Mechanisms and Intermediates in the True Liquid Crystal Templating Synthesis of Mesoporous Silica Materials

Abstract

Mesoporous silica materials (MSMs) produced by true liquid crystal templating (TLCT) are often considered as direct inverted replicas of the initial lyotropic liquid crystal (LLC) phase. However, the predictive design of tailor-made MSMs requires the full knowledge of the TLCT process, which is still incomplete. Here, we tackle this issue by monitoring the structural evolution during the templating process by small-angle X-ray scattering, showing that after the addition of the silica source the reaction mixture is first isotropic and then an intermediary liquid crystal phase appears, which is the key to the success of the templating process, namely the formation of ordered MSMs. We analyze the structure and the formation dynamics of this intermediary phase and present a simple theoretical model, which allows us to connect the structural parameters of the initial LLC and the MSM. These results provide an enhanced understanding of the TLCT process and are an important step toward the predictable synthesis of new MSMs in the future.

Synthesis and Characterization of Zinc Oxide Doped Mesoporous Silica SBA-16 and Anti-bacterial Property

“…SBA-16 ZnO nanocomposite also represented SAXS data with a single peak at a frequency of 0.99° but with (111) relatively low amplitude. The second highest peak in this pattern resolved due to the introduction of nanoparticles of ZnO into the pores of SBA-16 (Bruckner et al, 2021).…”

Predictive design of ordered mesoporous silica with well-defined, ultra-large mesopores

“…Furthermore, there is a direct correlation between the hexagonal lattice parameters a LLC of the LLC phase and a OMS of the OMS underlining their close relation. 65 Both values can be found in Table S1. ‡ A sketch of the TLCT process can be found in Fig.…”

“…In contrast to the conventional liquid crystal templating, the TLCT process leads to the formation of one massive block of hybrid material via an intermediary LLC phase and thus, needs so be grinded to obtain a powder. 65,74 Subsequently, the polyethers were removed from the pores by calcination. Exemplary scanning electron micrographs of the hybrid material and the grinded OMS are depicted in Fig.…”

“…Additionally, we achieve exceptionally narrow pore size distributions, by applying a variant of the typically used liquid crystal templating approach, the so-called true liquid crystal templating (TLCT), in which the formation of the mesoporous material is mediated via an intermediary formed lyotropic liquid crystal phase. 64,65…”

The Chemical-Physical Processes Behind Self-assembly

“…They are only an intermediate phase of the dynamic self-assembly process, which is substantially guided by the progress of the silica condensation. However, it is possible to use another approach for self-assembly which is defined as "direct" or True Liquid Crystal Templating [9]. In this case the surfactant concentrations in the starting solution are very high and can reach up 30-60% in volume, thus allowing the formation of crystalline liquid phases in binary water-surfactant systems.…”