Theory of flow orientation effects in Langmuir-Blodgett films: examination of the local thermal equilibrium approximation

The angular distribution function for the case of one single substrate in a large trough is numerically calculated allowing for the deviation from the local thermal equilibrium. The function obtained for the line-sink potential on the water surface is found to disagree with that of the previous model derived using the local thermal equilibrium approximation. As for the transfer from the water surface to the substrate, two different models are introduced, the abrupt connection and a smooth connection. The smooth connection model leads to a satisfactory agreement with the predictions from the previous model, and, at the same time, to a semi-quantitative coincidence with the experimentally observed dichroic behavior for the previously obtained values of the viscoelastic parameters. These results indicate that the line-sink potential with local thermal equilibrium approximation, if not strictly relevant to the process on the water surface, is effective for describing the angular distribution in LB films.