Monte Carlo simulations of chain molecules in confined environments

The conformational and thermodynamic properties of lattice chain molecules in confined environments have been studied by Monte Carlo simulations. In the case of homopolymers with purely repulsive interactions with the walls the scaling laws proposed by Daoud and deGennes for the free energy of confinement, from three dimensions to one dimension and for two dimensions to one dimension, have been confirmed. The number of self-avoiding walks (SAW) of a chain with n segments for each film thickness d has been found to follow an effective relationship of the form N_SAW(d) ∝ z_eff ⁿ(d)n^γ(d)-1, where z_eff(d) is a thickness dependent effective lattice coordination number and γ(d) is the d dependent enhancement exponent. In the case of triblock copolymers in which the segments of the end blocks have attractions with the walls of the confined media it was found that for strong enough attractive interactions there is a minimum in the effective interactions between parallel walls. The distance at which the interaction potential has its minimum corresponds to the bulk end-to-end distance of the middle (nonattractive) block. This turns out to also be the distance at which the chains have the maximum number of bridging configurations between the two surfaces.