Preparation Of Hollow Silica Microspheres With Controlled Wall Thickness With The Assistance Of Supercritical CO₂

Nowadays, nanomaterials have attracted much attention because of their special structure and morphology. As one of them, porous capsules combining the merits of hollow and porous structures present improved flow performance and high surface areas. They also have an inerior void as a storge space or a reaction chamber that can encapsulate various substances. The channel on the shell could effectively control the release of substances, including drugs, genes, dyes, inks, cosmetics, pesticides and food, and has became research highlight. The silica material is one of them. In addition, supercritical carbon dioxide has excellent mass tranfer, permeability and nontoxic, cheap and other characteristics, which is widely used in the preparation and modification of materials. In this work, we focus on the preparation and structure tunability of hollow silica microspheres with the assistance of supercrical carbon dioxide.In chapter two, firstly, we prepared cross-linked polystyrene microspheres with free emulsion polymerization method. These particles can be used as hard template for the preparation of hollow silica microspheres with uniform size and structural integrity. We selected some appropriate SCCO2 conditions which can keep the polymer microspheres from distortion. The precursors of silica (Tetraethyl orthosilicate TEOS) were carried into the solid polymer templates to form TEOS/polymer composites with the assistance of SCCO2. After the process of hydrolysis, the surface of template was covered with uniform silica shell. Finally, we obtained hollow silcia microspheres with uniform shell thickness after calcination. In addition, we explored the formation mechanism in depth of the hollow microspheres.In chapter three, we can change the the wall thickness of the hollow silica spheres by tuing the TEOS/PS ratio. Based on this, we also adjust and control the thickness of hollow silica spheres not only by change the amount of TEOS in the process of supercritical treatment and hydrolysis, but also adjust the pressure and treatment time of the supercritical process, in which the amount of TEOS infiltrated into the template can be varied. Finally, the shell thickness was successfully controlled in small and large range by multiple means.Drug delivery of hollow mesoporous silica microspheres has become one of the research highlight. According to the relavant literature, the pore size plays an important role in the drug choice and release kinetics. Thus, in chapter four, based on the above-mentioned work, we obtained hollow mesoporous silica microspheres with the pore size of about 3nm using cetyltrimethyl ammonium bromide (CTAB) as porogen. Combined with cooperative self-assemble mechanism proposed by Stucky and Huo, we discussed the possible mechanism in the mesoporous forming process. Also, through changing the amount of TEOS in the hydrolysis process, the shell thickness can be controlled in the range of 37nm and 60nm. By the addition of tetradecane, the mesoporous size increased from 2.97nm to 4.76nm. This work laid the foundation for the further reseach of the effect of thickness and pore size on drug delivery.In summary, we studied the feasibility of prepare hollow silica microspheres with the assistance of supercritical canbon dioxid e in this work. Using this technique, we realized the tunability of the morphology structure and the wall thickness successfully. Based on the above work, we extended this technique to prepared hollow mesopores silica microspheres with controlled wall thickness, pore size and cavity volume, which laid the foundation for the reseach of the effect of thickness and pore size on drug delivery.