Papers by Andra Dedinaite
Journal of colloid and interface science, Jan 7, 2015
Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and ... more Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25-52°C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica-liquid interface has been followed ...
Soft Matter, 2012
ABSTRACT Hyaluronan has been found to play an important role in boundary lubrication in joints, b... more ABSTRACT Hyaluronan has been found to play an important role in boundary lubrication in joints, but model experiments have shown that free hyaluronan is reluctant to stay between surfaces. We show that hyaluronan, when assisted by a phospholipid bilayer, can act as a boundary lubricant, even at pressures well above those leading to breakdown of cartilage.
Progress in Colloid & Polymer Science, 1997
Interactions between negatively charged surfaces coated with cationic polyelectrolytes across sol... more Interactions between negatively charged surfaces coated with cationic polyelectrolytes across solutions containing an anionic surfactant, sodium dodecyl sulphate (SDS) have been studied. Polyelectrolytes with charge densities between 100% and 10%, counted per monomer unit, were used. At low ionic strength the polyelectrolytes adsorb in a flat conformation to neutralize the negative mica surface charge. The higher the linear charge density
Journal of Colloid and Interface Science, 2015
Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and ... more Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-snglycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25-52°C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica-liquid interface has been followed using X-ray reflectivity measurements, which suggests that the DPPC bilayer is in the gel phase at 25°C and 39°C and in the liquid disordered state at 55°C. Well-defined bilayer structures were observed for both phases. The deposited DPPC bilayers were also imaged using AFM PeakForce Tapping mode, and these measurements indicated a less homogeneous layer at temperatures below 37°C.
Journal of Colloid and Interface Science, 2015
Pre-adsorbed branched brush layers were formed on silica surfaces by adsorption of a diblock copo... more Pre-adsorbed branched brush layers were formed on silica surfaces by adsorption of a diblock copolymer consisting of a linear cationic block and an uncharged bottle-brush block. The charge of the silica surface was found to affect the adsorption, with lower amounts of the cationic polyelectrolyte depositing on less charged silica. Cleaning under basic conditions rendered surfaces more negatively charged (more negative zeta-potential) than acid cleaning and was therefore used to increase polyelectrolyte adsorption. The structure of adsorbed layers of the diblock copolymer was as determined by neutron reflectometry found to be about 70 nm thick and very water rich (97%). Interactions between the anionic surfactant sodium dodecylsulfate (SDS) and such pre-adsorbed diblock polymer layers were studied by neutron reflectometry and by optical reflectometry. Optical reflectometry was also used for deducing interactions between the individual blocks of the diblock copolymer and SDS at the silica/aqueous interface. We find that SDS is readily incorporated in the diblock copolymer layer at low SDS concentrations, and preferentially co-localized with the cationic block of the polymer next to the silica surface. At higher SDS concentrations some desorption of polyelectrolyte/surfactant complexes takes place.
Progress in Colloid and Polymer Science, 2006
... Andra Dedinaite · Joseph Iruthayaraj · Per M. Claesson (u) Department of Chemistry, Surface C... more ... Andra Dedinaite · Joseph Iruthayaraj · Per M. Claesson (u) Department of Chemistry, Surface Chemistry, Royal Institute of Technology, 100 44 Stockholm ... for a comb copolymer consisting of a polylysine backbone and poly(ethylene oxide), PEO, grafts [5]. Simi-lar results have ...
Langmuir, 1999
ABSTRACT Mixing the phospholipid soybean phosphatidyl ethanolamine (PE) with the triglyceride tri... more ABSTRACT Mixing the phospholipid soybean phosphatidyl ethanolamine (PE) with the triglyceride triolein and a trace amount of water leads to a spontaneous formation of isotropic aggregates. Evidence for the existence of such aggregates in pseudo-three-component systems is presented here for the first time. Dynamic light scattering and cryogenic temperature transmission electron microscopy reveal polydisperse spherical particles with radii in the range of 250−840 nm and a mean radius of the order 600 nm. From the results of both depolarized light scattering and time-resolved electro-optical birefringence (Kerr effect) the presence of aggregates with an optical anisotropy (rodlike or wormlike reverse micelles as well as particles with lamellar structure) can be excluded. The remaining possibilities are reverse vesicles and a dispersed cubic bicontinuous phase, where our results favor reverse vesicles. A necessary condition for the formation of reverse vesicles is a saturation of the PE−triolein mixture with water; at lower water content the particles are significantly smaller.
