In Situ FTIR Investigation of the Kinetics of Silica Polycondensation in Surfactant Templated, Mesostructured Thin Films

A detailed Fourier transform infrared spectroscopy (FTIR) study of the kinetics of polycondensation of surfactant-templated mesostructured silica thin films was carried out with the goal of understanding how to manipulate the synthesis and processing of these films to achieve a desired architecture. The evolution of silica condensation was followed both during the sol preparation process and in situ for a time period on the order of minutes to hours after initial film deposition. The kinetics were measured in the presence of three commonly used classes of surfactant templates: P123 [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer), Brij-56 (poly(ethylene oxide] [ n ∼ 10] hexadecyl ether), and CTAB (cetyltrimethylammonium bromide). The induction period for polycondensation (an initial period during which the rate of change of silanol content is slow) was different in each case, with P123 giving the longest induction time followed by Brij-56 and finally CTAB. Humidity was found to increase the induction time for polycondensation in general, and the initial period of up to 30 min after film deposition was identified as a critical “tunable steady state” interval during which conditions can be adjusted to tune the film properties for different applications, for instance, to alter the nature of the mesophase or its orientation by imposing external forces by confining interfaces or by electrical, magnetic, or flow fields.