly swollen, block-copolymer-templated, polyhedral silica foam material is investigated by a combination of transmission electron microscopy, nitrogen sorption, and NMR cryoporometry. The adsorption-desorption hysteresis and melting-freezing hysteresis data recorded by the respective methods provide pore volume and access channel sizes that virtually coincide for the two used methods. This provides a consistent picture where polyhedral foam cells of 60-70 nm diameter are interconnected by cylindrical access channels with several characteristic sizes for the latter.

  • 230. von Bahr, M
    et al.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Zhmud, B
    YKI – Ytkemiska institutet.
    Oscillations of sessile drops of surfactant solutions on solid substrates with differing hydrophobicity2003In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, p. 10109-10115Article in journal (Refereed)
    Abstract [en]

    The paper reports results of experimental studies on the dynamic behavior of surfactant solution drops on substrates with differing hydrophobicity. Contact angle oscillations observed immediately after the drop deposition are studied, and a mechanistic interpretation of this phenomenon is put forward. The major emphasis is put on the physicochemical aspects of surfactant action, including the dynamic wetting enhancement and the effect of surface tension relaxation on the frequency of drop oscillation, which are characteristic of surfactant solutions. Appropriate scaling relations describing the drop dynamics are derived.

  • 231.
    von Bahr, M
    et al.
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Zhmud, BV
    YKI – Ytkemiska institutet.
    Spreading dynamics of surfactant solutions1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 7069-7075Article in journal (Refereed)
    Abstract [en]

    The spreading behavior of microdrops of surfactant solutions at solid surfaces has been studied. The influence on the spreading of different factors, such as the drop lifetime prior to surface contact, surface tension dynamics, surface energy, and surfactant properties, was systematically investigated. The results obtained suggest the existence of two spreading regimes exhibiting different spreading characteristics: In the first, nondiffusive regime, the spreading is very rapid and controlled to different extents by inertia, gravity, and capillarity, depending on the drop size, impact energy, and interfacial tension balance. It is shown in this study that the initial drop surface tension, which is set by the surface tension decay rate and the drop lifetime prior to the surface impact, strongly influences the maximum spreading distance in the nondiffusive spreading regime. The second, diffusion-controlled regime, is characterized by slower concentration-dependent spreading rates. The spreading rate is, here, mainly controlled by the diffusive transport of surfactant to the expanding liquid-vapor interface. In this regime, the drop base radius exhibits an approximate rb2 t dependence on time. The spreading kinetics at hydrophobic surfaces has been discussed in the framework of a simplified theory. Depending on the assumptions regarding the drop shape, rb5/2 t to rb2 t spreading laws are obtained. This agrees reasonably with the experimentally observed relationship.

  • 232.
    Von Corswant, C.
    et al.
    SIK – Institutet för livsmedel och bioteknik.
    Olsson, C.
    Soderman, O.
    Microemulsions based on soybean phosphatidylcholine and isopropylmyristate-effect of addition of hydrophilic surfactants1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, no 24, p. 6864-6870Article in journal (Refereed)
    Abstract [en]

    This work reports the effect of the addition of n-alkyl ?-D-maltosides (C nG 2), sucrose monododecanoate, and sodium taurocholate on the phase behavior and microstructure of a microemulsion based on water, 1-propanol, soybean phosphatidylcholine (SbPC), and isopropylmyristate (IPM). The self-diffusion coefficients of the components were determined with the pulsed field gradient NMR technique. The spontaneous curvature (H 0) of the surfactant monolayer separating the aqueous and oil domains was found to increase with an increasing proportion of hydrophilic surfactant for all the hydrophilic surfactants studied. The microstructure of the microemulsion, deduced from the self-diffusion coefficients and the conductivity measurements, changed from an oil-continuous structure to oil-swollen micelles through a bicontinuous structure. The general phase behavior could be described with a simple model where H 0 was assumed to vary linearly with the changing weight fraction of hydrophilic surfactant. The molar ratio of C nG 2/SbPC needed to obtain a balanced microemulsion ? bal was found to increase linearly with n for n ? 10. The ? bal for C 12G 2 was 0.71. There was no observed difference in ? bal between sucrose monododecanoate and C 12G 2, but sucrose monododecanoate was found to increase the flexibility of the surfactant film to a greater extent than C 12G 2. Sodium taurocholate increased H 0 more effectively than C 12G 2 (? bal=0.22) but did not destabilize the surfactant film to the same degree.

