Influence of Compression Direction on the Shape-Memory Effect of Micro-Cylinder Arrays Prepared from Semi-Crystalline Po
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Influence of Compression Direction on the Shape-Memory Effect of Micro-Cylinder Arrays Prepared from Semi-Crystalline Polymer Networks Yi Jiang1,2, Liang Fang1,#, Karl Kratz1, Andreas Lendlein1,2 1 Institute of Biomaterial Science and Berlin-Brandenburg Center for Regenerative Therapies, Helmholtz Zentrum Geesthacht, Kantstr. 55, 14513, Teltow, Germany 2 Institute of Chemistry, University of Potsdam, 14476 Potsdam, Germany # Present address: State Key Laboratory of Materials-Oriented Chemical Engineering, College of Material Science and Engineering, Nanjing Tech University, 210009, Nanjing, China. ABSTRACT Microstructured polymeric surfaces capable of a thermally-induced shape-memory effect (SME) can perform on demand changes of surface properties such as wettability or adhesion. In this study, we explored the influence of the applied compression direction during programming, i.e. vertical compression and tilted compression, on the SME of microstructured crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) films comprising arrays of microcylinders with a height of 10 μm and different diameters of 10 μm, 25 μm, and 50 μm. The shape recovery of the microstructures during heating was visualized online by optical microscopy, while atomic force microscopy (AFM) was utilized to investigate the temperatureinduced shape change of single micro-cylinders. Here, the changes in micro-cylinder height and the characteristic angle T were followed and analyzed for quantification of the shape-memory performance. Both compression modes resulted in almost flat programmed surfaces as indicated by high shape fixity ratios of Rf ≥ 93±1%. A nearly complete recovery of the micro-cylinders was obtained for all investigated cPEVA samples documented by high shape recovery values of Rr ≥ 97±1%, while the obtained shape change of the micro-cylinders during recovery almost reversely recalled the applied deformation during programming. The presented capability of SMP microstructured substrates to memorize the way of deformation during programming could be a new tool for controlling particular shape changes of microstructures during recovery and in such a way the generated local recovery forces can be adjusted. INTRODUCTION Shape-memory polymers (SMPs) are a prominent class of thermo-sensitive materials, which are capable of active movements. While in the last decade the majority of SMP research was focused on the investigation of macroscopic effects [1], more recently micro- and
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nanostructured SMP films have been explored as novel type of intelligent surface [2-9]. In this context smart films have been reported showing i.e. a switchable wettability [2] or adhesion [3, 9], allow controlled changes in optical elements [4, 5], can be applied as intelligent microfluidics [6] or utilized
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