The Experts below are selected from a list of 135 Experts worldwide ranked by ideXlab platform
Christy F. Landes - One of the best experts on this subject based on the ideXlab platform.
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Single molecule spectroscopy reveals heterogeneous transport mechanisms for molecular ions in a Polyelectrolyte Polymer brush.
The journal of physical chemistry. B, 2009Co-Authors: Carmen Reznik, Rigoberto C. Advincula, Nicel C. Estillore, Christy F. LandesAbstract:Single molecule polarization and fluorescence correlation spectroscopy were used to evaluate heterogeneous transport mechanisms of molecular ions within supported Polyelectrolyte brushes. Modes of diffusive transport include periods of significantly restricted rotational motion, often maintained over tens of milliseconds; periods of fast molecular rotation; and occasional adsorption of fluorescent probe molecules in the brush. The studies reveal rapid switching between orientational states during each observed mode of motion. Through quantitative analysis of state occupation times, the rate constants for transitions from weakly associated to strongly associated states were extracted. Additionally, the pH dependence of the ion transport rates in the brush exhibits an abrupt, rather than continuous, trend. These single molecule studies demonstrate the presence of dynamic anisotropic interactions between the charged molecular probe and the Polymer brush and provide experimental evidence of stimuli responsive...
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Single ion diffusive transport within a Poly(styrene sulfonate) Polymer brush matrix probed by fluorescence correlation spectroscopy.
The journal of physical chemistry. B, 2008Co-Authors: Carmen Reznik, Qusai Darugar, Andrea Wheat, Tim Fulghum, Rigoberto C. Advincula, Christy F. LandesAbstract:Diffusive transport within complex environments is a critical piece of the chemistry occurring in such diverse membrane systems as proton exchange and bilayer lipid membranes. In the present study, fluorescence correlation spectroscopy was used to evaluate diffusive charge transport within a strong Polyelectrolyte Polymer brush. The fluorescent cation rhodamine-6G was used as a counterion probe molecule, and the strong Polyelectrolyte poly(styrene sulfonate) was the Polymer brush. Such strong Polyelectrolyte brushes show promise for charge storage applications, and thus it is important to understand and tune their transport efficiencies. The Polymer brush demonstrated preferential solvation of the probe counterion as compared to solvation by the aqueous solvent phase. Additionally, diffusion within the Polymer brush was strongly inhibited, as evidenced by a decrease in diffusion constant of 4 orders of magnitude. It also proved possible to tune the transport characteristics by controlling the solvent pH, and thus the ionic strength of the solvent. The diffusion characteristics within the charged brush system depend on the brush density as well as the effective interaction potential between the probe ions and the brush. In response to changes in ionic strength of the solution, it was found that these two properties act in opposition to each other within this strong Polyelectrolyte Polymer brush environment. A stochastic random walk model was developed to simulate interaction of a diffusing charged particle with a periodic potential, to show the response of characteristic diffusion times to electrostatic field strengths. The combined results of the experiments and simulations demonstrate that responsive diffusion characteristics in this brush system are dominated by changes in Coulombic interactions rather than changes in brush density. More generally, these results support the use of FCS to evaluate local charge transport properties within Polyelectrolyte brush systems, and demonstrate that the technique shows promise in the development of novel Polyelectrolyte films for charge storage/transport materials.
Jeffrey B. Sokoloff - One of the best experts on this subject based on the ideXlab platform.
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Discrete model studies of two grafted Polyelectrolyte Polymer hydrogels pressed in contact.
The Journal of chemical physics, 2013Co-Authors: Jeffrey B. Sokoloff, Mark J. StevensAbstract:The interaction between two grafted Polymer gels was investigated. We studied a defect-free network of diamond-like topology containing 8 tetra-functional nodes linked by 16 non-crossing chains. In order to explain the very low friction coefficient observed for Polyelectrolyte hydrogels, we computed the monomer density profile of these Polymer gels, the interpenetration between two Polymer gels (defined as the percentage of monomers belonging to one gel which have penetrated the second gel), the normal force per unit area, and the radial distribution function of the interacting monomers. Low monomer density in the interface region separating the two gels and low interpenetration of the gels similar to that found in our simulations are likely to be responsible for the small friction coefficients observed for Polyelectrolyte Polymer gels.