  • 233. Wakeham, D
    et al.
    Niga, P
    Warr, GG
    Rutland, MW
    YKI – Ytkemiska institutet.
    Atkin, R
    Nonionic surfactant adsorption at the ethylammonium nitrate surface: A neutron reflectivity and vibrational sum frequency spectroscopy study2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 11, p. 8313-8318Article in journal (Refereed)
    Abstract [en]

    The adsorbed layers of polyoxyethylene n-alkyl ether surfactants C 12E4, C14E4, and C16E4 at the EAN surface have a headgroup layer that is thin and compact (only ∼ 30 vol % EAN). The headgroups do not adopt a preferred orientation and are disordered within the ethylene oxide layer. Alkyl tails contain a significant number of gauche defects indicating a high degree of conformational disorder. The thickness of the tail layer increases with increasing alkyl chain length, while the headgroup layer shows little change. Lowering the C12E 4 concentration from 1 to 0.1 wt % decreases the adsorbed amount, and the headgroup layer becomes thinner and less solvated, whereas C 14E4 and Ci6E4 adsorbed layers are unaffected by dilution over the same concentration range. The C16E4 layer thickness increases and area per molecule decreases on warming to 60 °C, but the adsorbed layer structures of C12E4 and C 14E4 are unchanged. Both effects are attributed to surfactant solubility.

  • 234.
    Wallin, Maria
    et al.
    Chalmers University of Technology, Sweden.
    Altskär, Annika
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Food and Bioscience, Structure Design.
    Nordstierna, Lars
    Chalmers University of Technology, Sweden.
    Andersson, Martin
    Chalmers University of Technology, Sweden.
    Meso-ordered PEG-based particles2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 1, p. 13-16Article in journal (Refereed)
    Abstract [en]

    We report on the formation of meso-ordered hydrogel particles by cross-linking poly(ethylene glycol) diacrylate (PEG-DA) in the presence of surfactants in a confined environment. The results demonstrated that well-ordered mesoporous hydrogel particles having a pore size of about 5 nm could be formed. It is suggested that these meso-ordered hydrogel particles might have unique drug-delivery capabilities

  • 235.
    Wallqvist, V
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Claesson, PM
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Swerin, A
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Ostlund, C
    RISE, STFI-Packforsk.
    Schoelkopf, J
    Gane, PAC
    Influence of surface topography on adhesive and long-range capillary forces between hydrophobic surfaces in water2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 16, p. 9197-9207Article in journal (Refereed)
    Abstract [en]

    We report on the interactions between a hydrophobic probe particle and surfaces with nanoscopic surface features. These surfaces have been prepared by spin-coating of nanoparticles and by polishing. The surface topography was characterized by AFM, using the methods of high-resolution imaging, low-resolution imaging using the probe particle, and by the rolling ball method. The spin-coated surfaces can be characterized as nanostructured due to the high density of nanoparticles that on a short length scale provides a regular pattern of crevices and hills. On these surfaces a larger waviness is also distinguished. In contrast, the polished surfaces display sharp nanoscopic peaks and hardly any crevices. In all cases the dominant force at short separations was found to be a capillary attraction due to the formation of an air/ vapor condensate. Our data show that the large-scale waviness of the surface does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. The large variation in adhesion force corresponds to a small variation in local contact angle of the capillary condensate at the surfaces. The report discusses how the nature of the surface topographical features influences the capillary attraction by influencing the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on whether the surface features exist in the form of crevices or as extending ridges.

  • 236.
    Wallqvist, V
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Swerin, A
    YKI – Ytkemiska institutet.
    Schoelkopf, J
    Gane, PAC
    Influence of wetting and dispersing agents on the interaction between talc and hydrophobic particles2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 12, p. 6909–6915-Article in journal (Refereed)
    Abstract [en]

