The photon transmission method was used to probe the time evolution of film formation from latex particles, Two different latex films were prepared from high molecular weight (HM) and low molecular weight (LM) polystyrene particles at room temperature and were annealed at various temperatures in 2.5-min time intervals above the glass transition. The increase in the transmitted photon intensity (I-tr) is attributed to the increase in "crossing density" at the junction surface. The Prager-Tirrell model was employed to interpret the increase in crossing density at the junction surface. The back and forth activation energies were measured for HM and LM films and found to be around 59 and 87 kcal/mol for a reptating polymer chain across the junction surface. Monte Carlo simulations were performed for photon transmission through a rectangular lattice. The number of transmitted photons (N-tr) was calculated as a function of the mean free path of photons. It was observed that N-tr, similar to I-tr, increases as the square of the mean free path of photons is increased. (C) 1999 Academic Press.