| 1. |
- An, Junxue, et al.
(författare)
-
Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers
- 2017
-
Ingår i: Journal of Colloid and Interface Science. - : Academic Press. - 0021-9797 .- 1095-7103. ; 487, s. 88-96
-
Tidskriftsartikel (refereegranskat)abstract
- Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperatures <40 °C. A local force minimum at short separation develops at 40 °C and a strong attraction due to capillary condensation of a polymer-rich phase is observed close to the bulk phase separation temperature. The friction forces decrease in the cooling stage due to rehydration of the PIPOZ chain. A consequence of the adsorption hysteresis is that the friction forces measured at 25 °C are significantly lower after exposure to a temperature of 40 °C than prior to heating, which is due to higher polymer chain density on the surface after heating.
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| 2. |
- An, Junxue, et al.
(författare)
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Comparison of a Brush-with-Anchor and a Train-of-Brushes Mucin on Poly(methyl methacrylate) Surfaces : Adsorption, Surface Forces, and Friction
- 2014
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 15:4, s. 1515-1525
-
Tidskriftsartikel (refereegranskat)abstract
- Interfacial properties of two types of mucins have been investigated at the aqueous solution/poly(methyl methacrylate) (PMMA) interface. One is commercially available bovine submaxillary mucin, BSM, which consists of alternating glycosylated and nonglycosylated regions. The other one is a recombinant mucin-type fusion protein, PSGL-1/mIgG(2b), consisting of a glycosylated mucin part fused to the Fc part of an immunoglobulin. PSGL-1/mIgG(2b) is mainly expressed as a (timer upon production. A quartz crystal microbalance with dissipation was used to study the adsorption of the mucins to PMMA surfaces. The mass of the adsorbed mucin layers, including the adsorbed mucin and water trapped in the layer, was found to be significantly higher for PSGL-1/mIgG(2b) than for BSM. Atomic force microscopy with colloidal probe was employed to study interactions and frictional forces between mucin-coated PMMA surfaces. Purely repulsive forces of steric origin were Observed between PSGL-1/mIgG(2b) mucin layers, whereas a small adhesion was detected between BSM layers and attributed to bridging. Both mucin layers reduced the friction force between PMMA surfaces in aqueous solution. The reduction was, however, significantly more pronounced for PSGL-1/mIgG(2b). The effective friction coefficient between PSGL-1/mIgG(2b)-coated PMMA surfaces is as low as 0.02 at low loads, increasing to 0.24 at the highest load explored, 50 nN. In contrast, a friction coefficient of around 0.7 was obtained between BSM-coated PMMA surfaces. The large differences in interfacial properties for the two mucins are discussed in relation to their structural differences.
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| 3. |
- An, Junxue, et al.
(författare)
-
Influence of Glycosylation on Interfacial Properties of Recombinant Mucins : Adsorption, Surface Forces, and Friction
- 2017
-
Ingår i: Langmuir. - : American Chemical Society. - 0743-7463 .- 1520-5827. ; 33:18, s. 4386-4395
-
Tidskriftsartikel (refereegranskat)abstract
- Interfacial properties of two brush-with-anchor mucins, C-P55 and C-PSLex, have been investigated at the aqueous solution/poly(methyl methacrylate) (PMMA) interface. Both are recombinant mucin-type fusion proteins, produced by fusing the glycosylated mucin part of P-selectin glycoprotein ligand-1 (PSLG-1) to the Fc part of a mouse immunoglobulin in two different cells. They are mainly expressed as dimers upon production. Analysis of the O-glycans shows that the C-PSLex mucin has the longer and more branched side chains, but C-P55 has slightly higher sialic acid content. The adsorption of the mucins to PMMA surfaces was studied by quartz crystal microbalance with dissipation. The sensed mass, including the adsorbed mucin and water trapped in the layer, was found to be similar for these two mucin layers. Atomic force microscopy with colloidal probe was employed to study surface and friction forces between mucin-coated PMMA surfaces. Purely repulsive forces of steric origin were observed between mucin layers on compression, whereas a small adhesion was detected between both mucin layers on decompression. This was attributed to chain entanglement. The friction force between C-PSLex-coated PMMA is lower than that between C-P55-coated PMMA at low loads, but vice versa at high loads. We discuss our results in terms of the differences in the glycosylation composition of these two mucins.
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| 4. |
- An, Junxue, et al.
(författare)
-
Influence of Glycosylation on Interfacial Properties of Recombinant Mucins: Adsorption, Surface Forces and Friction
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Interfacial properties of two brush-with-anchor mucins, C-P55 and C-PSLex, have been investigated at the aqueous solution/poly(methylmethacrylate) (PMMA) interface. Both are recombinant mucin-type fusion proteins, produced by fusing the glycosylated mucin part of P-selectin glycoprotein ligand-1 (PSLG-1) to the Fc part of a mouse immunoglobulin in two different cells. They are mainly expressed as dimers upon production. Analysis of the O-glycans shows that the C-PSLex mucin has the longer and more branched side chains, but C-P55 has slightly higher sialic acid content. The adsorption of the mucins to PMMA surfaces was studied by quartz crystal microbalance with dissipation. The sensed mass, including the adsorbed mucin and water trapped in the layer, was found to be similar for these two mucin layers. Atomic force microscopy with colloidal probe was employed to study surface and friction forces between mucin-coated PMMA surfaces. Purely repulsive forces of steric origin were observed between mucin layers on compression, whereas a small adhesion was detected between both mucin layers on decompression. This was attributed to chain entanglement. The friction force between C-PSLex-coated PMMA is lower than that between C-P55-coated PMMA at low loads, but vice versa at high loads. We discuss our results in terms of the differences in the glycosylation composition of these two mucins.
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| 5. |
- An, Junxue, et al.
(författare)
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Temperature-Dependent Adsorption and Adsorption Hysteresis of a Thermoresponsive Diblock Copolymer
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:15, s. 4333-4341
-
Tidskriftsartikel (refereegranskat)abstract
- A nonionic-cationic diblock copolymer, poly(2-isopropyl-2-oxazoline)(60)-b-poly((3-acrylamidopropyl)- trimethylammonium chloride)(17), (PIPOZ(60)-b-PAMPTMA(17)), 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 PAMPTMA(17) 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 degrees C and then back to 25 degrees C. Possible causes for this temperature hysteresis are discussed.
