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  • 251.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Herder, PC
    Berg, JM
    Christenson, HK
    The state of fluorocarbon surfactant monolayers at the air-water interface and on Mica surfaces1990Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 136, s. 541-555Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Monolayers of a cationic, double-chained fluorocarbon surfactant (N-(α-trimethylammonioacetyl)-O-O'-bis (1H, 1H, 2H, 2H-perfluorodecyl)-L-glutamate chloride) were studied at the air-water interface and adsorbed on the muscovite mica basal plane. The stability of the monolayer at the air-water interface was considerably higher on a 10-2 M KBr subphase than on pure water. Fluorocarbon surfactant-coated mica surfaces were obtained either by Langmuir-Blodgett (LB) deposition or by adsorption from a polar solvent. The adsorbed layer was characterized by means of ESCA, transfer ratio and contact angle measurements. A more densely packed layer could be obtained by LB deposition than by adsorption from solution. For this surfactant the preferential conformation of the molecule in layers adsorbed from solution is different from that in LB layers. At low adsorption denseties the advancing contact angle increases rapidly with the adsorbed amount. The receding angle is hardly affected until the area per molecule is less than about 140 Å2. At higher adsorption densities, the receding contact angle is more sensetive to the adsorbed amount than the advancing angle. The reason for the low salt stability, the low adhesion force in water, and the numerous cavities forming around the contact region when surfaces coated by this fluorocarbon surfactant are brought together in water is proposed to be due to (molecular size) heterogeneities in the surfactant layer.

  • 252.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Herder, PC
    Rutland, MW
    YKI – Ytkemiska institutet.
    Waltermo, Å
    Anhede, B
    Amine functionalized surfactants - pH effects on adsorption and interaction1992Inngår i: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 88, s. 64-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interactions between layers of two hydrolyzable surfactants, dodecylamine (DA) and tetraoxyethylene dodecylamine (TEDA), adsorbed on negatively charged muscovite mica have been investigated. It was found that the variation of the interaction and adsorption as a function of pH was similar, but not identical, for the two kinds of surfactants. At a concentration of 10-4 M at low pH (below 8) both types of surfactants adsorb electrostatically to form a monolayer. The resulting surfaces have a hydrophobic character, particularly in the case of dodecylamine. A series of events takes place as the pH is increased. For DA the first event is that uncharged molecules adsorb within the monolayer. This does not occur to any significant degree for TEDA due to steric hindrance within the adsorbed layer. In the next step a bilayer builds up on the surface. The binding of the outer layer is stronger for DA than for TEDA. The DA bilayer becomes uncharged at pH 10.3, and liquid dodecylamine droplets, which phase separate from the bulk solution at this pH-value, precipitate on the surface. At pH-values above 11-12 the affinity between both types of surfactants and the surface decreases significantly, resulting in a less ordered first layer. In addition a strong surface charge develops that prevents multilayer build-up.

  • 253.
    Claesson, PM
    et al.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Kjellin, Mikael
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Rojas, OJ
    Stubenrauch, C
    Short-range interactions between non-ionic surfactant layers2006Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 8, s. 5501-5514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 254.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Kjellin, URM
    Studies of interactions between interfaces across surfactant solutions employing various surface force techniques1999Inngår i: Modern Characterization Methods of Surfactant Systems / [ed] Binks, BP, Marcel Dekker, 1999, s. 255-333Kapittel i bok, del av antologi (Fagfellevurdert)
  • 255.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Makuska, R
    Varga, I
    Meszaros, R
    Titmuss, S
    Linse, P
    Bottle-brush polymers: Adsorption at surfaces and interactions with surfactants2010Inngår i: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 155, nr 1-2, s. 50-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solution and adsorption properties of both charged and uncharged bottle-brush polymers have been investigated. The solution conformation and interactions in solution have been investigated by small-angle scattering techniques. The association of the bottle-brush polymers with anionic surfactants has also been studied. Surfactant binding isothermmeasurements,NMR, surface tensionmeasurements, aswell as SAXS, SANS and light scattering techniques were utilized for understanding the association behaviour in bulk solutions. The adsorption of the bottle-brush polymers onto oppositely charged surfaces has been explored using a battery of techniques, including reflectometry, ellipsometry, quartz crystal microbalance, and neutron reflectivity. The combination of these techniques allowed determination of adsorbedmass, layer thickness,water content, and structural changes occurring during layer formation. The adsorption ontomicawas found to be very different to that on silica, and an explanation for this was sought by employing a lattice mean-field theory. The model was able to reproduce a number of salient experimental features characterizing the adsorption of the bottle-brush polymers over a wide range of compositions, spanning fromuncharged bottle-brushes to linear polyelectrolytes. This allowed us to shed light on the importance of electrostatic surface properties and non-electrostatic surface-polymer affinity for the adsorption. The interactions between bottle-brush polymers and anionic surfactants in adsorbed layers have alsobeen elucidated using ellipsometry, neutron reflectivity and surface force measurements.

  • 256.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Lindman, B
    Forces between hydrophobic surfaces coated with ethyl(hydroxyethyl)cellulose in the presence of an ionic surfactant1991Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 7, s. 1441-1446Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The forces between hydrophobic surfaces across an aqueous solution containing 0.25% ethyl(hydroxyethyl)cellulose (EHEC) and 4 mM SDS have been studied and compared with the situation in the absence of SDS. A long-range repulsive force (measurable at distances smaller than 1200 Å) is present already after an adsorption time of 30 minutes. The range of the repulsive force increases with time indicating that the adsorption process is rather slow. After 20 hours equilibration, the repulsion was measurable at separations smaller than 2500 Å. The force is rather insensitive to temperature and decays at large separations essentially exponentially, with a decay-length of approximately 300 Å. The force measured on compression is always slightly larger than the one observed on decompression. Hence, the forces are not measured in a true equilibrium situation. The system behaves strikingly different in the absence of SDS (Malmsten and Claesson, Langmuir, in press). Without any surfactant in the EHEC solution less long-range and completely reversible forces are observed. Hence, SDS causes the polymer conformation to be more extended, and is responsible for the non-equilibrium effects observed (e.g. by decreasing the polymer-surface affinity). The adsorbed amount in the presence of SDS was found to be about 1.7 mg/m2 at adsorption equilibrium, independent of temperature (20°-35°C). This is considerably less than in the absence of surfactants (5 mg/m2 at 20°C, 15 mg/m2 at 37°C).

  • 257.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Ninham, BW
    pH-dependent interactions between adsorbed chitosan layers1992Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 8, s. 1406-1412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chitosan is a cationic polyelectrolyte obtained after N-deacetylation of chitin by alkaline treatment. The adsorption of chitosan and the interaction between chitosan layers have been investigated using a surface force technique. Negatively charged mica surfaces were immersed in a 0.01 wt % acetic acid solution containing 0.01 wt % chitosan. The adsorption of chitosan results in a flat adsorbed layer and a reversal of the sign of the surface charge. The adsorption is essentially irreversible with respect to subsequent dilution. After dilution, the pH dependence of the forces acting between the adsorbed chitosan layers was investigated. The chitosan-mica system is uncharged around pH 6.2 (the pKa of chitosan is around 6.5) At this pH there is a weak attractive interaction between the chitosan-coated surfaces. The minimum in the force vs distance curve is located at a separation of about 20-25 Å. A steric repulsion is observed at smaller separations. At lower and higher pH values the long-range interaction is dominated by a repulsive double-layer force originating from charges on chitosan and on the mica surface, respectively. The information obtained from surface force measurements allows us to suggest a structure of the irreversibly adsorbed layer at various pH values. The pH dependence of the layer structure is rationalized in terms of changes in segment-segment and segment-surface interactions.

