Thick mesostructured films via light induced self-assembly

Abstract

As an alternative to solvent evaporation, we show that UV light can serve as a stimulus to promote self-assembly during the formation of surfactant-templated silica films. Despite practical and conceptual advantages, the Light Induced Self-Assembly (LISA) route has been poorly described in comparison with its evaporation induced analogue. In this article, we give an exhaustive overview of the potentiality of this photoinduced process using a range of PEO-b-PPO-b-PEO amphiphilic triblock copolymers, and investigating systematically the structural (²⁹Si MAS NMR, XRD) and textural properties (TEM, N₂ sorption) of the resultant worm-like mesostructured films. Practically, UV irradiation is applied directly to isotropic micrometric films consisting of a nonhydrolyzed alkoxide-amphiphilic copolymer-photoacid generator mixture, obviating the addition of solvent and water. Photoliberation of Brønsted photoacid generates on demand hydrophilic silica species, driving the micellization of the copolymer. The process is single-step and fast, yielding transparent mesostructured films within a few seconds. A target addressed in this feature is to investigate the film structural evolution resulting from the UV irradiation by in situ Fourier transformed infrared analysis (FTIR). Without the interference of solvent, this powerful technique provides a new perspective on the course of the sol–gel process in mesostructured films. For the first time, hydrolysis is assessed kinetically as well as the silica network condensation and the water content of the film.