pH值和前驱体用量对核壳结构PSt/SiO_2复合微球结构形态的影响

INFLUENCES OF pH AND AMOUNT OF PRECURSOR ON THE MORPHOLOGY OF PSt/SiO_2 CORE-SHELL COMPOSITE MICROSPHERES

首先通过无皂乳液聚合法制得表面含羧基、粒径为360 nm的单分散聚苯乙烯(PSt)种子乳液,并在EtOH/H2 O混合介质中用γ-氨丙基三乙氧基硅烷(KH-550)对其进行改性,制得表面含有活性硅乙氧基并带有正电荷的改性PSt乳胶粒,然后再加入原硅酸乙酯(TEOS)进行共水解与共缩聚反应,制备出了核壳结构PSt/SiO2复合微球.系统研究了聚合体系pH和前驱体TEOS用量对复合微球结构形态的影响.研究表明,对于改性PSt乳胶粒和TEOS反应体系,只有在碱性条件下才能制备出具有核壳结构的PSt/SiO2复合微球,当pH值为8.5时,可得到包覆完整、SiO2壳层厚度均一的核壳结构PSt/SiO2复合微球,此后随着体系pH值的升高,被部分包覆复合微球的比例增加;固定PSt种子乳胶粒的用量为1.5 g,随着TEOS用量从2.5 g增加到15 g,复合微球壳层厚度从17 nm逐渐增加到68 nm,微球表面也逐渐变得粗糙.

Monodispersed carboxyl-containing PSt seed latex with the diameter of 360 nm was first synthesized via batch emulsifier-free emulsion polymerization, and the positively charged PSt latex particles with surface reactive ethoxylsilyl groups were then prepared in the medium of ethanol and water using γ-aminopropyl triethoxysilane （KH-550） as modifier, then PSt/SiO2 core-shell composite microspheres were obtained by dropwise adding tetraethoxysilane （TEOS） into the above system. Influences of pH and TEOS amount on the morphology of PSt/SiO2 core-shell composite microspheres were investigated using TEM and SEM. Results showed that the PSt/SiO2core-shell composite mierospheres were generated only under alkaline conditions. When the amounts of PSt seed particles and TEOS was 1.5 g and 5.0 g, respectively,and pH was controlled at 8.5 ,the encapsulation of PSt seed particles with SiO2 was intact,and the uniform SiO2 shell with about 35 nm was obtained, and after that, the percentage of the composite microspheres partially encapsulated by SiO2 increased with the increase of pH value. With the increase of TEOS amount from 2.5 g to 15 g, the thickness of PSt/SiO2core-shell composite mierospheres gradually increased from 17 nm to 68 nm, but their surface gradually became rough.