    The interactions between a natural talc surface and a model hydrophobic particle have been investigated in aqueous solutions by employing the atomic force microscopy (AFM) colloidal probe technique. The results demonstrate the presence of long-range attractive forces due to bridging via preadsorbed or induced bubbles/cavities. Due to the natural heterogeneity of talc, and the stochastic nature of the bubble bridging process, the variability in the range and magnitude of the attraction is larger than that for cases when other interactions predominate or than that when only model surfaces are used. Addition of poly(acrylic acid), a common dispersing agent, did not affect the measured forces. Thus, we conclude that poly(acrylic acid) does not adsorb to the basal plane of talc. In sharp contrast, addition of Pluronic PE6400, a nonionic triblock polymer used as wetting agent, resulted in complete removal of the bubble-induced attractive force. Instead, a short-range steric repulsion is the dominating feature. Clearly, Pluronic PE6400 is able to displace air bubbles from the surface and prevent their formation when the particles come into contact. These are suggested to be important features of efficient wetting agents.

  • 237.
    Wallqvist, V
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Swerin, A
    YKI – Ytkemiska institutet.
    Schoelkopf, J
    Gane, PAC
    Interaction forces between talc and pitch probed by Atomic Force Microscopy2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 8, p. 4248-4256Article in journal (Refereed)
    Abstract [en]

    Colloidal wood resin components present in pulp are collectively called “pitch”. The presence of pitch may cause severe problems due to deposits in and on the paper machine. There is thus a need for controlling pitch aggregation and adsorption. To be able to develop more efficient pitch control systems, one needs to develop the understanding of pitch-pitch interactions and of the interactions between pitch and other materials. With this general goal in mind, we present methods for preparing geometrically well-defined pitch particles attached to atomic force microscopy tips. This has enabled us to investigate the interactions between pitch and talc, an additive commonly used for pitch control. We have used model pitch particles consisting of one component only (abietic acid), a mixture of components (collophonium), and particles prepared from real pitch deposits. We show that the forces acting between pitch and talc are attractive and, once the initial approach is made, exert this attraction out to large distances of separation. We present evidence that the formation of bridging air bubbles or cavities is responsible for this interaction.

  • 238. Waltermo, Å
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Simonsson, S
    Manev, E
    Johansson, I
    Bergeron, V
    Foam and thin-liquid-film studies of alkyl glucoside systems1996In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 12, p. 5271-5278Article in journal (Refereed)
    Abstract [en]

    The foaming behaviour of nonionic alkyl glucosides, in terms of foamability and foam stability, has been investigated using various methods. Three different foam tests, two dynamic methods: the Bikerman cylinder and the Watkins funnel, and one static method, have been employed for measuring the foamability and foam stability of nonionic surfactant solutions made from either the linear octyl b-glucoside, the linear octyl a-glucoside, or the branched octyl a-glucoside, 2-ethylhexyl a-glucoside. At low surfactant concentration there is only a small difference between the surfactants, which remains when the salt concentration increases. At high surfactant concentration octyl b-glucoside is observed to be the major foaming agent. The stability of the individual foam lamellae have also been studied with the Thin-Film-Balance technique (TFB). The stabilizing forces in these nonionic foam films is, in most cases, electrostatic double-layer forces. The thickness dependence of the repulsive forces is consistent with Poisson Boltzmann theory. As the salt concentration is increased the range of the double-layer force measured with the TFB technique decreases. This correlates with a reduction in foam stability as noticed by measuring the decay of foams formed by a shaking method. Furthermore, for the octyl b-glucoside close to cmc, only a very weak double-layer force is observed, and in this case Newton black films stabilized by steric/hydration forces are formed as noticed by TFB measurements.

  • 239.
    Walther, Bernhard
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Loren, Niklas
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Nyden, M.
    Hermansson, Ann-Marie
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Influence of ?-carrageenan gel structures on the diffusion of probe molecules determined by transmission electron microscopy and NMR diffusometry2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 19, p. 8221-8228Article in journal (Refereed)
    Abstract [en]