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| 6. |
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| 7. |
- An, Junxue, et al.
(författare)
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Tethered Poly(2-isopropyl-2-oxazoline) Chains : Temperature Effects on Layer Structure and Interactions Probed by AFM Experiments and Modeling
- 2015
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:10, s. 3039-3048
-
Tidskriftsartikel (refereegranskat)abstract
- Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 degrees C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature.
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| 8. |
- Bastardo Zambrano, Luis Alejandro, et al.
(författare)
-
Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
- 2007
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 312, s. 21-33
-
Tidskriftsartikel (refereegranskat)abstract
- A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO45 MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 Å. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO45 MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.
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| 9. |
- Beldowski, Piotr, et al.
(författare)
-
Albumin-Hyaluronan Interactions : Influence of Ionic Composition Probed by Molecular Dynamics
- 2021
-
Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 22:22
-
Tidskriftsartikel (refereegranskat)abstract
- The lubrication mechanism in synovial fluid and joints is not yet fully understood. Nevertheless, intermolecular interactions between various neutral and ionic species including large macromolecular systems and simple inorganic ions are the key to understanding the excellent lubrication performance. An important tool for characterizing the intermolecular forces and their structural consequences is molecular dynamics. Albumin is one of the major components in synovial fluid. Its electrostatic properties, including the ability to form molecular complexes, are closely related to pH, solvation, and the presence of ions. In the context of synovial fluid, it is relevant to describe the possible interactions between albumin and hyaluronate, taking into account solution composition effects. In this study, the influence of Na+, Mg2+, and Ca2+ ions on human serum albumin-hyaluronan interactions were examined using molecular dynamics tools. It was established that the presence of divalent cations, and especially Ca2+, contributes mostly to the increase of the affinity between hyaluronan and albumin, which is associated with charge compensation in negatively charged hyaluronan and albumin. Furthermore, the most probable binding sites were structurally and energetically characterized. The indicated moieties exhibit a locally positive charge which enables hyaluronate binding (direct and water mediated).
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| 10. |
- Bełdowski, Piotr, et al.
(författare)
-
Collagen type II-hyaluronan interactions - the effect of proline hydroxylation: a molecular dynamics study
- 2022
-
Ingår i: Journal of materials chemistry. B. - : Royal Society of Chemistry. - 2050-750X .- 2050-7518. ; 10:46, s. 9713-9723
-
Tidskriftsartikel (refereegranskat)abstract
- Hyaluronan-collagen composites have been employed in numerous biomedical applications. Understanding the interactions between hyaluronan and collagen is particularly important in the context of joint cartilage function and the treatment of joint diseases. Many factors affect the affinity of collagen for hyaluronan. One of the important factors is the ratio of 3- or 4-hydroxy proline to proline residues. This article presents the results from molecular dynamics calculations of HA-collagen type II interactions with hyaluronan. The applied protocol employed docking and geometry optimization of complexes built using collagen structures with different numbers of hydroxyl groups attached to proline moieties. It was established that the hydroxyproline/proline ratio affects both structural and energetic features of the collagen-hyaluronan complex. Proline hydroxylation was found to significantly influence the number of all identified types of molecular forces, hydrophobic interactions, water bridges and hydrogen bonds, which can be formed between collagen and hyaluronan. Importantly, an increase in the hydroxyproline/proline ratio in the collagen chain increases the binding affinity for hyaluronan. This is illustrated by the linear correlation between the binding free energy and the hydroxylation degree. A comparison of the results obtained for 3 and 4 hydroxylation of proline indicates that the hydroxyl group attachment position plays a minor role in complex stabilization. However, a slightly stronger affinity was observed for 4 hydroxylation. In order to evaluate the effect of the aqueous environment on the collagen-hyaluronan complex stability, the enthalpic and entropic contributions to the free energy of solvation were analyzed.
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| 11. |
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| 12. |
- Bełdowski, Piotr, et al.
(författare)
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Interactions of a short hyaluronan chain with a phospholipid membrane
- 2019
-
Ingår i: Colloids and Surfaces B. - : Elsevier B.V.. - 0927-7765 .- 1873-4367. ; 184
-
Tidskriftsartikel (refereegranskat)abstract
- Hyaluronic acid and phospholipids are two components that are present in the synovial fluid, and both are implicated as important facilitators of joint lubrication. In this work we aim to clarify how hyaluronic acid interacts with a phospholipid bilayer through their molecular interactions at the bilayer surface. To this end we performed molecular dynamics simulations of one hyaluronic acid molecule at a phospholipid bilayer in aqueous solution. The simulations were carried out for two aqueous solutions of equal concentrations, containing either NaCl or CaCl2. We analyzed hydrogen bonds, hydrophobic contacts and cation mediated bridges to clarify how hyaluoronic acid binds to a phospholipid bilayer. The analysis shows that calcium ions promote longer lasting bonds between the species as they create calcium ion bridges between the carboxylate group of hyaluronic acid and the phosphate group of the phospholipid. This type of additional bonding does not significantly influence the total number of contact created, but rather stabilizes the contact. The presented results can facilitate understanding of the role of hyaluronic acid and phospholipid interactions in terms of lubrication of articular cartilage.
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| 13. |
- Bełdowski, Piotr, et al.
