FORCES BETWEEN ASYMMETRIC POLYMER BRUSHES

We study the equilibrium compression of asymmetric polymer brushes grafted on flat plates, under athermal and theta solvent conditions, using a lattice self-consistent field (SCF) approach. We find that the separation d between two plates coated asymmetrically with brushes of type 1 and 2, as a function of the force F, obeys the 'bisection rule', d(F) = (d1(F) + d2(F)) /2 where d1(F) and d2(F) are the corresponding separations for the symmetric brushes of type 1 and 2 respectively. The bisection rule is easily esplained if one assumes no interpenetration of the two brushes. However, a study of the polymer volume fraction profiles suggests that the bisection rule is well obeyed even where there is strong interpenetration. The relevance of this work to recent experiments on asymmetric brushes is discussed.