(573e) Nanostructured Polymer Gels and Brushes Via 2 Color Interference Lithography

Optical interference lithography has remained an attractive technique to cheaply and rapidly pattern three dimensional features in polymer photoresists despite both resolution and feature size being limited by diffraction. In the past few years, Stimulated Emission Depletion Microscopy (STED) inspired lithography schemes have shown the ability to direct-write features well below the diffraction limit using visible light. However, the high intensity required for effective photoinhibition limits their use to point by point writing.

Recently, we have shown that combining the reversibly saturable photoisomerization of spirothiopyran with thiol-Michael addition chemistry can be used to formulate writing systems with desired low threshold characteristics. Adapting the spirothiopyran writing chemistry for polyethylene glycol monomers allows us to synthesize photoresponsive gels where crosslinking can be initiated and inhibited using two different wavelengths of light with spatial control obtained by controlling the relative intensity of the activating and deactivating wavelengths. Photokinetic modeling of such systems demonstrate the potential to fabricate nanostructured gels with feature sizes less than 50 nm over ranges spanning hundreds of microns by tuning the kinetics of spirothiopyran photoswitching using a 2W 532 nm light source. Nanopatterning using spirothiopyran functionalized systems is experimentally demonstrated by spatially localizing the Michael addition product over 1D patterns spanning large areas (>500 µm²) using a 2-color interference lithography setup. The feature size of the written patterns is shown to be tunable by controlling the relative intensity of the initiation and inhibition wavelengths. Secondary patterning on such nanostructured gels using unreacted photochromic brushes in conjunction with bifunctional maleimide linker molecules can be used to tailor the patterned surfaces to desired chemical functionalities. These experiments demonstrate the versatility of spirothiopyran based photochromic polymer systems for fabricating large area chemically tunable nanostructured gels