Reorganisation of layer structures formed from amphiphilic molecules

Abstract

Two closely related amphiphilic compounds have been deposited as multilayers by evaporation in vacuo, the structures of which have been studied as a function of time using low-angle X-ray diffraction and polarising microscopy. The material consisting of the shorter of the two molecules forms a structure in which the repeat unit corresponds to a monolayer but, initially, there are two phases present with slightly different d spacings. At room temperature this material reorganises over a period of 1 week so that it consists entirely of one of these phases. The material consisting of the longer molecule forms a structure in which the repeat unit is a bilayer (a Y structure). On storing for 1 week at room temperature the first-order Bragg peak disappears but the second-and third-order Bragg peaks remain. A possible explanation for this remarkable behaviour is proposed.