Finite-stretching corrections to the Milner-Witten-Cates theory for polymer brushes.

ABSTRACT

This paper investigates finite-stretching corrections to the classical Milner-Witten-Cates theory for semi-dilute polymer brushes in a good solvent. The dominant correction to the free energy originates from an entropic repulsion caused by the impenetrability of the grafting surface, which produces a depletion of segments extending a distance mu proportional to L(-1) from the substrate, where L is the classical brush height. The next most important correction is associated with the translational entropy of the chain ends, which creates the well-known tail where a small population of chains extend beyond the classical brush height by a distance xi proportional to L(-1/3). The validity of these corrections is confirmed by quantitative comparison with numerical self-consistent field theory.