Polymer brush bilayer under stationary shear: A joint DFT, scaling theory and MD

Abstract

The problem of polymer brush bilayer under stationary shear is studied by using the DFT, the scaling theory and MD simulations. Both theory and simulations confirm that the shear stress follows the universal power law [Formula] for the brush bilayers with interpenetration and in the absence of the interpenetration, the shear stress scales linearly with the shear rate. It is also revealed that the presence of explicit solvent molecules prevents the brushes to form and interpenetration zone and therefore with explicit solvents the shear stress scales linearly with shear rate. Therefore, this study strongly confirms that there is no sublinear regime in the world of polymer brush bilayer, neither by solvents nor by hydrodynamic effects. As long as there is an interpenetration zone, the superlinear regime dominates and in the absence of the interpenetration zone the linear regime dominates. Therefore, polymer brushes are not a good candidate for lubrication and all works suggesting that this system is a super lubricant are completely wrong.