Void closure and interdiffusion in latex film formation by photon transmission and fluorescence methods

Steady state fluorescence (SSF) and photon transmission methods were used t o study void closure and interdiffusion processes during film formation fro m hard latex particles. Latex films were prepared separately by annealing p yrene (P-y) labeled and unlabeled poly (methyl methacrylate) (PMMA) particl es above the glass transition temperature. Direct fluorescence emission of excited pyrene from labeled latex films was monitored as a function of anne aling temperature to detect void closure and interdiffusion. The increase i n fluorescence intensity against temperature was used to determine the acti vation energy for viscous flow (Delta H congruent to 47 kcal/mol). The decr ease in I-op above the void closure temperature was used to produce the bac kbone activation energy (Delta E congruent to 44 kcaI/moi) for the interdif fusing chains. Unlabeled PMMA particles were used to prepare films for UW m easurements. Transmitted photon intensity from these films increased as the annealing temperature was increased. Monte Carlo simulations were performe d for photon transmission through a rectangular lattice. The number of tran smitted and scattered photons were calculated as a function of disappeared particle-particle interfaces. The increase in the transmitted photon intens ity (I-tr) is attributed to the increase in 'crossing density' at the junct ion surface. The backbone activation energy (LTE) was measured and found to be around 33 kcal/mol for a diffusing polymer chain across the junction su rface. (C) 1999 Elsevier Science B.V. All rights reserved.