(författare)
-
Physical crosslinking of hyaluronic acid in the presence of phospholipids in an aqueous nano-environment
- 2018
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 14:44, s. 8997-9004
-
Tidskriftsartikel (refereegranskat)abstract
- Hyaluronic acid and phospholipids are two components in the synovial joint cavity that contribute to joint lubrication synergistically. Molecular dynamics simulations were performed and hydrogen bonds in hyaluronic acid were analyzed to identify specific sites that are responsible for its physical cross-linking. Two molecular masses of hyaluronic acid, 10 kDa and 160 kDa, were considered. We use molecular dynamics simulations and the small world network approach to investigate dynamic couplings using a distance map applied to oxygen atoms in a chain of hyaluronic acid in the presence of phospholipids and water. The distance characterizing the coupling can be defined in various ways to bring out the most evident differences between various scenarios of the polymer chain conformation We show herein a physical distance understood as H-bond length and classes of these distances which are defined in a coarse-grained picture of the molecule. Simulation results indicate that addition of phospholipids has little influence on hyaluronic acid crosslinking. However, longer chains and addition of lipids promote appreciably long lasting (resilient) networks that may be of importance in biological systems. Specific sites for hydrogen bonding of phospholipids to hyaluronic acid have also been identified.
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| 14. |
- Bodvik, Rasmus, et al.
(författare)
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Aggregation and network formation of aqueous methylcellulose and hydroxypropylmethylcellulose solutions.
- 2010
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 354:1-3, s. 162-171
-
Tidskriftsartikel (refereegranskat)abstract
- Solution properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) have been investigated as a function of temperature and concentration using a broad range of experimental techniques. Novelties include the extensive comparison between MC and HPMC solutions as well as the combination of techniques, and the use of Cryo transmission electron microscopy (Cryo-TEM). The correlation between rheology and light scattering results clearly demonstrates the relation between viscosity change and aggregation. Cryo-TEM images show the network structures formed. Viscosity measurements show that for both MC and HPMC solutions sudden changes in viscosity occur as the temperature is increased. The onset temperature for these changes depends on polymer concentration and heating rate. For both MC and HPMC solutions the viscosity on cooling is very different compared to on heating, demonstrating the slow equilibration time. The viscosity changes in MC and HPMC solutions are dramatically different; for MC solutions the viscosity increases by several orders of magnitude when a critical temperature is reached, whereas for HPMC solutions the viscosity decreases abruptly at a given temperature, followed by an increase upon further heating. Light and (SAXS) small-angle X-ray scattering shows that the increase in viscosity, for MC as well as for HPMC solutions, is due to extensive aggregation of the polymers. Light scattering also provides information on aggregation kinetics. The SAXS measurements allow us to correlate aggregation hysteresis to the viscosity hysteresis, as well as to extract some structural information. Cryo-TEM images give novel information that a fibrillar network is formed in MC solutions, and the strong viscosity increase occurs when this network spans the whole solution volume. For HPMC solutions the behaviour is more complex. The decrease in viscosity can be related to the formation of compact objects, and the subsequent increase to formation of fibrillar structures, which are more linear and less entangled than for MC.
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| 15. |
- Claesson, Per, et al.
(författare)
-
Association between Polyelectrolytes and Oppositely Charged Surfactants in Bulk and at Solid/Liquid Interfaces
- 2007
-
Ingår i: Colloid Stability and Application in Pharmacy. - Weinheim : Wiley-VCH Verlagsgesellschaft. ; , s. 337-395
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Mixtures of polyelectrolytes and oppositely charged surfactants find applications in many processes and products that are used in our daily life. Such systems also show many interesting features from a scientific point of view. Due to the combined technological relevance and scientific challenge, considerable research efforts have been made in this area in recent years. This has resulted in new theoretical approaches, the development of simulation methods and new experimental techniques and, of course, a large body of new findings. Together, these efforts have increased the understanding significantly, especially during the last 5 years. This chapter reviews some aspects of this topic, focusing on bulk association and association at solid/liquid interfaces. The review is focused on developments during the 21st century, even though in some cases a historical perspective is also offered.
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| 16. |
- Claesson, P. M., et al.
(författare)
-
Association between Polyelectrolytes and Oppositely Charged Surfactants in Bulk and at Solid/Liquid Interfaces
- 2010
-
Ingår i: Colloids and Interface Science Series. - Weinheim, Germany : Wiley-Blackwell. - 9783527631193 - 9783527314614 ; , s. 337-395
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Mixtures of polyelectrolytes and oppositely charged surfactants find applications in many processes and products that are used in our daily life. Such systems also show many interesting features from a scientific point of view. Due to the combined technological relevance and scientific challenge, considerable research efforts have been made in this area in recent years. This has resulted in new theoretical approaches, the development of simulation methods and new experimental techniques and, of course, a large body of new findings. Together, these efforts have increased the understanding significantly, especially during the last 5 years. This chapter reviews some aspects of this topic, focusing on bulk association and association at solid/liquid interfaces. The review is focused on developments during the 21st century, even though in some cases a historical perspective is also offered.
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| 17. |
|
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| 18. |
- Claesson, Per M., et al.
(författare)
-
Association between Polyelectrolytes and Oppositely Charged Surfactants in Bulk and at Solid/Liquid Interfaces : Chapter 11
- 2011
-
Ingår i: Colloid Stability and Application in Pharmacy. - : Wiley-VCH Verlag GmbH & Co. KGaA. - 9783527314638 ; , s. 337-395
-
Bokkapitel (refereegranskat)abstract
- Mixtures of polyelectrolytes and oppositely charged surfactants find applications in many processes and products that are used in our daily life. Such systems also show many interesting features from a scientific point of view. Due to the combined technological relevance and scientific challenge, considerable research efforts have been made in this area in recent years. This has resulted in new theoretical approaches, the development of simulation methods and new experimental techniques and, of course, a large body of new findings. Together, these efforts have increased the understanding significantly, especially during the last 5 years. This chapter reviews some aspects of this topic, focusing on bulk association and association at solid/liquid interfaces. The review is focused on developments during the 21st century, even though in some cases a historical perspective is also offered.
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| 19. |
- Claesson, Per M., et al.
