Viscoelastic necking dynamics between attractive microgels
Viscoelastic necking dynamics between attractive microgels
复制标题
有吸引力的微凝胶之间的粘弹性颈缩动力学
DOI：
10.1016/j.jcis.2022.03.048
复制
发表时间：
2022
影响因子：
9.9
通讯作者：
Yong, Xin
中科院分区：
文献类型：
--
作者：
Chen, Shensheng;Pirhadi, Emad;Yong, Xin
假设微凝胶可以变形和互穿，并表现出胶体/聚合物的二元性。微凝胶在崩塌状态下的有效相互作用是由聚合物-溶剂界面张力和体弹性的相互作用决定的。连接颈被证明介导微凝胶相互作用，但其时间进化尚未得到解决。我们假设吸引微凝胶的颈缩动力学在不同的时间和长度尺度上表现出液体或固体样的行为。实验用耗散粒子动力学模拟了不同交联密度的吸引微凝胶在显式溶剂中的合并和挤压。研究了微凝胶的时间聚结动力学，并与简单液体和聚合物液滴进行了比较。我们利用聚合物弛豫的Maxwell模型对长时间尺度的颈部生长进行了建模，并将理论预测与模拟数据进行了比较。颈部的机械强度通过操纵分子动力学模拟微凝胶的掐断来系统地表征。研究结果表明，在聚结动力学中存在交叉反应，反映了微凝胶的粘弹性特征。与粘弹性材料在短时间尺度上的弹性反应不同，微凝胶颈部的早期膨胀表现为线性行为，类似于液滴的粘性聚结。然而，动力学阻滞的后期状态类似于固体颗粒的烧结。通过将微凝胶动力学与颈部生长联系起来的分析模型，我们表明，长期行为是由颈部区域聚合物的应力松弛控制的，并预测了生长速率的指数衰减，这与模拟结果非常吻合。与聚结不同的是，微凝胶破碎过程中丝线变薄主要体现了微凝胶的聚合特性。
HypothesisMicrogels can deform and interpenetrate and display colloid/polymer duality. The effective interaction of microgels in the collapsed state is governed by the interplay of polymer–solvent interfacial tension and bulk elasticity. A connecting neck is shown to mediate microgel interaction, but its temporal evolution has not been addressed. We hypothesize that the necking dynamics of attractive microgels exhibits liquid-like or solid-like behavior over different time and length scales.ExperimentsWe simulate the merging and pinching of attractive microgels with different crosslinking densities in explicit solvent using dissipative particle dynamics. The temporal coalescence dynamics of microgels is investigated and compared with simple liquid and polymeric droplets. We model the neck growth on long time scales using Maxwell model of polymer relaxation and compare the theoretical prediction with simulation data. The mechanical strength of the neck is characterized systematically via simulated pinch-off of microgels by steered molecular dynamics.FindingsWe evidence a crossover in the coalescence dynamics reflecting the viscoelastic signature of microgels. In contrast to the common knowledge that viscoelastic materials respond elastically on short time scales, the early expansion of the microgel neck exhibits a linear behavior, similar to the viscous coalescence of liquid droplets. However, the late regime with arrested dynamics resembles sintering of solid particles. Through an analytical model relating microgel dynamics to neck growth, we show that the long-term behavior is governed by stress relaxation of the polymers in the neck region and predict an exponential decay in the rate of growth, which agrees favorably with the simulation. Different from coalescence, the thread thinning in microgel breakup primarily highlights its polymeric characteristics.