  • 258.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Parker, JL
    Fröberg, JC
    New surfaces and techniques for studies of interparticle forces1994Inngår i: Journal of Dispersion Science and Technology, ISSN 0193-2691, E-ISSN 1532-2351, Vol. 15, s. 375-397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several methods of preparing surfaces suitable for interparticle surface forces measurements are presented. Treatment of muscovite mica surfaces with a water vapour plasma introduces surface hydroxyl groups. These groups can react with chlorosilanes to form organo functionalized surfaces. The forces between water vapour plasma treated mica surfaces in aqueous solutions are well described by DLVO theory except for the presence of a short-range (D < 10 Å) additional repulsion. After reaction with a fluorocarbon containing silane the surfaces become hydrophobic and a long-range attraction acts between the surfaces in water. Smooth glass spheres can be obtained by melting a glass rod in a gas burner. These surfaces are ideal substrates for a new type of surface force apparatus that uses a bimorph force sensor for measuring surface forces. The chemistry of the glass surfaces is readily modified by reactions with chlorosilanes. The similarities and the differences between the forces acting between glass and water vapour plasma treated mica surfaces before and after silanation are discussed. We also report on the use of a cold plasma process to produce thin, smooth organic films that can be investigated with the surface force technique.

  • 259.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Paulson, OEH
    Blomberg, E
    YKI – Ytkemiska institutet.
    Burns, NL
    Surface properties of poly(ethylene imine)-coated mica surfaces - salt and pH effects1997Inngår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 123, s. 341-353Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of a branched weak polybase, poly(ethylene imine) (PEI), on the basal plane of muscovite mica was investigated using surface force measurements, electro-osmotic measurements, and ESCA. The use of this combination of techniques allows us to obtain information about adsorbed amount, interfacial charges, average structure of adsorbed layers and the most important types of forces acting between PEI-coated surfaces. The system was studied under two different conditions. The adsorbed layer adopts a flat conformation at low ionic strength ant at low pH owing to the predominance of electrostatic forces. The interfacial properties of PEI-coated surfaces are compared with those of strong polyelectrolytes as well as with a linear weak polybase studied previously under similiar conditions. At higher pH-values the adsorbed amount increases owing to a reduction in the polyelectrolyte charge density. This results in a thicker layer and in the increased importance of repulsive steric forces. Finally, the interaction between one polyelectrolyte-coated surface and a bare mica surface was investigated and compared with recent theoretical predictions.

  • 260.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Poptoshev, E
    Blomberg, E
    YKI – Ytkemiska institutet.
    Dédinaité, A
    YKI – Ytkemiska institutet.
    Polyelectrolyte-mediated surface interactions2005Inngår i: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 114-115, s. 173-187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current understanding of interactions between surfaces coated with polyelectrolytes is reviewed. Experimental data obtained with various surface force techniques are reported and compared with theoretical predictions. The majority of the studies concerned with interactions between polyelectrolyte-coated surfaces deal with polyelectrolytes adsorbed to oppositely charged surfaces, and this is also the main focus of this review. However, we also consider polyelectrolytes adsorbed to uncharged surfaces and to similarly charged surfaces, areas where theoretical predictions are available, but relevant experimental data are mostly lacking. We also devote sections to interactions between polyelectrolyte brush-layers and to interactions due to non-adsorbing polyelectrolytes. Here, a sufficient amount of both theoretical and experimental studies are reported to allow us to comment on the agreement between theory and experiments. A topic of particular interest is the presence of trapped non-equilibrium states that often is encountered in experiments, but difficult to treat theoretically.

  • 261.
    Corkery, Robert W
    YKI – Ytkemiska institutet.
    Aspects of the differential geometry and topology of bicontinuous liquid-crystalline phase: Chapter 52005Inngår i: Bicontinuous Liquid Crystals / [ed] Matthew L . Lynch and Patrick T . Spicer, CRC Press, 2005, s. 99-125Kapittel i bok, del av antologi (Fagfellevurdert)
  • 262.
    Corkery, Robert W
    et al.
    YKI – Ytkemiska institutet.
    Blute, Irena A
    Friberg, Stig E
    Guo, Rong
    Emulsion inversion in the PIT range: Quantitative phase variations in a two-phase emulsion2010Inngår i: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 55, nr 10, s. 4471-4475Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The phase-inversion temperature (PIT) phenomenon is for the first time given a quantitative treatment for systems having a sufficiently small surfactant content to be limited to two phases at the PIT. The results show that the early opinion of a phase transfer of the surfactant as the major event in the transversal of the temperature range is not entirely correct; the major phenomenon is instead an expulsion of water from the low-temperature aqueous micellar solution. In addition, the results unexpectedly give an indication of the existence of three phases at temperatures beneath the PIT, in spite of the the fact that system consists of only two phases at the actual PIT.

  • 263.
    Corkery, RW
    YKI – Ytkemiska institutet.
    Metal organic framework (MOF) liquid crystals. 1D, 2D and 3D ionic coordination polymer structures in the thermotropic mesophases of metal soaps, including alkaline earth, transition metal and lanthanide soaps2008Inngår i: Current Opinion in Colloid & Interface Science, ISSN 1359-0294, E-ISSN 1879-0399, Vol. 13, nr 4, s. 288-302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Taken together, the body of existing literature on metal soap crystal structures and mesophases supports the view that much is to be gained by treating the soaps as metal organic frameworks (MOF's) when relating their structure and liquid crystallinity. We argue that metal soaps mesophases often consist of disordered metal organic (carboxylate) frameworks (MOF's). Metal atoms are linked by bridging carboxylates, and the metal–oxygen networks form semi-flexible rods, chains and sheets of M–O polyhedra within their co-bonded, mesotructured, self-assemblies of lipidic chains. The packing of the molten hydrocarbon chains allows otherwise unconnected MOF networks to coexist as spatially isolated units in the same unit cell. For instance the lamellar phases are true 2D MOF's or layers of 1-D MOF's. The phase transitions can then be regarded as coupled disordering/re-ordering transitions involving rotational and conformational disordering of the hydrocarbon chains balanced with disordering of MOF symmetries, MOF topological transformations, depolymerizations and dimensionality reductions ultimately leading to anisotropic melts. By way of demonstration, thermotropic phase transitions of homologous series of lanthanide soaps are systematically studied using a variety of experimental methods, and the data are used in a topological model for testing the consistency with the MOF concept of metal soap crystal structures and thermotropic mesophases. Finally, an interpenetrating bicontinuous MOF comprised of SrO6 polyhedral rods is presented as an atomically resolved model for the network topology of the cubic mesophase of strontium soaps. Metal soaps are therefore shown to afford a bridge between liquid crystals and metal organic framework (MOF) materials.

  • 264.
    Corkery, RW
    et al.
    YKI – Ytkemiska institutet.
    Fogden, A
    On the formation and structure of nanometric polyhedral foams: Toward the dry limit2008Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, s. 10443-10452Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High surface area, high porosity, nanometric polygonal silica foams with hierarchically connected and uniformly sized pore systems are reported here. We observe a remarkable increase in foam cell sizes from mesoscopic to macroscopic dimensions upon swelling the self-assembled template with oil. The resultant structures resemble classical macroscopic soap foams and display, among other features, Plateau borders and volume fractions approaching the dry limit of 100%. In well-developed foams of this kind, dimensionally isometric polyhedral cells are connected by relatively short, flat cylindrical mesopores through polyhedral faces and micropores through the walls. For one sample, with approximately 75 nm diameter primary foam cells, we infer three separate sets of cell-connecting mesopores puncturing tetragonal, pentagonal, and hexagonal faces of the component polyhedra. A multiple step model of foam formation is discussed where an organic silica precursor progressively hydrolyzes and condenses as a growing flexible shell from the core-corona interface of oil-swollen triblock copolymer micelles or microemulsion droplets, inducing a clouding phenomena in the otherwise stabilizing poly(ethylene oxide) chains, leading to aggregation, deformation, and jamming to high volume fractions.

