Neda Maghsoodi

ABSTRACT Liquid crystal elastomers (LCEs) combine molecular anisotropy with elastic softness, enabling programmable and reversible shape transformations that make them promising candidates for soft robotics. However, achieving localized, rapid, and remotely controlled actuation of LCEs without embedded components is a continuing challenge. Here, we introduce focused ultrasound (FUS) as a non‐invasive stimulus for remotely actuating pre‐programmed LCEs. We demonstrate that a pre‐programmed LCE strip exposed to FUS undergoes rapid and reversible bending deformation driven by a localized acousto‐thermomechanical effect, wherein acoustic energy is converted into heat within the viscoelastic network, triggering the nematic–isotropic transition and inducing contraction along the nematic director. We characterize the FUS‐induced temperature field and dynamic response to reveal how the LCE geometry, crosslinking density, and ultrasound parameters govern the actuation kinetics. The results expose three key advantages: ultrasound enables remote and wireless actuation; the response relies solely on the intrinsic viscoelasticity of the LCE– without the need to embed optical or magnetic components in LCEs; and the spatiotemporal tunability of FUS allows localized and sequential activation within LCEs. Together, these findings establish an acoustic‐based actuation paradigm for LCEs, paving the way toward intelligent, reconfigurable, and remotely powered soft robotic systems.

Abstract This paper investigates the effect of intrinsic (built-in) bending curvature on the dynamics, energetics, and stability of photomechanical fibers, which deform in response to illumination. We develop a multiphysics dynamic model based on the nonlinear Kirchhoff's rod theory to capture the coupled photomechanical response of the curved fibers. Using two canonical examples—the bending of a clamped-free strip and the periodic flapping of a clamped–clamped strip—we demonstrate how intrinsic curvature fundamentally affects the spatiotemporal deformation of the strips subject to steady illumination. Our findings reveal that the dynamic behavior of intrinsically curved photomechanical fibers differs both qualitatively and quantitatively from their intrinsically flat counterparts, underscoring the importance of initial geometry in the design and control of photomechanical systems. In particular, in the case of the clamped–clamped strips, although both the prestressed strip and stress-free curved strip exhibit self-sustained periodic flapping motions when subject to steady illumination, the stress-free curved strip requires higher input energy (i.e., greater light intensity), oscillates at a lower frequency, and exhibits a largely asymmetric deformation pathway per cycle. Moreover, the range of illumination angles that can trigger self-sustained oscillations in stress-free curved strips is narrower compared to the prestressed case.

Abstract Curved fibers (beams or strips) play essential functional roles in micro-devices such as valves, clips, threshold switches, and memory cells. Fabricating stress-free curved fibers, as opposed to pre-stressed ones, can be more cost-effective and practical for bulk manufacturing; however, their dynamic behavior may be significantly influenced by their intrinsic (built-in) geometry. This study investigates the effect of intrinsic bending curvature on the dynamics, energetics, and stability of photomechanical fibers, which deform in response to illumination. We develop a multi-physics dynamic model based on the nonlinear Kirchhoff’s rod theory to capture the coupled photomechanical response of the curved fibers. Using two canonical examples—the bending of a clamped-free strip and the periodic flapping of a clamped-clamped strip—we demonstrate how intrinsic curvature fundamentally affects the spatiotemporal deformation of the strips subject to steady illumination. Our findings reveal that the dynamic behavior of intrinsically curved photomechanical fibers differs both qualitatively and quantitatively from their intrinsically flat counterparts, underscoring the importance of initial geometry in the design and control of photomechanical systems. In particular, in the case of the clamped-clamped strips, although both the pre-stressed strip and stress-free curved strip exhibit self-sustained periodic flapping motions when subject to steady illumination, the stress-free curved strip requires higher input energy (i.e., greater light intensity), oscillates at a lower frequency, and exhibits a largely asymmetric deformation pathway per cycle. Moreover, the range of illumination angles that can trigger self-sustained oscillations in stress-free curved strips is narrower compared to the pre-stressed case.

Reversible dry adhesion is exploited by lizards and insects in nature, and is of interest to robotics and bio-medicine. In this paper, we use numerical simulation to study how the soft elasticity of liquid crystal elastomers can affect its adhesion and provide a technological opportunity. Liquid crystal elastomers are cross-linked elastomer networks with liquid crystal mesogens incorporated into the main or side chain. Polydomain liquid crystalline (nematic) elastomers exhibit unusual mechanical properties like soft elasticity, where the material deforms at nearly constant stress, due to the reorientation of mesogens. Our study reveals that the soft elasticity of nematic elastomers dramatically affects the interfacial stress distribution at the interface of a nematic elastomer cylinder adhered to a rigid substrate. The stress near the edge of the nematic cylinder under tensile load deviates from the singular behavior predicted for linear elastic materials, and the maximum normal stress reduces dramatically. This suggests that nematic elastomers should display extremely high, but controllable adhesion, consistent with the available experimental observations.

Optomechanical materials directly generate work from light through physical deformation upon illumination. Here, we report an optical fiber-based optomechanical actuator that undergoes bending when illuminated by actinic light. A model for light-induced bending curvature as a function of geometrical and material properties was developed to aid in design. Polymer fibers were fabricated and filled directly during the draw with a molten azobenzene derivative. Upon illumination, photoactivated motion is observed and quantified with an optical lever beam approach.