TY - JOUR A1 - Lendlein, Andreas A1 - Heuchel, Matthias T1 - Shape-memory polymers designed in view of thermomechanical energy storage and conversion systems BT - Effective temporary shape fixation by strain-induced formation of supramolecular nanostructures enables high energy density one-way shape-memory polymers JF - ACS central science KW - Actuators KW - Deformation KW - Energy KW - Energy storage KW - Polymers Y1 - 2021 U6 - https://doi.org/10.1021/acscentsci.1c01032 SN - 2374-7951 VL - 7 IS - 10 SP - 1599 EP - 1601 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sauter, Tilman A1 - Kratz, Karl A1 - Heuchel, Matthias A1 - Lendlein, Andreas T1 - Fiber diameter as design parameter for tailoring the macroscopic shape-memory performance of electrospun meshes JF - Materials and design N2 - Fibrous shape-memory polymer (SMP) scaffolds were investigated considering the fiber as basic microstructural feature. By reduction of the fiber diameter in randomly oriented electrospun polyetherurethane (PEU) meshes from the micro-to the nano-scale, we observed changes in the molecular orientation within the fibers and its impact on the structural and shape-memory performance. It was assumed that a spatial restriction by reduction of the fiber diameter increases molecular orientation along the orientation of the fiber. The stress-strain relation of random PEU scaffolds is initially determined by the 3D arrangement of the fibers and thus is independent of the molecular orientation. Increasing the molecular orientation with decreasing single fiber diameter in scaffolds composed of randomly arranged fibers did not alter the initial stiffness and peak stress but strongly influenced the elongation at break and the stress increase above the Yield point. Reduction of the single fiber diameter also distinctly improved the shape-memory performance of the scaffolds. Fibers with nanoscale diameters (< 100 nm) possessed an almost complete shape recovery, high recovery stresses and fast relaxation kinetics, while the shape fixity was found to decrease with decreasing fiber diameter. Hence, the fiber diameter is a relevant design parameter for SMP. KW - Nanofiber KW - Shape-memory polymer KW - Electrospinning KW - Function by design KW - Molecular orientation Y1 - 2021 U6 - https://doi.org/10.1016/j.matdes.2021.109546 SN - 1873-4197 VL - 202 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Izraylit, Victor A1 - Heuchel, Matthias A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Non-woven shape-memory polymer blend actuators JF - MRS advances : a journal of the Materials Research Society (MRS) N2 - The hierarchical design approach provides various opportunities to adjust the structural performance of polymer materials. Electrospinning processing techniques give access to molecular orientation as a design parameter, which we consider here in view of the shape-memory actuation performance. The aim of this work is to investigate how the reversible strain epsilon'(rev) can be affected by a morphology change from a bulk material to an electrospun mesh. epsilon'(rev) could be increased from 5.5 +/- 0.5% to 15 +/- 1.8% for a blend from a multiblock copolymer with poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA) segments with oligo(D-lactide) (ODLA). This study demonstrates an effective design approach for enhancing soft actuator performance, which can be broadly applied in soft robotics and medicine. Y1 - 2021 U6 - https://doi.org/10.1557/s43580-021-00063-8 SN - 2059-8521 VL - 6 IS - 33 SP - 781 EP - 785 PB - Springer Nature Switzerland AG CY - Cham ER - TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Heuchel, Matthias A1 - Lendlein, Andreas T1 - Thin-layer studies on surface functionalization of polyetherimide BT - hydrolysis versus amidation JF - Journal of materials research : JMR / Materials Research Society N2 - Among the high-performance and engineering polymers, polyimides and the closely related polyetherimide (PEI) stand out by their capability to react with nucleophiles under relatively mild conditions. By targeting the phthalimide groups in the chain backbone, post-functionalization offers a pathway to adjust surface properties such as hydrophilicity, solvent resistance, and porosity. Here, we use ultrathin PEI films on a Langmuir trough as a model system to investigate the surface functionalization with ethylene diamine and tetrakis(4-aminophenyl)porphyrin as multivalent nucleophiles. By means of AFM, Raman spectroscopy, and interfacial rheology, we show that hydrolysis enhances the chemical and mechanical stability of ultrathin films and allows for the formation of EDC/NHS-activated esters. Direct amidation of PEI was achieved in the presence of a Lewis acid catalyst, resulting in free amine groups rather than cross-linking. When comparing amidation with hydrolysis, we find a greater influence of the latter on material properties. KW - Membrane KW - Nanostructure KW - Polymer KW - Raman spectroscopy KW - Scanning probe microscopy (SPM) KW - Surface reaction KW - Thin film Y1 - 2021 U6 - https://doi.org/10.1557/s43578-021-00339-7 SN - 0884-2914 SN - 2044-5326 VL - 37 IS - 1 SP - 67 EP - 76 PB - Springer CY - Berlin ER - TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Heuchel, Matthias A1 - Lendlein, Andreas T1 - Hydrolytic stability of polyetherimide investigated in ultrathin films JF - Journal of materials research : JMR / Materials Research Society N2 - Increasing the surface hydrophilicity of polyetherimide (PEI) through partial hydrolysis of the imide groups while maintaining the length of the main-chain was explored for adjusting its function in biomedical and membrane applications. The outcome of the polymer analogous reaction, i.e., the degree of ring opening and chain cleavage, is difficult to address in bulk and microstructured systems, as these changes only occur at the interface. Here, the reaction was studied at the air-water interface using the Langmuir technique, assisted by atomic force microscopy and vibrational spectroscopy. Slow PEI hydrolysis sets in at pH > 12. At pH = 14, the ring opening is nearly instantaneous. Reduction of the layer viscosity with time at pH = 14 suggested moderate chain cleavage. No hydrolysis was observed at pH = 1. Hydrolyzed PEI films had a much more cohesive structure, suggesting that the nanoporous morphology of PEI can be tuned via hydrolysis. KW - 2D materials KW - Membrane KW - Polymer KW - Water KW - Nanostructure Y1 - 2021 U6 - https://doi.org/10.1557/s43578-021-00267-6 SN - 0884-2914 SN - 2044-5326 VL - 36 IS - 14 SP - 2987 EP - 2994 PB - Springer CY - Berlin ER -