Rheo-Optical Study on the Viscoelastic Relaxation Modes of a Microgel Particle Suspension around the Liquid?Solid Transition Regime
Rheo-Optical Study on the Viscoelastic Relaxation Modes of a Microgel Particle Suspension around the Liquid?Solid Transition Regime
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微凝胶颗粒悬浮液液-固转变体系粘弹性弛豫模式的流变光学研究
DOI：
10.1021/acs.macromol.0c02205
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发表时间：
2021
期刊：
影响因子：
5.5
通讯作者：
Inoue Tadashi
中科院分区：
文献类型：
--
作者：
Shangwei Li;Urakawa Osamu;Inoue Tadashi
研究了微凝胶体系在液-固转变浓度附近的动态粘弹性和动态双折射，以阐明微凝胶体系粘弹性响应的分子来源。当浓度c低于无规密堆积微凝胶时，复数模数表现出粘弹性类液体行为，而粘弹性类固体行为则表现为类粘弹性。在类液体区域，复数应变光学系数的虚部随角频率ω的增大而变化，这表明应力和双折射涉及三种弛豫机制。利用应力-光学规则，对于每个松弛过程，将复合剪切模量值从高频依次分解为暂时接触微凝胶中网状链的取向应力、颗粒变形和重分布过程。另一方面，在类似固体的情况下，普通的SOR具有单一的应力光学系数C，这意味着只有一个应力来源是主导的，这可以归因于致密堆积的微凝胶在永久接触中的取向应力。使用Onuki-Doi理论评估的应变光学系数定性地再现了测量结果，并支持这些指定。
Dynamic viscoelasticity and dynamic birefringence of a microgel system were investigated around the liquid–solid transition concentration to clarify the molecular origin of the viscoelastic response of the microgel system. The complex modulus showed viscoelastic liquid-like behavior at concentrations,c, below a thresholdcjammingfor random close packing of the microgels, whereas viscoelastic solid-like behavior atc>cjamming. The imaginary part of the complex strain-optical coefficient changed its sign with increasing angular frequency ω in a liquid-like regime, suggesting that the stress and birefringence involved three relaxation mechanisms. Utilizing the stress-optical rule, SOR, for each relaxation process, the complex shear modulus atc<cjammingwas separated into the orientational stress of network strands in temporary contacted microgels, deformation of particle, and the redistribution process, from high frequencies in this order. On the other hand, in a solid-like regime atc>cjamming, the ordinary SOR held well with a single stress-optical coefficient,C, implying that only one stress origin is dominant, which can be attributed to the orientational stress of densely packed microgels in permanent contact. The strain-optical coefficients evaluated using the Onuki–Doi theory reproduced the measurements qualitatively and supported these assignments.