TY  - JOUR
A1  - Frieß, Fabian
A1  - Lendlein, Andreas
A1  - Wischke, Christian
T1  - Switching microobjects from low to high aspect ratios using a shape-memory effect
JF  - Soft matter
N2  - Spherical particles from shape-memory polymers (SMP) can be stretched to ellipsoids with high aspect ratio (AR) and temporarily stabilized. They can switch back to low AR upon thermal stimulation. Here, the creation of an alternative shape-switching capability of particles from low to high AR is introduced, where a SMP matrix from polyvinyl alcohol (PVA) is used to create crosslinked high AR particles and to program the embedded micrometer-sized particles from a second SMP (oligo(epsilon-caprolactone) micronetworks, MN) with a low switching temperature T-sw. This programming proceeds through shape-recovery of the PVA matrix, from which the MN are harvested by PVA matrix dissolution. The use of a dissolvable SMP matrix may be a general strategy to efficiently create systems with complex moving capabilities.
Y1  - 2021
U6  - https://doi.org/10.1039/d1sm00947h
SN  - 1744-6848
VL  - 17
IS  - 41
SP  - 9326
EP  - 9331
PB  - Royal Society of Chemistry
CY  - London
ER  - 
TY  - JOUR
A1  - Nöchel, Ulrich
A1  - Reddy, Chaganti Srinivasa
A1  - Wang, Ke
A1  - Cui, Jing
A1  - Zizak, Ivo
A1  - Behl, Marc
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers
JF  - Journal of Materials Chemistry A, Materials for energy and sustainability
N2  - Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units.
Y1  - 2015
U6  - https://doi.org/10.1039/c4ta06586g
SN  - 2050-7488
SN  - 2050-7496
VL  - 16
IS  - 3
SP  - 8284
EP  - 8293
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  -