Polymer-brush lubricated surfaces with colloidal inclusions under shear inversion.
ABSTRACT We characterize the response of compressed, sheared polymer-brush bilayers with colloidal inclusions to highly nonstationary inversion processes by means of molecular dynamics simulations and scaling theory. Bilayers with a simple (dimeric) solvent reveal an overshoot for the shear stress, while simulations of dry brushes without explicit solvent molecules fail to display this effect. We demonstrate that mechanical instabilities can be controlled by the inclusion of macromolecular structures, such as colloids of varying softness. Based on a recently developed theory, we suggest a scaling approach to determine a characteristic time for conformational and collective responses.
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ABSTRACT: We report on the design of microchannels made of glass capillary coated with polymer brushes elaborated by the so-called "grafting-from" technique. We present measurements of velocity profiles for pressure-driven flows of water in such "hairy" capillaries. We show that the flow reduction induced by the presence of the brush is unexpectedly greater than what could be anticipated from simple geometric arguments on the reduction of the effective capillary diameter or from predictions by models describing the brush layer as a poro-elastic boundary.Langmuir 08/2012; 28(38):13758-64. · 4.19 Impact Factor
Article: Polymer Brushes under High Load[show abstract] [hide abstract]
ABSTRACT: Polymer coatings are frequently used to provide repulsive forces between surfaces in solution. After 25 years of design and study, a quantitative model to explain and predict repulsion under strong compression is still lacking. Here, we combine experiments, simulations, and theory to study polymer coatings under high loads and demonstrate a validated model for the repulsive forces, proposing that this universal behavior can be predicted from the polymer solution properties.PLoS ONE 03/2013; 8(3):e58392. · 4.09 Impact Factor