Coalescence and Film Formation of Soft-Core–Hard-Shell Polyacrylate Latex

In the present study, we examine the coalescence between model soft-core (Tg ≈ −15 °C) and hard-“shell” (Tg ≈ 100 °C) polyacrylate (PA) particles (90 nm) prepared using a two-stage emulsion polymerization. To assess the coalescence in this rather complex system, we employed Förster resonance energy transfer (FRET), where donor and acceptor dyes were selectively placed in either the “shell” or core of the PA particles. FRET studies revealed some mixing between the high Tg “shell” polymer, while the lower Tg core had modest mixing when aged at room temperature and annealed at elevated (55 °C) temperatures. These results support the notion that the PA core–“shell” particle has a patchy shell. The phase behavior between the “shell” and core of the PA particles was also studied by FRET and atomic force microscopy. Both studies provide strong evidence of phase separation. These results present insights into the phase behavior in core–“shell” PA latexes.