Abstract
Temperature-memory technology was utilized to generate flat substrates with a programmable stiffness pattern from cross-linked poly(eth-ylene-co-vinyl acetate) substrates with cylindrical microstructures. Programmed substrates were obtained by vertical compression at temperatures in the range from 60 to 100 °C and subsequent cooling, whereby aflat substrate was achieved by compression at 72 °C, as documented by scanning electron microscopy and atomic force microscopy (AFM). AFM nanoindentation experiments revealed that all programmed substrates exhibited the targeted stiffness pattern. The presented technology for generating polymeric substrates with programmable stiffness pattern should be attractive for applications such as touchpads, optical storage, or cell instructive substrates.
Highlights
Programmed substrates were obtained by vertical compression at temperatures in the range from 60 to 100 °C and subsequent cooling, whereby a flat substrate was achieved by compression at 72 °C, as documented by scanning electron microscopy and atomic force microscopy (AFM)
The uniformity of the microcylinders was visualized by scanning electron microscopy (SEM), showing arrays of identical cylinders across the substrate area, while an average height of the cylinders of 10.0 ± 0.1 μm was determined by AFM (Fig. 1)
A pronounced maximum in the tan δ temperature curve was found at −15 °C in dynamic mechanical thermal analysis (DMTA) experiments, which can be attributed to the glass transition of cPEVA
Summary
Polymeric substrates comprising local mechanical stiffness pattern or nanostructural features are intensively investigated in the context of applications such as haptic displays (touchpads), stretchable electronics, mechanical and optical data storage devices,[1,2,3,4,5,6,7,8] or as instructive cell substrates guiding mechanosensitive (stem) cells.[9,10,11,12,13,14,15] While individual cells can react to structural features of few nanometers in size and mechanical differences in the Pascal (Pa) range,[9,14] the tactile sensitivity of a human finger is only capable of detecting structural features above 10 nm and local mechanics in the kPa regime.[16,17,18,19,20]Mechanically patterned surfaces can be realized by variation of the polymer’s chemical composition (e.g., phase separated blends)[2] or crosslinking density (e.g., hydrogels).[9,21] Another approach is based on placing rigid microstructures or defined closed cavities (pores)[22] under soft/elastic polymeric materials and applying pressure.[11]In most technical applications (i.e., touchpads or data storage) the programmability of the material’s surface is a central requirement. Programmed substrates were obtained by vertical compression at temperatures in the range from 60 to 100 °C and subsequent cooling, whereby a flat substrate was achieved by compression at 72 °C, as documented by scanning electron microscopy and atomic force microscopy (AFM). In this study we explored whether flat polymeric substrates with a distinct mechanical pattern can be obtained by applying temperature-memory programming to microstructured polymer substrates.
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