GROWTH OF HIGHLY ORDERED THIN SILICATE FILMS AT THE AIR-WATER-INTERFACE

The growth of thin silicate-organic films at the air-water interface o f surfactant solutions has been studied in situ by X-ray and neutron r eflectivity to a resolution of ca. 5 Angstrom. Surfactant in the solut ion and the air-water interface itself are involved in directing the g rowth and final structure of the films. Hexadecyltrimethylammonium chl oride (C(16)TAC) and bromide (C(16)TAB) have been used as the templati ng surfactants, and the film structure is independent of the anions un der the conditions used. In situ X-ray and neutron reflectivity measur ements at an early stage of film growth show a slow development of str ucture in the top 100 Angstrom of the solution, which is consistent wi th a monolayer of tilted surfactant molecules at the air-water interfa ce, a layer of partly silicated material, and an interdigitated surfac tant bilayer or layer of cylindrical micelles oriented with their long axes parallel to the surface. Following this induction period a rapid crystallization occurs to give a structure with a crystallographic re peat distance of 45 Angstrom perpendicular to the surface and composed of alternating surfactant layers and silicate material. The very narr ow observed diffraction peaks indicate that the final silicate film is highly ordered.