Steady state fluorescence (SSF) and photon transmission methods were used to study void closure and interdiffusion processes during film formation from hard latex particles. Latex films were prepared separately by annealing pyrene (P-y) labeled and unlabeled poly (methyl methacrylate) (PMMA) particles above the glass transition temperature. Direct fluorescence emission of excited pyrene from labeled latex films was monitored as a function of annealing temperature to detect void closure and interdiffusion. The increase in fluorescence intensity against temperature was used to determine the activation energy for viscous flow (Delta H congruent to 47 kcal/mol). The decrease in I-op above the void closure temperature was used to produce the backbone activation energy (Delta E congruent to 44 kcaI/moi) for the interdiffusing chains. Unlabeled PMMA particles were used to prepare films for UW measurements. Transmitted photon intensity from these films increased as the annealing temperature was increased. Monte Carlo simulations were performed for photon transmission through a rectangular lattice. The number of transmitted and scattered photons were calculated as a function of disappeared particle-particle interfaces. The increase in the transmitted photon intensity (I-tr) is attributed to the increase in 'crossing density' at the junction surface. The backbone activation energy (LTE) was measured and found to be around 33 kcal/mol for a diffusing polymer chain across the junction surface. (C) 1999 Elsevier Science B.V. All rights reserved.