Periodic evaporation-induced self-assembly

Recently, preparation of well-ordered periodic meso-structured hybrid materials was reported with (MeO)3Si-R-Si(OMe)3(R = alkylene, phenylene and 2-butylene) precursors210. Using an evaporation-induced self-assembly, thin films with a mesoporous organization can be prepared, and their physical properties (thickness, dielectric constant, modulus and hardness) are closely dependent on the nature of the R group. 

The tailored design of the titanium-coordinated surfactant and its application in an evaporation-induced self-assembly process followed by heat treatment enabled the preparation of periodic mesoporous silica-based films with a high loading and good dispersion of tetrahedral titanium atoms within the silica matrix. This approach is also feasible for a variety of other transition metal oxides. 

In these syntheses the films with mesophase order form spontaneously at an interface from a dilute solution ofsurfactant micelles and sihca precursor via a co-assembly route. The surfactant concentration is higher than that used for evaporation induced self-assembly, and the concentration of volatile solvents is lower. Films will self-assemble from these solutions in closed containers and on submerged substrates, so the development ofmesoscale order does not rely on evaporation as in the work described above. These films form after an extended induction period, the length of which is dependent on solution concentration, ionic strength, inorganic surfactant ratio, pH and surface to volume ratio. Most of the work on films grown at the solution/air interface concerns the formation mechanisms of these films, and since these are likely to be similar for solid/solution interface films, film growth at the solution/air interface will be treated first. 

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