Mechanical and Civil Engineering Seminar

Abstract:
Liquid crystal elastomers (LCEs) have the unique feature that the macroscopic shape (deformation) and the liquid crystal alignment (director) are strongly correlated with each other due to the coupling of rubber elasticity and liquid crystallinity. This feature enables us to drive the macroscopic deformation of LCEs by various types of external stimulus to alter the LC alignment. Furthermore, the induced deformation mode can be controlled by the director configuration in the fabrication of LCEs. We introduce the thermally driven change in helical shape for the LCEs with twist LC alignment[1], and the thermally induced periodical surface undulation for the cholesteric LCE films whose helical axis is parallel to the film surface[2].
The LCEs show the markedly nonlinear stress-strain relations due to the coupling of imposed strain and director realignment. Earlier studies showed that the uniaxial stress- strain curves of nematic elastomers with polydomain texture (prepared in the high- temperature isotropic state) (I-PNEs) show a plateau region with markedly low magnitude over a finite range of strain[3]. The low plateau stress reflects the realignment process of the local directors in the stretching direction, which has often been called "soft elasticity"[4]. Recently, we reveal the nonlinear stress-strain relations of the I-PNEs under various types of stretching using a custom-built biaxial tester.
We also introduce the electrically driven large deformation of I-PNEs using the soft elasticity[5], the electro-opto-mechanical behavior of the swollen cholesteric elastomers (cholesteric gels)[6], and the mechano-optical effects in the cholesteric elastomers [7].
[1] Sawa et al., PNAS (2011); [2] Nagai et al., Macromolecules (2016); [3] Urayama et al., Macromolecules (2009); [4] Biggins, et al., Phys. Rev. Lett. (2009).[5] Okamoto et al, Soft Matter (2011); [6] Fuchigami, et al., ACS Macro Lett. (2015); [7] Varanytsia et al., Sci. Rep. (2014).

Short Bio:
Kenji Urayama is a professor in Department of Macromolecular Science and Engineering at Kyoto Institute of Technology in Japan. He was a faculty member at Department of Materials Chemistry at Kyoto University until 2013. His current research focuses on the nonlinear viscoelasticity of soft solids such as elastomers and gels, especially characterized by a custom built biaxial tester, and the rheology of dense microgel suspensions, and the stimulus-response behavior of liquid crystal elastomers and gels. His honor includes the John H. Dillon Medal in 2006 from the Division of Polymer Physics in American Physical Society, and the Wiley Award in 2008 from the Society of Polymer Science, Japan, and the Bridgestone Soft Materials Frontier Award in 2012.