TY  - JOUR
A1  - Ghobadi, Ehsan
A1  - Heuchel, Matthias
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Simulating the shape-Memory behavior of amorphous switching domains of Poly(L-lactide) by molecular dynamics
JF  - Macromolecular chemistry and physics
N2  - The thermally induced shape-memory effect of polymers is typically characterized by cyclic uniaxial thermomechanical tests. Here, a molecular-dynamics (MD) simulation approach of such a cyclic uniaxial thermomechanical test is presented for amorphous switching domains of poly(L-lactide) (PLLA). Uniaxial deformation of the constructed PLLA models is simulated with a Parinello-Rahman scheme, as well as a pragmatic geometrical approach. We are able to describe two subsequent test cycles using the presented simulation approach. The obtained simulated shape-memory properties in both test cycles are similar and independent of the applied deformation protocols. The simulated PLLA shows high shape fixity ratios (Rf 94%), but only a moderate shape recovery ratio is obtained (Rr 30%). Finally, the structural changes during the simulated test are characterized by analysis of the changes in the dihedral angle distributions.
KW  - molecular modeling
KW  - polyesters
KW  - shape-memory properties
KW  - stimuli-sensitive polymers
KW  - thermomechanical properties
Y1  - 2013
U6  - https://doi.org/10.1002/macp.201200450
SN  - 1022-1352
VL  - 214
IS  - 11
SP  - 1273
EP  - 1283
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Zhang, Quanchao
A1  - Sauter, Tilman
A1  - Fang, Liang
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Shape-Memory Capability of Copolyetheresterurethane Microparticles Prepared via Electrospraying
JF  - Macromolecular materials and engineering
N2  - Multifunctional thermo-responsive and degradable microparticles exhibiting a shapememory effect (SME) have attracted widespread interest in biomedicine as switchable delivery vehicles or microactuators. In this work almost spherical solid microparticles with an average diameter of 3.9 +/- 0.9 mm are prepared via electrospraying of a copolyetheresterurethane named PDC, which is composed of crystallizable oligo(p-dioxanone) (OPDO) hard and oligo(e-caprolactone) (OCL) switching segments. The PDC microparticles are programmed via compression at different pressures and their shapememory capability is explored by off-line and online heating experiments. When a low programming pressure of 0.2 MPa is applied a pronounced thermally-induced shape-memory effect is achieved with a shape recovery ratio about 80%, while a high programming pressure of 100 MPa resulted in a weak shape-memory performance. Finally, it is demonstrated that an array of PDC microparticles deposited on a polypropylene (PP) substrate can be successfully programmed into a smart temporary film, which disintegrates upon heating to 60 degrees C.
KW  - biomaterials
KW  - microparticles
KW  - processing
KW  - stimuli-sensitive polymers
KW  - shape-memory effect
Y1  - 2015
U6  - https://doi.org/10.1002/mame.201400267
SN  - 1438-7492
SN  - 1439-2054
VL  - 300
IS  - 5
SP  - 522
EP  - 530
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Yan, Wan
A1  - Fang, Liang
A1  - Nöchel, Ulrich
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Influence of programming strain rates on the shape-memory performance of semicrystalline multiblock copolymers
JF  - Journal of polymer science : B, Polymer physics
N2  - Multiblock copolymers named PCL-PIBMD consisting of crystallizable poly(epsilon-caprolactone) segments and crystallizable poly[oligo(3S-iso-butylmorpholine-2,5-dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape-memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL-PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL-PIBMD. Programming was conducted at 50 degrees C by elongation to epsilon(m)=50% with strain rates of 1 or 10 or 50 mmmin(-1). The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X-ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain-induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape-memory polymers with designed recovery forces. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1935-1943
KW  - atomic force microscopy (AFM)
KW  - crystal structures
KW  - crystallization
KW  - multiblock copolymer
KW  - stimuli-sensitive polymers
KW  - SAXS
KW  - shape-memory effect
KW  - WAXS
KW  - X-ray scattering
Y1  - 2016
U6  - https://doi.org/10.1002/polb.24097
SN  - 0887-6266
SN  - 1099-0488
VL  - 54
SP  - 1935
EP  - 1943
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -