The Experts below are selected from a list of 1266 Experts worldwide ranked by ideXlab platform
Yoav Tsori - One of the best experts on this subject based on the ideXlab platform.
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experimental demonstration of the Stabilization of Colloids by addition of salt
arXiv: Soft Condensed Matter, 2014Co-Authors: Sela Samin, Manuela Hod, Eitan Melamed, Moshe Gottlieb, Yoav TsoriAbstract:We demonstrate a general non--Derjaguin-Landau-Verwey-Overbeek method to stabilize Colloids in liquids. By this method, colloidal particles that initially form unstable suspension and sediment from the liquid are stabilized by the addition of salt to the suspending liquid. Yet, the salt is not expected to adsorb or directly interact with the surface of the Colloids. For the method to work, the liquid should be a mixture, and the salt needs to be antagonistic such that each ion is preferentially solvated by a different component of the mixture. The Stabilization may depend on the salt content, mixture composition, or distance from the mixture's coexistence line.
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experimental demonstration of the Stabilization of Colloids by addition of salt
Physical review applied, 2014Co-Authors: Sela Samin, Manuela Hod, Eitan Melamed, Moshe Gottlieb, Yoav TsoriAbstract:Controlling the stability of a colloidal suspension is key to processing and using materials ranging from ferrofluids to gemstones. Suspended particles can be stabilized either sterically by adding short surfactant molecules or polymers, or electrostatically via repulsion, if the particles bear a common charge. In the latter case, addition of salt generally decreases the repulsion between particles and leads to their coagulation. However, here researchers demonstrate and explain how addition of salt to a colloidal suspension actually can $s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}z\phantom{\rule{0}{0ex}}e$ it.
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Stabilization of charged and neutral Colloids in salty mixtures
Journal of Chemical Physics, 2013Co-Authors: Sela Samin, Yoav TsoriAbstract:We present a mechanism for the Stabilization of Colloids in liquid mixtures without use of surfactants or polymers. When a suitable salt is added to a solvent mixture, the coupling of the colloid's surface chemistry and the preferential solvation of ions leads to a repulsive force between Colloids that can overcome van der Waals attraction. This repulsive force is substantial in a large range of temperatures, mixture composition, and salt concentrations. The increased repulsion due to addition of salt occurs even for charged Colloids. This mechanism may be useful in experimental situations where steric Stabilization with surfactants or polymers is undesired.
Keith P Johnston - One of the best experts on this subject based on the ideXlab platform.
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electrostatic Stabilization of Colloids in carbon dioxide electrophoresis and dielectrophoresis
Langmuir, 2005Co-Authors: Won Ryoo, Jasper L Dickson, Varun V Dhanuka, S E Webber, Roger T Bonnecaze, Keith P JohnstonAbstract:Over the past decade, steric Stabilization has been achieved for a variety of inorganic and organic Colloids in supercritical fluid carbon dioxide (scCO2). Herein we demonstrate that Colloids may also be stabilized in CO2 by electrostatic forces, despite the ultralow dielectric constant of 1.5. Zeta potentials of micrometer-sized water droplets, measured in a microelectrophoresis cell, reached −70 mV corresponding to a few elementary charges per square micrometer of droplet surface. This degree of charge was sufficient to stabilize water/CO2 emulsions for an hour, even with water volume fractions of 5%. Hydrogen ions partition preferentially, relative to bicarbonate ions, from the emulsion droplets to the cores of surfactant micelles in the diffuse double layer surrounding the droplets. The micelles, formed with a low molecular weight branched hydrocarbon surfactant, prevent ion pairing of the hydrogen counterions to the negatively charged emulsion droplets. Dielectrophoresis of the water droplets at a fr...
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steric Stabilization of Colloids by poly dimethylsiloxane in carbon dioxide effect of cosolvents
Journal of Colloid and Interface Science, 2000Co-Authors: Matthew Z Yates, Keith P Johnston, Parag S Shah, Kwon Taek Lim, S E WebberAbstract:Abstract Steric Stabilization and flocculation of Colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO2 at pressures up to 345 bar at 25°C and 517 bar at 65°C without stirring. The addition of 15 wt% hexane to CO2 led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1–2 μm PMMA particles. The critical flocculation pressure of the Colloids in the hexane/CO2 mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS–CO2 system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO2 with PDMS-based surfactants.
S E Webber - One of the best experts on this subject based on the ideXlab platform.
