Pattern formation in polymer via electrohydrodynamic instabilities and glassy fracture

Fabrication of micro and nano structures from polymeric materials has attracted significant attention due to their promise of inexpensive, fast throughput and ease of integration into existing fabrication processes. This dissertation describes our contributions to two such processes.; In the first process, electrohydrodynamic flow drives a thin polymer film sandwiched between electrodes with an intervening gap into multidomained, hexagonally packed pillars or concentric rings. We model the initial stages of formation by performing a linear stability analysis under the lubrication approximation. We find the presence of free charge at the free interface both decreases the pillar-to-pillars spacing and increases the growth rate. We examined the possible sources of electrostatic field in the absence of an applied voltage to find static charge to be the most likely candidate. In practice, however, the lubrication approximation may not strictly apply in the situations of greatest interest. Accordingly, we contrasted results of the linear stability analysis with and without the lubrication approximation to show that the approximation fails where surface tension is small and electric fields are large, typical of experiments with a polymer/organic liquid instead of air in the gap---precisely the conditions that predict the smallest pillar arrays. Motivated by the discovery of concentric rings, we adapted the form of the perturbation from sinusoids to Bessel functions to predict constant ring-to-ring spacings, constant annular widths and growth rates in agreement with experiment.; In the second patterning technique, a thin film sandwiched between two substrates fractures into periodic ridges upon insertion of a razor blade. We investigated the conditions that selected for the presence or absence of the gratings, their fractional coverage, their period, and their alignment. Our key findings indicated that the gratings form from all glassy materials tested with periods of approximately four times the film thickness. We took the first step towards a theoretical understanding of the phenomena by constructing a model under the Griffith criterion. The model indicates the stress at fracture to depend strongly on the period to film thickness ratio and provides an explanation for the dearth of periods less than 100 nm.