  • 265.
    Corkery, RW
    et al.
    YKI – Ytkemiska institutet.
    Rousseau, D
    Smith, P
    YKI – Ytkemiska institutet.
    Pink, DA
    Hanna, CB
    A case for discotic liquid crystals in molten triglycerides2007Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, s. 7241-7246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To date, essentially only two structural models have been proposed and debated in detail for explaining the liquid state order of triglycerides, and both invoke a form of thermotropic liquid crystalline order in triglyceride melts. These are the paralamellar model of Larsson et al. (J. Am. Oil Chem. Soc. 1992, 69, 835) and the nematic model of Cebula et al. (J. Am. Oil Chem Soc. 1992, 69, 130). An alternative discotic model is proposed here that adequately accounts for the broad small-angle X-ray diffraction peak often observed in the liquid state of fats and oils. In this alternative model, triglyceride molecules exist in the liquid state with fully splayed chains, approximating "Y"-shapes (Y-conformers). These are loosely bound within discs that stack into flexible, relatively short cylindrical rods of colloidal dimension, which in turn assemble into rod-packings with short-range order akin to disordered versions of thermotropic discotic liquid crystalline phases in other lipidic systems.

  • 266. Costas, M
    et al.
    Kronberg, B
    YKI – Ytkemiska institutet.
    Thermodynamics of aliphatic and aromatic hydrocarbons in water1998Inngår i: Biophysical Chemistry, ISSN 0301-4622, E-ISSN 1873-4200, Vol. 74, s. 83-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Makhatadze and Privalov have analyzed the thermodynamics of transfer of aliphatic and aromatic hydrocarbons from the gas phase into water. Finding that the hydration free energy of aliphatic and aromatic hydrocarbons trave different signs, they conclude that the mechanism causing hydrophobicity of these solutes is of a different nature. Here, we offer an alternative analysis of the dissolution of these non-polar compounds into water based on a recently published interpretation scheme for thermodynamic transfer functions. Our analysis shows that the hydrophobicity of aromatic and aliphatic hydrocarbons is qualitatively the same, i.e. its causes are the same namely the extremely high cohesive energy of water which overcomes the favorable solute-solute and solute-water interactions. However, both analyses conclude that the experimentally observed quantitative difference between the interactions of water with aliphatic and aromatic hydrocarbons, can be assigned to the formation of aromatic ring-water H-bonds.

  • 267. Craig, VSJ
    et al.
    Plunkett, M
    YKI – Ytkemiska institutet.
    Determination of coupled solvent mass in quartz crystal microbalance measurements using deuterated solvents2003Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 262, s. 126-129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simple method is described for determining of the contribution of hydrodynamically coupled solvent to the adsorbed film mass determined in a quartz crystal microbalance (QCM) when operated in liquid. The method requires no additional apparatus and utilizes the change in QCM resonant frequency response between measurements made in nondeuterated and deuterated solvents. The mass of coupled water in a polymer film has been determined and is found to agree with that determined by XPS analysis of the dried polymer film

  • 268. Cranston, ED
    et al.
    Gray, DG
    Rutland, MW
    YKI – Ytkemiska institutet.
    Direct surface force measurements of polyelectrolyte multilayer films containing nanocrystalline cellulose2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 22, s. 17190-17197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyelectrolyte multilayer films containing nanocrystalline cellulose (NCC) and poly(allylamine hydrochloride) (PAH) make up a new class of nanostructured composite with applications ranging from coatings to biomedical devices. Moreover, these materials are amenable to surface force studies using colloid-probe atomic force microscopy (CP-AFM). For electrostatically assembled films with either NCC or PAH as the outermost layer, surface morphology was investigated by AFM and wettability was examined by contact angle measurements. By varying the surrounding ionic strength and pH, the relative contributions from electrostatic, van der Waals, steric, and polymer bridging interactions were evaluated. The ionic cross-linking in these films rendered them stable under all solution conditions studied although swelling at low pH and high ionic strength was inferred. The underlying polymer layer in the multilayered film was found to dictate the dominant surface forces when polymer migration and chain extension were facilitated. The precontact normal forces betweenasilica probe and an NCC-capped multilayer film were monotonically repulsiveatpH values where the material surfaces were similarly and fully charged. In contrast, at pH 3.5, the anionic surfaces were weakly charged but the underlying layer of cationic PAH was fully charged and attractive forces dominated due to polymer bridging from extended PAH chains. The interaction with an anionic carboxylic acid probe showed similar behavior to the silica probe; however, for a cationic amine probe with an anionic NCC-capped film, electrostatic doublelayer attraction at low pH, and electrostatic double-layer repulsion at high pH, were observed. Finally, the effect of the capping layer was studied with an anionic probe, which indicated that NCC-capped films exhibited purely repulsive forces which were larger in magnitude than the combination of electrostatic double-layer attraction and steric repulsion, measured for PAH-capped films. Wherever possible, DLVO theory was used to fit the measured surface forces and apparent surface potentials and surface charge densities were calculated.

  • 269. Cárdenas, M
    et al.
    Valle-Delgado, JJ
    KTH Royal Institute of Technology, Sweden.
    Hamit, J
    Rutland, MW
    YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Arnebrant, T
    Interactions of hydroxyapatite surfaces: Conditioning films of human whole saliva2008Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 14, s. 7262-7268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydroxyapatite is a very interesting material given that it is the main component in tooth enamel and because of its uses in bone implant applications. Therefore, not only the characterization of its surface is of high relevance but also designing reliable methods to study the interfacial properties of films adsorbed onto it. In this paper we apply the colloidal probe atomic force microscopy method to investigate the surface properties of commercially available hydroxyapatite surfaces (both microscopic particles and macroscopic discs) in terms of interfacial and frictional forces. In this way, we find that hydroxyapatite surfaces at physiological relevant conditions are slightly negatively charged. The surfaces were then exposed to human whole saliva, and the surface properties were re-evaluated. A thick film was formed that was very resistant to mechanical stress. The frictional measurements demonstrated that the film was indeed highly lubricating, supporting the argument that this system may prove to be a relevant model for evaluating dental and implant systems.

  • 270. Dahlberg, C
    et al.
    Millqvist-Fureby, A
    YKI – Ytkemiska institutet.
    Schuleit, M
    Surface composition and contact angle relationships for differently prepared solid dispersions2008Inngår i: European journal of pharmaceutics and biopharmaceutics, ISSN 0939-6411, E-ISSN 1873-3441, Vol. 70, nr 2, s. 478-485Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid dispersions are promising drug delivery forms which offer the possibility to disperse a hydrophobic drug in a hydrophilic matrix and thereby improve the dissolution behavior and the bioavailability of the drug. One important aspect and a prerequisite in understanding the drug dissolution mechanism from solid dispersions is a better analytical monitoring of the solid dispersion surface properties, such as powder surface composition and water adsorption properties. In this paper, we have considered chemical and structural surface analysis data for solid dispersions processed by spray drying or roto-evaporation and compared these data with information obtained by contact angle measurements. Firstly, we establish the usefulness and suitability of X-ray photoelectron spectroscopy (XPS) for determination of surface chemical composition and scanning electron microscopy (SEM) for determining the structure of solid dispersions composed of different types of carriers, drugs and drug concentrations. Secondly, we measure contact angles of solid dispersions to describe wettability, to finally establish a link between the surface chemical composition, the powder structure and the wetting behavior. These experimental methods offer a rapid screening tool for the selection of carrier, drug concentration and/or process in early development. In addition, they provide a useful tool for investigating structural aspects of solid dispersions which have intrinsic relevance for drug dissolution and stability.

