Concentration-Dependent Formation Mechanisms in Mesophase Silica−Surfactant Films

Abstract

The development of surfactant-templated mesoporous films grown at the air/water interface was investigated using specular and off-specular X-ray reflectivity techniques. The samples were prepared in acidic conditions using cetyltrimethylammonium bromide (CTABr, 0.075 M) and different concentrations (0.27−0.88 M) of tetramethyloxysilane (TMOS). At CTABr/TMOS molar ratio between 0.277 and 0.093, the final films exhibited at least three orders of diffraction, corresponding to a real space repeat distance of 46 Å. This long-range order was not observed when the TMOS content was increased to 0.88 M at constant CTABr concentration. In each case, the induction period prior to film formation was monitored using diffuse X-ray scattering. The intensity of the specular reflectivity peak, first and second-order diffraction peaks, and Yoneda wing were recorded as a function of time. The reflected intensity of the specular peak oscillated during the lengthy induction period, indicating that at some concentrations the films nucleate at the surface through a phase separation mechanism followed by growth of ordered arrays. This oscillation has been modeled as a surface layer having increasing thickness and roughness with time. The evolution of the first-order diffraction peak displays different characteristics depending on the TMOS content. For the shortest induction times (corresponding to a molar ratio of 0.139) the film formation mechanism appears to be bulk driven, but for longer development periods the film forms through assembly of ordered arrays at the surface.

Ordered Mesoporous Materials Based on Interfacial Assembly and Engineering

“…The resultant films showed a hexagonal mesostructure with the channels in an orientation parallel to the interface and a continuous morphology with the resilience to withstand significant bending as well as flexibility to be transferred onto substrates of different shapes. Later on, the majority of work in regard of the synthesis of mesoporous silica films at the air‐solution interface concern films formed from acidic solutions using an alkoxysilane (e.g., TEOS, tetramethoxysilane, TMOS) as a silica source and a cationic surfactant (e.g., C n TAB, C n TAC) as a template in terms of the growth time, concentration, film thickness and mesostructures 176–180. Until 2004, Park et al .…”

Spontaneous Formation of Hierarchically Structured Curly Films of Nickel Carbonate Hydrate through Drying

“…According to the above results, the formation process of curly films is dependent on the polymer concentration, which is similar to that reported previously for the formation of surfactanttemplated mesoporous films grown at the air/water interface. 18 When the polymer concentration increases, the included polymer content in the structures increases, and thus the coiling degree of film is also increasing. This is evidence for polymer interaction with the mineral.…”

Synthesis and characterization of the air–water interfacial TiO2/ZrO2 binary oxide film

“…5a). The formation scheme of the TiO 2 /ZrO 2 film [21], showing the effect of the surfactant SDS as a template, is shown in Fig. 5b.…”