Particle size effect on the film‐forming process of PS/PBA composite latexes

In this work, the effect of hard particle size and blend ratio on the film formation behavior of hard polystyrene (PS) and soft poly( n ‐butyl acrylate) (PBA) latex blends was studied by means of steady‐state fluorescence and UV–visible techniques in conjunction with atomic force microscopy. Three different sets of latexes were synthesized: PBA latex (diameter 97 nm), pyrene (P)‐labeled large PS (LgPS; diameter 900 nm), and small PS (SmPS; diameter 320 nm). Two different series of latex blends (LgPS/PBA and SmPS/PBA) were prepared with varying blend composition at room temperature separately. Films were then annealed at elevated temperatures above glass transition ( T g ) temperature of PS. Fluorescence intensity ( I P ) from P and photon transmission intensity ( I tr ) were measured after each annealing step to monitor the stages of film formation. The results showed that a significant change occurred in I P and I tr at a certain critical weight fraction ( R c ) of PBA. Below R c , two distinct film formation stages, which are named as void closure and interdiffusion, were seen. However, at PBA concentrations nearer to or above R c , no film formation can be achieved. Comparing to the LgPS/PBA, the sintering process of SmPS/PBA particles occurred at much lower temperatures. Film formation stages for R < R c were modeled, and related activation energies were calculated. Void closure (Δ H ) and interdiffusion (Δ E ) activation energies for SmPS/PBA were also found smaller in comparing with LgPS/PBA series. However, Δ H and Δ E values were not changed much with the blend composition for both series. POLYM. COMPOS., 31:1637–1652, 2010. © 2009 Society of Plastics Engineers