O-TADROS:COLLOIDS VOL 3 O-BK, 2007
ABSTRACT
Surface and Interfacial Forces – From Fundamentals to Applications, 2008
The AFM colloidal probe technique has been utilized in order to investigate the forces acting bet... more The AFM colloidal probe technique has been utilized in order to investigate the forces acting between preadsorbed mucin layers on uncharged, hydrophobic mercaptohexadecane-coated gold surfaces. Layers with some highly extended tails are formed when the adsorption proceeds from 25 ppm mucin solution in 30 mM NaNO3. The effects of salt concentration and cation valency on the interactions have been explored using NaCl,
Progress in Colloid & Polymer Science, 1997
Interactions between negatively charged surfaces coated with cationic polyelectrolytes across sol... more Interactions between negatively charged surfaces coated with cationic polyelectrolytes across solutions containing an anionic surfactant, sodium dodecyl sulphate (SDS) have been studied. Polyelectrolytes with charge densities between 100% and 10%, counted per monomer unit, were used. At low ionic strength the polyelectrolytes adsorb in a flat conformation to neutralize the negative mica surface charge. The higher the linear charge density
Journal of Colloid and Interface Science, 2015
Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and ... more Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-snglycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25-52°C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica-liquid interface has been followed using X-ray reflectivity measurements, which suggests that the DPPC bilayer is in the gel phase at 25°C and 39°C and in the liquid disordered state at 55°C. Well-defined bilayer structures were observed for both phases. The deposited DPPC bilayers were also imaged using AFM PeakForce Tapping mode, and these measurements indicated a less homogeneous layer at temperatures below 37°C.
Berichte der Bunsengesellschaft für physikalische Chemie, 1996
The interferometric surface force technique has been utilized for studying the interaction betwee... more The interferometric surface force technique has been utilized for studying the interaction between negatively charged surfaces coated with a cationic polyelectrolyte across solutions of anionic surfactant, sodium dodecyl sulphate (SDS). The polyelectrolyte used was poly ([2-(propionyloxy)ethyl]trimethylammonium chloride), PCMA, which has one positive charge per segment. At low ionic strength the polyelectrolyte adsorbs in a flat conformation and neutralizes the negative mica surface charge. The interaction forces between the polyelectrolyte-coated surfaces are dominated by a strongly attractive force at distances shorter than about 150 A.
Journal of Colloid and Interface Science, 2015
Pre-adsorbed branched brush layers were formed on silica surfaces by adsorption of a diblock copo... more Pre-adsorbed branched brush layers were formed on silica surfaces by adsorption of a diblock copolymer consisting of a linear cationic block and an uncharged bottle-brush block. The charge of the silica surface was found to affect the adsorption, with lower amounts of the cationic polyelectrolyte depositing on less charged silica. Cleaning under basic conditions rendered surfaces more negatively charged (more negative zeta-potential) than acid cleaning and was therefore used to increase polyelectrolyte adsorption. The structure of adsorbed layers of the diblock copolymer was as determined by neutron reflectometry found to be about 70 nm thick and very water rich (97%). Interactions between the anionic surfactant sodium dodecylsulfate (SDS) and such pre-adsorbed diblock polymer layers were studied by neutron reflectometry and by optical reflectometry. Optical reflectometry was also used for deducing interactions between the individual blocks of the diblock copolymer and SDS at the silica/aqueous interface. We find that SDS is readily incorporated in the diblock copolymer layer at low SDS concentrations, and preferentially co-localized with the cationic block of the polymer next to the silica surface. At higher SDS concentrations some desorption of polyelectrolyte/surfactant complexes takes place.
Langmuir, 2014
A nonionic-cationic diblock copolymer, poly(2-isopropyl-2-oxazoline)60-b-poly((3-acrylamidopropyl... more A nonionic-cationic diblock copolymer, poly(2-isopropyl-2-oxazoline)60-b-poly((3-acrylamidopropyl)trimethylammonium chloride)17, (PIPOZ60-b-PAMPTMA17), was utilized to electrostatically tether temperature-responsive PIPOZ chains to silica surfaces by physisorption. The effects of polymer concentration, pH, and temperature on adsorption were investigated using quartz crystal microbalance with dissipation monitoring and ellipsometry. The combination of these two techniques allows thorough characterization of the adsorbed layer in terms of surface excess, thickness, and water content. The high affinity of the cationic PAMPTMA17 block to the negatively charged silica surface gives rise to a high affinity adsorption isotherm, leading to (nearly) irreversible adsorption with respect to dilution. An increase in solution pH lowers the affinity of PIPOZ to silica but enhances the adsorption of the cationic block due to increasing silica surface charge density, which leads to higher adsorption of the cationic diblock copolymer. Higher surface excess is also achieved at higher temperatures due to the worsening of the solvent quality of water for the PIPOZ block. Interestingly, a large hysteresis in adsorbed mass and other layer properties was observed when the temperature was cycled from 25 to 45 °C and then back to 25 °C. Possible causes for this temperature hysteresis are discussed.
Progress in Colloid and Polymer Science, 2006
... Andra Dedinaite · Joseph Iruthayaraj · Per M. Claesson (u) Department of Chemistry, Surface C... more ... Andra Dedinaite · Joseph Iruthayaraj · Per M. Claesson (u) Department of Chemistry, Surface Chemistry, Royal Institute of Technology, 100 44 Stockholm ... for a comb copolymer consisting of a polylysine backbone and poly(ethylene oxide), PEO, grafts [5]. Simi-lar results have ...
