Two-Way Reversible Shape Memory in a Semicrystalline Network
详细信息 查看全文
- 作者：Taekwoong Chung ; Angel Romo-Uribe ; Patrick T. Mather
- 刊名：Macromolecules
- 出版年：2008
- 出版时间：January 8, 2008
- 年：2008
- 卷：41
- 期：1
- 页码：184 - 192
- 全文大小：240K
- 年卷期：v.41,no.1(January 8, 2008)
- ISSN：1520-5835
文摘
Cooling-induced crystallization of cross-linked poly(cyclooctene) films under a tensile load resultsin significant elongation and subsequent heating to melt the network reverses this elongation (contracting), yieldinga net two-way shape memory (2W-SM) effect. The influence of cross-linking density on the thermal transitions,mechanical properties, and the related 2W-SM effect was studied by varying the concentration of cross-linkingagent dicumyl peroxide (DCP) and using differential scanning calorimetry (DSC), gel fraction measurements,dynamic mechanical analysis (DMA), and customized 2W-SM analysis. The latter showed that there iscrystallization-induced elongation on cooling and melting-induced shrinkage on heating (2W-SM), with lowercross-link density leading to higher elongation at the same applied stress. For a given cross-link density, however,increasing the tensile stress applied during cooling resulted in greater stress-induced crystallization. We furtherobserved that the onset temperatures for elongation on cooling (Tc) and contraction on heating (Tm) shifted tohigher temperatures with decreasing cross-link density. Similarly, the degree of molecular orientation achievedupon deformation was found to increase with decreasing cross-link density. The impact of stress on the 2W-SMeffect was examined using wide-angle X-ray diffraction (WAXD), revealing a transition from bimodal to unimodalorientation. As the crystalline structure evolves from bimodal (low stress) to unimodal (high stress), thecrystallization occurs along a single preferred orientation thus inducing greater elongation along the stretchingdirection. We anticipate that the observed 2W-SM property in a semicrystalline network will enable applicationsheretofore possible only with costly shape memory alloys and liquid crystalline elastomers.