  In both research and industrial settings spin coating is extensively used to
prepare highly uniform thin polymer films. However, under certain conditions,
spin coating results in films with non-uniform surface morphologies. Although
the spin coating process has been extensively studied, the origin of these
morphologies is not fully understood and the formation of non-uniform spincast
films remains a practical problem. Here we report on experiments demonstrating
that the formation of surface instabilities during spin coating is dependent on
temperature. Our results suggest that non-uniform spincast films form as a
result of the Marangoni effect, which describes flow due to surface tension
gradients. We find that both the wavelength and amplitude of the pattern
increase with temperature. Finally, and most important from a practical
viewpoint, the non-uniformities in the film thickness can be entirely avoided
simply by lowering the spin coating temperature.
