TY - JOUR A1 - Bothe, Martin A1 - Pretsch, Thorsten T1 - Bidirectional actuation of a thermoplastic polyurethane elastomer JF - Journal of materials chemistry A N2 - Herein, we report on how to teach a thermoplastic polyurethane elastomer completely stress-free, bidirectional motion. Briefly spoken, we applied training, consisting of extensive tensile deformation in the specimen's viscoelastic state, initiating deformation-induced crystallization. Once unloaded, thermo-reversible specimen expansion and contraction could be detected. Following the microstructural evolution of such a trained specimen by in situ wide-angle X-ray scattering gave evidence for progressive growth of oriented crystallites during cooling. Upon heating, crystallite melting resulted in structural disorder. Beyond this, modification of the training method was used to introduce a geometrically more complex crystalline order. Here, actuation in the form of a decrease and an increase in sample thickness and specimen twisting and untwisting were witnessed. The novel semi-crystalline polymer actuator highlights an enormous potential for realizing versatile reversible shape changes in elastomers. KW - Bidrectional actuation KW - Thermoplastic polyurethane elastomer KW - Shape memory polymer KW - Training KW - Reversible shape changes KW - In situ wide-angle X-ray scattering KW - Hermann's orientation function KW - Mechanical properties KW - Phase change KW - Polymorphism KW - Poly(ester urethane) KW - Poly(1,4-butylene adipate) KW - Semi-crystallinity KW - Stimuli-sensitive polymer KW - Two-way actuator KW - Two-way shape memory KW - Microscopic model PY - 2013 DO - https://doi.org/10.1039/c3ta13414h SN - 2050-7496 SN - 2050-7488 VL - 1 IS - 46 SP - 14491 EP - 14497 PB - RSC CY - London [u.a.] AN - OPUS4-29641 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bothe, Martin A1 - Pretsch, Thorsten T1 - Two-way shape changes of a shape-memory poly(ester urethane) JF - Macromolecular chemistry and physics N2 - Phase-segregated PEU exhibits two-way shape changes under various constant stresses. Most distinct actuation (expansion on cooling and contraction on heating) can be detected between +60 and -20 °C when the maximum stress applied during a thermo-mechanical pretreatment approached the point where deformation-induced crystallization of the PBA soft segment sets in. The driving forces for the strain-related two-way shape changes consist of PBA crystallization and PBA melting-induced entropy elasticity. At low constant stresses (<1.5 MPa), entropy elasticity also contributes to specimen expansion on cooling. The results of multiple- cycling experiments imply that PEU is an appropriate candidate for the fabrication of thermoresponsive actuators working under constant stress conditions. KW - Actuation KW - Entropy elasticity KW - Mechanical properties KW - Phase change KW - Polymorphism KW - Poly(ester urethane) KW - Poly(1,4-butylene adipate) KW - Semi-crystallinity KW - Shape memory polymers KW - Stimuli-sensitive polymers KW - Stress KW - Two-way actuator KW - Two-way shape memory PY - 2012 DO - https://doi.org/10.1002/macp.201200096 SN - 1022-1352 SN - 1521-3935 VL - 213 IS - 22 SP - 2378 EP - 2385 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-27074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -