聚电解质水凝胶在空间非均匀电场下的收缩响应
Contraction response of a polyelectrolyte hydrogel under spatially nonuniform electric fields
AI总结：
本研究通过粗粒化分子动力学模拟揭示了聚电解质水凝胶在空间非均匀正弦电场下的可逆单轴收缩行为，发现可通过调节电场参数控制收缩效率，为快速柔性致动组件提供了新方法。
摘要：
当代材料科学面临的主要挑战之一是构建能够模拟响应性生物组织（如人造皮肤和肌肉）的合成结构。聚电解质水凝胶在外部电场下能够提供此类机电响应。然而，它们对这类刺激的响应，特别是在分子尺度上，尚未被完全揭示。在此，我们通过广泛的粗粒化分子动力学模拟，研究了半无限聚电解质水凝胶板对瞬态和空间非均匀正弦电场的机械响应。我们的模拟表明，如果电场施加在水凝胶板的一个小体积区域上，整个水凝胶板将在垂直于电场的方向上发生可逆且单轴的收缩。水凝胶收缩至几乎其无场初始长度的一半，随后恢复至原始尺寸，最终其尺寸波动呈类似的指数衰减。当电场施加在水凝胶板边界以外的区域时，收缩达到最大。此外，通过调节电场频率和振幅，可以控制收缩时间和效率。利用隐式溶剂模拟，对不同静电参数和盐浓度下的收缩时间和效率进行分析，证实了该现象的鲁棒性，同时突出了流体动力学的重要性。我们的结果证明了空间非均匀电场在操控均质水凝胶结构方面的有效性，适用于需要快速柔性致动组件的应用场景。
英文摘要：
One of the major challenges in contemporary materials science is to build synthetic structures that can mimic responsive biological tissues, such as artificial skins and muscles. Polyelectrolyte hydrogels can provide such mechanoelectrical responses under external electric fields. Yet, their response to such stimuli, particularly at the molecular scales, is not fully revealed. Here, we study the mechanical response of a semi-infinite polyelectrolyte hydrogel slab to transient and spatially nonuniform sinusoidal electric fields by using extensive coarse-grained molecular dynamics simulations. Our simulations show that if the electric field is exerted on a small volumetric section of the hydrogel slab, the entire slab contracts reversibly and uniaxially in the direction perpendicular to the field. The hydrogel contracts almost half of its field-free initial length before retracting its original size, and eventually, its size fluctuations decay similarly exponentially. A contraction maximises when the electric field is applied away from the boundaries of the hydrogel slab. Further, by tuning the electric field frequency and amplitude, both contraction times and efficiency can be controlled. Analyses of contraction times and efficiency with implicit solvent simulations for various electrostatic parameters and salt concentrations confirm the robustness of the phenomenon while highlighting the importance of hydrodynamics. Our results demonstrate the effectiveness of spatially nonuniform electric fields' effectiveness in manipulating homogenous hydrogel structures for applications requiring rapid and soft actuation components.
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