热可逆微凝胶中刚度依赖的介电弛豫：温度与应变的影响
Stiffness-dependent Dielectric Relaxation in Thermoreversible Microgels: Effects of Temperature and Strain
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中文总结 AI 辅助
本研究通过介电谱与流变测量，揭示PNIPAM微凝胶刚度调控微观与宏观弛豫动力学，为设计自适应软材料提供框架。
中文摘要 AI 辅助
我们研究了在温度变化和大振幅振荡剪切作用下，热响应性PNIPAM微凝胶致密悬浮液中，粒子刚度如何控制与长度尺度相关的弛豫动力学。通过将介电谱与流变测量相结合，我们直接将微观极化涨落动力学与宏观力学弛豫关联起来。高度交联、较硬的微凝胶在较宽的温度范围内表现出更长的介电弛豫时间，并出现应变诱导的减慢现象，而较软、开网络结构的微凝胶则表现出几乎与应变无关的介电动力学。在体积相变温度（VPTT）以下，宏观体积应力弛豫实验表明，最软粒子的悬浮液弛豫最快。然而，对于较硬的微凝胶悬浮液，动力学发生解耦：体积应力弛豫随刚度增加而加快，而介电弛豫却减慢。在VPTT以上，较软的粒子经历更大的体积塌缩，导致非常快速的体积应力弛豫。除了表现出较慢的应力衰减外，较硬的微凝胶悬浮液在变形后期还经历剪切诱导的结构再生。这些发现表明，粒子刚度和内部结构控制了微观和宏观长度尺度上的弛豫路径，从而为设计自适应软超材料、应力耗散涂层和自修复机器人材料提供了框架。
英文摘要
We investigate how particle stiffness governs length-scale-dependent relaxation dynamics in dense suspensions of thermoresponsive PNIPAM microgels subjected to temperature variations and large amplitude oscillatory shear. By combining dielectric spectroscopy with rheometric measurements, we directly correlate microscopic polarization fluctuation dynamics with macroscopic mechanical relaxation. Highly crosslinked, stiffer microgels exhibit longer dielectric relaxation times across a broad temperature range and strain-induced slowing down, whereas softer, open-network microgels exhibit nearly strain-independent dielectric dynamics. Below the volume phase transition temperature (VPTT), macroscopic bulk stress relaxation experiments reveal that suspensions of the softest particles relax most rapidly. For the stiffer microgel suspensions, however, the dynamics decouple: bulk stress relaxation speeds up with increasing stiffness even as dielectric relaxation slows down. Above the VPTT, softer particles undergo greater volume collapse, leading to very rapid bulk stress relaxation. Besides exhibiting slower stress decay, stiffer microgel suspensions also undergo shear-induced structural regeneration during the later stages of deformation. These findings demonstrate that particle stiffness and internal architecture govern relaxation pathways across microscopic and macroscopic length scales, thereby providing a framework for designing adaptive soft metamaterials, stress-dissipative coatings, and self-healing robotic materials.
发表机构
- Raman Research Institute（拉曼研究所）
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