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Martin Malmsten - One of the best experts on this subject based on the ideXlab platform.
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Ellipsometry and TIRF studies of enzymatic degradation of interfacial proteinaceous Layers
Langmuir, 2001Co-Authors: I Cecilia Hahn Berg, Dries Muller, † Thomas Arnebrant, Martin MalmstenAbstract:Ellipsometry and total internal reflectance fluorescence spectroscopy (TIRF) have been employed to investigate the Layer structure of gelatin Adsorbed from aqueous solutions onto silica/glass and methylated silica/glass, as well as the effects of addition of the proteolytic enzymes krillase and trypsin, in relation to temperature, enzyme concentration, and enzymatic activity. The results for the hydrophilic substrates show that homogeneous and heterogeneous exchange occurs readily, as does autolysis of trypsin at the interface. At the hydrophobic substrates, the effect of exchange is limited and a residual gelatin fraction is present at the interface throughout. The interfacial behavior of gelatin above and below the helix formation temperature (Thelix) shows that more extended surface Layers are formed at both substrates below Thelix. At the hydrophilic substrates, the higher Adsorbed Layer Thickness below Thelix is mainly due to the adsorption of more gelatin than at the higher temperature, whereas, at ...
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Tumor cell locomotion and metastatic spread
Microscopy research and technique, 1998Co-Authors: Günter Siegel, Martin Malmsten, Dietrich KlüßendorfAbstract:The cytoskeletal filament proteins alpha-actinin, filamin, desmin, and filamin-desmin aggregates were Adsorbed to a hydrophobic silica surface. The Adsorbed amount as measured by ellipsometric methods after rinsing and equilibration was 2.7 mg/m2 for alpha-actinin and 0.4 mg/m2 for filamin plus desmin, respectively. Adsorbed Layer Thicknesses in physiological salt solution were about 107 nm, 89 nm, 108 nm and 93 nm for alpha-actinin, filamin, desmin, and cross-linked filamin-desmin, respectively. Ca2+ ions in a concentration of 10(-4), 10(-3), and 2.52 mmol/l had no effect on the Adsorbed amount, refractive index, and Adsorbed Layer Thickness of the individual intermediate filament proteins. Cross-linked filamin-desmin, however, reacted markedly upon the addition of these Ca2+ concentrations with a change in refractive index and Adsorbed Layer Thickness. The Layer formed by the filamin-desmin complex contracted by 2-3, 6-7, and 6-7 nm, respectively. The maximum shortening occurred at 1 pmol/l Ca2+. The Ca(2+)-dependent Adsorbed Layer changes of cross-linked filamin-desmin supports the contractile mechanisms in muscular tissues and forms the basis for migration and motility in nonmuscular cells. These motional events are crucially involved in peripheral organ perfusion, inflammation, and tumor invasion and metastasis.
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Adsorption of Complement Protein C3 at Polymer Surfaces
Journal of Colloid and Interface Science, 1996Co-Authors: Martin Malmsten, Bo Lassen, Jerker Westin, Carl-gustaf Gölander, Rolf Larsson, Ulf R. NilssonAbstract:The adsorption of C3 at poly(methyl methacrylate) (PMMA) and poly(styrene) (PS) surfaces was investigated within situellipsometry and compared to that at (hydrophilic and negatively charged) silica and (hydrophobic) methylated silica. The adsorption of C3 at PMMA was higher than that at PS, while the Adsorbed Layer Thickness was the same for the two surfaces. For both PMMA and PS the Adsorbed Layer Thickness (10 ± 2 nm) corresponds rather closely to that of end-on oriented C3 molecules. The adsorption of C3 at PMMA and PS was found to be intermediate between that at silica and methylated silica, although the Adsorbed Layer Thickness was similar for all surfaces. The competitive adsorption among C3, human serum albumin (HSA), and factor B was investigated with ellipsometry and total internal reflection fluorescence spectroscopy (TIRF). Addition of HSA after C3 preadsorption resulted in fractional C3 desorption for both PMMA and PS. Factor B deposition at PS after preadsorption of C3 and blocking with HSA was found to be largely due to specific binding to C3/C3b, while in the case of PMMA, factor B was largely accumulated through passive (displacement) adsorption.
