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Extreme Mechanics of Soft Functional Materials
August 16, 2022 @ 6:00 pm - 7:00 pm PDT
Free – $5
- Prof. Lihua Jin, Mechanical and Aerospace Engineering, University of California, Los Angeles
- Sponsored by the Golden Gate Polymer Forum
- August 16, 6-7pm, Online via Zoom, Free/$5 Donation, Registration required (Deadline Aug. 15@1pm)
Soft robotics and stretchable electronics are transforming the fields of robotics and biomedical devices, in that they are capable of sustaining large deformation and interacting safely with fragile objects and human beings. Soft functional materials, as the building blocks of soft robotics and stretchable electronics, are typically subjected to extreme mechanical conditions, such as large deformation, cyclic loading, and fracture. In this seminar, I will present our recent progress in modeling and charactering extreme mechanics of soft functional materials. Liquid crystal elastomers (LCEs) are special polymers combining cross-linked elastomers with rod-like liquid crystal mesogens, aligning in a certain direction, called the director. Combining theory and experiments, we show that the directors of a LCE can reorient with stress in a highly rate-dependent manner. We further investigate the coupling between stress and director fields at a crack tip, and observe significant and highly inhomogeneous director rotation, resulting in crack-tip stress and strain distributions of LCEs distinct from those of regular elastomers. Stretchable carbon nanotube electrodes are used in various stretchable electronic devices. When deformed, they show characteristic resistance–strain hysteresis. We use coarse-grained molecular simulations together with experiments to unravel the microstructural origin of the resistance–strain hysteresis. Finally, we study fracture of thin conducting/semiconducting films. We have developed a new testing methodology to measure the fracture energy of free-standing ultrathin films. We further demonstrate that the fracture strain of a thin film is not an intrinsic material property, but can be significantly augmented by tuning interfacial properties.
Speaker Background & Research Interests:
Lihua Jin is an assistant professor in the Department of Mechanical and Aerospace Engineering at the University of California, Los Angeles (UCLA). Before joining UCLA in 2016, she was a postdoctoral scholar at Stanford University. In 2014, she obtained her PhD degree in Engineering Sciences from Harvard University. Prior to that, she earned her Bachelor’s and Master’s degrees from Fudan University in 2006 and 2009. Jin’s group conducts research on mechanics of soft materials, stimuli-responsive materials, instability and fracture, soft robotics, and biomechanics. Lihua was the winner of Haythornthwaite Research Initiative Grant from American Society of Mechanical Engineers in 2016, Extreme Mechanics Letters Young Investigator Award in 2018, Hellman Fellowship in 2019, UCLA Faculty Career Development Award in 2020, and NSF CAREER Award in 2021.