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Comparison of the kinetic friction of planar neutral and Polyelectrolyte Polymer brushes using molecular dynamics simulations.
Physical Review E, 2012Co-Authors: Jeffrey B. Sokoloff, Mark J. StevensAbstract:We have simulated the relative shear motion of both neutral and Polyelectrolyte end-grafted Polymer brushes using molecular dynamics. The flexible neutral Polymer brush is treated as a bead-spring model, and the Polyelectrolyte brush is treated the same way except that each bead is charged and there are counterions present to neutralize the charge. We investigated the friction coefficient, monomer density, and brush penetration for both Polyelectrolyte and neutral brushes with both equal grafting density and equal normal force under good solvent conditions. We found that Polyelectrolyte brushes had a smaller friction coefficient and monomer penetration than neutral Polymer brushes with the identical grafting density and chain length, and the Polyelectrolyte brushes supported a much higher normal load than the neutral brushes for the same degree of compression. Charged and neutral brushes with their grafting densities chosen so that they support the same load exhibited approximately the same degree of interpenetration, but the Polyelectrolyte brush exhibited a significantly lower friction coefficient. We present evidence that the reason for this is that the extra normal force contribution provided by the counterion osmotic pressure that exists for Polyelectrolyte brushes permits them to support the same load as an identical neutral Polymer brush of higher grafting density. Because of the resulting lower monomer density for the charged brushes, fewer monomer collisions take place per unit time, resulting in a lower friction coefficient.
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Theory of the observed ultralow friction between sliding Polyelectrolyte brushes.
The Journal of chemical physics, 2008Co-Authors: Jeffrey B. SokoloffAbstract:It is shown using a method based on a modified version of the mean field theory of Miklavic and Marcelja [J. Phys. Chem. 92, 6718 (1988)] that it should be possible for osmotic pressure due to the counterions associated with the two Polyelectrolyte Polymer brush coated surfaces to support a reasonable load (i.e., about 10(6) Pa) with the brushes held sufficiently far apart to prevent entanglement of Polymers belonging to the two brushes, thus avoiding what is believed to be the dominant mechanisms for static and dry friction.
Mark J. Stevens - One of the best experts on this subject based on the ideXlab platform.
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Discrete model studies of two grafted Polyelectrolyte Polymer hydrogels pressed in contact.
The Journal of chemical physics, 2013Co-Authors: Jeffrey B. Sokoloff, Mark J. StevensAbstract:The interaction between two grafted Polymer gels was investigated. We studied a defect-free network of diamond-like topology containing 8 tetra-functional nodes linked by 16 non-crossing chains. In order to explain the very low friction coefficient observed for Polyelectrolyte hydrogels, we computed the monomer density profile of these Polymer gels, the interpenetration between two Polymer gels (defined as the percentage of monomers belonging to one gel which have penetrated the second gel), the normal force per unit area, and the radial distribution function of the interacting monomers. Low monomer density in the interface region separating the two gels and low interpenetration of the gels similar to that found in our simulations are likely to be responsible for the small friction coefficients observed for Polyelectrolyte Polymer gels.
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Comparison of the kinetic friction of planar neutral and Polyelectrolyte Polymer brushes using molecular dynamics simulations.
