Layering transitions and reentrant-like phenomenon in thin films of three-block organosiloxane smectogens at the air/water interface

The surface pressure induced layering transition of three-block amphiphilic smectogens at the air/water interface is observed and characterized by film balance measurements, Brewster angle microscopy and X-ray reflectivity. Since the systems possess a fluid smectic A bulk phase the transition is reversible with little hysteresis and occurs layer by layer. Whereas the monolayer at the air/water interface exhibits polar smectic C-like order the multilayer is in a smectic A arrangement equivalent to that in bulk. The reentrant-like transition can be ascribed to a loss of order of water surrounding the hydrophilic head when removing molecules from the water surface. The thickness uniformity and stability may be ascribed to the line tension related to a domain boundary and to long-range van der Waals forces between interfaces. The mono- as well as multilayers can be transferred onto solid substrate apparently without any major structural changes.