  • 271. Dahlberg, C
    et al.
    Millqvist-Fureby, A
    YKI – Ytkemiska institutet.
    Schuleit, M
    Dvinskikh, SV
    Furó, I
    Polymer mobilization and drug release during tablet swelling. A 1H NMR and NMR microimaging study2007Inngår i: Journal of Controlled Release, ISSN 0168-3659, E-ISSN 1873-4995, Vol. 122, s. 199-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of this study was to investigate the swelling characteristics of a hydroxypropyl methylcellulose (HPMC) matrix incorporating the hydrophilic drug antipyrine. We have used this matrix to introduce a novel analytical method, which allows us to obtain within one experimental setup information about the molecular processes of the polymer carrier and its impact on drug release. Nuclear magnetic resonance (NMR) imaging revealed in situ the swelling behavior of tablets when exposed to water. By using deuterated water, the spatial distribution and molecular dynamics of HPMC and their kinetics during swelling could be observed selectively. In parallel, NMR spectroscopy provided the concentration of the drug released into the aqueous phase. We find that both swelling and release are diffusion controlled. The ability of monitoring those two processes using the same experimental setup enables mapping their interconnection, which points on the importance and potential of this analytical technique for further application in other drug delivery forms.

  • 272.
    Dahlberg, Carina
    et al.
    YKI – Ytkemiska institutet.
    Dvinskikh, Sergey V
    Schuleit, Michael
    Furo, Istvan
    Polymer swelling, drug mobilization and drug recrystallization in hydrating solid dispersion tablets studied by multinuclear NMR microimaging and spectroscopy2011Inngår i: Molecular Pharmaceutics, ISSN 1543-8384, E-ISSN 1543-8392, Vol. 8, nr 4 Spec. iss., s. 1247-1256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the advantages offered by solid dispersions, the marketed products based on this technology are few. The most frequent concern is the stability of the amorphous drug. The state of the drug in solid dispersions is, in general, poorly characterized as the number of characterization techniques available to monitor nanometer-sized drug particles embedded in a matrix are limited. Here we present a combination of localized NMR spectroscopic and NMR imaging techniques which allow in situ monitoring of the state of the drug during tablet disintegration and dissolution. F-19 NMR relaxation is shown to be sensitive to both the crystalline/amorphous state and the size of the model nanoparticles made of the drug substance flutamide. The time course of drug mobilization and recrystallization is detected with spatial resolution within swelling solid dispersion tablets. Comparing results from spatially resolved F-19, H-2 and H-1 NMR experiments, recrystallization is related to its enabling factors such as local hydration level and local mobility of the polymer matrix. The initially amorphous drug may recrystallize either by nanoparticle coalescence or by ripening of crystalline grains.

  • 273. Dahlberg, Carina
    et al.
    Millqvist-Fureby, Anna
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Schuleit, Michael
    Furó, Istvan
    Polymer-drug interactions and wetting of solid dispersions2010Inngår i: European Journal of Pharmaceutical Sciences, ISSN 0928-0987, E-ISSN 1879-0720, Vol. 39, nr 1-3, s. 125-133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate the ability of drugs to influence the wetting of solid dispersion tablets in unexpected ways. Five model drugs of different water solubility and ability to interact with the involved polymers were incorporated in hydrophilic polymer matrices, made of either hydroxypropyl methylcellulose (HPMC) or polyvinyl pyrrolidone (PVP). The physical mixtures of all combinations of drug and polymer presented Surface hydrophobicities, as measured by the equilibrium advancing contact angle of water, which are expected for materials that do not influence the interactions of each other with water. However, the solid dispersions containing HPMC deviated from this regular behaviour and displayed contact angles below those of the pure compounds involved. either drug or polymer. This behaviour is explained by changed surface exposure of HPMC side groups, as a result of changes in intermolecular hydrogen bonds. In addition to water contact angle measurements, we employed NMR imaging to monitor the time course of water ingress and swelling.

  • 274. Dahlberg, Carina
    et al.
    Millqvist-Fureby, Anna
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Schuleit, Michael
    Furó, Istvan
    Relationships between solid dispersion preparation process, particle size and drug release - An NMR and NMR microimaging study2010Inngår i: European journal of pharmaceutics and biopharmaceutics, ISSN 0939-6411, E-ISSN 1873-3441, Vol. 76, nr 2, s. 311-319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid dispersion tablets prepared by either spray drying or rotoevaporation and exhibiting different grain and pore sizes were investigated under the process of hydration-swelling-gelation. H-2 and H-1 NMR microimaging experiments were used to selectively follow water penetration and polymer mobilization kinetics, respectively, while the drug release kinetics was followed by H-1 NMR spectroscopy. The obtained data, in combination with morphological information by scanning electron microscopy (SEM), reveal a complex process that ultimately leads to release of the drug into the aqueous phase. We find that the rate of water ingress has no direct influence on release kinetics, which also renders air in the tablets a secondary factor. On the other hand, drug release is directly correlated with the polymer mobilization kinetics. Water diffusion into the originally dry polymer grains determines the rate of grain swelling and the hydration within the grains varies strongly with grain size. We propose that this sets the stage for creating homogeneous gels for small grain sizes and heterogeneous gels for large grain sizes. Fast diffusion through water-rich sections of the inhomogeneous gels that exhibit a large mesh size is the factor which yields a faster drug release from tablets prepared by rotoevaporation.

  • 275. Dahlenborg, H
    et al.
    Millqvist-Fureby, Anna
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Brandner, Birgit D
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Bergenståhl, B
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Study of the porous structure of white chocolate by confocal Raman microscopy2012Inngår i: European Journal of Lipid Science and Technology, ISSN 1438-7697, E-ISSN 1438-9312, Vol. 114, nr 8, s. 919-926Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Confocal Raman microscopy has been shown to be a useful technique for investigation of white chocolate surfaces. The appearance of protrusions and pores, and the distribution of fat, sucrose, and milk powder at and below the surface of white chocolate pralines were investigated using confocal Raman microscopy. Raman horizontal and depth scans showed that the protrusions and pores continue at least 10μm into the chocolate shell and that some protrusions and channels mainly consist of fat, while some consisted of a fat layer, leaving a hollow space underneath. Further, the pores and their continuing channels consisted of nothing but air. These findings indicate that the protrusions might be connected to channels where we suggest a pressure driven convective flow of liquid fat from within the chocolate matrix that, depending on temperature, moves up to the surface or goes back into the matrix, leaving an empty pore with a shell of fat at the surface, which in some cases collapse and leaves a hollow pore and channel. Therefore, these findings support that the protrusions could be connected to oil migration in chocolate and, thus, further to fat bloom development.