    The influence of the microstructures of different ?-carrageenan gels on the self-diffusion behavior of poly(ethylene glycol) (PEG) has been determined by nuclear magnetic resonance (NMR) diffusometry and transmission electron microscopy (TEM). It was found that the diffusion behavior was determined mainly by the void size, which in turn was defined by the state of aggregation of the ?-carrageenan. The ?-carrageenan concentration was held constant at 1 w/w%, and the aggregation was controlled by the amount of potassium and/or sodium chloride and, for samples containing potassium, also by the cooling rate. Gels containing potassium formed microstructures where ?-carrageenan strands are rather evenly distributed over the image size, while sodium gels formed dense biopolymer clusters interspersed with large openings. In a gel with small void sizes, relatively slow diffusion was found for all PEG sizes investigated. Extended studies of the self-diffusion behavior of the 634 g mol-1 PEG showed that there is a strong time dependence in the measured PEG diffusion. An asymptotic lower time limit of the diffusion coefficient was found in all gels when the diffusion observation time was increased. According to the ratio, D/D0, where D0 is the diffusion coefficient in D2O and D is the diffusion coefficient in the gels, the gels could be divided into three classes: small, medium, and large voids. For quenched ?-carrageenan solutions with salt concentrations of 20 mM K+, 100 mM K+, or 20 mM K+/200 mM Na + as well as slowly cooled solutions with only 20 mM K+, D/D0 ratios between 0.18 and 0.29 were obtained. By quenching a ?-carrageenan solution with 100 mM K+, the D/D0 was 0.5, while D/D0 ratios between 0.9 and 1 were obtained in a quenched solution with 250 mM Na+ and slowly cooled samples with 20 mM K +/200 mM Na+ or 250 mM Na+. © 2006 American Chemical Society.

  • 240. Wang, J-H
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Parker, JL
    Yasuda, H
    Dynamic contact angles and contact angle hysteresis of plasma polymers1994In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 10, p. 3887-3897Article in journal (Refereed)
    Abstract [en]

    Dynamic advancing and receding contact angles and the contact angle hysteresis for different plasma polymers deposited on microscope cover glasses were investigated by the Wilhelmy plate method. The hysteresis loops observed by this dynamic method show two major factors: (1) the meniscus change at the transition region; (2) the wettability change of solid surfaces. The first factor is due to the fact that three-phase contact line does not move in the transition region while the water level is forced to rise up or lower down. The second factor is due to the change of surface state of the solid. Moreover, this factor can be related to the Fstep change» at the buoyancy slope of a hysteresis loop when the wetting line is moved from a "prewetted» area to a adry" area of the same sample and also to the gap between the first and second immersion loops. Both factors are caused by the interaction forces between solid surface and water molecules at the solid/liquid interface . Plasma polymer of the tetrafluoroethylene (TFE) showed the largest hysteresis loop primarily due to the significant change of surface state after water immersion. Plasma polymer of hexamethyldisiloxane (HMDSO) showed the smallest hysteresis loop due to the minimal change in the surface state after water immersion. Water contact angles of plasma polymers were clearly dependent on plasma conditions manifested by the discharge energy density.

  • 241. Weissenborn, PK
    et al.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Surface tension and bubble coalescence phenomena of aqueous solutions of electrolytes1995In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, p. 1422-1426Article in journal (Refereed)
    Abstract [en]

    The inhibition of bubble coalescence by electrolytes beyond a critical transition concentration has been assessed by the relationship between transition concentration and surface tension gradients of electrolytes (d(Ay)/dc) and gas solubility. The correlation between transition concentration and [d(Ay)/dc]~2 was mediocre (0.74), suggestingthatthe Gibbs-Marangoni effect cannot fully account forinhibition of bubble coalescence. Preliminary bubbling experiments on mixed electrolytes supported this conclusion. A much better correlation was found between the transition concentration and gas solubility (represented by the exponential decay coefficient of 02 solubility with increasing electrolyte concentration). Hence, the inhibition of bubble coalescence may be linked with the decreased dissolved gas concentration in the electrolyte solution.

  • 242. Williams, M.A.K.
    et al.
    Fabri, D.
    Hubbard, C.D.
    Lundin, Leif
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Loren, Niklas
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Hermansson, Ann-Marie
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Kinetics of droplet growth in gelatin/maltodextrin mixtures following thermal quenching2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 11, p. 3412-3418Article in journal (Refereed)
    Abstract [en]

    Rates of droplet growth, following the thermal quenching of gelatin/maltodextrin mixtures into the incompatible region of the phase diagram, have been obtained from turbidity measurements. The results from experiments carried out at temperatures that prohibit the involvement of biopolymer conformational ordering and gelation are in good agreement with those obtained by similar studies of binary synthetic polymer systems and with theoretical predictions. For mixtures that would phase separate at temperatures above the gelatin ordering temperature (T0) but which are quenched directly to temperatures below this, droplet growth shows modified kinetics owing primarily to restrictions imposed by the viscosifying continuous phase. However, for a mixture that was initially observed to be miscible following quenches to temperatures below T0, it is proposed that biopolymer ordering induces phase separation, which was found to occur after significant delay periods.

