2025 SES James R. Rice Medal Lecture

Modeling the Complex Thermoviscoelastic Response of Monodomain Liquid Crystal Elastomers

Liquid crystalline elastomers (LCEs), composed of mesogens bound in an elastomeric network, combine the anisotropic self-ordering behavior of liquid crystals with the dissipative viscoelastic behavior of the polymer network. This synergy produces unique behaviors, including temperature-activated large reversible shape changes, a rate-dependent soft stress response, and enhanced dissipation compared to traditional elastomers. A broad range of functionalities can be programmed by patterning the local mesogen alignment, such as reversible shape morphing, actuation, and energy absorption. To facilitate the design and optimization of LCE actuators and shape-morphing devices, we have developed a thermoviscoelastic model for LCEs based on a novel viscoelastic microstretch theory that describes the coupled mechanisms of viscous mesogen ordering, viscous director rotation, and viscoelastic network deformation. To demonstrate the behavior of this coupled theory, we specified evolution equations for the order parameter, director orientation, and viscous deformation gradient; applied the neoclassical potentials for the equilibrium and nonequilibrium free energy densities of the network; and utilized the Frank energies for the gradient of the director and order parameter fields. The model was implemented in COMSOL and used to investigate the effects of heating/cooling rates and preload on the deformation response of various patterned LCE structures during the nematic-isotropic transition. 

Bio of the speaker: Thao (Vicky) Nguyen received her S.B. from MIT in 1998, and M.S. and Ph.D. from Stanford in 2004, all in mechanical engineering. She was a research scientist at Sandia National Laboratories in Livermore from 2004- 2007 before joining Johns Hopkins University, where she is currently a Professor in Mechanical Engineering with secondary appointments in Materials Science and Engineering and Ophthalmology. She is also Deputy Director of the Hopkins Extreme Materials Institute. Dr. Nguyen’s research encompasses the mechanics of soft tissues, stimuli-responsive soft materials, and engineering polymers. Her lab currently studies the biomechanics of the optic nerve head in glaucoma, the mechanics of recycled polymers, and the mechanical behavior of liquid crystal elastomers and DNA hydrogels. Dr. Nguyen has received numerous awards, including the  2008 Presidential Early Career Award for Scientists and Engineers (PECASE) and the NNSA Office of Defense Programs Early Career Scientists and Engineer Awards for her work on modeling the thermomechanical behavior of shape memory polymers. In 2013, she received the NSF CAREER award for studying the micromechanisms of growth and remodeling of collagenous tissues, the Eshelby Mechanics Award for Young Faculty, and the Sia Nemat-Nasser Early Career Medal from the Materials Division of ASME.  She received the T.J.R. Hughes Young Investigator Award from the ASME Applied Mechanics Division in 2015, the Van C. Mow Medal from the ASME Bioengineering Division in 2024, and the James R. Rice Medal from the Society of Engineering Science and the Centennial Mid-Career Award from the ASME Materials Division in 2025.  She is a Fellow of ASME and the American Institute for Medical and Biological Engineering (AIMBE). She served as the President of the Society of Engineering Science (SES) in 2020 and is currently the  Editor-in-Chief of the Journal of Biomechanical Engineering.