Preparation and Structural Modifications of Organo-functionalized Silica Particles

Abstract

Organic-inorganic composite silica particles represent a significant advancement in material science, surpassing the limitations of conventional silica particles by incorporating organic functional groups. These composite particles have diversified applications across catalysts, dyes, filter fillers, electrochemical materials, sensors, and pharmaceuticals. Ongoing research aims to harness these particles' properties, structures, and morphologies, extending their utility to even more fields. Traditionally, manufacturing organic-inorganic composite silica particles involved surface modification of genuine silica particles to impart functional groups. However, drawbacks of this process, including the need for a two-step reaction process and the limited properties of surface-modified particles, prompted exploration of ORMOSIL particles, synthesized from organic silane as a raw material, circumventing the surface modification approach. This study investigates a novel manufacturing process of ORMOSIL particles based on the emulsion-based method, diverging from conventional silica manufacturing process which is known as Stöber process. It explores the potential for expanded applications in new fields by modifying silica particles created through this innovative process. In this thesis, Chapter 1 briefly contrasts the emulsion process with other methods, elucidating its advantages in organosilane-based particle preparation. Chapter 2 delves into the emulsion process of hydrophobic phenyltrimethoxysilane (PTMS)-based particles, detailing the production of hollow organosilica particles. Unlike conventional methods requiring an additional template for hollow particle formation, this self-template process selectively removes particle interiors by controlling PTMS condensation. It offers advantages of simplicity, scalability for mass production, and precise control over particle size and shell thickness. In Chapter 3, the emulsion-based sol-gel process for methyl-, vinyl-, and mercaptopropyl-based silica particles forms OMROSIL particles which proviode the basis for the preparation of SiC-based particles with controllable hollowness throiugh magnesiothermic reduction. While SiC boasts robust physical, thermal, and electromagnetic properties, its complex manufacturing process and low processability necessitate the addition of carbon to Si-based structures. This chapter demonstrates the preparation of ORMOSIL-based hollow particles, offering a simpler process and enhanced structural control. Chapter 4 elucidates the creation of nano graphitic carbon and nano hexagonal SiC structures during magnesiothermic reduction of PTMS-based particles, showcasing the recombination of nano graphene. This novel process leads to the growth of carbon structures, revealing insights into varying reduction process conditions. Lastly, Chapter 5 explores the potential applications of PTMS-based particles in various forms by their softness and Tg characteristics. This investigation confirms the versatility of these particles, enabling the production of 1D polygonal particles, 2D plate-type or film-type structures, and even intricate 3D shapes. This versatility transcends the structural constraints of conventional spherical particles, paving the way for novel applications in diverse fields. This thesis comprises multiple chapters aimed at presenting the emulsion process of ORMOSIL as a solution to the constraints posed by traditional solution-based silica preparation methods. The process yielded spherical organosilica particles characterized by high monodispersity. These particles, exhibiting varying synthesis mechanisms and hydrophobicity based on their functional groups, offer diverse properties and applications. Furthermore, this research explores augmenting the particle production process to create hollow particles or to generate SiC structures or graphitic carbon from organic functional groups and Si-O via reduction. By leveraging the processability of certain organosilica particles, a wide variety of structures can be achieved. The significance of these fabrication methods lies in their potential to broaden the limited applications of silica. They stand out for their simplicity in comparison to conventional methods, suitability for mass production, ease of size and shape control, and the possibility of further modifications through organic functional groups.