Physical Review E, 2012Co-Authors: Jeffrey B. Sokoloff, Mark J. StevensAbstract:We have simulated the relative shear motion of both neutral and Polyelectrolyte end-grafted Polymer brushes using molecular dynamics. The flexible neutral Polymer brush is treated as a bead-spring model, and the Polyelectrolyte brush is treated the same way except that each bead is charged and there are counterions present to neutralize the charge. We investigated the friction coefficient, monomer density, and brush penetration for both Polyelectrolyte and neutral brushes with both equal grafting density and equal normal force under good solvent conditions. We found that Polyelectrolyte brushes had a smaller friction coefficient and monomer penetration than neutral Polymer brushes with the identical grafting density and chain length, and the Polyelectrolyte brushes supported a much higher normal load than the neutral brushes for the same degree of compression. Charged and neutral brushes with their grafting densities chosen so that they support the same load exhibited approximately the same degree of interpenetration, but the Polyelectrolyte brush exhibited a significantly lower friction coefficient. We present evidence that the reason for this is that the extra normal force contribution provided by the counterion osmotic pressure that exists for Polyelectrolyte brushes permits them to support the same load as an identical neutral Polymer brush of higher grafting density. Because of the resulting lower monomer density for the charged brushes, fewer monomer collisions take place per unit time, resulting in a lower friction coefficient.
Hongyu Zhang - One of the best experts on this subject based on the ideXlab platform.
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Biodegradable lubricating mesoporous silica nanoparticles for osteoarthritis therapy
Friction, 2020Co-Authors: Li Wan, Xiaolong Tan, Yulong Sun, Jing Luo, Yi Wang, Hongyu ZhangAbstract:Osteoarthritis is characterized by lubrication failure of the articular cartilage and severe inflammation of the joint capsule. Lubricating mesoporous silica nanoparticles (MSNs) have been developed for the treatment of osteoarthritis based on enhanced lubrication and local drug delivery. However, MSNs are difficult to degrade in vivo in a short time, resulting in potential toxic effect due to bioaccumulation. In this study, biodegradable MSNs (bMSNs) were prepared through an oil-water biphase stratification method, and modified with poly(2-methacryloyloxyethyl phosphocholine) (PMPC) to synthesize lubricating drug-loaded nanoparticles (bMSNs-NH2@PMPC) by photoPolymerization. The in vitro degradation test demonstrated that the bMSNs and bMSNs-NH2@PMPC almost degraded within 7 days. The tribiological test showed that the lubrication property of the bMSNs-NH2@PMPC was greatly improved, with a reduction of 50% in the friction coefficient (COF) compared with the bMSNs. It was attributed to hydration lubrication mechanism by which a tenacious hydration layer is formed surrounding the zwitterionic headgroups (N+(CH3)3 and PO4−) in PMPC Polyelectrolyte Polymer. Additionally, the bMSNs-NH2@PMPC maintained excellent lubrication property under degradation and achieved sustained drug release behavior compared with the bMSNs. In summary, the biodegradable bMSNs-NH2@PMPC developed in this study with the properties of enhanced lubrication and drug delivery may be a promising approach for osteoarthritis therapy.
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Lubrication and drug release behaviors of mesoporous silica nanoparticles grafted with sulfobetaine-based zwitterionic Polymer.
Materials science & engineering. C Materials for biological applications, 2020Co-Authors: Li Wan, Xiaolong Tan, Tao Sun, Yulong Sun, Jing Luo, Hongyu ZhangAbstract:Osteoarthritis, which is characterized by irreversible destruction of articular cartilage and severe inflammation of joint capsule, may be effectively treated via the synergistic therapy of lubrication restoration and local drug intervention. In this study, zwitterionic Polymer-grafted mesoporous silica nanoparticles (MSNs@pSBMA) with the property of enhanced lubrication and sustained drug release were successfully synthesized via photoPolymerization of 3-[dimethyl-[2-(2-methylprop-2-enoyloxy) ethyl] azaniumyl] propane-1-sulfonate Polymer (pSBMA) on the surface of MSNs. The tribiological test showed that the lubrication performance of MSNs@pSBMA was remarkably improved, with a reduction of 80% in friction coefficient compared with MSNs. It was attributed to hydration lubrication mechanism by which a tenacious hydration layer was formed surrounding the N+(CH2)2(CH3)2 and SO3- headgroups in the pSBMA Polyelectrolyte Polymer. Additionally, the surface morphology analysis of the tribopairs demonstrated that MSNs@pSBMA were endowed with excellent anti-wear performance. Importantly, the drug release test illustrated that, compared with MSNs, MSNs@pSBMA achieved good sustained drug release behavior. In summary, the MSNs@pSBMA nanoparticles developed herein, as an injectable lubricant with enhanced lubrication and drug delivery, may represent a promising approach for the treatment of osteoarthritis.
