The intercelluar diffusion of poly(butyl methacrylate) (PBMA; glass tr
ansition temperature (T-g) = 21 degrees C) at 60 degrees C was monitor
ed by fluorescence energy transfer in films formed from blends of PBMA
latex and a high-T-g (hard) latex. Two types of hard latexes were use
d in blends: one composed of poly(methyl methacrylate) (PMMA) and the
other having a high-T-g shell made of styrene and acrylic monomer unit
s with a large central void (Rohm & Haas Ropaque, ROP). The diffusion
rate of PBMA is significantly decreased in the presence of hard partic
les. The mean apparent diffusion coefficient (D-app) decreased from 0.
3 to 0.2 nm(2)/s when 35 vol % ROP particles (400 Mn) are present in t
he film and to 0.1 nm(2)/s at 75 vol % ROP. The presence of similar-si
zed PMMA (400 nm) particles showed a slightly larger effect than ROP o
n the PBMA diffusion: D-app decreased by a factor of 2 at 35 vol % PMM
A and a factor of 4 at 75 vol % PMMA. At a constant volume fraction of
the hard particle additive, the PBMA diffusion rate decreases signifi
cantly when the diameter of PMMA particles is reduced from 400 to 67 n
m. These effects can be explained in terms of a model in which a more
rigid PBMA layer forms, with a slower diffusion rate, near the hard pa
rticle surface.