  • 276. Dahlenborg, Hanna
    et al.
    Millqvist-Fureby, Anna
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Bergenståhl, Björn
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Kalnin, Daniel JE
    Investigation of chocolate surfaces using profilometry and low vacuum scanning electron microscopy2011Inngår i: Journal of the American Oil Chemists Society, ISSN 0003-021X, E-ISSN 1558-9331, Vol. 88, nr 6, s. 773-783Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study we establish the use of optical non-contact profilometry combined with low vacuum scanning electron microscopy (LV SEM) for the investigation of lipid surfaces. We illustrate, by using profilometry, a methodology for investigation of chocolate surface topology as a function of time, in the same area of interest. Both qualitative and quantitative data analysis has been performed for profilometry data. Further, relating these results to LV SEM images provides complementary topological information and hence a useful toolkit for the study of the chocolate surface prior and post fat bloom formation. For the demonstration of the successful combination of these two analytical techniques, white chocolate pralines were stored at two temperature-controlled conditions (at 18 °C, and cycled between 15 and 25 °C). Surface properties were then investigated during 36 weeks of storage. The surface images and the roughness parameters indicated distinct development of surface characteristics for the two storage conditions. From the results it is suggested that some imperfections, in the form of pores or protrusions, could play a role in fat bloom development and that there may be different main mechanisms of fat migration taking place for the different storage environments. In the present work, a positive correlation of profilometry data to chocolate surface characteristics and early bloom development has been established. There are indications that early prediction of fat bloom can be possible, however further work needs to be done to quantify prediction of fat bloom.

  • 277.
    Dahlgren, MAG
    YKI – Ytkemiska institutet.
    Direct measurement of attractive forces in an asymmetric polyelectrolyte system1996Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 181, s. 654-656Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article are presented results form direct measurements of interactions between one polyelectrolyte covered mics surface and one bare mica surface. There is a strong and long ranged attraction between the bare mica surface and the mica surface neutralized by adsorbed polyelectrolyte. The attraction is stronger and more long ranged in this asymmetric system than in a corresponding symmetric system. This attraction is of the same magnitude in strength in both 0.1 mM KBr and 10 mM KBr solution. The results support the findings from Monte Carlo simulations and mean field calculations presented in the preceeding article by Sjöström and Åkesson.

  • 278.
    Dahlgren, MAG
    YKI – Ytkemiska institutet.
    Effect of counterion valency and ionic strength on polyelectrolyte adsorption1994Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 10, s. 1580-1583Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of cationic polyelectrolytes onto negatively charged mica from solutions of variable ionic strength was studied using the interferometric surface force technique. The results show that the structure of the adsorbed layer of polyelectrolyte is strongly dependent on the ionic strength of the solution from which the initial adsorption takes place, rather than the valency of the counter-ion. Within the time for one experiment (1 week) it was not feasible to achieve the same layer structure by a stepwise increase of the ionic strength, as was obtained when the adsorption of the polyelectrolyte was carried out directly from the solution of the higher ionic strength. A mechanism for attraction due to counter-ion-bridges when large, flexible counter-ions are present in the solution is suggested.

  • 279.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Surface forces between adsorbed polyelectrolytes in salt solution1993Inngår i: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 93, s. 206-208Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Highly charged cationic polyelectrolyte was adsorbed onto mica from 10-4 M KBr and 10-4 M K2SO4 solutions. The results show that the structure of the adsorbed layer and the total amount adsorbed is dependent on the anion valency. Both the layer thickness and the adsorbed amount increase when the salt anion is of higher valency. Desorption over several days into 10-4 M K2SO4 solution was followed. This indicates the adsorbed layer initially overcompensates the mica lattice charge. After some time, the sign of the charge is re-reversed, due to desorption. Adhesion between the adsorbed layers increase during the desorption process. This adhesion is attributed to bridging of entropic origin.

  • 280.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Audebert, R
    Highly charged cationic polyelectrolytes on mica: Influence of polyelectrolyte concentration on surface forces1994Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 166, s. 343-349Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface force apparatus was used to study the effects of polyelectrolyte concentration on the interaction between mica sheets immersed in aqueous polyelectrolyte solution. We have found that at low polyelectrolyte concentration, adsorption of cationic polyelectrolyte to negatively charged mica leads to extremely flat adsorbed layers in solution of low ionic strength. There is a repulsion between the surfaces at separations between about 100 and 10 nm. This force is of electrostatic origin when the polyelectrolyte concentration is lower than that needed to neutralize the surface charge. When increasing the polyelectrolyte concentration above the charge neutralization point, cnp, only a slight additional adsorption takes place in low ionic strength solution. In these systems, a steric component in the interaction force appears. The adsorption at the cnp is approximately 20 % below that at the plateau level in the adsorption isotherm, which is found by ESCA measurements.

  • 281.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Audebert, R
    Interaction and adsorption of polyelectrolytes on mica1993Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 8, s. 62-67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Interaction and adsorption of different polyelectrolytes onto mica was studied using the surface force technique. For highly charged polyelectrolytes in dilute aqueous salt solution, the adsorbed layer neutralizes the mica surface charge at a bulk concentration of 10-50 ppm. Upon dilution the adsorbed layers desorb slowly. When the indifferent salt concentration of the solution is increased at a constant polyelectrolyte concentration, additional adsorption takes place. Attractive interactions are present between two layers of adsorbed polyelectrolytes with a charge density of 30% or more as long as the substrate surface charge is not overcompensated strongly. This attraction, which is mainly due to bridging, is considerably stronger than the van der Waals interaction. For uncharged polyelectrolyte/surface systems, the thickness of the polyelectrolyte equilibrium layer increases with decreasing charge density. For the fully charged polyelectrolyte, the range of bridging and steric interaction indicates that the polyelectrolytes adsorb in a flat conformation on the mica surface. Desorption of the polyelectrolytes into a dilute aqueous salt solution is a slow process. For an initially slightly overcompensated system, the long-range and adhesive forces vary with time in contact with a polyelectrolyte-free solution. Initially, the adhesion force increases as the net surface charge decreases. This is due to an increased bridging attraction.

  • 282.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Hollenberg, HCM
    Polyelectrolytes interacting with interfaces: Surface forces and theoretical results1996Inngår i: Berichte Der Bunsen-Gesellschaft: Physical Chemistry, Chemical Physics, ISSN 0005-9021, Vol. 100, s. 1004-1007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The order in which salt and polyelectrolyte is added to a solution influences the structure of the adsorbed polyelectrolyte on surfaces in contact with the solution, and the interactions between surfaces across such solutions. These effects were investigated using the interferometric surface force technique. The results show that in low ionic strength (0.1mM KBr), there is a strong attraction between two mica surfaces covered with oppositely charged polyelectrolytes. When the ionic strength is increased (up to 100 mM KBr), a long-ranged repulsion is developing. This repulsion is more long ranged and larger in magnitude when the salt is added before the polyelectrolyte than when salt is added to a system which already contains polyelectrolyte. This indicates a more extended adsorbed layer when the adsorption is carried out directly from the higher ionic strength solution. This more extended adsorbed layer is irreversibly compressed upon the first approach of the surfaces. Mean field calculations (Scheutjens-Fleer model) were used to rationalize experimental findings. The results from these calculations show that the adsorbed layer is much more extended in high ionic strength solutions, which is in good agreement with the experimental results.