  • 243. Wågberg, L.
    et al.
    Decher, G.
    Norgren, M.
    Lindström, Tom
    RISE, STFI-Packforsk.
    Ankerfors, Mikael
    RISE, STFI-Packforsk.
    Axnäs, K.
    The build-up of polyelectrolyte multilayers of microfibrillated cellulose and cationic polyelectrolytes2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 3, p. 784-795Article in journal (Refereed)
    Abstract [en]

    A new type of nanocellulosic material has been prepared by high-pressure homogenization of carboxymethylated cellulose fibers followed by ultrasonication and centrifugation. This material had a cylindrical cross-section as shown by transmission electron microscopy with a diameter of 5-15 nm and a length of up to 1 ÎŒm. Calculations, using the Poisson-Boltzmann equation, showed that the surface potential was between 200 and 250 mV, depending on the pH, the salt concentration, and the size of the fibrils. They also showed that the carboxyl groups on the surface of the nanofibrils are not fully dissociated until the pH has reached pH = ∌10 in deionized water. Calculations of the interaction between the fibrils using the Derjaguin-Landau-Verwey-Overbeek theory and assuming a cylindrical geometry indicated that there is a large electrostatic repulsion between these fibrils, provided the carboxyl groups are dissociated. If the pH is too low and/or the salt concentration is too high, there will be a large attraction between the fibrils, leading to a rapid aggregation of the fibrils. It is also possible to form polyelectrolyte multilayers (PEMs) by combining different types of polyelectrolytes and microfibrillated cellulose (MFC). In this study, silicon oxide surfaces were first treated with cationic polyelectrolytes before the surfaces were exposed to MFC. The build-up of the layers was monitored with ellipsometry, and they show that it is possible to form very well-defined layers by combinations of MFC and different types of polyelectrolytes and different ionic strengths of the solutions during the adsorption of the polyelectrolyte. A polyelectrolyte with a three-dimensional structure leads to the build-up of thick layers of MFC, whereas the use of a highly charged linear polyelectrolyte leads to the formation of thinner layers of MFC. An increase in the salt concentration during the adsorption of the polyelectrolyte results in the formation of thicker layers of MFC, indicating that the structure of the adsorbed polyelectrolyte has a large influence on the formation of the MFC layer. The films of polyelectrolytes and MFC were so smooth and well-defined that they showed clearly different interference colors, depending on the film thickness. A comparison between the thickness of the films, as measured with ellipsometry, and the thickness estimated from their colors showed good agreement, assuming that the films consisted mainly of solid cellulose with a refractive index of 1.53. Carboxymethylated MFC is thus a new type of nanomaterial that can be combined with oppositely charged polyelectrolytes to form well-defined layers that may be used to form, for example, new types of sensor materials.

  • 244. Yaminsky, VV
    et al.
    Yaminskaya, KB
    YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Thermodynamic analysis of solute effects on contact angles : Equilibrium adsorption of cationic surfactants at silica - water and silica - air interfaces1995In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, p. 936-941Article in journal (Refereed)
    Abstract [en]

    It is shown that the equilibrium wetting tension, defined thermodynamically as the difference between the solid -vapor and solid-liquid interfacial tensions, can be measured to the same high degree of certainty and accuracy as the surface tension of liquids. Just as for surface tension isotherms the wetting tension isotherms can be analyzed through the Gibbs adsorption equation. This allows for unambiguous evaluation of the adsorption difference at the two interfaces. As an example we have investigated the wetting of smooth and homogeneous silica glass surfaces by solutions of cetyltrimethylammonium bromide (CTAB). At small concentrations (below the point of zero charge) equilibrium monolayer adsorption is larger at the solid-vapor interface than at the solid-liquid interface. At higher concentrations (near the critical micelle concentration) the adsorption difference changes sign due to formation of bilayer at a solid-liquid interface. Adsorption reequilibration within the hydrophobic monolayer occurs when a three-phase contact line is displaced. This reequilibration is slow and explains large contact angle hysteresis typically observed when measurements are done under nonequilibrium conditions.

