聚苯乙烯胶乳颗粒的成膜过程及尺寸效应

Particle Size Effect on the Filming Process of Polystyrene Latex

聚合物乳液成膜过程可分为介质蒸发、颗粒形变和相邻颗粒间高分子的扩散融合三个阶段[1,2]. 一般认为, 环境温度达到或高于高分子的玻璃化转变温度(Tg)时颗粒才可能发生形变[1, 2]. Goudy等[3]研究了粒径为0.24～1.05 μm的聚苯乙烯(PS)胶乳的成膜过程, 发现PS颗粒在368 K(Tg约 373 K)热处理很长时间也不发生形变, 而在378 K热处理后, 粒径较小的颗粒融合速度快于较大颗粒. 本文通过对粒径为742 nm的PS颗粒和粒径为29 nm的纳米PS(记为NPS)颗粒成膜过程的形态观察, 发现NPS颗粒的形变温度远低于PS本体的Tg, 而且成膜速度快, 成膜温度明显降低.

The film formation process of micro-PS particles (diameter 742 nm) and nano-PS particles (diameter 29 nm) was studied by means of AFM and DSC. During a step heating process, the particles were annealed for 0. 5 h at each selected temperature. It is found that the deformation and interdiffusion temperatures are ca. 393-403 K and 413-423 K for the micro-PS particles, 363 K and 373-383 K for the nano-PS particles respectively. Comparing to the micro-PS particles, the sintering process of nano-PS particles occurs at much lower temperature determined by the confined state of polymer chains with less interactions between segments, leading to a higher conformational energy, and completed in much narrower temperature range driven mainly by the larger total surface energy.