(författare)
-
Mixtures of cationic polyelectrolyte and anionic surfactant studied with small-angle neutron scattering
- 2000
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:49, s. 11689-11694
-
Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering (SANS) data for solutions containing a highly charged cationic polyelectrolyte and an anionic surfactant are presented. The scattering data were obtained in pure D2O, emphasizing the scattering from the polyelectrolyte, and in a H2O/D2O mixture that contrast matches the polyelectrolyte. In the absence of surfactant, a broad scattering peak due to the mesh size of the polyelectrolyte solution is the most characteristic feature. This peak moves to larger q-values (smaller distances) as the polyelectrolyte concentration is increased, as expected for a semidilute polyelectrolyte solution. Addition of a small amount of surfactant reduces and finally removes this peak. Instead a sharp diffraction peak appears at high q-values. This Bragg peak corresponds to a characteristic distance of 37-39 Angstrom, and it is observed when either the polyelectrolyte or the surfactant is contrast matched by the solvent. Once this peak has appeared, its position does not change when the surfactant concentration is increased. The intensity of the peak grows, however, until a stoichiometric polyelectrolyte-surfactant complex has been formed. The Bragg peak remains in excess surfactant solution. These results are discussed in relation to the structure of the polyelectrolyte-surfactant aggregates and in connection with recent results from surface force and turbidity measurements using the same polyelectrolyte-surfactant pair.
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| 20. |
- Claesson, Per M., et al.
(författare)
-
Polyelectrolyte-mediated surface interactions
- 2005
-
Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 114, s. 173-187
-
Forskningsöversikt (refereegranskat)abstract
- 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.
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| 21. |
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| 22. |
- Claesson, Per M., et al.
(författare)
-
Polyelectrolytes as adhesion modifiers
- 2003
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 104, s. 53-74
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorbed layers of polyelectrolytes have been studied with atomic force microscopy (AFM) and the interferometric surface force apparatus (SFA). Particular emphasis was put on determining the effect of the polyelectrolyte charge density on surface topography, and the effect of the polyelectrolyte coating on the adhesive properties. The AFM was employed to image individual polymer chains at low adsorption densities and to characterize the layer topography and coverage at higher adsorption densities. The adhesive properties between two polyelectrolyte-coated surfaces in air were determined as a function of the number of contacts made at any given spot. The data provide evidence for formation of electrostatic bridges, particularly when highly charged polyelectrolytes are used. Further, material transport between the surfaces is observed when the polyelectrolyte is either highly charged or have a very low charge density. For intermediate charge densities we could not observe any indication of material transfer. The adhesion between one polyelectrolyte-coated surface and one bare surface was initially higher than that between two polyelectrolyte-coated surfaces. However, due to material transfer between the two surfaces the adhesion decreased significantly with the number of times that the surfaces were driven into contact. For the polyelectrolytes of the lowest charge density the results suggest that entanglement effects contribute to the adhesive interaction. The modification of the adhesion by polyelectrolytes in practical systems such as in the case of dry-strength additives to improve paper resistance is also considered.
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| 23. |
- Claesson, Per M, et al.
(författare)
-
The dynamic nature of natural and fatty acid modified calcite surfaces
- 2024
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 26:4, s. 2780-2805
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Tidskriftsartikel (refereegranskat)abstract
- Calcium carbonate, particularly in the form of calcite, is an abundant mineral widely used in both human-made products and biological systems. The calcite surface possesses a high surface energy, making it susceptible to the adsorption of organic contaminants. Moreover, the surface is also reactive towards a range of chemicals, including water. Consequently, studying and maintaining a clean and stable calcite surface is only possible under ultrahigh vacuum conditions and for limited amounts of time. When exposed to air or solution, the calcite surface undergoes rapid transformations, demanding a comprehensive understanding of the properties of calcite surfaces in different environments. Similarly, attention must also be directed towards the kinetics of changes, whether induced by fluctuating environments or at constant condition. All these aspects are encompassed in the expression “dynamic nature”, and are of crucial importance in the context of the diverse applications of calcite. In many instances, the calcite surface is modified by adsorption of fatty acids to impart a desired nonpolar character. Although the binding between carboxylic acid groups and calcite surfaces is strong, the fatty acid layer used for surface modification undergoes significant alterations when exposed to water vapour and liquid water droplets. Therefore, it is also crucial to understand the dynamic nature of the adsorbed layer. This review article provides a comprehensive overview of the current understanding of both the dynamics of the calcite surface as well as when modified by fatty acid surface treatments. Calcium carbonate, particularly in the form of calcite and surface modified calcite, is an abundant mineral widely used in both human-made and biological systems.
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| 24. |
- Dédinaité, Andra, 1966-, et al.
(författare)
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Biolubrication synergy : Hyaluronan – Phospholipid interactions at interfaces
- 2019
-
Ingår i: Advances in Colloid and Interface Science. - : Elsevier B.V.. - 0001-8686 .- 1873-3727. ; 274
-
Tidskriftsartikel (refereegranskat)abstract
- The manner in which nature has solved lubrication issues has fascinated scientists for centuries, in particular when considering that lubrication is achieved in aqueous media. The most outstanding system in this respect is likely the synovial joint, where close to frictionless motion is realized under different loads and shear rates. This review article focuses on two components present in the synovial area, hyaluronan and phospholipids. We recapitulate what has been learned about their interactions at interfaces from recent experiments, with focus on results obtained using reflectivity techniques at large scale facilities. In parallel, modelling experiments have been carried out and from these efforts new detailed knowledge about how hyaluronan and phospholipids interact has been gained. In this review we combine findings from modelling and experiments to gain deeper insight. Finally, we summarize what has been learned of the lubrication performance of mixtures of phospholipids and hyaluronan. © 2019
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| 25. |
- Dédinaité, Andra
(författare)
-
Biomimetic lubrication
- 2012
-
Ingår i: Soft Matter. - 1744-683X .- 1744-6848. ; 8:2, s. 273-284
-
Forskningsöversikt (refereegranskat)abstract
- The lubrication of synovial joints is extremely efficient, allowing smooth motion to be performed between relatively soft and vulnerable cartilage surfaces for close to 100 years. A failure of this system leads to significant pain and loss of life quality. The ultrastructure of cartilage is complex and of functional significance. The molecules that are involved in the lubrication process are of many types, and they associate with each other in a complex fashion. This review focuses on the lubricating molecules, both biolubricants and biomimetic ones that share some features of the biolubricants. It discusses the conditions that must be fulfilled for achieving low friction in aqueous media and emphasizes the importance of load bearing capacity and self-healing ability.