  • 245.
    Zhmud, BV
    et al.
    YKI – Ytkemiska institutet.
    Poptoshev, E
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Role of hydration and conformational changes in adsorption dynamics of ethyl(hydroxyethyl)cellulose at the air/solution interface1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 3620-3624Article in journal (Refereed)
    Abstract [en]

    Previous studies have discussed the kinetics of the reduction in surface tension of ethyl(hydroxyethyl)cellulose (EHEC) at the air/aqueous solution interface in terms of configuration changes involved in the transfer of individual polymer segments between soluted and adsorbed state. It was suggested that the process kinetics were governed by a substantially high activation barrier. In the present study, based on molecular mechanic simulations, it is shown that a nearly activation-free path between configurations exists for EHEC due to the extreme flexibility of the polymer chain. Hence, the relatively slow kinetics of the process should rather be attributed to the step-wise transformation between conformations which is expressed as a sequence of elementary processes involving a large number of intermediate steps. This occurs over an extended time period. Also, the configuration changes involved in the uncoiling of the polymer at the interface are related to the hydration effects.

  • 246.
    Zhmud, BV
    et al.
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Kizling, J
    YKI – Ytkemiska institutet.
    Dynamic surface tension in concentrated solutions of CnEm Surfactants: A comparison between the theory and experiment2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 2557-2565Article in journal (Refereed)
    Abstract [en]

    Dynamic surface tension (DST) measurements have been carried out with a series of CnE6-type surfactants with varying alkyl chain length (n = 10 to 16). Major emphasis has been placed on the DST relaxation in complex solutions containing both the micellar and monomer forms of surfactant. This paper also provides a step-by-step guidance to the theoretical interpretation of DST data for micellar solutions. Distributions of monomers and micelles in the vicinity of the gas/liquid interface, adsorption kinetics, and DST relaxation curves have been simulated in the framework of the Fainerman theory (Fainerman, V.B. Kolloid. Zhur. 1981, 43, 94) explicitly allowing for monomer/micelle interconversation. A thorough numerical analysis has shown that although the Fainerman theory can follow the general experimental trends, it clearly lacks the flexibility needed to provide a self-consistent and quantitatively-correct description of the process. Possible reasons for this disagreement are discussed.

  • 247.
    Zhmud, BV
    et al.
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Kizling, J
    YKI – Ytkemiska institutet.
    Long-time interfacial relaxation in aqueous butanol solutions2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 7685-7690Article in journal (Refereed)
    Abstract [en]

    The long-time relaxation of the dynamic surface tension (DST) in aqueous solutions of four structural isomers of butyl alcohol has been observed with the aid of the maximum bubble pressure technique. Diffusion-controlled kinetics was found to allow an apparently successful (in terms of the quality of fitting) description of the observed DST dynamics, but it leads to an unrealistically low value of the diffusion coefficient, 10-11-10-13 m2 s-1. Conversely, the activation-controlled kinetics fails to explain the slow damping of DST curves observed over long time periods. A comprehensive theoretical analysis supported by numerical simulations has conclusively shown that neither diffusion nor mixed diffusion-activation kinetics can adequately account for the observed slower DST relaxation. As an alternative explanation, the presence of packing defects in the adsorbed layer is proposed.

  • 248. Östmark, E
    et al.
    Macakova, L
    YKI – Ytkemiska institutet.
    Auletta, T
    Malkoch, M
    Malmström, E
    Blomberg, E
    YKI – Ytkemiska institutet.
    Dendritic structures based on bis(hydroxymethyl)propionic acid as platforms for surface reactions2005In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, p. 4512-4519Article in journal (Refereed)
    Abstract [en]

    In this paper we present results related to the self-assembly of different generations of disulphide-cored 2,2-bis-(methylol)propionic acid-based dendritic structures onto gold surfaces. These molecular architectures, ranging from generation 1 (G#1) to generation 3 (G#3), contain removable acetonide protecting groups at their periphery that are accessible for hydrolysis with subsequent formation of OH-terminated surface-attached dendrons. The deprotection has been investigated in detail as a versatile approach to accomplish reactive surface platforms. A special focus has been devoted to the comparison of the properties of the layers formed by hydrolysis of the acetonide moieties directly on the surface and in solution, prior to the layer formation.

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