Statistical Thermodynamics of Short-Chain Molecule Interphases. 2. Configurational Properties of Amphiphilic Aggregates

In the preceding paper, formal expressions for configurational properties of short-chain molecule interphases have been derived. In the present work, expressions giving positional and orientational probability distributions of chain segments and bonds are evaluated for the case of planar systems (representing monolayers at an oil/water interface or bilayers). Configurational properties (e.g., order parameter, chain segment distributions, and probabilities of chain bends) are evaluated as a function of bending energy, length, and surface density of the chains. Results of neutron diffraction experiments on widths of segment position distributions are compared to predictions of the model and are found to be in good agreement. Calculated chain-averaged properties (order parameter and bends/chain averaged over the interphase) are presented as functions of area/chain and are found to fit simple exponential functions remarkably well. For planar systems, chain stiffness is predicted to have relatively little effect on configurational properties, which are determined largely by intermolecular constraints.