Multiscale pattern generation in viscoelastic polymer films by spatiotemporal modulation of electric field and control of rheology

Abstract

Electric-field-induced hierarchical, multiscale patterning of incompletely cross-linked viscoelastic polydimethylsiloxane (PDMS) films is achieved by spatiotemporal variation of the field, which produces a multiplicity of complex mesopatterns from the same electrode. Experiments and simulations are employed to uncover pathways of hierarchical pattern formation. Spatial modulation of the field is introduced by employing different types of simply patterned electrodes: stripes, elevated concentric circular rings, and box-patterned ridges. Multiscale complex structures consisting of increasingly finer primary, secondary, and tertiary hierarchical structures are fabricated by progressively ramping up the electric field while maintaining the integrity of the already formed structures. The latter is achieved by partially cross-linking the films before patterning, which engenders optimal viscosity to prevent a rapid ripening and coalescence of earlier formed patterns. These multiscale structures can be controlled by the geometry and periodicity of patterned electrodes, the strength of the electric field, and its programmable temporal variation. The PDMS patterns are made permanent by complete cross-linking after a desired multiscale structure is obtained. Based on experiments and simulations, a spatiotemporally modulated electric field is shown to be usable for large-area microfabrication of hierarchical multiscale patterns in thin viscoelastic films. Increasingly finer structures are produced by progressive ramping up of applied voltage while preserving the coarser structures already produced by a partial cross-linking of polydimethysiloxane (PDMS) films. Final multiscale micropatterns are stabilized by complete cross-linking. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.