AI 中文总结
该研究通过计算机模拟发现，交联剂浓度约1%的微凝胶在体积相变附近出现负泊松比特性，超低交联微凝胶的负泊松比为其固有属性，有望推动相关实验验证。
AI 中文摘要
负泊松比（auxetic behavior）是一种表现为负泊松比的反常力学响应，除其他体系外，特定聚合物网络也会呈现该特性。本文通过计算机模拟研究了热响应微凝胶在体积相变过程中，交联剂浓度变化（直至超低条件）下的力学响应，该超低交联剂（ULC）浓度区域此前尚未被探索。针对极具挑战性的ULC情况——即非常稀疏且形状各向异性的网络，我们优化了基于平衡形状涨落估算弹性模量的方法，最终证明交联剂浓度约为1%的微凝胶在体积相变附近会出现负泊松比特性。此外，我们发现ULC微凝胶在整个溶胀区间内呈现轻微的负泊松比。进一步检查网络内部区域的负泊松比响应后，我们还证明ULC微凝胶的该特性在所有长度尺度上均存在，表明其是弱连接聚合物网络的固有属性。本研究结果有望推动新的实验研究，旨在测量单个低及超低交联微凝胶的泊松比，以验证这些有趣的数值预测。
英文摘要
Auxetic behavior, characterized by a negative Poisson's ratio, is a counterintuitive mechanical response exhibited, among other systems, by certain polymer networks. Here, through in silico simulations we investigate the mechanical response of thermoresponsive microgels across the volume phase transition upon varying crosslinker concentration down to ultralow conditions, a regime so far unexplored. After refining the method to estimate the elastic moduli based on equilibrium shape fluctuations for the challenging case of ULCs, which are very sparse networks with rather anisotropic shape, we are able to show the onset of auxetic behavior near the volume phase transition for microgels with crosslinker concentration of ~ 1%. In addition, we find that ULC microgels exhibit a slightly negative Poisson's ratio across the whole swollen regime. Further examining the auxetic response within the inner region of the network, we also demonstrate that, for ULC microgels, this extends at all length scales, suggesting that it is an intrinsic property of the weakly connected polymer network. The present findings should likely stimulate novel experimental investigations, aiming to measure the Poisson's ratio of individual low and ultralow crosslinked microgels, to verify these intriguing numerical predictions.
