title: Humidity and temperature effects on CTAB-templated mesophase silicate films at the air-liquid interface.
abstract: Off-specular X-ray reflectivity measurements were carried out to follow the in situ development of surfactant-templated silica thin films at the air-water interface under conditions of controlled relative humidity and temperature, using an enclosed sample cell designed for this purpose. The results suggest a strong dependence of formation time and growth mechanism on ambient conditions. Thin films were synthesized at the air-water interface using cetyltrimethylammonium bromide (CTAB, 0.075 M) and a silica precursor, tetramethoxysilane (TMOS, 0.29-0.80 M) in an acidic medium. The studied humidity range was from 50 to 100%, the temperature was between 25 and 40 degrees C, and the TMOS/CTAB molar ratio was between 3.3 and 10.7. We observed that high humidity slows down the growth process due to lack of evaporation. However, increasing the temperature results in a decrease in the film-formation time. We proposed a formation mechanism for film growth as a consequence of phase separation, organic array assembly, and silica polymerization.
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Cristina
authors.initials: C
authors.lastname: Fernandez-Martin
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Edler
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Roser
mesh_terms: D000388:Air; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D006813:Humidity; D008567:Membranes, Artificial; D016062:Porosity; D017640:Silicates / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D002593:Cetrimonium Compounds; D008567:Membranes, Artificial; D017640:Silicates; D014867:Water; D000077286:Cetrimonium