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9. Dynamics of Main Chain Liquid Crystal Elastomers |
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Main chain liquid crystal elastomers (MCLCEs) are cross linked polymer networks that incorporate liquid crystal mesogens into the polymer backbone via covalent bonding. They uniquely combine anisotropic order of liquid crystals and elastic properties of cross linked polymers. We investigated the structural response and relaxation dynamics of several siloxane-based smectic-C (SmC) MCLCEs immediately upon the application of strain, after removal of strain, and with temperature using x-ray scattering. These elastomers relaxed under constant strain as evident from the changes in the tilt angle of the SmC phase, most likely due to annealing of strain-induced instabilities and conformational changes. At low strains, the MCLCEs exhibited reversible elastic behavior but had anelastic response beyond a threshold strain of 50%. The MCLCE films’ structure gradually changed with increasing strain at RT and revealed a strain dependent enhancement of the smectic order. At strains beyond 50%, a monodomain structure from an initially polydomain state was obtained. Quantitative analysis of the structural evolution with strain, time and temperature provide important insight into molecular level relaxation in these materials.
Figure. Small angle XRD patterns in the Sm C phase of siloxane-based liquid crystal elastomer stretched to 120%; (a) immediately after stretching and after (b) 3 (c) 7 (d) 11 (e) 17 and (f) 24 minutes. Azimuthal scans of these peaks shown in (g) illustrate the time dependence of the smectic tilt angle. The direction of stretching is in the vertical direction.
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1. Dual relaxation and structural changes under uniaxial strain in main-chain smectic-C liquid crystal elastomer, D.M. Agra-Kooijman, M. Fisch, L. Joshi, W. Ren, P. McMullan, A. Griffin and Satyen Kumar, Phys. Chem. Chem. Phys. 17, 191(2015). 2. Strain Dependent Relaxation of Main-Chain Liquid Crystal Elastomer (Oral), D. M. Agra-Kooijman, S. Dey, W. Ren, P. McMullan, A. Griffin, and Satyen Kumar, 25th International Liquid Crystal Conference, Dublin, Ireland, June 29-July 4 (2014). 3. Soft Elasticity in Main Chain Liquid Crystal Elastomers, S. Dey, D.M. Agra-Kooijman, W. Ren, P.J. McMullan, A. C. Griffin, and S. Kumar, Crystals 3, 363-390, (2013). 4. Structural Dynamics of Siloxane-Based Main Chain Liquid Crystal Elastomer Revealed by Synchrotron X-ray Scattering, D. M. Agra-Kooijman, L. Joshi, S. Dey, W. Ren, W.Kline, A. Griffin, and S. Kumar, Oral Presentation, 23rd International Liquid Crystal Conference, Krakow, Poland, July 11–16 (2010) 5. Dynamics of Main Chain Liquid Crystal Elastomers Revealed by Synchrotron X-ray Scattering, Dena Mae Agra-Kooijman, Leela Joshi, Sonal. Dey, and Satyendra Kumar, Wanting Ren, Whitney Kline, and A. Griffin, APS March meeting, Portland, OR, March 15-19 (2010). 6. Dynamics of Main Chain Liquid Crystal Elastomers, D. M. Agra-Kooijman, L. Joshi, S. Dey, and S. Kumar, Synposium on “Anisotropic Soft Matter in bulk and under Confinement: Challenges in Integrating Theory, Simulations and Experiments”, Georgia Institute of Tech, Atlanta, Jan 28-29 (2010). 7. Strain and Temperature Dependence of Liquid Crystalline Order in Elastomers, D.M. Agra-Kooijman, S. Dey, L. Joshi, and S. Kumar, 16th National LC Conference, Lucknow, India, Oct. 26-28 (2009). |
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Publications and Presentations |
