Finite-N effects for ideal polymer chains near a flat impenetrable wall.

This paper addresses the statistical mechanics of ideal polymer chains next to a hard wall. The principal quantity of interest, from which all monomer densities can be calculated, is the partition function, G(N)(z) , for a chain of N discrete monomers with one end fixed a distance z from the wall. It is well accepted that in the limit of infinite N , G(N)(z) satisfies the diffusion equation with the Dirichlet boundary condition, G(N)(0) = 0, unless the wall possesses a sufficient attraction, in which case the Robin boundary condition, G(N)(0) = - xi G(N)(')(0), applies with a positive coefficient, xi. Here we investigate the leading N(-1/2) correction, Delta G (N)(z). Prior to the adsorption threshold, Delta G(N)(z) is found to involve two distinct parts: a Gaussian correction (for z approximately <or= aN(1/2) with a model-dependent amplitude, A, and a proximal-layer correction (for z approximately <or= a described by a model-dependent function, B(z).