Fluorescence and UV techniques for studying neck growth and equilibration processes during latex film formation

Steady state fluorescence (SSF) and UV-visible techniques have been used to study neck growth and equilibration processes during the coalescence of ha rd latex particles. Latex films were prepared separately by annealing pyren e (P-y) labelled and unlabelled poly(methyl methacrylate) (PMMA) particles above their glass transition temperature. During the annealing processes, t he optical clarity of the films increased considerably. Direct fluorescence emission of excited pyrene from labelled latex films was monitored as a fu nction of annealing temperature to detect this change. Void closure tempera ture (T-c) and time (t(c)) were determined at the point where the fluoresce nce emission intensity became maximal. Below this point, the increase in fl uorescence intensity (I-op) against temperature was used to determine the a ctivation energy for viscous flow (Delta H approximate to 47 kcal mol(-1)). The decrease in I-op above the void closure temperature was used to determ ine the backbone activation energy (BE approximate to 44 kcal mol(-1)) for the interdiffusing chains. Unlabelled PMMA particles were used to prepare f ilms for UV-vis measurements. The transmitted photon intensity (I-tr) from these films increased as the annealing temperature was increased. This beha viour was also used to determine the backbone activation energy (Delta E ap proximate to 35 kcal mol(-1)) for the interdiffusing chains. (C) 1998 Socie ty of Chemical Industry..