Structure and properties of hexadecyltrimethylammonium chloride monolayers in contact with oil films with different thicknesses

We report a study on the effects of the amount of oil (100, 300, and 1372 1,2-dichloroethane molecules) spread on a hexadecyltrimethylammonium (CTA) chloride monolayer adsorbed on water. There are some related experimental results, namely, by neutron reflection on the Langmuir interface (air/water interface), that could be used carefully to understand the behavior of monolayers adsorbed at liquid/liquid interfaces. With this work we make a bridge between the Langmuir and the liquid/liquid interfaces. The addition of a small amount of DCE molecules changes dramatically various properties, namely, the distribution of the width of the chains, the distribution of the distance between the chain heads and tails, and the distribution of the tilt angle. On the other hand, the in-plane mean square distribution and the diffusion coefficient of the nitrogen atom are very similar in the systems studied, except for the system containing the largest amount of DCE molecules, which corresponds to the water/DCE interface.