Particle size effect on the filming process of polystyrene latex

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.