Session: VIB-01/MSNDC-08-03

Paper Number: 148391

148391 - Photomechanical Actuation of Fibers 

The design of remotely activated untethered devices without onboard power is a continuing challenge in soft robotics. Photomechanical liquid crystal elastomers (LCEs) can convert light directly into mechanical deformation, making them attractive candidates for soft actuators capable of remote and multi-mode actuation. This presentation describes a method of generating periodic motions in pre-stressed photomechanical liquid crystal elastomer fibers using steady illumination (constant light intensity and direction) that can be exploited for propulsion and mixing. LCEs are rubbery networks composed of crosslinked polymer chains that contain liquid-crystalline mesogens in their main or inside chains. LCEs containing light-sensitive molecules, such as azobenzene (azo) photochromes, exhibit a reversible photomechanical behavior: they absorb light energy and convert it into mechanical energy by changing their shape. This fascinating photomechanical effect arises from the trans-cis isomerization of azobenzene dyes, a process in which the azo molecules absorb light energy and change their conformation from a linear trans isomer to a bent cis isomer. The steric interaction between the azo and LC molecules consequently changes the LC ordering leading to a photo-induced shape change. Upon removing the light, the cis isomers thermally relax to the trans state leading to a reversal of the photo-induced shape change. Recent works demonstrate the potential of photomechanical materials for soft robotics because of their remarkable features: 1) properly synthesized photomechanical materials can undergo large, reversible deformation upon light irradiation, 2) these materials are lightweight and soft, and hence, appropriate to generate flexible motion in soft robotics, 3) light is a clean power source that can actuate a photomechanical object from distance, thereby eliminating the need for on-board power or tethers, and 4) light-induced deformations can be controlled by changing light intensity, wavelength, or polarization thereby providing a platform for multiplexing and control. In this study, we develop a theoretical framework to investigate the dynamical response of the pre-stressed LCE fibers under illumination. We build the model by coupling the three-dimensional Kirchhoff rod theory with the microscale photochemical reaction of azobenzene photochromes. We use the model to show that pre-stressed fibers immersed in a fluid can undergo periodic motion under steady illumination. We show that such motion can be exploited in developing remotely controlled bio-inspired micro-swimmers and novel micromixers. We analyze the photo-driven spatiotemporal pattern and stability of the periodic deformation and provide a parametric study. Finally, we show that we can control the photo-response using illumination conditions (light intensity and direction), pre-stressed configuration of fiber (twist and bending), and cross-sectional shape (circular and rectangular). These provide opportunities to design micro-actuators for different conditions, and for control. Together, the model and the results open a new avenue for the development of remotely actuated and controlled soft actuators.

 

Presenting Author: Neda Maghsoodi University of Southern California

Presenting Author Biography: Neda Maghsoodi is an Assistant Professor of Aerospace and Mechanical Engineering at the University of Southern California (USC). Before joining USC in 2023, Neda pursued her postdoctoral research at the California Institute of Technology, Department of Mechanical and Civil Engineering (2021-2022) and Harvard University, Department of Molecular and Cellular Biology (2019-2020). She received her Ph.D. in Mechanical Engineering (2019) and M.Sc. in Biomedical Engineering (2017) from the University of Michigan-Ann Arbor. Neda’s research lies at the interface of applied mechanics, materials science, and biology. She employs a combination of theory, experiment, and simulation to elucidate the dynamics of soft biological structures and soft active materials.

Authors:

Neda Maghsoodi University of Southern California