Multiscale Pattern Generation in Viscoelastic Polymer Films by Spatiotemporal Modulation of Electric Field and Control of Rheology

Electric-fi eld-induced hierarchical, multiscale patterning of incompletely cross-linked viscoelastic polydimethylsiloxane (PDMS) fi lms is achieved by spatiotemporal variation of the fi eld, 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 fi eld is introduced by employing different types of simply patterned electrodes: stripes, elevated concentric circular rings, and boxpatterned ridges. Multiscale complex structures consisting of increasingly fi ner primary, secondary, and tertiary hierarchical structures are fabricated by progressively ramping up the electric fi eld while maintaining the integrity of the already formed structures. The latter is achieved by partially cross-linking the fi lms 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 fi eld, and its programmable temporal variation. The PDMS patterns are made permanent by complete cross-linking after a desired multiscale structure is obtained.