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electrostatic Stabilization of Colloids in carbon dioxide electrophoresis and dielectrophoresis
Langmuir, 2005Co-Authors: Won Ryoo, Jasper L Dickson, Varun V Dhanuka, S E Webber, Roger T Bonnecaze, Keith P JohnstonAbstract:Over the past decade, steric Stabilization has been achieved for a variety of inorganic and organic Colloids in supercritical fluid carbon dioxide (scCO2). Herein we demonstrate that Colloids may also be stabilized in CO2 by electrostatic forces, despite the ultralow dielectric constant of 1.5. Zeta potentials of micrometer-sized water droplets, measured in a microelectrophoresis cell, reached −70 mV corresponding to a few elementary charges per square micrometer of droplet surface. This degree of charge was sufficient to stabilize water/CO2 emulsions for an hour, even with water volume fractions of 5%. Hydrogen ions partition preferentially, relative to bicarbonate ions, from the emulsion droplets to the cores of surfactant micelles in the diffuse double layer surrounding the droplets. The micelles, formed with a low molecular weight branched hydrocarbon surfactant, prevent ion pairing of the hydrogen counterions to the negatively charged emulsion droplets. Dielectrophoresis of the water droplets at a fr...
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steric Stabilization of Colloids by poly dimethylsiloxane in carbon dioxide effect of cosolvents
Journal of Colloid and Interface Science, 2000Co-Authors: Matthew Z Yates, Keith P Johnston, Parag S Shah, Kwon Taek Lim, S E WebberAbstract:Abstract Steric Stabilization and flocculation of Colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO2 at pressures up to 345 bar at 25°C and 517 bar at 65°C without stirring. The addition of 15 wt% hexane to CO2 led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1–2 μm PMMA particles. The critical flocculation pressure of the Colloids in the hexane/CO2 mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS–CO2 system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO2 with PDMS-based surfactants.
Sela Samin - One of the best experts on this subject based on the ideXlab platform.
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experimental demonstration of the Stabilization of Colloids by addition of salt
arXiv: Soft Condensed Matter, 2014Co-Authors: Sela Samin, Manuela Hod, Eitan Melamed, Moshe Gottlieb, Yoav TsoriAbstract:We demonstrate a general non--Derjaguin-Landau-Verwey-Overbeek method to stabilize Colloids in liquids. By this method, colloidal particles that initially form unstable suspension and sediment from the liquid are stabilized by the addition of salt to the suspending liquid. Yet, the salt is not expected to adsorb or directly interact with the surface of the Colloids. For the method to work, the liquid should be a mixture, and the salt needs to be antagonistic such that each ion is preferentially solvated by a different component of the mixture. The Stabilization may depend on the salt content, mixture composition, or distance from the mixture's coexistence line.
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experimental demonstration of the Stabilization of Colloids by addition of salt
Physical review applied, 2014Co-Authors: Sela Samin, Manuela Hod, Eitan Melamed, Moshe Gottlieb, Yoav TsoriAbstract:Controlling the stability of a colloidal suspension is key to processing and using materials ranging from ferrofluids to gemstones. Suspended particles can be stabilized either sterically by adding short surfactant molecules or polymers, or electrostatically via repulsion, if the particles bear a common charge. In the latter case, addition of salt generally decreases the repulsion between particles and leads to their coagulation. However, here researchers demonstrate and explain how addition of salt to a colloidal suspension actually can $s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}z\phantom{\rule{0}{0ex}}e$ it.
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Stabilization of charged and neutral Colloids in salty mixtures
Journal of Chemical Physics, 2013Co-Authors: Sela Samin, Yoav TsoriAbstract:We present a mechanism for the Stabilization of Colloids in liquid mixtures without use of surfactants or polymers. When a suitable salt is added to a solvent mixture, the coupling of the colloid's surface chemistry and the preferential solvation of ions leads to a repulsive force between Colloids that can overcome van der Waals attraction. This repulsive force is substantial in a large range of temperatures, mixture composition, and salt concentrations. The increased repulsion due to addition of salt occurs even for charged Colloids. This mechanism may be useful in experimental situations where steric Stabilization with surfactants or polymers is undesired.
Helmut Colfen - One of the best experts on this subject based on the ideXlab platform.
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double hydrophilic block copolymers synthesis and application as novel surfactants and crystal growth modifiers
Macromolecular Rapid Communications, 2001Co-Authors: Helmut ColfenAbstract:Double-hydrophilic block copolymers are a new class of amphiphilic molecules of rapidly increasing importance with unique and fascinating properties poten tially connecting materials science, pharmacy, biochemistry and polymer science. Characteristic of these polymers is their application in aqueous environments and that amphiphilicity is just induced in the presence of a subtrate or by temperature and pH changes, respectively, Their chemical structure may be turned for a wide range of applications covering as different aspects as Stabilization of Colloids, crystal growth modification, indnced micelle formation, polyelectrolyte complexing towards novel drug carrier systems. As the potential of this novel polymer class is relatively unexplored vet it can be expected that more applications will arise due to the possibility to adapt the chemical structure to either the desired substrate in contact with water or the stimulus for the induction of structural changes. This review describes the synthetic strategies to wards these AB block copolymers, as well as their applications.