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| 26. |
- Dédinaité, Andra
(författare)
-
Biomimetic lubrication
- 2012
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 8:2, s. 273-284
-
Tidskriftsartikel (refereegranskat)abstract
- The lubrication of synovial joints is extremely efficient, allowing smooth motion to be performed between relatively soft and vulnerable cartilage surfaces for close to 100 years. A failure of this system leads to significant pain and loss of life quality. The ultrastructure of cartilage is complex and of functional significance. The molecules that are involved in the lubrication process are of many types, and they associate with each other in a complex fashion. This review focuses on the lubricating molecules, both biolubricants and biomimetic ones that share some features of the biolubricants. It discusses the conditions that must be fulfilled for achieving low friction in aqueous media and emphasizes the importance of load bearing capacity and self-healing ability.
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| 27. |
- Dedinaite, Andra, et al.
(författare)
-
Chitosan-SDS interactions at a solid-liquid interface : Effects of surfactant concentration and ionic strength
- 2003
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 107:32, s. 8181-8188
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of ionic strength on adsorption of chitosan on mica as well as the impact of addition of an anionic surfactant, SDS, on the adsorbed chitosan layers is explored. It is demonstrated by chemical surface analysis (ESCA) and surface force measurements (SFA) that an elevated salt concentration leads to larger adsorbed amounts and thicker adsorption layers of this cationic polyelectrolyte. It is also shown that in contrast to the bulk, the binding of oppositely charged surfactant to the polyelectrolyte adsorbed on a negatively charged surface is facilitated by elevated ionic strength. Thus, the association process in bulk and at solid-liquid interfaces is rather different. The main point of difference is that at the solid-liquid interface one also has to consider interactions between the polyelectrolyte and the surface as well as between the surfactant and the surface.
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| 28. |
- Dedinaite, Andra, et al.
(författare)
-
Effect of sodium dodecyl sulfate on adsorbed layers of branched polyethylene imine
- 2004
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:31, s. 11645-11653
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of an anionic surfactant, sodium dodecyl sulfate, SDS, on the properties of adsorbed layers of a cationic highly branched polyelectrolyte, polyethylene,imine, PEI, has been investigated using surface force measurements, atomic force microscopy, and ESCA. The strategy used was to preadsorb PEI on negatively charged muscovite mica surfaces from a 20 ppm polyelectrolyte solution in 10 mM NaCl. The adsorption of PEI under these conditions gives rise to a strong recharging of the surface, i.e. after adsorption of PEI the surface carries a net positive charge. This conclusion was supported by ESCA measurements. Despite the high molecular weight of PEI (1.8 x 10(5) g/mol), the adsorbed layer is found to be very flat, and a repulsive double-layer force dominates at large separations. At smaller separation a strong attractive force is the main feature. Addition of SDS to a concentration of 0.01 cmc results in a nearly complete removal of the double-layer force, an increase in compressed layer thickness, and an increase in the magnitude of the adhesion force. Hence, significant SDS incorporation in the adsorbed layer occurs already at this low surfactant concentration. A recharging of the layer occurs at higher surfactant concentrations. At 0.5 cmc, the compressed thickness of the adsorbed layer is increased significantly and the adhesion between the surfaces has disappeared. We argue that each layer now is coated with an outer SDS layer oriented with the polar groups toward solution. In fact, there are striking similarities between the interfacial association between SDS and PEI and the adsorption of an ionic surfactant to an oppositely charged mineral surface. AFM imaging reveals that the adsorbed PEI layer is somewhat nonhomogeneous and contains polyelectrolyte patches. These surface features are smoothed out by addition of SDS to a concentration of 6 mM (1 cmc in 10 mM NaCl). ESCA measurements showed that exposure of the preadsorbed PEI layer to SDS concentrations around the cmc resulted in a limited desorption; about 15% of the initially adsorbed polyelectrolyte was removed after 16 h.
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| 29. |
- Dédinaité, Andra, et al.
(författare)
-
Friction in aqueous media tuned by temperature-responsive polymer layers
- 2010
-
Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:11, s. 2489-2498
-
Tidskriftsartikel (refereegranskat)abstract
- An atomic force microscope colloidal probe technique has been employed to probe normal and friction forces between silica surfaces coated with adsorbed layers of a diblock copolymer of the composition poly(N-isopropylacrylamide)(48)-block-poly(3-acrylamidopropyl)trimethyla mmonium chloride)(20), abbreviated PNIPAAM(48)-b-PAMPTMA(+)(20). The interactions between the PNIPAAM(48)-b-PAMPTMA(+)(20)-coated surfaces across a 0.1 mM NaCl (pH 6) solution at 25 degrees C are purely repulsive, due to a combination of steric and electrostatic double-layer forces. However, when the temperature is increased to 35 degrees C, and subsequently to 45 degrees C, an attractive force develops at short separations due to the unfavourable PNIPAAM-water interaction at these temperatures. The temperature-dependent polymer-water interaction has implications for the friction force between the layers. At 25 degrees C a frictional force that increases linearly with increasing load is observed once the surfaces are brought into close contact. At higher temperatures significantly higher friction forces appear as a consequence of attractive segment-segment interactions. Further, a clearly expressed hysteresis between friction forces encountered on loading and unloading is detected. Our results demonstrate that both normal and friction forces between surfaces can be controlled by temperature changes when temperature-responsive polymers are employed, and friction forces can be adjusted as required from low to high.
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| 30. |
- Dedinaite, Andra, et al.
(författare)
-
How synergistic aqueous lubrication is mediated by natural and synthetic molecular aggregates
- 2019
-
Ingår i: IOP Conference Series. - : Institute of Physics Publishing.
