Newly homogenized film-forming dispersions, containing 1.5 g
of total solids, were spread evenly over a Teflon casting plate (15 cm
diameter) resting on a level surface. Films were formed by drying
for approximately 60 h at 45% RH and 20 C. These conditions were
established after previous experiments to ensure that homogeneous,
flawless films were obtained. At a higher relative humidity,
films did not dry adequately. Dry films could be peeled intact from
the casting surface. Film thickness was measured with a Palmer
digital micrometer to the nearest 0.0025 mm at 6 random
positions.