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Structure of Protein Layers during Competitive Adsorption
Journal of Colloid and Interface Science, 1996Co-Authors: Bo Lassen, Martin MalmstenAbstract:Abstract The formation of protein Layers during competitive adsorption was studied with ellipsometry. Single, binary, and ternary protein solutions of human serum albumin (HSA), IgG, and fibrinogen (Fgn) were investigated at concentrations corresponding to blood plasma diluted 1/100. As a model surface, hydrophobic hexamethyldisiloxane (HMDSO) plasma polymer modified silica was used. By using multiambient media measurements of the bare substrate prior to protein adsorption the Adsorbed amount as well as the Thickness and refractive index of the Adsorbed protein Layer could be followedin situand in real time. Under conditions used in these experiments neither IgG nor fibrinogen could fully displace serum albumin from the interface. The buildup of the protein Layer occurred via different mechanisms for the different protein systems. Fgn Adsorbed in a rather flat orientation at low Adsorbed amounts, while at higher surface coverage the protein reoriented to a more upright orientation in order to accommodate more molecules in the Adsorbed Layer. IgG adsorption proceeded mainly end-on with little reorientation or conformational change on adsorption. Finally, for HSA an Adsorbed Layer Thickness greater than the molecular dimensions was observed at high concentrations (although not at low), indicating that aggregates or multiLayers formed on HMDSO plasma polymer surfaces. For all protein mixtures the Adsorbed Layer structure and buildup indicated that Fgn was the protein dominating the Adsorbed Layer, although HSA partially blocked the adsorption of this protein. At high surface concentration, HSA/Fgn mixtures show an abrupt change in both Adsorbed Layer Thickness and refractive index suggesting, e.g., an interfacial phase transition of the mixed protein Layer. A similar but less pronounced behavior was observed for HSA/IgG. For IgG/Fgn and HSA/IgG/Fgn a buildup of the Adsorbed Layer similar to that displayed by Fgn alone was observed.
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Ellipsometry Studies of Interfacial Film Formation in Emulsion Systems
Journal of Colloid and Interface Science, 1995Co-Authors: Martin Malmsten, Anna-lena Lindström, Torbjörn WärnheimAbstract:Abstract The possibility of using in situ ellipsometry for studies of the formation of interfacial films in emulsion systems was investigated. It was found that ellipsometry studies on dilute emulsions can provide information on the adsorption kinetics, the Adsorbed Layer structure, and the mechanisms of formation of the Adsorbed Layer. At high electrolyte concentrations, the adsorption from a model o/w emulsion stabilized by egg lecithin was found to be more pronounced at hydrophilic and negatively charged silica than at hydrophobic methylated silica. Furthermore, the Adsorbed Layer Thickness at both surfaces is smaller than the average droplet size, corresponding to either small or "flattened" droplets or liposomes. The Adsorbed Layer Thickness is smaller at methylated silica than at silica, presumably due to a larger degree of emulsion droplet or liposome spreading at this surface. In both cases, the Adsorbed Layer Thickness is independent of the Adsorbed amount, i.e., the Adsorbed Layer formation proceeds by attachment of droplets, which pack more densely with an increasing Adsorbed amount.
Paschalis Alexandridis - One of the best experts on this subject based on the ideXlab platform.
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Nanoparticle surface modification by amphiphilic polymers in aqueous media: Role of polar organic solvents
Journal of colloid and interface science, 2013Co-Authors: Biswajit Sarkar, Vinithra Venugopal, Andrew M. Bodratti, Marina Tsianou, Paschalis AlexandridisAbstract:We investigate the role of three polar organic solvents (dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), and glycerol) on the interfacial behavior of Pluronic P105 poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymers on protonated silica nanoparticles in an aqueous dispersion. The polymer adsorption and self-assembly have been assessed from critical surface micelle concentration (csmc, measured by pyrene fluorescence spectroscopy) and Adsorbed Layer Thickness (measured by capillary viscometry) data. Above its csmc, PEO–PPO–PEO block copolymers form hydrophobic domains on the nanoparticle surface. Below a critical concentration in water (known as critical displacer concentration, cdc), organic solvents act as displacers (molecules that can displace Adsorbed polymer from a solid surface). The critical displacer concentration is obtained from the csmc and the polymer Adsorbed Layer Thickness data. The cdc is found to be dependent on both the amount of nanoparticles present in the system as well as the nature of the displacer. Below the cdc, the csmc increases and the Adsorbed polymer Layer Thickness decreases with increasing organic solvent concentration. Interfacial free energy calculations suggest that DMF, DMSO, and glycerol can adsorb onto the silica particles by displacing Adsorbed PEO. These calculations are consistent with the experimental results in that, as a displacer, glycerol is the most effective and DMF is the least effective. Above the cdc, the influence of glycerol or DMSO on csmc is opposite to that of DMF which is attributed to the cosolvent effect.
