Mechanistic study on latex film formation in the presence of alkali-soluble resin using atomic force microscopy

The mechanism of film formation of emulsifier-free monodisperse poly(n-buty l methacrylate) (PBMA) latex in the presence of postadded alkali-soluble re sin (ASR), namely poly(styrene/alpha-methylstyrene/acrylic acid) (SAA) was followed using atomic force microscopy (AFM). The film morphology and peak- to-valley distance (Delta z) of latex particles in the film was monitored a t different annealing temperatures as a function of annealing duration. The Delta z of the PBMA particles in films containing SAA was found to be high er than those in the pure PBMA films. The AFM results suggest very strongly the formation of a hard surface layer of SAA over the soft PBMA particle, and the migration of free SAA to the latex film surface during annealing. T he SAA layer adsorbed on and surrounding each PBMA particle retards the vis coelastic flow of the PBMA particles and slows down the gradual coalescence of the particles in film formation. Annealing at high temperature, the PBM A particles fuse at a faster rate than the SAA due to its lower T-g compare d to that of SAA. The difference in the rates of fusion of the SAA and PBMA phases leads to the formation of indentations on individual particles at h igh annealing temperature and long annealing duration.