Journal of Colloid and Interface Science, 2011
We analyzed the interaction between chemically grafted polysaccharide layers in aqueous solutions... more We analyzed the interaction between chemically grafted polysaccharide layers in aqueous solutions. To fabricate such layers, an end-terminated dextran silane coupling agent was synthesized and the polydextran was grafted to oxidized silicon wafers and to silica particles. This resulted in the formation of a 28 nm thick layer (in air) and a grafted amount of 40 mg/m2 as determined by ellipsometry. The physical properties of the grafted layer were investigated in aqueous solutions by atomic force microscope imaging and colloidal probe force measurements. Surface and friction forces were measured between one bare and one polydextran coated silica surface. A notable feature was a bridging attraction due to affinity between dextran and the silica surface. Surface interactions and friction forces were also investigated between two surfaces coated with grafted polydextran. Repulsive forces were predominant, but nevertheless a high friction force was observed. The repulsive forces were enhanced by addition of sodium dodecyl sulfate (SDS) that associates with the tethered polydextran layers. SDS also decreased the friction force. Our data suggests that energy dissipation due to shear-induced structural changes within the grafted layer is of prime importance for the high friction forces observed, in particular deformation of protrusions in the surface layer.The effect of a grafted polysaccharide layer and the presence of a surfactant on the surface and friction forces between two silica surfaces was investigated by the AFM using two bare silica surfaces, a bare- and a polysaccharide grafted silica surface, and two polysaccharide grafted silica surfaces in the absence and presence of sodium dodecyl sulfate.► We study interactions between chemically grafted polysaccharide layers in water. ► We synthesize and graft an end-terminated dextran silane coupling agent to silica. ► A bridging attraction was seen between a silica surface and a polydextran surface. ► Repulsive forces and high friction were seen between two polydextran surfaces. ► Addition of surfactant enhanced the repulsive forces and decreased the friction.
Langmuir, 1999
ABSTRACT Mixing the phospholipid soybean phosphatidyl ethanolamine (PE) with the triglyceride tri... more ABSTRACT Mixing the phospholipid soybean phosphatidyl ethanolamine (PE) with the triglyceride triolein and a trace amount of water leads to a spontaneous formation of isotropic aggregates. Evidence for the existence of such aggregates in pseudo-three-component systems is presented here for the first time. Dynamic light scattering and cryogenic temperature transmission electron microscopy reveal polydisperse spherical particles with radii in the range of 250−840 nm and a mean radius of the order 600 nm. From the results of both depolarized light scattering and time-resolved electro-optical birefringence (Kerr effect) the presence of aggregates with an optical anisotropy (rodlike or wormlike reverse micelles as well as particles with lamellar structure) can be excluded. The remaining possibilities are reverse vesicles and a dispersed cubic bicontinuous phase, where our results favor reverse vesicles. A necessary condition for the formation of reverse vesicles is a saturation of the PE−triolein mixture with water; at lower water content the particles are significantly smaller.
Interactions between negatively charged surfaces coated with cationic polyelectrolytes across sol... more Interactions between negatively charged surfaces coated with cationic polyelectrolytes across solutions containing an anionic surfactant, sodium dodecyl sulphate (SDS) have been studied. Polyelectrolytes with charge densities between 100% and 10%, counted per monomer unit, were used. At low ionic strength the polyelectrolytes adsorb in a flat conformation to neutralize the negative mica surface charge. The higher the linear charge density of the polyelectrolyte, the thinner adsorbed layers are obtained. In no case could any desorption be detected when the polyelectrolyte containing solution was replaced with an aqueous polyelectrolyte-free solution. The presence of SDS at concentrations considerably below the critical micellar concentration (cmc) does in all cases result in a recharging and a considerable swelling of the adsorbed layer. This is due to a cooperative association of surfactants in the preadsorbed polyelectrolyte layer. In case of the 100% charged PCMA, the force versus distance profile displays clear oscillations. We interpret these oscillations as being caused by the spatial arrangement of SDS micelles induced by the polyelectrolyte. The oscillations in the force curve remain as the SDS concentration is increased to twice the cmc. No similar oscillations in the force distance curve are observed when the surfaces are precoated with less charged polyelectrolytes. In these cases a strong swelling of the polyelectrolyte layer is observed once the surfactant concentration reaches a critical value (well below the cmc).
Colloid and Polymer Science, 1997
Interactions between negatively charged surfaces coated with cationic polyelectrolytes across sol... more Interactions between negatively charged surfaces coated with cationic polyelectrolytes across solutions containing an anionic surfactant, sodium dodecyl sulphate (SDS) have been studied. Polyelectrolytes with charge densities between 100% and 10%, counted per monomer unit, were used. At low ionic strength the polyelectrolytes adsorb in a flat conformation to neutralize the negative mica surface charge. The higher the linear charge density
O-TADROS:COLLOIDS VOL 3 O-BK, 2007
ABSTRACT
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Papers by Andra Dedinaite