-
Konferensbidrag (refereegranskat)abstract
- Nature lubricates in aqueous environment, and thus the example of a human synovial joint with its seamless function has been a fascination for scientists since the times of the birth of modern science. Here, inspired by nature, we investigate the mechanistic function of three different types of synergistic molecular aggregates. Firstly, we show how simple phospholipids lubricate hydrophilic model surfaces of silica and how this lubrication is facilitated further by the presence of an anionic polysaccharide, hyaluronan, due to the enhanced surface build-up of lubricant material. Next, we mimic natural polylectrolytesurfactant aggregation by employing a highly positively charged polyelectrolyte and anionic surfactant that strongly associate both in the bulk and at the surfaces by building structured aggregates that lubricate due to hydration lubrication. This occurs despite of the presence of strong attraction between the lubricated surfaces. This is an example of synergistic lubrication due to particular internal structural arrangement of the aggregates. Finally, we investigate the case of synergistic lubrication due to preferential surface ordering of two biological polyelectrolytes, cartilage oligomeric matrix protein and lubricin, that leads to favourable lubrication.
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| 31. |
- Dedinaite, Andra, et al.
(författare)
-
Interactions between mica surfaces across triglyceride solution containing phospholipid and polyglycerol polyricinoleate
- 2000
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:5, s. 2248-2253
-
Tidskriftsartikel (refereegranskat)abstract
- 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 a PE/PGPR mixture are presented. It was shown that PE adsorbed on mica from anhydrous triolein and thus rendered the surface nonpolar. 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 Angstrom. 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 nonpolar 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.
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| 32. |
- Dedinaite, Andra, et al.
(författare)
-
Interfacial properties of aggregates formed by cationic polyelectrolyte and anionic surfactant
- 2000
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:4, s. 1951-1959
-
Tidskriftsartikel (refereegranskat)abstract
- Interactions between mica surfaces across aqueous solutions containing mixtures of a highly positively charged polyelectrolyte and an anionic surfactant were studied by use of a surface force apparatus. The investigation was carried out with a constant polyelectrolyte concentration (20 ppm) and a wide range of surfactant concentrations [0-1 times the critical micelle concentration (cmc)]. The chemical composition of the adsorbed polyelectrolyte-surfactant layers was analyzed by x-ray photoelectron spectroscopy (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 times 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 times cmc, the polyelectrolytes adsorb on mica surfaces with loops acid 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 times 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 (greater than or equal to 0.4 times cmc) highly negatively charged aggregates adsorb on the surfaces in rather thin layers, resulting in purely repulsive forces of mixed electrostatic and steric origin.
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| 33. |
- Dédinaité, Andra, et al.
(författare)
-
Interfacial properties of chitosan-PEO graft oligomers: Surface competition with unmodified chitosan oligomers
- 2006
-
Ingår i: Progress in Colloid and Polymer Science. - Berlin/Heidelberg : Springer-Verlag. - 0340-255X .- 1437-8027. ; 132, s. 124-130
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 34. |
- Dédinaité, Andra, 1966-
(författare)
-
Interfacial properties of mucins
- 2010. - 2
-
Ingår i: Encyclopedia of Surface and Colloid Science. - : Tailor and Francis. ; , s. 1-17, s. 1-17
-
Bokkapitel (refereegranskat)abstract
- Mucins are a very abundant class of glycoproteins present on most internal interfaces in most organisms in the animal kingdom. They fulfill many functions related to hydration, lubrication, and protection and also in recognition events and cell signaling. Despite the great importance of mucins, it is fair to say that even today the understanding of the interfacial properties of mucins is limited. One reason for this is the great variation in mucin structure. Mucins can be secreted or they can be membrane‐bound, their molecular weight can be vastly different, and their charge density varies, but most importantly, the unlimited number of ways that the carbohydrate moieties can be assembled provides a structural variation that is enormous. Thus, different mucins behave differently in solution, they aggregate differently, and they have very different interfacial properties. This has yet not been investigated in a systematic manner and thus the structure–property relations are not fully clear. However, different mucins do show general structural similarities, and some general features of their interfacial properties also display similarities. This review seeks to elucidate these similarities and tries to relate them to common physical chemical characteristics, which are also key elements for their functions in living organisms.
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| 35. |
|
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| 36. |
- Dedinaite, Andra, et al.
(författare)
-
Lubrication by organized soft matter
- 2010
-
Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:7, s. 1520-1526
-
Tidskriftsartikel (refereegranskat)abstract
- The AFM-colloidal probe technique has been used to explore surface interactions and friction forces between polyelectrolyte-coated surfaces immersed in aqueous solutions in the absence and presence of surfactant. It is found that the nature of the load bearing forces is decisive for the lubricating properties of the layers. Low frictional forces are obtained when the load is carried by a force that allows the interfacial layer to have a high fluidity, whereas attractive surface forces most often increase the friction. Highly charged polyelectrolytes and oppositely charged surfactants associate in bulk solution to form complexes with a well-defined internal structure. At the surface, similarly structured polyelectrolyte-surfactant layers are spontaneously formed. Such layers have a high load bearing capacity, and the friction coefficient is very low as long as the integrity of the layer remains intact. Interestingly, when the load is increased step-wise the friction force as a function of load displays some sharp peaks, which are identified as being due to structural rearrangements in the polyelectrolyte-surfactant layer. On unloading very low frictional forces are obtained despite the presence of an adhesion between the layers. To maintain the favorable lubricating properties it is essential to have surfactants present in solution, whereas, after the initial adsorption step, there is no need to have the polyelectrolyte present in the bulk. The reason for this is the essentially irreversible adsorption of the polyelectrolyte.
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| 37. |
- Dédinaité, Andra
(författare)
-
Monolayer Properties Probed by Surface Forces Measurements
- 2007
-
Ingår i: Advanced chemistry of monolayers at interfaces. - : Elsevier. - 9780123725707 ; , s. 23-53
-
Bokkapitel (refereegranskat)abstract
- In a review like this it is impossible to refer to even a small fraction of all the interesting work that has been done with the SFA. Anyway, I hope to have illustrated some selected areas in which the SFA has played a major role for increasing our understanding. It is fascinating to see how the development of the "basic SFA" is continued in many laboratories. One clear focus of modern developments is towards studies of dynamic phenomena, another is to combine the SFA with spectroscopy in order to gain further molecular understanding of matter in confinement. The coming years will be exciting and promise new developments that will allow us to develop our understanding of colloids, biophysical systems and complex liquids at and between interfaces.