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Adsorption of a polymeric siloxane surfactant on carbon black particles dispersed in mixtures of water with polar organic solvents.
Journal of colloid and interface science, 2002Co-Authors: Yining Lin, Thomas W. Smith, Paschalis AlexandridisAbstract:Abstract The adsorption of a rake-type polymeric siloxane surfactant (polydimethylsiloxane-graft-polyether copolymer) on carbon black (CB) particles dispersed in mixtures of water with polar organic solvents (ethanol, formamide, or glycerol) has been investigated. The adsorption obeys the Langmuir isotherm at low surfactant concentrations (below the critical micelle concentration, CMC). At these conditions, the average surface area occupied by one siloxane surfactant follows the sequence water+glycerol mixture>plain water>water+ethanol mixture. At higher surfactant concentrations in the solution in contact with the particles, a sharp increase in the Adsorbed amount is observed. The Adsorbed Layer Thickness has been determined by dynamic light scattering. Below the CMC the Adsorbed Layer Thickness is less than 10 nm. Above the CMC, the Adsorbed Layer Thickness increases to 20–30 nm, a length scale comparable to the diameter of the siloxane surfactant micelles in aqueous solution. This fact, together with SANS data that we have obtained in the absence of added polar organic solvent, indicates that the structure of the Adsorbed Layer is similar to that of micelles. The findings presented here are relevant to waterborne coatings and ink formulations, where polymeric surfactants are used in conjunction with polar organic solvents.
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Adsorption of a Rake-Type Siloxane Surfactant onto Carbon Black Nanoparticles Dispersed in Aqueous Media
Langmuir, 2002Co-Authors: Yining Lin, Thomas W. Smith, Paschalis AlexandridisAbstract:The adsorption properties of a rake-type siloxane surfactant (consisting of a poly(dimethylsiloxane) backbone with grafted polyether) on carbon black (CB) nanoparticles have been investigated. The CB particles have fractal structure according to transmission electron microscopy and small-angle neutron scattering (SANS) data. Surface compositions, determined by X-ray photoelectron spectroscopy, indicate that the CB surface is partly oxidized, prove the adsorption of the siloxane surfactant onto the CB particles, and suggest that the surface coverage is incomplete. The adsorption obeys the Langmuir isotherm at low filtrate concentrations (below the critical micelle concentration, cmc). At higher filtrate concentrations, a sharp increase in the Adsorbed amount is observed. The Adsorbed Layer Thickness was determined by viscometry and dynamic light scattering. These two methods give good agreement on the Adsorbed Layer Thickness (∼30 nm) at surfactant concentrations above the cmc. This Thickness is comparable...
Tharwat F. Tadros - One of the best experts on this subject based on the ideXlab platform.
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Viscoelastic properties of sterically stabilised emulsions and their stability.
