Structure development in octadecyl trimethylammonium templated silicate films grown at the air/water interface

The mechanism of growth of silicate films at the air/liquid interface has been investigated in situ by a series of grazing incidence diffraction experiments using a 20 × 25 cm² imaging plate as the detector. C₁₈TAX (X = Br^- or Cl^-) has been used as the film templating surfactant. The formation of a layered phase, prior to growth of the hexagonal mesophase in C₁₈TABr templated films, has been seen. This layered structure has a significantly shorter d spacing compared to the final hexagonal film (43 versus 48 Å, respectively). The correlation lengths associated with the development of the hexagonal in-plane diffraction spots are much longer in-plane than perpendicular to the air/liquid interface (300 Å versus 50 Å). This implies that the film forms via the growth or aggregation of islands that are initially only a micelle or two thick, which then grow down into the solution.