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| 38. |
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| 39. |
- Dedinaite, Andra, et al.
(författare)
-
Polyelectrolyte-surfactant layers : Adsorption of preformed aggregates versus adsorption of surfactant to preadsorbed polyelectrolyte
- 2000
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:12, s. 5257-5266
-
Tidskriftsartikel (refereegranskat)abstract
- 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 is reached only after 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, poly{(propionyloxy)ethyl}trimethylammonium chloride (PCMA), and an anionic surfactant, sodium dodecyl sulfate (SDS). The adsorbed layer properties were determined using mainly surface force measurements and atomic force microscope (AFM) imaging. We also present some small-angle neutron scattering data for bulk PCMA-SDS complexes formed between the polyelectrolyte and the surfactant. They demonstrate the presence of a characteristic correlation length of about 37-39 Angstrom. A similar characteristic length scale is also observed in some of the adsorbed layers, both employing the AFM and the surface force apparatus. It may be interpreted as the distance between surfactant loaded polyelectrolyte chains.
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| 40. |
- Dedinaite, Andra, et al.
(författare)
-
Solution properties of bottle-brush polyelectrolytes
- 2007
-
Ingår i: PROCEEDINGS OF BALTIC POLYMER SYMPOSIUM 2007. - 9789955331506 ; , s. 112-116
-
Konferensbidrag (refereegranskat)abstract
- Aqueous solution properties of bottle brush polyelectrolytes, where side-chains are attached to a polymer backbone, have been studied. The side chains consist of 45 units long poly(ethylene oxide) groups and the backbone is of the methacrylate type. Small-angle X-ray scattering (SAXS) was used to elucidate the solution conformation of this class of polymer and how it is affected by the side chain density and charge density. The effect of temperature on the solution conformation, and in particular the side chain extension, has also been quantified. At higher concentrations the interactions between the polymer chains in solution affects the scattering, and it is shown that this interaction is well described by a model originally developed for wormlike micelles.
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| 41. |
- Dedinaite, Andra
(författare)
-
Surface force studies of association phenomena at solid-liquid interfaces
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main topics of this thesis, association phenomena inbulk and at solid-liquid interfaces in polar and non-polarmedia, were studied by a range of methods. Direct forcemeasurements employing the interferometric surface forceapparatus (SFA) was the chief technique. In addition, atomicforce microscopy (AFM), X-ray photoelectron spectroscopy (XPS),small angle neutron scattering (SANS), dynamic light scattering(DLS), turbidimetric and electrophoretic mobility measurementswere also applied. These techniques give complementaryinformation, and together they can provide a rather detailedpicture of the fairly complex systems studied.The first system studied was designed to explore particleinteractions in non-polar media. It consisted of polar or,alternatively, non-polar surfaces immersed in a non-polarmedium, triolein, in some cases containing additives such asphospholipids, polyglycerol polyricinoleate (PGPR), and traceamounts of water. It was investigated how triolein mediates thesurface interactions and how these interactions are affected bythe presence of additives. Triolein adsorbs onto mica surfacesthus producing a barrier against flocculation of the particles.The additives mentioned interact with the surfaces and witheach other, thus altering the surface interactions. Water, forinstance, being strongly polar, preferentially adsorbs ontomica and disturbs the triolein ordering at the mica surfacescausing the barrier against flocculation to vanish. Owing tocapillary condensation of water, a strong adhesion between thesurfaces is instead developed. On the other hand, it could beshown that in the presence of phospholipids, the effect ofwater was opposite: long-range repulsive forces develop due toweakly adsorbed reversed phospholipid aggregates.The second type of system studied contained cationicpolyelectrolytes and oppositely charged surfactants. Suchsystems occur in numerous technological processes: wastewatertreatment and ore recovery as well as laundry and body care.Polyelectrolytes and surfactants associate in bulk solution,and they also adsorb on surfaces. Thus, the relation betweenthe bulk properties of polyelectrolyte-surfactant mixtures andtheir properties at the solid-liquid interface is of greatscientific and industrial interest. The bulk properties ofpolyelectrolyte-surfactant aggregates were characterised byDLS, SANS, turbidimetry and electrophoretic mobilitymeasurements. It was concluded that to a certain extent theinterfacial properties of polyelectrolyte-surfactant aggregatescan be rationalised by considering their bulk properties.However, it was also shown that the presence of a surfaceaffects the association between polyelectrolytes andsurfactants. The chemical composition of adsorbed aggregates isdifferent from that of aggregates in solution, and, moreover,the structure of surface-bound polyelectrolyte-surfactantaggregates changes slowly with time.Keywords:Triolein, phosphatidiylethanolamine,phospholipid, lecithin, capillary condensation, polyglycerolpolyricinoleate, aggregation, adsorption, surface forces,structural forces, mica, polar surface, non-polar surface,polyelectrolyte, surfactant, sodium dodecyl sulphate,polyelectrolyte-surfactant association, turbidity,electrophoretic mobility, AFM, SANS, DLS, SFA.
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| 42. |
- Dédinaité, Andra, et al.
(författare)
-
Synergies in lubrication
- 2017
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:35, s. 23677-23689
-
Tidskriftsartikel (refereegranskat)abstract
- To slide surfaces against each other with application of a minimum force and minimum wear has been important since ancient times, and it remains equally important today. The use of oil-soluble lubricants is widely spread in technology, whereas living organisms have developed water-soluble lubricants to facilitate sliding motions. In this perspective article we focus on water-based lubrication in the boundary lubrication regime, and particularly lubrication synergies. This focus has, of course, found inspiration from the outstanding lubrication properties of synovial joints. It has ignited significant amount of research, mostly aimed at answering the question: Which molecule is the magic biolubricant? Different research groups have advocated different answers, and the debate has been intensive. In this article we argue that the question in itself is inappropriate. The relevant question is rather the following: How do molecules work in synergy to provide superior lubrication?
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| 43. |
- Dobryden, Illia, et al.
(författare)
-
Bioinspired Adhesion Polymers : Wear Resistance of Adsorption Layers.
