The Structure and Conformation of n-Hydrocarbon Chains in Bilayer Systems in the “Fluid” Phase

Abstract

A realistic computer model of a bilayer of hexadecyl groups at a surface area per chain corresponding to that present in systems of biological interest has been obtained using the Monte Carlo technique. Properties evaluated from the model are in good agreement with results of deuterium magnetic resonance (d.m.r.) and X-ray and neutron diffraction experiments, showing that the distribution of matter and the degree of order in the model are not too far from those in real bilayer systems.

The structure of the model bilayer consists of two “single layer” regions, closely related to the plateau of the d.m.r. order parameters, separated by a large interpenetra-tion zone. The conformation of the alkyl chains, though extended along the normal to the layers, is not perturbed to a great extent with respect to the unperturbed model. A uniform filling of the space is obtained in the model in the absence of long range orientational correlations such as the collective tilt postulated in the literature.