  • 283.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Hollenberg, HCM
    Claesson, PM
    YKI – Ytkemiska institutet.
    The order of adding polyelectrolyte and salt affects surface forces and layer structures1995Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, s. 4480-4485Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The order in which salt and polyelectrolyte is added to a solution influences the structure of adsorbed layers on surfaces in contact with the solution and the interactions between surfaces across such solutions. By performing surface force measurements, it is shown that the strong attraction observed between polyelectrolyte coated surfaces in low ionic strength solutions is changed into a long ranged repulsion at solution of high ionic strength. This repulsion is more long ranged and larger in magnitude when the salt is added before the polyelectrolyte than when additions are done in the reverse order. When increasing the ionic strength in steps, the layer thickness and short range repulsion increases. We suggest that this is due to an increased adsorption of the polyelectrolyte. Mean field calculations (Scheutjens-Fleer model) were used to rationalize experimental findings. The results show that the adsorbed layer is much more extended in high ionic strength solutions. Furthermore, we show that the adsorption of polyelectrolyte is increased with ionic strength when the non-electrostatic interaction between polymer segments and the solvent is unfavourable.

  • 284.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Leermakers, FAM
    Depletion zones in polyelectrolyte systems: polydispersity effects and colloidal stability1995Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, s. 2996-3006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have used the Scheutjens-Fleer theory for polymers at interfaces to study depletion zone effects in polyelectrolyte systems. The segment density profiles of depletion regions are independent of the chain length, $N$, and the depletion interaction is often fully repulsive. In polyelectrolyte systems, a depletion zone develops both at adsorbing and at non-adsorbing interfaces, especially at low ionic strengths. Interactions which are repulsive at some surface separations and attractive at others can also be found, e. g. for intermediate ionic strength conditions or for very low charge density in the chain. At very high ionic strength or very low charge density, the classical neutral polymer depletion layers develop, causing attraction between particles in solution. Effects of polydispersity of the polyelectrolytes on the segment density profiles are small. There is a minor effect on the depletion region at low ionic strengths, provided that there is not a large fraction of very short chainspresent. Only depletion zones near adsorbing surfaces tend to be preferentially populated by low molecular weight polymer. Under these conditions, long chains are still depleted from this filled-up depletion region, which has immediate implications for the equilibration of the adsorbed layer: The diffusion of long chains through this region to the surface is slow. At an adsorbing surface, preferential adsorption of the longer polyelectrolytes over the shorter ones results in a fractionation of the chains at the adsorbing interface, if equilibrium can be reached.

  • 285.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Waltermo, Å
    Blomberg, E
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Sjöström, L
    Åkesson, T
    Salt effects on the interaction between adsorbed cationic polyelectrolyte layers - Theory and experiment1993Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 97, s. 11769-11775Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of inert salt concentration on polyelectrolyte adsorption from aqueous solutions onto oppositely charged surfaces, and the interactions between such surfaces were studied experimentally using a surface force technique and compared to theoretical predictions from Monte Carlo simulations. At a polyelectrolyte concentration of 10 ppm and a low inert salt concentration (10-4 M) the polyelectrolytes adsorb in a flat conformation and the force acting between the surfaces is close to zero down to a separation of 10-15 nm, where the surfaces jump inwards. The attractive force observed at separations below 10 nm is stronger than the expected van der Waals force. The magnitude and range of the attraction agrees with forces obtained from Monte Carlo simulation and we interpret the attraction as being due to bridging polyelectrolytes. When the salt concentration is increased, additional polyelectrolyte adsorption takes place. This gives again rise to a repulsive force, which is significantly larger than what is observed between bare surfaces. The extra repulsion is due to adsorbed polyelectrolytes stretching out from the surfaces and is also predicted from simulations.

  • 286.
    Dahlvik, P
    et al.
    YKI – Ytkemiska institutet.
    Ström, G
    YKI – Ytkemiska institutet.
    Eklund, D
    Variations in calcium ion concentration and pH influencing coating colour rheology, dewatering and immobilization1997Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 12, s. 61-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Interparticle interactions in a coating colour are largely influeced by electrolyte concentration and suspension pH. The degree of interaction is reflected in the rheological and dewatering properties of the colour as well as in the structural properties of the immobilized coating layer. In the present study an attempt is made to correlate the degree of interparticle interaction created within coating colours by variation in calcium ion concentration and pH with the atomic absorption spectroscopy were applied to gain further information about the degree of interaction. Results showed that coating colours of a mix of calcium carbonate and clay exhibit a pronounced elastic character. The elastic response increased with calcium ino concentration. This is due to calcium calcium ions binding to the dispersing agent, making it less effective. A further cauce is the decrease in the thickness on the diffuse layer of counter ions surrounding the pigment particles. A pH-reducation further strenghened the created intrinsic three-dimensional network structure. An increase in calcium ion concentration resulted in a reduced water retention, slightly pronounced by a higher pH. The immobilization solids content as did also a lower pH. Characterization of coated layers drawn down on polyester film confirmed that a combination of a high calcium ion concentration and a reduction of pH results in a pronounced pigment interaction, reflected in a thicker layer with lower density and higher roughness.

  • 287.
    Dahlvik, P
    et al.
    YKI – Ytkemiska institutet.
    Ström, G
    YKI – Ytkemiska institutet.
    Karathanasis, M
    Hermansson, E
    Eklund, D
    Interactions in coating colours induced by a thermally active cellulosic polymer1999Inngår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 25, s. 229-234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A thermally active polymer, ethyl hydroxyethyl cellulose (EHEC), was evaluated with respect to its ability to generate temperature-induced interactions between components in coating colors. At low temperatures the polymer is water soluble, providing a good flow behavior to the color. As the temperature is raised a phase separation of the polymer takes place, inducing an interaction between the components in the color. Rheological measurements showed that using EHEC as thickener resulted in a significant temperature-induced viscosity increase of the coating color. The increase in viscosity was found to be a result of interactions taking place between the three-component system consisting of EHEC, latex and pigment. The increase in viscosity with increasing temperature was further shown to correlate with the styrene/butadiene ratio in the latex. It was also found that a higher amount of EHEC was adsorbed on English clay than on ground calcium carbonate. This affected the degree of interaction within the three-component system EHEC-latex-pigment, in that the increase in viscosity with temperature was lower when English clay was used. However, when delaminated US clay was used, a strong temperature effect was detected.

  • 288. Darcovich, K
    et al.
    Toll, FN
    Meurk, A
    YKI – Ytkemiska institutet.
    Sintering effects on the porous characteristics of functionally gradient ceramic membrane structures2001Inngår i: Journal of porous materials, ISSN 1380-2224, E-ISSN 1573-4854, Vol. 8, s. 215-223Artikkel i tidsskrift (Fagfellevurdert)
  • 289. de Peppo, GM
    et al.
    Palmquist, A
    Borchardt, P
    YKI – Ytkemiska institutet.
    Lennerås, M
    Hyllner, J
    Snis, A
    Lausmaa, J
    YKI – Ytkemiska institutet.
    Free-form-fabricated commercially-pure Ti and Ti6Al4V porous scaffolds support the growth of human embryonic stem cell-derived medsodermal progenitors2012Inngår i: The Scientific World Journal, ISSN 2356-6140, Vol. 2012, artikkel-id art. ID 646417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Commercially-pure titanium (cp-Ti) and the titanium-aluminum-vanadium alloy (Ti6Al4V) are widely used as reconstructive implants for skeletal engineering applications, due to their good mechanical properties, biocompatibility and ability to integrate with the surrounding bone. Electron beam melting technology (EBM) allows the fabrication of customized implants with tailored mechanical properties and high potential in the clinical practice. In order to augment the interaction with the biological tissue, stem cells have recently been combined with metallic scaffolds for skeletal engineering applications. We previously demonstrated that human embryonic stem cell-derived mesodermal progenitors (hES-MPs) hold a great potential to provide a homogeneous and unlimited supply of cells for bone engineering applications. This study demonstrates the effect of EBM-fabricated cp-Ti and Ti6Al4V porous scaffolds on hES-MPs behavior, in terms of cell attachment, growth and osteogenic differentiation. Displaying different chemical composition but similar surface properties, EBM-fabricated cp-Ti and Ti6Al4V scaffolds supported cell attachment and growth, and did not seem to alter the expression of genes involved in osteogenic differentiation and affect the alkaline phosphatase activity. In conclusion, interfacing hES-MPs to EBM-fabricated scaffolds may represent an interesting strategy for design of third-generation biomaterials, with the potential to promote implant integration in clinical conditions characterized by poor bone quality. Copyright 2012 G. M. de Peppo et al.

