Effect of Soft Filler Particles on Polymer Diffusion in Poly(butyl methacrylate) Latex Films

We examine the influence of small (56 nm diameter) cross-linked poly(butyl acrylate) (xPBA) particles as fillers on the diffusion rate of poly(butyl methacrylate) (PBMA) molecules in PBMA latex films. For the high-M PBMA sample (M<INF>w</INF> = 400 000), the presence of soft, elastic particles strongly decreases the diffusion rate of the PBMA molecules across the intercellular boundaries. The retardation effect increases linearly with xPBA content, with the surface-to-volume ratio for xPBA particles of different size, and is best explained as an obstacle effect on the PBMA diffusion rate. For the low-M PBMA sample (M<INF>w</INF> = 35 000), the presence of 30 vol % cross-linked PBA particles increases the diffusion rate of the PBMA polymer, whereas in the presence of 60 vol % cross-linked PBA particles, the PBMA diffusion rate is the same as that in the latex film without filler. Thus, the overall effect of soft filler particles on polymer diffusion is a combination of an obstacle effect, which retards polymer diffusion, and a second effect, probably a free volume effect, which promotes polymer diffusion. This effect is much smaller for the high-M PBMA sample. Depending on which of these effects dominates, one can observe an increase or decrease in the polymer diffusion rate.