Hypothesis

Soft microgel colloids can be densely packed since particle networks can compress and interpenetrate. This evolution of the particle’s internal structure associated with packing is expected to determine the linear viscoelastic properties and the yielding behavior of dense suspensions of microgel colloids.

Experiments

We investigated the volume fraction-dependent linear and non-linear rheological response of suspensions of soft core-shell particles formed by a poly(N-isopropylacrylamide) (PNIPAM) microgel core and a thin poly(ethylene glycol) (PEG) shell.

Findings

The linear viscoelasticity of suspensions reveals a transition from a fluid to a jammed glass state. Increasing volume fraction within the jammed state, the linear storage modulus and the yield stress show distinct regimes associated with the evolution of particle contacts, which involve progressive compression and interpenetration of the shell and core. The yielding of jammed suspensions occurs in two-steps: At small strains jammed cages are rearranged, while full disentanglement of interpenetrating networks only occurs at large deformations and results in fluidization. Yield strains and stresses increase with increasing shear rate or frequency, suggesting a progressive dominance of the timescale associated with shear over that associated with the internal dynamics of the system.

中文翻译：

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胶体和聚合物对致密微凝胶悬浮液产量的贡献

假设

软的微凝胶胶体可以紧密堆积，因为颗粒网络可以压缩并互穿。与填充相关的颗粒内部结构的这种演变预计将决定线性粘弹性和微凝胶胶体致密悬浮液的屈服行为。

实验

我们研究了由聚（N-异丙基丙烯酰胺）（PNIPAM）微凝胶核和薄的聚（乙二醇）（PEG）壳形成的软核-壳颗粒悬浮液的体积分数依赖性线性和非线性流变响应。

发现

悬浮液的线性粘弹性揭示了从流体状态到玻璃堵塞状态的转变。在卡塞状态下，体积分数的增加，线性储能模量和屈服应力显示出与粒子接触演化有关的不同机制，这涉及壳和核的逐渐压缩和互穿。堵塞的悬浮液的屈服分为两个步骤：在较小的应变下，将堵塞的笼子重新排列，而互穿网络的完全解缠仅在较大的变形下发生，并导致流化。屈服应变和应力随着剪切速率或频率的增加而增加，这表明与剪切相关的时间尺度逐渐超过与系统内部动力学相关的时间尺度。