  • 290.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Bastardo, L
    Interactions between mucin and surfactants at solid-liquid interfaces2002Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, s. 9383-9392Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The association between mucin and surfactants at the solid-liquid interface has been investigated employing reflectometry. The study is particularly aimed at understanding the removal of preadsorbed mucin layers by surfactant addition. To this end we investigated the effect of three different surfactants, one anionic surfactant, sodium dodecylsulfate (SDS), and two nonionic ones, penta(oxy ethylene) dodecyl ether (C12E5 ) and n-dodecylß -D-maltopyranoside (C12-mal). All three surfactants were found to be potent in removing mucin from hydrophobic surfaces. On the other hand, C12-mal was found to have a very limited effect on mucin adsorbed to hydrophilic negatively charged surfaces, whereas the mucin layer was removed by SDS and C12E5 . The association between mucin and the three different surfactants was also investigated by means of dynamic light scattering and surface tension measurements. It was concluded that SDS associates readily with mucin above a critical surfactant concentration, about 0.2 cmc, whereas the nonionic surfactants associate with mucin to a very limited degree. The results obtained with the different techniques allow us to propose that C12E5 removes mucin from silica surfaces by competitive adsorption, whereas the removal of mucin by SDS is due to formation of mucin/SDS complexes that have reduced surface affinity and increased water solubility compared to mucin alone

  • 291.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Campbell, B
    Interactions between mica surfaces across triglyceride solution containing phospholipid and polyglycerol polyricinoleate2000Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, s. 2248-2253Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results obtained by direct measurements of the forces acting between polar mica surfaces interacting across solutions of triolein containing phosphatidylethanolamine (PE), polyglycerol polyricinoleate (PGPR), and PE/PGPR mixture are presented. It was shown that PE adsorbed on mica >from anhydrous triolein and thus rendered the surface non-polar. The change in ordering of the liquid triolein molecules induced by bringing two such surfaces together gives rise to a structural force with two force barriers. In contrast, the adsorption of PGPR from anhydrous triolein resulted in a steric force barrier with a range of 120 Å. It was also found that from the mixture of PE and PGPR in triolein both additives adsorbed as a complex on mica surfaces. The presence of these aggregates on the surfaces gave rise to a very long-range strong repulsive force. We discuss the implication of the measured forces to colloidal stability of particle dispersion in non-polar media and compare the efficiency of additives as dispersion stabilizers. We also show, that the presence of water has an effect on the adsorbed layer structures. When PE is used as a dispersing agent, water induces formation of aggregates, which would provide strong repulsive barriers between the particles. In contrast, when PGPR is used as additive, water preferentially adsorbs on the polar mica surface and at water saturation gives rise to a capillary formation around the surface contact position. Finally, when a mixture of PE and PGPR is used, water is found to result in formation of a viscous, sticky adsorbed layer that would flocculate the particles.

  • 292.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Interfacial properties of aggregates formed by cationic polyelectrolyte and anionic surfactant2000Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, s. 1951-1959Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Interactions between mica surfaces across aqueous solutions containing mixtures of a highly positively charged polyelectrolyte and an anionic surfactant were studied using a surface force apparatus. The investigation was carried out using a constant polyelectrolyte concentration (20 ppm) and a wide range of surfactant concentrations (0 - 1 cmc). The chemical composition of the adsorbed polyelectrolyte-surfactant layers was analysed by XPS. The properties of polyelectrolyte-surfactant aggregates formed in bulk were studied by measurements of turbidity and electrophoretic mobility. The aggregates formed at low surfactant concentrations (<0.04 cmc) were positively charged, whereas at higher surfactant concentrations the aggregates carried a net negative charge. It was shown that polyelectrolyte-surfactant aggregates rapidly adsorb on negatively charged mica surfaces regardless of the sign of their charge. At surfactant concentrations up to 0.01 cmc, the polyelectrolytes adsorb on mica surfaces with loops and tails stretching out into solution and repulsive steric forces are generated. The thickness of the layer decreases with time and we suggest that this conformational change is accompanied by some expulsion of surfactant >from the adsorbed layers. Thick adsorbed layers were formed in the surfactant concentration range 0.02 - 0.1 cmc. In this concentration regime the measurement of equilibrium forces was inaccessible due to a very slow layer relaxation. During compression the forces were repulsive and during separation an attraction developed. We attribute this to formation of interlayer surfactant bridges. Finally, at high surfactant concentrations (≥ 0.4 cmc) highly negatively charged aggregates adsorb on the surfaces in rather thin layers, resulting in purely repulsive forces of mixed electrostatic and steric origin.

  • 293.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Campbell, B
    Mays, H
    Interactions between modified mica surfaces in triglyceride media1998Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, s. 5546-5554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results obtained from surface force measurements using modified nonpolar mica surfaces immersed in triolein are presented. The force vs distance curves were determined for different water activities in the interaction medium. Two oscillations with a periodicity of 20 Å were observed in the force curve measured across anhydrous triolein. The force barriers appear at separations of 45-40 and 20-30 Å. It is suggested that triolein has no clear preferential orientation of the oleic acid chains outside a nonpolar surface. This is different from outside a polar mica surface where triolein adopts conformations with the three oleic acid residues directed toward the bulk. At high water contents the triolein molecules outside nonpolar surfaces suddenly change their orientation when a high compressive force is applied. The forces acting between mica surfaces were measured in triolein solutions containing phospholipids at different water activities. It was shown that the phospholipid self-assembled onto the mica surfaces and rendered them nonpolar. The forces between such surfaces in anhydrous triolein are similar to those observed between mica hydrophobized using the Langmuir-Blodgett technique. In addition, at high water activities a weak long range repulsive force was observed. This force was interpreted as being due to weakly adsorbed phospholipid aggregates. We discuss the implications of the results for the stability and physical properties of colloidal particle dispersions in nonpolar media. Adsorption isotherms for the phospholipid from refined vegetable oil at low water activity on mica and sucrose crystals are presented. They show that the phospholipid adsorbs in a monolayer on mica. On sucrose more than monolayer coverage is observed, which we interpret in terms of a phase separation of phospholipid into crevices and cracks.

  • 294.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Bergenståhl, B
    YKI – Ytkemiska institutet.
    Campbell, B
    Interactions between hydrophilic surfaces in triglyceride media - information obtained from surface force measurements1997Inngår i: Food Hydrocolloids, ISSN 0268-005X, E-ISSN 1873-7137, Vol. 11, s. 7-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The application of surface force measurements for modelling the behaviour of food colloid system, in particular dispersions of hydrophilic particles in oil continuous media, is discussed. Interactions between two mica surfaces across a triglyceride, triolein, in anhydrous state and containing different amounts of dissolved water, have been investigated. The water content influences the layering of triolein molecules at the surfaces and whereby their interactions. The relation between surface force data (e.g. the magnitude of the force barrier and the adhesion force) to the properties of colloidal systems is discussed. Further, the importance of capillary condensation for particle interactions in triolein saturated with water is demonstrated.

