Tunable Upper Critical Solution Temperature of Poly(N-isopropylacrylamide) in Ionic Liquids for Sequential and
Soonyong So1,2, Ryan C Hayward1
1Department of Polymer Science and Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
Abstract:
We demonstrate sequential folding of micropatterned polymer actuators by tuning the upper critical solution temperature (UCST) of poly(N-isopropylacrylamide) (PNIPAM) copolymers in the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl) imide. Incorporation of comonomers having different hydrogen-bonding capacities, acrylic acid and methyl acrylate, is shown to shift the UCST of PNIPAM to higher and lower temperatures, respectively. Relying on the ability to tune the transition temperature through copolymerization along with the wide thermal range afforded by the IL as a solvent, we fabricated a photopatterned self-folding device which shows reversible and sequential bending of three sets of hinges. Such sequential and reversible bending of microactuators offers potential for the design of complex self-folding origami and soft robots.
