Surface morphology of latex film formed from poly(butyl methacrylate) latex in the presence of alkali-soluble resin

The film morphology of emulsifier-free poly(n-butyl methacrylate) (PI)MA) l atex in the presence of post-added alkali-soluble resin (ASR) was studied u sing atomic force microscopy (AFM). The film morphology was monitored, from the nascent stage after water was evaporated from the dispersion, as a fun ction of annealing temperature and its duration. The AFM: results suggest s trongly the formation of a hard shell of ASR, namely poly(styrene/alpha-met hylstyrene/acrylic acid) (SAA) over the soft PBMA particle. During annealin g, the incompatibility of the two polymers leads to the migration and accum ulation of SAA at the interstices and interfacial regions among the arrays of PBMA particles, and also at the film surface, The hard shell of SAA reta rds the diffusion of the PBMA molecules across the particle/particle interf ace and slows down the gradual coalescence of film formation. Annealing at high temperature ruptures the SAA shells and the PBMA particles interdiffus e at a faster rate than the SAA due to its lower T-g compared to that of SA A, The difference in the rates of fusion of the SAA and PBMA phases leads t o the formation of indentations on individual particles at high annealing t emperature and long annealing duration. The occurrence of this feature incr eases with the annealing temperature and its duration. These indentations a re eventually transformed into 'depressions' on the latex films when the in dentations at the top of the individual particles sag inwords at sufficient ly high annealing temperature and long annealing time. The surface enrichme nt of SAA is confirmed by the results of fainer transform infrared spectros copy with attenuated internal reflectance of the film surface. Copyright (C ) 1999 John Whey & Sons, Ltd.