Mechanical deformations of a liquid crystal elastomer at director angles between 0° and 90°: Deducing an empirical model encompassing anisotropic nonlinearity

• Published in: Journal of polymer science. Part B, Polymer physics Vol. 57; no. 20; pp. 1367 - 1377
• Main Authors: Mistry, Devesh, Gleeson, Helen F.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 15.10.2019; Wiley Subscription Services, Inc
• Subjects: anisotropic elasticity; Anisotropy; Deformation; Elastomers; empirical model; liquid crystal elastomer; Liquid crystals; Mechanical analysis; Mechanical properties; nonlinear elasticity; Nonlinearity; Polymer physics; Rotating liquids; Strain; Tensile tests
• DOI: 10.1002/polb.24879
• ISSN: 0887-6266

ABSTRACT Despite the wealth of studies reporting mechanical properties of liquid crystal elastomers (LCEs), no theory can currently describe their complete mechanical anisotropy and nonlinearity. Here, we present the first comprehensive study of mechanical anisotropy in an all‐acrylate LCE via tensile tests that simultaneously track liquid crystal (LC) director rotation. We then use an empirical approach to gain a deeper insight into the LCE's mechanical responses at values of strain, up to 1.5, for initial director orientations between 0° and 90°. Using a method analogous to time–temperature superposition, we create master curves for the LCE's mechanical response and use these to deduce a model that accurately predicts the load curve of the LCE for stresses applied at angles between 15° and 70° relative to the initial LC director. This LCE has been shown to exhibit auxetic behavior for deformations perpendicular to the director. Interestingly, our empirical model predicts that the LCE will further demonstrate auxetic behavior when stressed at angles between 54° and 90° to the director. Our approach could be extended to any LCE; so it represents a significant step forward toward models that would aid the further development of LCE theory and the design and modeling of LCE‐based technologies. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1367–1377 A comprehensive study of the mechanical anisotropy and nonlinearity of a liquid crystal elastomer was performed, and an empirical model which describes a wide range of the material's tensile mechanical behaviour was developed. The methods and model developed will aid the future design and development of LCE‐based mechanical devices.