Polymer diffusion in latex films at ambient temperature

Polymer diffusion across interfaces at room temperature (21 degrees C) was analyzed by direct nonradiative energy transfer (DET) in labeled latex films. Two model latex polymers were examined: poly(butyl methacrylate) [PBMA, M-w, = 3.5 x 10(4), T-g (dry) = 21 degrees C] and a copolymer of 2-ethylhexyl methacrylate with 10 wt % (acetoacetoxy)ethyl methacrylate [P(EHMA-co-AAEM), M-w = 4.8 x 10(4), T-g (dry) = -7 degrees C]. Little energy transfer due to polymer diffusion was detected for the P(EHMA-co-AAEM) latex samples in the dispersed state or dried to solids content below ca. 90%, but above 90% solids, diffusion occurs among particles. For PBMA, diffusion occurs only after the film is dried (>97% solids) and aged. In the dry PBMA films, it requires 4-5 days at 21 degrees C to reach a significant extent of mixing (f(m) = 0.3-0.4). This corresponds to an estimated penetration depth d(app) of 30-40 nm and a mean apparent diffusion coefficient (D-app) of 5 x 10(-4) nm(2)/s. The corresponding D-app value for the dry P(EHMA-co-AAEM) sample is 5 x 10(-2) nm(2)/s, and it takes about 25-40 min for this polymer to reach f(m) of of 20-30 nm. (C) 1998 John Wiley & Sons, Inc.