Photocurable Pillar Arrays Formed via Electrohydrodynamic Instabilities

Abstract

Low viscosity, photocurable liquids are demonstrated as ideal materials for the formation of pillar arrays generated spontaneously by field-assisted assembly. Pillars form spontaneously via electrohydrodynamic instabilities that arise from the force imbalance at a film−air interface generated by an applied electric field. Conventional polymer films form pillars slowly as a result of their relatively large viscosities and are often process-limited by a requirement of heat to modulate rheological properties. In contrast, low viscosity liquids require no heat and form pillars orders of magnitude faster, as predicted by theory. The resulting structures are preserved by photopolymerization, eliminating the lengthy heating−cooling cycle necessary to process most polymers. The combination of nearly instantaneous formation and rapid photocuring at room temperature is ideal for patterning. Epoxy, vinyl ether, acrylate, and thiol-ene systems were evaluated for pillar formation. Relevant material properties were characterized (viscosity, dielectric constant, interfacial energy, kinetics) to explain the phenomenological behavior of each system during electrohydrodynamic patterning. The thiol-ene system formed pillar arrays nearly instantaneously and cured rapidly under ambient conditions. These are nearly ideal characteristics for pillar formation.

Optically induced electrohydrodynamic instability-based micro-patterning of fluidic thin films

“…In order to circumvent the problems associated with high temperatures (such as polymer degradation by thermal oxidation) which arise due to long processing times, methods, such as ''solvent annealing'' (Harkema and Steiner 2005) and low viscosity, photocurable liquids, were introduced into the EHDI process (Dickey et al 2006). Localized laser heating also provided an environmentfriendly approach (Lyutakov et al 2009) for EHDI-based fabrication.…”

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

“…[ 47 , 48 , 52 , 56 , 65 , 66 ] The dependence of λ on ψ , h and d can be found in the Equation (4) reducing its T g by a solvent vapor followed by patterning and then reducing the temperature below T g to freeze the structures, [ 47 ] or b) by patterning soft photo/UV curable liquid polymers followed by their rapid curing before removal of the top electrode. [ 70 ] Laser heating for self-organization in thin metallic fi lms is another possibility, not yet explored for polymer fi lms. [ 19 ] Patterned cross-linkable polymers such as PDMS are of course the mainstay of a variety of soft lithography techniques requiring moulds, stamps, templates and masters.…”

Electrohydrodynamic Assembly of Multiscale PDMS Microlens Arrays

“…An easy technique to produce lateral structures at microscale in polymer films was recently developed by using EHD instability [18], [19] or by optically induced electrohydrodynamic instability [20]. Indeed, EHD assembling is an innovative micromanufacturing process that makes use of the instability of viscous polymeric thin films when exposed to non-uniform electrostatic fields.…”