TY  - JOUR
A1  - Farhan, Muhammad
A1  - Rudolph, Tobias
A1  - Nöchel, Ulrich
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Extractable Free Polymer Chains Enhance Actuation Performance of Crystallizable Poly(epsilon-caprolactone) Networks and Enable Self-Healing
JF  - Polymers
N2  - Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(epsilon-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5-60 wt % of non-crosslinked polymer chains, which freely interpenetrate the crosslinked network, were achieved leading to differences in the resulting phase of the bulk material. This can be described as "sponge-like" with open or closed compartments depending on the amount of interpenetrating polymer. The crosslinking density and the average network chain length remained in a similar range for all network structures, while the theoretical accessible volume for reptation of the free polymer content is affected. This feature could influence or introduce new functions into the material created by thermomechanical treatment. The effect of interpenetrating PCL in cPCLs on the reversible actuation was analyzed by cyclic, uniaxial tensile tests. Here, high reversible strains of up to Delta epsilon = 24% showed the enhanced actuation performance of networks with a non-crosslinked PCL content of 30 wt % resulting from the crystal formation in the phase of the non-crosslinked PCL and co-crystallization with network structures. Additional functionalities are reprogrammability and self-healing capabilities for networks with high contents of extractable polymer enabling reusability and providing durable actuator materials.
KW  - shape-memory polymer actuators
KW  - soft actuators
KW  - self-healing
KW  - poly(epsilon-caprolactone)
KW  - thermoplastics
Y1  - 2018
U6  - https://doi.org/10.3390/polym10030255
SN  - 2073-4360
VL  - 10
IS  - 3
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Razzaq, Muhammad Yasar
A1  - Behl, Marc
A1  - Heuchel, Matthias
A1  - Lendlein, Andreas
T1  - Matching magnetic heating and thermal actuation for sequential coupling in hybrid composites by design
JF  - Macromolecular rapid communications
N2  - Sequentially coupling two material functions requires matching the output from the first with the input of the second function. Here, magnetic heating controls thermal actuation of a hybrid composite in a challenging system environment causing an elevated level of heat loss. The concept is a hierarchical design consisting of an inner actuator of nanocomposite material, which can be remotely heated by exposure to an alternating magnetic field (AMF) and outer layers of a porous composite system with a closed pore morphology. These porous layers act as heat insulators and as barriers to the surrounding water. By exposure to the AMF, a local bulk temperature of 71 degrees C enables the magnetic actuation of the device, while the temperature of the surrounding water is kept below 50 degrees C. Interestingly, the heat loss during magnetic heating leads to an increase of the water phase (small volume) temperature. The temperature increase is able to sequentially trigger an adjacent thermal actuator attached to the actuator composite. In this way it could be demonstrated how the AMF is able to initiate two kinds of independent actuations, which might be interesting for robotics operating in aqueous environments.
KW  - artificial muscles
KW  - magnetosensitivity
KW  - nanocomposites
KW  - soft actuators
Y1  - 2019
U6  - https://doi.org/10.1002/marc.201900440
SN  - 1022-1336
SN  - 1521-3927
VL  - 41
IS  - 1
PB  - Wiley-VCH
CY  - Weinheim
ER  -