Characterization Methods for Shape-Memory Polymers
- Wolfgang WagermaierAffiliated withCenter for Biomaterial Development, Institute of Polymer Research, GKSS Research Center Geesthacht GmbH
- , Karl KratzAffiliated withCenter for Biomaterial Development, Institute of Polymer Research, GKSS Research Center Geesthacht GmbH
- , Matthias HeuchelAffiliated withCenter for Biomaterial Development, Institute of Polymer Research, GKSS Research Center Geesthacht GmbH
- , Andreas LendleinAffiliated withCenter for Biomaterial Development, Institute of Polymer Research, GKSS Research Center Geesthacht GmbH Email author
Shape-memory polymers (SMPs) are able to fix a temporary deformed shape and recover their original permanent shape upon application of an external stimulus such as heat or light. A shape-memory functionalization can be realized for polymer based materials with an appropriate morphology by application of a specific shape-memory creation procedure (SMCP). Specific characterization methods have been tailored to explore the structure-function relations of SMPs in respective applications. This paper reviews characterization methods on different length scales from the molecular to the macroscopic level.
On the molecular morphological level SMPs are comprised of netpoints determining the permanent shape and reversible crosslinks fixing the temporary shape. For polymers with covalent permanent netpoints the crosslinking density plays an important role, which can be quantified by means of swelling experiments or nuclear magnetic resonance (NMR) methods. In contrast, thermoplastic SMPs are typically phase-segregated polymers, where each domain is related to a different thermal transition, which can be explored by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Further suitable techniques for investigations of the SMP morphology on different levels of hierarchy are polarized light microscopy (POM), scanning or transmission electron microscopy (SEM, TEM) and atomic force microscopy (AFM) as well as wide and small X-ray scattering (WAXS, SAXS).
On the macroscopic level the extent to which a temporary deformation can be fixed and the recovery of the permanent shape or the recovery stress are the most important characteristics of the shape-memory effect (SME), which can be quantified in cyclic, thermomechanical tensile tests or bending tests. Such cyclic tests consist of a SMCP module that can be performed either under stress or strain control followed by a recovery module under stress-free or constant strain conditions. The obtained shape-memory properties are strongly influenced by temperature dependent test parameters like deformation and fixation temperature or applied heating and cooling rate. In addition cyclic, photomechanical testing of light-induced dual-shape polymers, where the temporary shape is fixed by photoreversible chemical crosslinks and the testing of magnetically-induced shape-memory composites are described. In contrast multi-phase polymer networks, which exhibit a triple-shape effect, are explored in cyclic, thermomechanical experiments utilizing a specific two-step SMCP. Furthermore a selection of application-oriented tests for characterization of SME is presented.
Finally, as part of a comprehensive characterization, modeling approaches for simulating the thermomechanical behavior of SMPs are presented. At the beginning linear viscoelastic models were applied consisting of coupled spring, dashpot and frictional elements. More recent approaches consider in detail the specific molecular transition underlying the SME, e.g. glass or melting transition. Currently models that incorporate the strain rate dependence and time dependent behavior are under development.
KeywordsShape-memory effect Shape-memory polymer morphology Thermomechanical tests
- Characterization Methods for Shape-Memory Polymers
- Book Title
- Shape-Memory Polymers
- pp 97-145
- Print ISBN
- Online ISBN
- Series Title
- Advances in Polymer Science
- Series Volume
- Series ISSN
- Springer Berlin Heidelberg
- Copyright Holder
- Springer-Verlag Berlin Heidelberg
- Additional Links
- Shape-memory effect
- Shape-memory polymer morphology
- Thermomechanical tests
- Industry Sectors
- eBook Packages
- Andreas Lendlein (ID1)
- Editor Affiliations
- ID1. Geesthacht GmbH, Institut für Chemie, GKSS Forschungszentrum
- Author Affiliations
- 1. Center for Biomaterial Development, Institute of Polymer Research, GKSS Research Center Geesthacht GmbH, Kantstr. 55, 14513, Teltow, Germany
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