| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 99 === In this study, polystyrene latex was prepared by emulsifier free polymerization. Methacryl oxypropyl trimethoxy silane ( MPS ) and divinylbenzene ( DVB ) were added in the reaction medium at the 80 % conversion of styrene polymerization to provide silane functional groups for further reaction with tetraethoxylsilane ( TEOS ) to construct the shell. Therefore, a core-shell structure was formed in the PS-silica latex. Furthermore, a porous hollow silica sphere was obtained by removing PS core by solvent extraction followed by calcination step.
The PS latex particles are nearly monodispersed based on DLS data. The surface of PS-silica latex is more rough and uneven than that of the PS latex. The collapsed structure on the surface of hollow silica is shown. TGA was used to evaluate the amount of PS chains remained on the silica shell, indicating that the addition of MPS will introduce more PS chains on the silica shell due to the enhancing compatibility of MPS between PS and silica. BET measurements show the surface area of 39.01 m2/g for PS-silica latex and 603.30 m2/g for hollow silica sphere after calcination. The organic PS chains are removed and voids between these small silica nanoparticles are observed. Porous hollow silica with an average pore diameter of 7.72 nm by BJH method in the shell for PSM0.1-T3-E-C which was synthesized with polycondensation of TEOS took place at the PS/MPS latex surface and removing PS core by extraction and calcination steps. A BJH average pore size of 4.12 nm is obtained PSM0.1D-T3-E-C which was made from modification PS with MPS and DVB. This indicates that the addition of DVB can reach a partial crosslinking of polystyreneand prevent the sphere shell from breaking during extraction and calcination step. Furthermore, We also focused on the encapsulation of ascorbic acid into hollow silica studdied their controlled release behavior. Release data were analyzed with the zero order model, the first order model, the Higuchi model. The kinetic release model fits with the zero order model. The kinetic constant (k1) in the first 3 hours was 25.89, and k2 was 2.40 after 3 hours.
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