Excluded volume effects in rotational-isomeric-state chains

Abstract

An algorithm improving the accuracy of Monte-Carlo calculations of the configurations of off-lattice polymer chains is described. It is used to investigate excluded-volume effects in rotational-isomeric-state polymethylene chains perturbed by Sutherland potentials and a particular Lennard-Jones potential. The importance of accounting properly for chain structure when determining expansion factors is clearly shown. The effective value of the segmental cluster integral is discussed in detail showing that it cannot be calculated directly from the potential function used but is strongly dependent on chain structure. Due to uneven chain expansion, i.e. the different perturbation of the various moments of the end-to-end distance distribution, θ-ranges rather than single θ-points are predicted at infinite chain length. The shortcomings of lattice models for chains are discussed, again emphasizing that chain structure must be included in calculations of chain expansion if meaningful interpretations of experimental expansion coefficients at different temperatures are to be achieved.