反应介质pH值和前驱体用量对PSt/TiO_2复合微球结构形态及TiO_2空心微球形貌的影响

首先用聚乙烯亚胺(PEI)对粒径为360 nm的单分散无皂聚苯乙烯(PSt)乳胶粒进行修饰,得到表面荷正电的PSt种子乳液,然后将其滴加到溶有钛酸正丁酯(TBT)的乙醇与水的混合介质中,通过溶胶-凝胶(sol-gel)法制备出了核壳结构PSt/TiO2复合微球,系统研究了体系pH和TBT用量对复合微球结构形态的影响.研究表明,酸性条件不利于核壳结构PSt/TiO2复合微球的形成;当体系pH值为7.2时,可得到包覆完整、TiO2壳层厚度均一的PSt/TiO2复合微球,此后随着体系pH值的升高,包覆厚度逐渐提高;当pH值升高到11.0时,壳层厚度达到最大,但出现了包覆层不完整的复合微球.在固定聚合体系pH为8.5,EtOH/H2O质量比为100/6,表面修饰PSt种子乳液用量为0.5 g(固含量为4%)的条件下,随着TBT用量从0.01 g增加到0.16 g,复合微球壳层厚度从约0 nm逐渐增加到60 nm;当TBT用量增加到0.32 g时,壳层厚度迅速降至12nm,微球表面变得粗糙,并出现大量未包覆微粒;此后随着TBT用量的增加,包覆层厚度逐渐减少,未包覆微球逐渐增多.结果显示,当复合微球中TiO2包覆层达到一定厚度时,经煅烧后才能得到形貌完整的TiO2中空微球.

INFLUENCES OF pH AND TBT AMOUNT ON THE MORPHOLOGY OF PSt/TiO2 CORE-SHELL COMPOSITE MICROSPHERES AND VOID TiO2 MICROSPHERES

A negatively charged monodisperse polystyrene(PSt) seed emulsion was first synthesized via batch emulsifier-free emulsion polymerization,and polyethyleneimine(PEI) aqueous solution was then added into the diluted emulsion to modify the particle surface at 25℃ to prepare the positively charged PSt seed particles.Then,the core-shell PSt/TiO2composite microspheres were obtained by adding the diluted modified PSt seed emulsion into the medium of ethanol containing certain amount of tetrabutyl titanate(TBT).Influences of pH and TBT amount on the morphology of PSt/TiO2 core-shell composite microspheres were investigated by TEM and SEM observation.Results showed that it was difficult to form PSt/TiO2 core-shell microspheres under acidic conditions,and a uniform TiO2 shell with about 29 nm in thickness was obtained when pH increased to 7.2,and then the thickness of the TiO2 shell increased with the increase of pH value.When pH was 11.0,the thickness of the TiO2 shell reached 70 nm,but some of the composite microspheres were partially encapsulated.With the increase of TBT amount from 0.01 g to 0.16 g,the thickness of PSt/TiO2core-shell composite microspheres gradually increased from about 0 nm to 60 nm when the amount of PSt seed emulsion was 0.5 g(solid content was 4% by weight) and pH was controlled at 8.5.While the TBT amount increased to 0.32 g,the thickness of the TiO2 shell reduced to 12 nm,and the surface of the composite microspheres became rough gradually.After that,with the increase of TBT amount,the thickness of the TiO2 shell decreased,and a number of TiO2 nanoparticles appeared.The voided TiO2 microspheres were obtained by calcining the PSt/TiO2 composite microspheres at 500℃ for 4 h when the thickness of TiO2 shell in the composite microspheres reached a certain level.