DENSITY DISCONTINUITIES IN SHORT POLYMER-CHAINS MODELED AS HARD-SPHERE SEQUENCES

Monte Carlo simulations of polymer chains containing up to fifteen hard-sphere repeat units have been carried out, the principal interest being the density distribution of the spheres in the neighbourhood of a rigid boundary. The density discontinuity recently reported by Croxton (1986), in the direction normal to the boundary and at a distance of one sphere diameter from it, is confirmed, although there are considerable differences in the calculated densities very close to the boundary. It is shown that the amplitude of the discontinuity is largely independent of the self-avoiding (excluded volume) condition imposed on the growing chain, but is approximately halved when the rigid boundary restraint is removed. The discontinuity originates mainly in the distribution of the second sphere of the chain sequence. The details of the configurational features of the chains are largely in agreement with Croxton's findings, although trains consisting of more than two spheres have been found. The exponent gamma in the expression (RN2) varies as (N-1)gamma, where (RN2) is the mean square end-to-end length of a chain containing N spheres, is evaluated at approximately 1.37 for 3<or=N<or=15.