COALESCENCE AT THE SURFACE OF A POLYMER BLEND AS STUDIED BY LASER CONFOCAL FLUORESCENCE MICROSCOPY

A blend of 10 vol % poly(methyl methacrylate) (PMMA) in a polystyrene (PS) matrix was prepared by mixing the polymers in the form of 1.0 mu m diameter latex particles, followed by melt pressing the powder at 11 0 degrees C into void-free films. These were annealed for various peri ods of time at 180 degrees C, and the aggregation and coalescence of t he PMMA. microspheres were followed by laser confocal fluorescence mic roscopy. Contrast was provided by a fluorescent dye attached to the PM MA polymer. Brownian motion as a contributor to aggregation could be r uled out. The major factor leading to particle aggregation was identif ied as flow within the sample, likely due to inhomogeneities on heatin g, leading to convective fluxes in the sample. At early stages of anne aling, Ostwald ripening contributed to the coarsening process.