6533b827fe1ef96bd1285999

RESEARCH PRODUCT

Friction between Polymer Brushes in Good Solvent Conditions:  Steady-State Sliding versus Transient Behavior

subject

description

Previous molecular dynamics simulations of friction between polymer brushes in relative sliding motion [Kreer, T.; Muser, M. H.; Binder, K.; Klein, J. Langmuir 2001, 17, 7804] are extended beyond steady-state conditions. We study two different protocols:  (i) stop and return and (ii) stop and go. In protocol (i), the relative, lateral motion between the two surfaces is stopped abruptly and reimposed opposite to the initial direction after the system could relax for some time. Protocol (ii) is similar except that the sliding direction is maintained. In the constant-velocity steady state, the average lateral extension lc of the polymers is found to be a power law of the sliding velocity v, namely, lc ∝ v0.3. When the sliding direction is inverted, a shear stress maximum is observed after the two walls have slid a relative distance of 2lc. This maximum occurs when the average inclination of the polymers is 90°, and it is accompanied by brush swelling. In protocol (ii), no brush swelling is found and shear st...