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Stretchable Chemical Templates for the Manipulation of Droplets and the Fabrication of Functional Polymeric Microstructures
Control over liquid droplets is important for applications ranging from heat transfer to soft lithography. Although many techniques exist to collect and manipulate droplets, most suffer from the inability to reconfigure the shape or position of the droplets easily. Here a set of core technologies based on stretchable chemical templates are described. The synthesis and operation of these materials in the assembly and manipulation of liquid droplets are elaborated and their application in the fabrication of functional polymeric microstructures detailed. Surface chemical patterns were created on elastomeric surfaces by exposing the surface to oxygen plasma through an etch mask. Silica layers produced by this process were etched away using a mild salt solution, yielding chemical patterns that were reconfigured using simple mechanical strain. The density of surface molecules was changed by either straining the substrate after the creation of the patterns or by straining it during oxidation and subsequently relaxing the polymer, decreasing the area of the derivatized regions and increasing the density of the surface functional groups simultaneously. These templates were used to collect and manipulate droplets for flexible and reconfigurable microlenses. Polymeric microdroplets were deposited, assembled, and polymerized on chemical templates to make polymeric microstructures, a process we call “surface molding.” We controlled the droplet geometry by simple mechanical strain of the substrate, accessing “families of patterns” which allowed for the production of geometrically related microstructures from the same mask pattern. Arrays of microgels were used to fabricate soft actuators with tailored bending responses. Functional fillers added to the prepolymer droplets allowed for multi-stimuli responsive actuators. Finally, we generated wettability gradients on strained, oxidized surfaces. These surfaces wrinkled upon release of strain and could be reversibly changed. Droplet transport on these surfaces was controlled via simple mechanical strain, enabling the turning “on” and “off” of motion. These surfaces are useful for self-cleaning surfaces, surface fluidics, and heat transfer.
Bowen, John J, "Stretchable Chemical Templates for the Manipulation of Droplets and the Fabrication of Functional Polymeric Microstructures" (2018). ETD collection for University of Nebraska - Lincoln. AAI13421231.