Kinetics and morphology of electric field -induced patterning in thin polymer films

• Main Author: Leach, Kathryn Amanda
• Language: ENG
• Published: ScholarWorks@UMass Amherst 2005
• Subjects: Polymers|Materials science
• Online Access: https://scholarworks.umass.edu/dissertations/AAI3194033

Electrohydrodynamic instabilities in thin liquid polymer films are generated when electrostatic pressure overcomes surface tension, leading to amplification of fluctuations at the polymer surface. The growth kinetics of these fluctuations are, in principle, similar to the growth in size of domains during phase separation of polymer mixtures. Consequently, an exponential dependence of fluctuation height on time, characterized by a time constant, can be predicted from the strength of the electric field and the characteristics of the polymer. Results for in situ measurements of fluctuation growth in polydimethylsiloxane show good agreement with theory at early stages and divergence from theory at later stages. At the early stages, the measured time constants shoe quantitative agreement with theory, using no adjustable parameters. Furthermore, a significant reduction in the rate of amplification was observed when a low-viscosity thiolene mixture was used. To preserve the fluctuations and patterned structures, the low molecular weight liquid could be polymerized using ultraviolet light. In situ observation of the growth and decay of electrohydrodynamic instabilities in varying electric fields showed that, since the time scales are predictable, they can be manipulated by varying the electric field. When the electric field was cycled between low and high, growth and decay of fluctuations in the varying electric fields was observed. Electric fields were also used to generate patterns in polymer/polymer/air trilayers with a PS film sandwiched between a silicon substrate and a layer of PMMA. The degree to which the viscosity of the polymer film at the substrate is smaller than that of the upper layer has a strong effect on the morphology of structure formation. Several unique three-dimensional microstructures are made possible by tuning electric-field induced fluctuations in concert with dewetting. The kinetics of structure formation were enhanced by this configuration resulting in much faster patterning than achieved in prior studies. External electric fields were also used to amplify fluctuations in bilayers with block copolymers added to reduce interfacial tension. A significant reduction in characteristic length scale for the instabilities was observed. This process shows promise for application to nanometer-scale lithography.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Windows MediaPlayer or RealPlayer.