Steady state fluorescence (SSF) and UV-visible techniques have been used to study neck growth and equilibration processes during the coalescence of hard latex particles. Latex films were prepared separately by annealing pyrene (P-y) labelled and unlabelled poly(methyl methacrylate) (PMMA) particles above their glass transition temperature. During the annealing processes, the optical clarity of the films increased considerably. Direct fluorescence emission of excited pyrene from labelled latex films was monitored as a function of annealing temperature to detect this change. Void closure temperature (T-c) and time (t(c)) were determined at the point where the fluorescence emission intensity became maximal. Below this point, the increase in fluorescence intensity (I-op) against temperature was used to determine the activation 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 determine the backbone activation energy (BE approximate to 44 kcal mol(-1)) for the interdiffusing chains. Unlabelled PMMA particles were used to prepare films for UV-vis measurements. The transmitted photon intensity (I-tr) from these films increased as the annealing temperature was increased. This behaviour was also used to determine the backbone activation energy (Delta E approximate to 35 kcal mol(-1)) for the interdiffusing chains. (C) 1998 Society of Chemical Industry..