Time and temperature dependence of void closure, healing and interdiffusion during latex film formation

A photon transmission method was used to probe the evolution of transparenc y during film formation from poly(methyl methacrylate) (PMMA) particles wit h different molecular weight. The latex films were prepared from low (LM) a nd high (HM) molecular weighted PMMA particles at room temperature and anne aled at elevated temperatures in various time intervals above glass transit ion (T-g). It was observed that transmitted photon intensities (I-tr) from these films increased as the annealing temperature was increased. It is see n from I-tr curves that there are two distinct film formation stages, which are named as void closure and interdiffusion processes, respectively. The activation energies for viscous Row and backbone motion were obtained using well-defined models. Viscous flow activation energies (DeltaH) were found to be around 150 and 134 kJ/mol for LM and HM films, respectively. Backbone activation energies (DeltaE(b)) were found to increase from 142 to 199 and 59 to 98 kJ/mol in time of annealing for LM and HM films, respectively. He aling points (tau (H),T-H) were determined and using these time-temperature pairs, healing activation energies (DeltaE(H)) were measured and found to be 188 and 117 kJ/mol for LM and HM films, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.