(166ak) A Simple Evaporative Deposition-Photopolymerization Approach for Facile Fabrication of Polymeric Hydrogel Films Containing Micropatterned Opal Structures
Subhash Kalidindi, Maurice Bukenya, and Hyunmin Yi
Department of Chemical and Biological Engineering, Tufts University, Medford, MA-02155, USA
Artificial opal structures have gained significant attention towards optical applications for sensing and detection due to the ready tunability and control of colors in response to stimuli. In specific, opal structure-based hydrogel platforms have shown great potential due to the reversible volume change they offer in response to external stimuli (e.g. temperature, pH, ionic strength).[2-5] However, existing techniques to fabricate these hydrogel platforms suffer from long opal deposition times and involve complicated procedures.
In order to address these challenges, we exploit a simple, reliable and robust fabrication technique: micromolding-based evaporation-polymerization method for fabrication of poly (ethylene glycol) (PEG)- based hydrogel films having micropatterned opal structures. First, deposition of uniform opal structures with intense colors is achieved by evaporation of polystyrene (PS) nanospheres in patterned polydimethylsiloxane (PDMS) micromolds. The uniformly deposited opal structures exhibit intense color via darkfield optical microscopy, and the wavelength of the opal color is confirmed using visible reflectance spectroscopy. Further, scanning electron microscopy (SEM) confirms uniform close hexagonal packing. The opal structures are then captured into hydrogel films via simple photopolymerization of PEG diacrylate monomers using a hand-held UV lamp. Dark field microscopy and SEM confirm reliable and consistent capture of the opal structure and robust nature of the films. By tuning simple parameters like monomer concentration and PS nanosphere size, wide color range in the visible spectrum is readily achieved, confirming rapid, reliable and robust nature of our simple evaporation-polymerization technique. Finally, incorporation of functional monomers like acrylic acid (AA) and methacrylic acid (MAA) leads to stimuli responsive opal-hydrogel films showing potential applications in the detection of pH and ionic strength. We envision that the simple evaporation â polymerization technique can be readily extended to manufacture a variety of functional materials for facile monitoring of environmental conditions.
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