Norouzikudiani Reza, Teresi Luciano, DeSimone Antonio
BioRobotics Institute, Scuola Superiore Sant'Anna, Viale Rinaldo Piaggio 34, Pontedera, Italy.
Dipartimento di Ingegneria Industriale, Elettronica e Meccanica, University Roma Tre, via della Vasca Navale 84, Rome, Italy.
J Elast. 2024;156(4-5):1243-1260. doi: 10.1007/s10659-024-10091-8. Epub 2024 Oct 9.
Liquid Crystal Elastomers (LCEs) are responsive materials that undergo significant, reversible deformations when exposed to external stimuli such as light, heat, and humidity. Light actuation, in particular, offers versatile control over LCE properties, enabling complex deformations. A notable phenomenon in LCEs is self-oscillation under constant illumination. Understanding the physics underlying this dynamic response, and especially the role of interactions with a surrounding fluid medium, is still crucial for optimizing the performance of LCEs. In this study, we have developed a multi-physics fluid-structure interaction model to explore the self-oscillation phenomenon of immersed LCE beams exposed to light. We consider a beam clamped at one end, originally vertical, and exposed to horizontal light rays of constant intensity focused near the fixed edge. Illumination causes the beam to bend towards the light due to a temperature gradient. As the free end of the beam surpasses the horizontal line through the clamp, self-shadowing induces cooling, initiating the self-oscillation phenomenon. The negative feedback resulting from self-shadowing injects energy into the system, with sustained self-oscillations in spite of the energy dissipation in the surrounding fluid. Our investigation involves parametric studies exploring the impact of beam length and light intensity on the amplitude, frequency, and mode of oscillation. Our findings indicate that the self-oscillation initiates above a certain critical light intensity, which is length-dependent. Also, shorter lengths induce oscillations in the beam with the first mode of vibration, while increasing the length changes the elasticity property of the beam and triggers the second mode. Additionally, applying higher light intensity may trigger composite complex modes, while the frequency of oscillation increases with the intensity of the light if the mode of oscillation remains constant.
液晶弹性体（LCEs）是一种响应性材料，当暴露于光、热和湿度等外部刺激时，会发生显著的、可逆的变形。特别是光驱动，能够对LCE的性能进行多种控制，实现复杂的变形。LCEs中一个值得注意的现象是在恒定光照下的自振荡。理解这种动态响应背后的物理原理，尤其是与周围流体介质相互作用的作用，对于优化LCE的性能仍然至关重要。在本研究中，我们开发了一个多物理场流固耦合模型，以探索浸没在液体中的LCE梁在光照下的自振荡现象。我们考虑一根一端固定的梁，最初是垂直的，暴露在聚焦于固定边缘附近的恒定强度的水平光线下。光照由于温度梯度使梁向光弯曲。当梁的自由端超过通过夹具的水平线时，自遮挡会导致冷却，从而引发自振荡现象。自遮挡产生的负反馈将能量注入系统，尽管周围流体存在能量耗散，但仍能持续自振荡。我们的研究包括参数研究，探索梁的长度和光强度对振荡幅度、频率和模式的影响。我们的研究结果表明，自振荡在一定的临界光强度以上开始，该临界光强度与长度有关。此外较短的长度会使梁以第一振动模式产生振荡，而增加长度会改变梁的弹性特性并触发第二模式。此外，施加更高的光强度可能会触发复合复杂模式，而如果振荡模式保持不变，振荡频率会随着光强度的增加而增加。