Carmen Reznik - One of the best experts on this subject based on the ideXlab platform.
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Single molecule spectroscopy reveals heterogeneous transport mechanisms for molecular ions in a Polyelectrolyte Polymer brush.
The journal of physical chemistry. B, 2009Co-Authors: Carmen Reznik, Rigoberto C. Advincula, Nicel C. Estillore, Christy F. LandesAbstract:Single molecule polarization and fluorescence correlation spectroscopy were used to evaluate heterogeneous transport mechanisms of molecular ions within supported Polyelectrolyte brushes. Modes of diffusive transport include periods of significantly restricted rotational motion, often maintained over tens of milliseconds; periods of fast molecular rotation; and occasional adsorption of fluorescent probe molecules in the brush. The studies reveal rapid switching between orientational states during each observed mode of motion. Through quantitative analysis of state occupation times, the rate constants for transitions from weakly associated to strongly associated states were extracted. Additionally, the pH dependence of the ion transport rates in the brush exhibits an abrupt, rather than continuous, trend. These single molecule studies demonstrate the presence of dynamic anisotropic interactions between the charged molecular probe and the Polymer brush and provide experimental evidence of stimuli responsive...
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Single ion diffusive transport within a Poly(styrene sulfonate) Polymer brush matrix probed by fluorescence correlation spectroscopy.
The journal of physical chemistry. B, 2008Co-Authors: Carmen Reznik, Qusai Darugar, Andrea Wheat, Tim Fulghum, Rigoberto C. Advincula, Christy F. LandesAbstract:Diffusive transport within complex environments is a critical piece of the chemistry occurring in such diverse membrane systems as proton exchange and bilayer lipid membranes. In the present study, fluorescence correlation spectroscopy was used to evaluate diffusive charge transport within a strong Polyelectrolyte Polymer brush. The fluorescent cation rhodamine-6G was used as a counterion probe molecule, and the strong Polyelectrolyte poly(styrene sulfonate) was the Polymer brush. Such strong Polyelectrolyte brushes show promise for charge storage applications, and thus it is important to understand and tune their transport efficiencies. The Polymer brush demonstrated preferential solvation of the probe counterion as compared to solvation by the aqueous solvent phase. Additionally, diffusion within the Polymer brush was strongly inhibited, as evidenced by a decrease in diffusion constant of 4 orders of magnitude. It also proved possible to tune the transport characteristics by controlling the solvent pH, and thus the ionic strength of the solvent. The diffusion characteristics within the charged brush system depend on the brush density as well as the effective interaction potential between the probe ions and the brush. In response to changes in ionic strength of the solution, it was found that these two properties act in opposition to each other within this strong Polyelectrolyte Polymer brush environment. A stochastic random walk model was developed to simulate interaction of a diffusing charged particle with a periodic potential, to show the response of characteristic diffusion times to electrostatic field strengths. The combined results of the experiments and simulations demonstrate that responsive diffusion characteristics in this brush system are dominated by changes in Coulombic interactions rather than changes in brush density. More generally, these results support the use of FCS to evaluate local charge transport properties within Polyelectrolyte brush systems, and demonstrate that the technique shows promise in the development of novel Polyelectrolyte films for charge storage/transport materials.