Electrochromic devices have seen widespread adoption in the automotive and aerospace industries and are increasingly considered for applications in the built environment, such as smart windows. Here, a distinctive approach is reported to realizing electrochromism in solid, polymeric materials. The optical elements are based on liquid crystalline elastomers (LCEs) that retain the cholesteric phase (CLCEs). By integrating flexible, optically transparent, and conductive electrodes the CLCEs are actuated as dielectric elastomer actuators. Application of an electric field causes a significant change in the reflection wavelength of fully solid CLCE. The electromechanical response (Maxwell stresses) is reversible. Both uniaxial and biaxial prestrain are shown to enhance and differentiate the stimuli‐response in the photonic device.
This content will become publicly available on May 1, 2025
The electrically‐directed, isothermal response of liquid crystal elastomers (LCEs) to an applied electric field is a compelling approach to realize spatially tailorable, sequence‐controllable, and high‐frequency deformation. The electromechanical response is facilitated by coating aligned LCEs with compliant electrodes. Upon application of an electric field, the electrodes attract and generate Maxwell stress. The directional difference in moduli for aligned LCEs produces directional deformation of the material and does not require mechanical bias or framing. Here, LCEs prepared from a newly reported thiol‐ene reaction are explored as DEAs with improved mechanical and dielectric properties. This report details that incorporating a difunctional liquid crystalline monomer composed of allyl ether functional groups reduces Young's modulus, increases the dielectric constant, and improves cyclic recovery compared to an analogous LCE prepared by thiol‐ene polymerization. Electrically‐induced, isothermal deformation of as much as 30% strain is reported. The facile chemistry and enhanced electromechanical response reported here may enable the functional integration of LCEs in applications such as robotics.
more » « less- Award ID(s):
- 2105369
- PAR ID:
- 10530660
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials Technologies
- Volume:
- 9
- Issue:
- 9
- ISSN:
- 2365-709X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Liquid crystalline elastomers (LCEs) are stimuli‐responsive materials capable of undergoing large deformations. The thermomechanical response of LCEs is attributable to the coupling of polymer network properties and disruption of order between liquid crystalline mesogens. Complex deformations have been realized in LCEs by either programming the nematic director via surface‐enforced alignment or localized mechanical deformation in materials incorporating dynamic covalent chemistries. Here, the preparation of LCEs via thiol‐Michael addition reaction is reported that are amenable to surface‐enforced alignment. Afforded by the thiol‐Michael addition reaction, dynamic covalent bonds are uniquely incorporated in chemistries subject to surface‐enforce alignment. Accordingly, LCEs prepared with complex director profiles are able to be programmed and reprogrammed by (re)activating the dynamic covalent chemistry to realize distinctive shape transformations.
-
more » « less
ABSTRACT Electrically induced mechanical stress was produced on a monolithic polycarbonate (PC) film when subjected to an instantaneous direct current voltage using a needle‐plane electrode setup. Three different experimental methods were used to investigate the electrically induced mechanical deformation on the glassy PC film, namely, morphological observation, energy loss analysis, and dielectric hysteresis study. It was found that the PC film exhibited elastic behavior at the nominal electric field below 200 MV m−1, showing no indentation on the film surface. When the nominal field was above 200 MV m−1, a spherical indentation was created. The depth and diameter of the deformation increased in response to the applied electric field. Subsequent thermal annealing of the deformed film revealed a recoverable “delayed elastic” and an unrecoverable “plastic” deformation. A three‐stage electrically induced mechanical deformation mechanism was proposed based on the experimental results, including a correlation between the energy loss and the deformed volume. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.
2020 ,137 , 48341. -
Liquid crystal elastomers (LCEs) are made of liquid crystal molecules integrated with rubber-like polymer networks. An LCE exhibits both the thermotropic property of liquid crystals and the large deformation of elastomers. It can be monodomain or polydomain in the nematic phase and transforms to an isotropic phase at elevated temperature. These features have enabled various new applications of LCEs in robotics and other fields. However, despite substantial research and development in recent years, thermomechanical coupling in polydomain LCEs remains poorly studied, such as their temperature-dependent mechanical response and stretch-influenced isotropic-nematic phase transition. This knowledge gap severely limits the fundamental understanding of the structure-property relationship, as well as future developments of LCEs with precisely controlled material behaviors. Here, we construct a theoretical model to investigate the thermomechanical coupling in polydomain LCEs. The model includes a quasi-convex elastic energy of the polymer network and a free energy of mesogens. We study the working conditions where a polydomain LCE is subjected to various prescribed planar stretches and temperatures. The quasi-convex elastic energy enables a “mechanical phase diagram” that describes the macroscopic effective mechanical response of the material, and the free energy of mesogens governs their first-order nematic-isotropic phase transition. The evolution of the mechanical phase diagram and the order parameter with temperature is predicted and discussed. Unique temperature-dependent mechanical behaviors of the polydomain LCE that have never been reported before are shown in their stress-stretch curves. These results are hoped to motivate future fundamental studies and new applications of thermomechanical LCEs.more » « less
-
more » « less
Abstract In our previous study, electrically induced mechanical stress was produced on monolithic polycarbonate (PC) films under a DC voltage using a needle‐plane electrode setup. This study investigated other materials with various structures and dielectric constants, in order to further understand the deformation mechanism. It was found that the elastic behavior occurred at electric fields intensities below that initiating measurable surface deformation. The amorphous materials, PS, and the semi‐crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar observable deformation onset electric field at 200 MV/m. While PVDF, having a dielectric constant of 10.0–12.0, showed an onset at only 30 MV/m. The data was also compared to our previous study on PC. The depth and diameter of the deformation for all materials increased relative to the applied electric field up to film breakdown. Thermal annealing of the deformed films revealed a recoverable “delayed elastic” component and an irreversible “plastic” component. A three‐stage electrically induced mechanical deformation mechanism was proposed for amorphous materials, while a two‐stage mechanism was proposed for the semi‐crystalline materials. The difference on the energy loss versus deformed volume for amorphous and semi‐crystalline polymers was also determined and discussed.
