Isomerization kinetics of azobenzene crosslinked to a liquid crystal polymer network
- Indian Inst. of Technology (IIT), Madras (India); University of Toulouse (France); Université Toulouse III-Paul Sabatier (France); Centre National de la Recherche Scientifique (CNRS), Toulouse (France). Laboratoire Softmat
- Indian Inst. of Technology (IIT), Madras (India); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Indian Inst. of Technology (IIT), Madras (India)
Azobenzene is an important chromophore having numerous applications that are a direct implication of its ability to change shape upon irradiation with a suitable wavelength. Here, in this study, photoisomerization kinetics of a diacrylate azobenzene molecule (A3MA) cross-linked to a liquid crystal polymer network (LCN) is investigated. Isomerization experiments were conducted on planar LCN thin films with varying cross-linking densities for a fixed azobenzene concentration. The experiments were conducted at approximately 26 °C, which is significantly below each film’s glass transition temperature. The forward trans-cis and reverse cis-trans isomerization slows down in crosslinked azobenzene liquid crystal polymer networks (ALCNs) as compared to a solution and an uncrosslinked polymer mixture. The observed slowdown is due to the reduction in the free volume and increased steric hindrances with an increase in crosslinking. A single-term first-order kinetics rate equation is known to describe the isomerization kinetics in solutions or uncrosslinked mixtures while the same form fails to represent the reaction kinetics in moderate to highly cross-linked ALCNs. Our results for the first time indicate that a two-term first-order reaction rate is an accurate way to describe the forward trans-cis and reverse thermal cis-trans isomerization in crosslinked azobenzene liquid crystal polymer networks. In addition, the effect of film thickness and incident intensities on the reaction kinetics is investigated. Finally, the two-term isomerization kinetics is incorporated into a finite element photo-chemo-mechanical model to reveal the consequent slowdown in the actuation response of ALCN films. The current findings will be of particular interest to theoreticians and experimentalists alike, for it will help predict and understand accurately the responses of azobenzene-based coatings, and actuators and may have potential applications in underwater soft robotics.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- Grant/Contract Number:
- 89233218CNA000001
- OSTI ID:
- 2589868
- Report Number(s):
- LA-UR--24-31290; 10.1016/j.polymer.2025.129057
- Journal Information:
- Polymer, Journal Name: Polymer Vol. 339; ISSN 0032-3861
- Publisher:
- Elsevier BVCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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