Programmable pattern transformation of reconfigurable polymer membranes

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NON-TECHNICAL SUMMARY:This project involves synthesizing polymeric materials that can respond to external stimuli by reconfiguring their shapes. These polymers will be processed so as to yield patterned microstructured membranes with regularly spaced holes. The study of structural change in response to external stimuli will provide important scientific insights into how to design reconfigurable nanomaterials. These could be used to create more complex, multifunctional microstructures. The resulting changes in physical properties (e.g. transparency and color change) may also make these materials relevant to novel technologies, including tunable optical windows, sensors, programmable sound and heat transfer, catalysis, drug delivery, and soft robotics. Students at all levels will be exposed to a diverse range of topics in chemistry, materials science and engineering, physics, soft mechanics, nanofabrication and computational modeling. Outreach will include underrepresented groups at local high schools and community colleges to carry out research on campus at the University of Pennsylvania. Research results will be showcased at the Philadelphia Materials Day and at other public outreach events. TECHNICAL SUMMARY:This project involves synthesis and study of microstructured polymer membranes that are responsive to external stimuli (e.g. pH, temperature and light), aimed at providing deeper understanding of the materials' mechanical responses in complex geometries (both isotropically and anisotropically). This in turn will allow for programming the evolution of complex chiral structures by considering the molecular structures of the polymers, the geometric parameters of the pore arrays in the membranes, and the application of external forces. Specifically, the research includes 1) preparation of a range of poly(2-hydroxyethyl methacrylate) (PHEMA) based hydrogel membranes with microscopic hole arrays of arbitrary feature size, spacing, aspect ratio, and arrangement; 2) examination of the solvent-swelling induced pattern transformation at different pH and temperature and its comparison to modeling; 3) synthesis of nematic liquid crystal monomers and crosslinkers to prepare microstructured nematic liquid crystal elastomers (NLCEs); 4) control of surface anchoring of the liquid crystal molecules within the membranes to maximize the strain response and comparison to modeling; 5) exploration of the internal instability in NLCE membranes at different temperatures in comparison to pattern transformation in PHEMA-based hydrogel membranes; 6) application of the same deformation principles to investigate light-responsive NLCE membranes with local spatial control of light and polarization.