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149 results on '"Rubinstein, Michael"'

3. Overlap Concentration in Salt-Free Polyelectrolyte Solutions

Author

Bollinger, Jonathan A., Grest, Gary S., Stevens, Mark J., and Rubinstein, Michael

Subjects
Chemical structure, Polymers, Counterions, Conformation, Polyelectrolytes
Abstract

For strongly charged polyelectrolytes in salt-free solutions, we use molecular dynamics simulations of a coarse-grained bead-spring model to calculate overlap concentrations c* and chain structure for polymers containing N = 10 to 1600 monomers. Over much of this range, we find that the end-to-end distance R* at c* increases faster than linearly with increasing N, as chains at the overlap concentration approach strongly extended conformations. This trend results in the overlap concentration c* decreasing as a stronger function of N than the classical prediction c* similar to N-2. This stronger dependence can be fit either by a logarithmic correction to scaling or by an apparent scaling c* similar to N-m, with m > 2.

Published
2021

7. Nonlinear Shear Rheology of Entangled Polymer Rings

Author

Parisi, Daniele, primary, Costanzo, Salvatore, additional, Jeong, Youncheol, additional, Ahn, Junyoung, additional, Chang, Taihyun, additional, Vlassopoulos, Dimitris, additional, Halverson, Jonathan D., additional, Kremer, Kurt, additional, Ge, Ting, additional, Rubinstein, Michael, additional, Grest, Gary S., additional, Srinin, Watee, additional, and Grosberg, Alexander Y., additional

Published
2021
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22. Influence of the Solvent Quality on Ring Polymer Dimensions

Author

Gooßen, Sebastian, primary, Brás, Ana R., additional, Pyckhout-Hintzen, Wim, additional, Wischnewski, Andreas, additional, Richter, Dieter, additional, Rubinstein, Michael, additional, Roovers, Jacques, additional, Lutz, Pierre J., additional, Jeong, Youncheol, additional, Chang, Taihyun, additional, and Vlassopoulos, Dimitris, additional

Published
2015
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36. Lubrication by Polyelectrolyte Brushes.

Author

Zhulina, Ekaterina B. and Rubinstein, Michael

Subjects
*LUBRICATION & lubricants, *POLYELECTROLYTES, *MONOMERS, *SOLVENTS, *VISCOSITY, *FRICTION
Abstract

We develop a scaling model relating the friction forces between two polyelectrolyte brushes sliding over each other to the separation between grafted surfaces, number of monomers and charges per chain, grafting density of chains, and solvent quality. We demonstrate that the lateral force between brushes increases upon compression, but to a lesser extent than the normal force. The shear stress at larger separations is due to solvent slip layer friction. The thickness of this slip layer sharply decreases at distances on the order of undeformed brush thickness. The corresponding effective viscosity of the layer sharply increases from the solvent viscosity to a much higher value, but this increase is smaller than the jump of the normal force resulting in the drop of the friction coefficient. At stronger compression we predict the second sharp increase of the shear stress corresponding to interpenetration of the chains from the opposite brushes. In this regime the velocity-dependent friction coefficient between two partially interpenetrating polyelectrolyte brushes does not depend on the distance between substrates because both normal and shear forces are reciprocally proportional to the plate separation. Although lateral forces between polyelectrolyte brushes are larger than between bare surfaces, the enhancement of normal forces between opposing polyelectrolyte brushes with respect to normal forces between bare charged surfaces is much stronger resulting in lower friction coefficient. The model quantitatively demonstrates how polyelectrolyte brushes provide more effective lubrication than bare charged surfaces or neutral brushes. [ABSTRACT FROM AUTHOR]

Published
2015
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