Formation of Wrinkled Silica Mesostructures Based on the Phase Behavior of Pseudoternary Systems

Abstract

Recently, mesoporous silica nanoparticles with radial wrinkle structures were introduced almost simultaneously by several groups. Wrinkled silica mesostructures (WSMs) have attracted much attention for their high accessibility to guest materials and large surface area due to those open pore structure. However, the mechanism study about synthesis of these WSMs is not proceeded enough yet. So in this dissertation, the tunable synthetic process of WSMs is investigated to determine the formation mechanism of WSMs. In Chapter 1, It is explained that the basic research backgrounds about synthesis of mesoporous silica mesostructures and phase behaviors of microemulsion and related systems. In Chapter 2, the formation mechanism of hierarchical mesoporous silica nanoparticles with wrinkle structure (wrinkled silica nanoparticles, WSNs) was studied and a method for substructure control of silica nanoparticles was proposed. We confirmed that WSNs were generated in the bicontinuous microemulsion phase of the Winsor III system. By using the phase behavior of Winsor III system, which depends on the water-oil-surfactant mixing ratio, and by adding various cosolvents (cosurfactants), we could precisely control the structure of silica nanoparticles, from the mesoporous to the wrinkle form

furthermore, we could control the inter-wrinkle distance. In Chapter 3, a profound investigation of water-oil-surfactant ternary systems which have various phase behaviors and substructures that depend on their chemical composition and component ratio is conducted. These substructures can be used as templates for the synthesis of a variety of nanostructures. In this chapter, the phase behavior of a pseudoternary system consisting of aqueous urea–cetyltrimethylammonium bromide (and n-butanol)–cyclohexane is analyzed. Additionally, wrinkled silica mesostructures (WSMs) with various morphologies are synthesized using the microemulsion layer in the multi-phase areas of the pseudoternary system with restricted degrees of freedom as a template. The particle size of the wrinkled silica nanoparticles (WSNs) and the connective morphology of the WSMs can be controlled via the catalytic conditions. In addition, some materials which are difficult to produce, such as radially branched WSNs and shuttlecock-shaped Janus nanoparticles, are prepared using a gradual seed-growth mechanism of silica in the emulsion system.