Advances in colloid and interface science, 2015Co-Authors: Tharwat F. TadrosAbstract:Abstract The interaction forces between emulsion droplets containing Adsorbed polymeric surfactants and the theory of steric stabilisation are briefly described. The results for the viscoelastic properties of O/W emulsions that are stabilised with partially hydrolysed poly(vinyl acetate) that is commonly referred to as poly(vinyl alcohol) (PVA) with 4% vinyl acetate are given. The effect of the oil volume fraction, addition of electrolytes and increasing temperature is described. This allows one to obtain various parameters such as the Adsorbed Layer Thickness, the critical flocculation concentration of electrolyte (CFC) and critical flocculation temperature (CFT) at constant electrolyte concentration. The viscoelastic properties of O/W emulsions stabilised with an A-B-A block copolymer of polyethylene oxide (A) and polypropylene oxide (B) are described. These emulsions behave as viscoelastic liquids showing a cross-over-point between G′ (the elastic component of the complex modulus) and G″ (the viscous component of the complex modulus) at a characteristic frequency. Plots of G′ and G″ versus oil volume fraction ϕ show the transition from predominantly viscous to predominantly elastic response at a critical volume fraction ϕ c . The latter can be used to estimate the Adsorbed Layer Thickness of the polymeric surfactants. Results are also shown for W/O emulsions stabilised with an A-B-A block copolymer of polyhydroxystearic acid (PHS, A) and polyethylene oxide (PEO, B). The viscosity volume fraction curves could be fitted to the Dougherty–Krieger equation for hard-spheres. The results could be applied to give an estimate of the Adsorbed Layer Thickness Δ which shows a decrease with increase of the water volume fraction. This is due to the interpenetration and/or compression of the PHS Layers on close approach of the water droplets on increasing the water volume fraction. The last section of the review gives an example of O/W emulsion stability using an AB n graft copolymer of polyfructose (A) to which several C 12 alkyl chains are grafted. The emulsions are stable both at high temperature and in the presence of high electrolyte concentrations (2 mol dm − 3 NaCl). This high stability is due to the strong adsorption (“anchoring”) of the graft copolymer with several C 12 alkyl chains and the strong hydration of the polyfructose chains both in water and in the presence of high electrolyte concentrations and temperature. Evidence for this high stability is obtained using disjoining pressure measurements which show a highly stable film between the emulsion droplets and absence of its rupture up to high pressures.
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viscoelastic properties of polystyrene and poly methyl methacrylate dispersions sterically stabilized by hydrophobically modified inulin polyfructose polymeric surfactant
Journal of Colloid and Interface Science, 2008Co-Authors: Jeremie Nestor, Marc Obiolsrabasa, Jordi Esquena, Conxita Solans, Bart Levecke, Karl Booten, Tharwat F. TadrosAbstract:Abstract Recently, steric repulsive forces induced by a new graft copolymer surfactant, which is based in inulin (polyfructose), have been described. Previous investigations by atomic force microscopy between solid surfaces covered with Adsorbed surfactant indicated strong repulsive forces even at high electrolyte concentration, due to the steric repulsion produced by the surfactant hydration. In the present paper, the colloidal stabilization provided by this surfactant is studied by rheology. The measurements were carried out on sterically stabilized polystyrene (PS) and poly(methyl methacrylate) (PMMA) containing Adsorbed surfactant (INUTEC®SP1). Steady-state shear stress as a function of shear rate curves was established at various latex volume fractions. The viscosity volume fraction curves were compared with those calculated using the Doughtry–Krieger equation for hard sphere dispersions. From the experimental η r – ϕ curves the effective volume fraction of the latex dispersions could be calculated and this was used to determine the Adsorbed Layer Thickness Δ. The value obtained was 9.6 nm, which is in good agreement with that obtained using atomic force microscopy (AFM). Viscoelastic measurements of the various latex dispersions were carried out as a function of applied stress (to obtain the linear viscoelastic region) and frequency. The results showed a change from predominantly viscous to predominantly elastic response at a critical volume fraction ( ϕ c ). The effective critical volume fraction, ϕ eff , was calculated using the Adsorbed Layer Thickness (Δ) obtained from steady-state measurements. For PS latex dispersions ϕ eff was found to be equal to 0.24 whereas for PMMA ϕ eff = 0.12 . These results indicated a much softer interaction between the latex dispersions containing hydrated polyfructose loops and tails when compared with latices containing poly(ethylene oxide) (PEO) Layers. The difference could be attributed to the stronger hydration of the polyfructose loops and tails when compared with PEO. This clearly shows the much stronger steric interaction between particles stabilized using hydrophobically modified inulin.
Chai Shan - One of the best experts on this subject based on the ideXlab platform.
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A continuous viscosity model for thin film lubrication
Tribology International, 2002Co-Authors: Qu Quingwen, Wang Mei, Wang Lihua, Chai ShanAbstract:The Thickness of Adsorbed molecular Layers is the most critical factor in studying thin film lubrication, and is a key feature that distinguishes thin from thick film lubrication analysis. A method is presented that enables the Adsorbed Layer Thickness to be calculated. This is based on adsorption theory and expressed in terms of molecular interaction energies. A continuous cross-gap viscosity model incorporating the Layer Thickness is introduced and used to calculate the load capacity and frictional characteristics of a simple bearing operating in the thin film regime.