  • 295.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Bergström, M
    YKI – Ytkemiska institutet.
    Polyelectrolyte-surfactant layers: Adsorption of preformed aggregates versus adsorption of surfactant to preadsorbed polyelectrolyte2000Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, s. 5257-5266Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The character of adsorbed layers containing both polyelectrolyte and surfactant depends on the type of polyelectrolyte used and the surfactant concentrations, as demonstrated by several recent studies. However, the layer properties also depend on the experimental pathway. This shows that the adsorbed layers can be trapped in quasi-equilibrium states, and that the true equilibrium state is only reached over experimentally inaccessible time scales. This has to be kept in mind when comparing different results reported in the literature. The present article highlights these effects using a system consisting of a highly charged cationic polyelectrolyte and an anionic surfactant. The adsorbed layer properties were determined using mainly surface force measurements and AFM imaging. We also present some new small angle neutron scattering data for bulk complexes formed between the polyelectrolyte and the surfactant, which demonstrates the presence of a characteristic correlation length of about 37-39 Å. A similar characteristic length-scale is also observed in some of the adsorbed layers, both employing the AFM and the surface force apparatus.

  • 296.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Nygren, J
    Iliopoulos, I
    Interactions between surfaces coated with cationic hydrophobically modified polyelectrolyte in the presence and the absence of oppositely charged surfactant2000Inngår i: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 116, s. 84-94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    (1) Department of Chemistry Surface Chemistry Royal Institute of Technology 100 44 Stockholm and Institute for Surface Chemistry, Box 5607, 114 86 Stockholm Sweden (2) Laboratoire de Physico-Chimie Macromoleculaire, UMR-7615, ESPCI CNRS, Universite Pierre et Marie Curie ESPCI, 10 Rue Vauquelin, 75231 Paris Cedex 5, France The association between a cationic hydrophobically modified polyelectrolyte and an anionic surfactant was investigated in bulk solution and at a negatively charged solid surface. The bulk association was followed by measurements of turbidity and electrophoretic mobility. The maximum turbidity of the solution was found to closely coincide with the point of zero electrophoretic mobility of the aggregates. The forces acting between negatively charged mica surfaces across a dilute aqueous solution of the hydrophobically modified polyelectrolyte were monitored using surface force measurements. The presence of hydrophobic side chains on the polyelectrolyte leads to adsorption in an inner rather compact layer and an outer extended layer. After dilution only the inner layer remains adsorbed to the surface. In the next step, sodium dodecyl sulphate (SDS) was added. It was found that the anionic surfactant is incorporated in the adsorbed layer even at very low bulk concentrations. As the surfactant concentration is increased stepwise the layer first swells and relaxes very slowly during compression. At higher SDS concentrations, desorption occurs. The interfacial properties of the hydrophobically modified polyelectrolyte alone and in mixtures with SDS are in many ways strikingly different to those of non-hydrophobically modified polyelectrolytes having a similar linear charge density. This is due to the importance of hydrophobic interactions between the hydrophobic side chains of the polyelectrolyte and between these groups and the nonpolar part of the surfactant

  • 297.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Iruthayara, J
    Gorochovceva, N
    Makuska, R
    Claesson, PM
    YKI – Ytkemiska institutet.
    Interfacial properties of chitosan-PEO graft oligomers: Surface competition with unmodified chitosan oligomers2006Inngår i: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 132, s. 124-130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Oligomers of chitosan carrying 45 units long poly(ethylene oxide), PEO, chains grafted to the C-6 position of the sugar units were prepared using a novel synthesis route. The graft density was high, close to one poly(ethylene oxide) chain grafted to each sugar unit of the chitosan oligomer but a small fraction of unreacted chitosan remained in the sample. The molecular weight distribution of the sample was determined using GPC. The interfacial properties of the chitosan-PEO graft oligomers were evaluated using X-ray photoelectron spectroscopy and surface force measurements. It was found that the small fraction of unreacted chitosan was significantly enriched at the solid-solution interface on negatively charged muscovite mica surfaces. The interactions between chitosan-PEO oligomer coated surfaces were found to be dominated by the extended PEO chains, and at high coverage the measured forces were consistent with those expected for polymer brushes. Addition of salt up to 10 mM did not result in any significant desorption of preadsorbed oligomer layers.

  • 298.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Lundin, M
    Macakova, L
    YKI – Ytkemiska institutet.
    Auletta, A
    Mucin-chitosan complexes at the solid-liquid interface: Multilayer formation and stability in surfactant solutions2005Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, s. 9502-9509Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of a biologically important glycoprotein, mucin, and mucin-chitosan complex layer formation on negatively charged surfaces, silica and mica, have been investigated employing ellipsometry, the interferometric surface apparatus, and atomic force microscopy techniques. Particular attention has been paid to the effect of an anionic surfactant sodium, dodecyl sulfate (SDS), with respect to the stability of the adsorption layers. It has been shown that mucin adsorbs on negatively charged surfaces to form highly hydrated layers. Such mucin layers readily associate with surfactants and are easily removed from the surfaces by rinsing with solutions of SDS at concentrations ≥0.2 cmc (1 cmc SDS in 30 mM NaCl is equal to 3.3 mM). The mucin adsorption layer is negatively charged, and we show how a positively charged polyelectrolyte, chitosan, associates with the preadsorbed mucin to form mucin-chitosan complexes that resist desorption by SDS even at SDS concentrations as high as 1 cmc. Thus, a method of mucin layer protection against removal by surfactants is offered. Further, we show how mucin-chitosan multilayers can be formed.

  • 299. Deguchi, Shigeru
    et al.
    Shimoshige, Hirokazu
    Tsudome, Mikiko
    Mukai, Sada-atsu
    Corkery, Robert W
    YKI – Ytkemiska institutet.
    Ito, Susumu
    Microbial growth at hyperaccelerations up to 403,627 x g2011Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 19, s. 7997-8002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is well known that prokaryotic life can withstand extremes of temperature, pH, pressure, and radiation. Little is known about the proliferation of prokaryotic life under conditions of hyperacceleration attributable to extreme gravity, however. We found that living organisms can be surprisingly proliferative during hyperacceleration. In tests reported here, a variety of microorganisms, including Gram-negative Escherichia coli, Paracoccus denitrificans, and Shewanella amazonensis; Gram-positive Lactobacillus delbrueckii; and eukaryotic Saccharomyces cerevisiae, were cultured while being subjected to hyperaccelerative conditions. We observed and quantified robust cellular growth in these cultures across a wide range of hyperacceleration values. Most notably, the organisms P. denitrificans and E. coli were able to proliferate even at 403, 627 x g. Analysis shows that the small size of prokaryotic cells is essential for their proliferation under conditions of hyperacceleration. Our results indicate that microorganisms cannot only survive during hyperacceleration but can display such robust proliferative behavior that the habitability of extraterrestrial environments must not be limited by gravity.

  • 300. Delgado, C
    et al.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Van Alstine, JM
    Analytical partitioning of poly(ethyleneglycol)-modified proteins1997Inngår i: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 692, s. 263-272Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Covalently grafting proteins with varying numbers (n) of poly(ethylene glycol) molecules (PEGs) often enhances their biomedical and industrial usefulness. Partition between the phases in aqueous polymer two-phase systems can be used to rapidly characterize polymer-protein conjugates in a manner related to various enhancements. The logarithm of the partition coefficient (K) approximates linearity over the range 0

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