- 2019
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 35:48, s. 15515-15525
-
Tidskriftsartikel (refereegranskat)abstract
- Mussel adhesive polymers owe their ability to strongly bind to a large variety of surfaces under water to their high content of 3,4-dihydroxy-l-phenylalanine (DOPA) groups and high positive charge. In this work, we use a set of statistical copolymers that contain medium-length poly(ethylene oxide) side chains that are anchored to the surface in three different ways: by means of (i) electrostatic forces, (ii) catechol groups (as in DOPA), and (iii) the combination of electrostatic forces and catechol groups. A nanotribological scanning probe method was utilized to evaluate the wear resistance of the formed layers as a function of normal load. It was found that the combined measurement of surface topography and stiffness provided an accurate assessment of the wear resistance of such thin layers. In particular, surface stiffness maps allowed us to identify the initiation of wear before a clear topographical wear scar was developed. Our data demonstrate that the molecular and abrasive wear resistance on silica surfaces depends on the anchoring mode and follows the order catechol groups combined with electrostatic forces > catechol groups alone > electrostatic forces alone. The devised methodology should be generally applicable for evaluating wear resistance or "robustness" of thin adsorbed layers on a variety of surfaces.
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| 44. |
- Dobryden, Illia, et al.
(författare)
-
Local Wear of Catechol-Containing Diblock Copolymer Layers : Wear Volume, Stick-Slip, and Nanomechanical Changes
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 125:38, s. 21277-21292
-
Tidskriftsartikel (refereegranskat)abstract
- Polymers containing catechol groups have gained a large interest, as they mimic an essential feature of mussel adhesive proteins that allow strong binding to a large variety of surfaces under water. This feature has made this class of polymers interesting for surface modification purposes, as layer functionalities can be introduced by a simple adsorption process, where the catechol groups should provide a strong anchoring to the surface. In this work, we utilize an AFM-based method to evaluate the wear resistance of such polymer layers in water and compare it with that offered by electrostatically driven adsorption. We pay particular attention to two block copolymer systems where the anchoring group in one case is an uncharged catechol-containing block and in the other case a positively charged and catechol-containing block. The wear resistance is evaluated in terms of wear volume, and here, we compare with data for similar copolymers with statistical distribution of the catechol groups. Monitoring of nanomechanical properties provides an alternative way of illustrating the effect of wear, and we use modeling to show that the stiffness, as probed by an AFM tip, of the soft layer residing on a hard substrate increases as the thickness of the layer decreases. The stick-slip characteristics are also evaluated. © 2021 The Authors.
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| 45. |
- Dobryden, Illia, et al.
(författare)
-
Thermoresponsive Pentablock Copolymer on Silica : Temperature Effects on Adsorption, Surface Forces, and Friction
- 2019
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 35:3, s. 653-661
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of hydrophilic or amphiphilic multiblock copolymers provides a powerful means to produce well-defined "smart" surfaces, especially if one or several blocks are sensitive to external stimuli. We focus here on an A-B-A-B-A copolymer, where A is a cationic poly((3-acrylamido-propyl)-trimethylammonium chloride) (PAMPTMA) block containing 15 (end blocks) or 30 (middle block) repeat units and B is a neutral thermosensitive water-soluble poly(2-isopropyl-2-oxazoline) (PIPOZ) block with 50 repeat units. X-ray reflectivity and quartz crystal microbalance with dissipation monitoring were employed to study the adsorption of PAMPTMA15-PIPOZ50-PAMPTMA30-PIPOZ50-PAMPTMA15 on silica surfaces. The latter technique was employed at different temperatures up to 50 °C. Surface forces and friction between the two silica surfaces across aqueous pentablock copolymer solutions at different temperatures were determined with the atomic force microscopy colloidal probe force and friction measurements. The cationic pentablock copolymer was found to have a high affinity to the negatively charged silica surface, leading to a thin (2 nm) and rigid adsorbed layer. A steric force was encountered at a separation of around 3 nm from hard wall contact. A capillary condensation of a polymer-rich phase was observed at the cloud point of the solution. The friction forces were evaluated using Amontons' rule modified with an adhesion term.
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| 46. |
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| 47. |
- Duner, Gunnar, et al.
(författare)
-
Attractive double-layer forces and charge regulation upon interaction between electrografted amine layers and silica
- 2012
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 385:1, s. 225-234
-
Tidskriftsartikel (refereegranskat)abstract
- Amine functionalities have been introduced on glassy carbon surfaces through electrografting of 4-(2-aminoethyl)benzenediazonium tetrafluoroborate. The grafted layers were characterized by ellipsometry and by nanomechanical mapping in air and aqueous solutions using the atomic force microscopy PeakForce QNM mode. The layer was found to be 2.5. nm thick with low roughness, comparable to that of the glassy carbon substrate. However, small semi-spherical features were observed in the topographical image, indicating a clustering of the grafted amine compound. The nanomechanical mapping also demonstrated some swelling of the layer in water and pointed toward an important contribution of electrostatic interactions for the tip-surface adhesion. The forces between an aminated glassy carbon surface and a μm-sized silica particle in aqueous solutions were measured at different ionic strength and pH-values. The results demonstrate that an attractive double-layer force predominates at large separations, and that the surface charge densities increase as the separation between the surfaces decreases. The degree of charge regulation on the aminated glassy carbon is significant. The relatively low surface charge density of the aminated glassy carbon is attributed to significant incorporation of counterions in the water-rich grafted layer.
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| 48. |
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| 49. |
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| 50. |
- Dunér, Gunnar, et al.
(författare)
-
Friction between surfaces - Polyacrylic acid brush and silica - mediated by calcium ions
- 2010
-
Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 31:10, s. 1285-1287
-
Tidskriftsartikel (refereegranskat)abstract
- With this letter, we report how friction can be controlled by inducing physical bonds solely within a polyelectrolyte brush layer, while keeping repulsive interactions between the brush layer and the bare surface that slides above. Our results imply that the nature of the bare surface is of minor importance as long as the repulsive surface interaction is maintained.
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