Johann Plank - One of the best experts on this subject based on the ideXlab platform.
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Adsorbed Layer Thickness of polycarboxylate and polyphosphate superplasticizers on polystyrene nanoparticles measured via dynamic light scattering
Journal of Colloid and Interface Science, 2020Co-Authors: Johannes Stecher, Johann PlankAbstract:Abstract Hypothesis Common superplasticizers (dispersants) for cementitious materials such as concrete include carboxylated comb polymers which strongly chelate Ca2+ ions. Thus, a substrate holding Ca2+ as docking site on its surface and of a narrow particle size distribution was expected to produce reliable values for the Adsorbed Layer Thickness (ALT) of polycarboxylate comb polymers, as measured via dynamic light scattering. ALT presents a key parameter which controls the dispersion power of these polymers and provides the steric hindrance effect between cement particles. Experiments Using octadecyl phosphate as emulsifier, phosphate modified polystyrene nanoparticles (dH(z) ~86 nm) of narrow size distribution were successfully synthesized and characterized via scanning electron microscopy, dynamic light scattering (DLS) and zeta potential measurements. The particles allowed to measure concentration dependent Adsorbed Layer Thicknesses of a series of structurally different, self-synthesized polycarboxylate superplasticizers. Findings The phosphate-modified polystyrene nanoparticles were found to present a suitable substrate for ALT measurements of Adsorbed polycarboxylate comb polymers. DLS measurements revealed that with progressing adsorption, these polymers develop a concentration-dependent isothermal ALT. At saturation point, Layer Thicknesses of 3 to 8 nm were observed. The values correlate well with molecular properties of the polymers whereby increasing side-chain length, side-chain density and molecular weight provoke higher ALTs.
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Adsorbed Conformations of PCE Superplasticizers in Cement Pore Solution Unraveled by Molecular Dynamics Simulations
Scientific Reports, 2017Co-Authors: Tsuyoshi Hirata, Alex Lange, Johann Plank, Paulo Branicio, Jianwei Zheng, Michael SullivanAbstract:The conformations of polycarboxylate ether (PCE) type superplasticizer polymers Adsorbed on the surface of MgO in cement pore solution are simulated by molecular dynamics (MD). Three types of PCEs commonly applied to concrete are simulated, namely a methacrylate type PCE (PCEM- P ), an allyl ether type PCE (PCEA- P ), and an isoprenyl ether type PCE (PCEI- P ) with ethylene oxide (EO) unit numbers ( P ) of 25, 34 and 25, respectively. It is observed that the Adsorbed Layer Thickness is inversely proportional to the experimentally measured Adsorbed amount at the initial paste flow of 26 ± 0.5 cm. Simulation results indicate that the Adsorbed Layer Thickness is sensitive to the initial polymer orientations against the model MgO surface. I.e., polymer molecules initially placed parallel/perpendicularly against the MgO surface gradually forms a train shaped or a loop and tail adsorption profile, respectively. As a result, the loop and tail shaped conformation gives a higher Layer Thickness.
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Determination of the Adsorbed Layer Thickness of functional anionic polymers utilizing chemically modified polystyrene nanoparticles
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2014Co-Authors: Constantin Tiemeyer, Alex Lange, Johann PlankAbstract:Abstract Dynamic light scattering (DLS) was found to present a facile method to directly measure the Adsorbed Layer Thickness (ALT) of various functional polymers. Monodisperse polystyrene nanoparticles ( d ∼ 77 nm) modified with zinc palmitate to attain a positive surface charge were identified as a suitable adsorbent. These particles are chemically inert and stable even at very high pH values, e.g. of ∼13. As polymers, two cement dispersants, two retarders and four water-retention admixtures were investigated. At first, adsorption isotherms were developed to probe whether single or multiple polymer Layers were present on the particles’ surfaces. Next, the Adsorbed Layer Thickness of each polymer on polystyrene nanoparticles was measured using DLS and the results were compared with the hydrodynamic radius of the polymers in solution. From this data, the Adsorbed conformation of the polymers was assessed. The method allows quick determination of the ALT at reasonable accuracy.