正交叠加流变法测量软核壳微胶束的流体机制
Orthogonal Superposition Rheometry of soft core-shell microgels
AI总结：
本研究利用正交叠加流变法探讨了软核壳微胶束在玻璃态与阻塞态之间的流动机制，揭示了剪切诱导结构松弛与微观失效机制的关系，并通过实验验证了Kramers-Kronig关系的应用。
摘要：
通过正交叠加流变法（OSR）探测了软粒子在玻璃转变体积分数以上的悬浮液以及在阻塞状态下的流动机制。在稳态剪切流上叠加一个小振幅振荡剪切流，允许在流动过程中监测受剪阻塞核壳微胶束的粘弹性谱。从粘弹性谱中推导出的特征交叉频率ωc提供了关于剪切诱导结构松弛时间的信息，这与微观的笼子破裂失效机制相关。交叉频率的剪切率演化用于实现所有谱的叠加，从而获得更深入的流动机制理解。尽管其固有柔软性，核壳混合微胶束表现出与硬球样流动行为的相似性，主要区别在于对于微胶束来说，从玻璃态到阻塞态的转变引入了体积分数对ωc与剪切率比例关系的依赖性。我们进一步检查了Kramers-Kronig关系在实验低应变振幅OSR数据中的应用，发现有良好的一致性。最后，通过开放底部细胞几何结构研究了高频响应在高应变率下的情况，并确定了仪器限制。基于这些限制，我们讨论了先前OSR数据和发现，在排斥性和吸引性胶体玻璃中的情况，并将其与当前软颗粒凝胶进行了比较。
英文摘要：
The mechanisms of flow in suspensions of soft particles above the glass-transition volume fraction and in the jammed state were probed using Orthogonal Superposition Rheometry (OSR). A small amplitude oscillatory shear flow is superimposed orthogonally onto a steady shear flow, which allows monitoring the viscoelastic spectra of sheared jammed core-shell microgels during flow. The characteristic crossover frequency ωc, deduced from the viscoelastic spectrum, provides information about the shear induced structural relaxation time, which is connected to the microscopic yielding mechanism of cage breaking. The shear rate evolution of the crossover frequency is used to achieve a superposition of all spectra and get a better insight of the flow mechanism. Despite their inherent softness, the hybrid core-shell microgels exhibit similarities with hard sphere-like flow behavior, with the main difference that for the microgels the transition from a glassy to a jammed state introduces a volume fraction dependence of the scaling of ωc with shear rate. We further check the application of the Kramers-Kronig relations on the experimental low strain amplitude OSR data finding a good agreement. Finally, the low frequency response at high strain rates was investigated with open bottom cell geometry and instrumental limits were identified. Based on these limits, we discuss previous OSR data and findings in repulsive and attractive colloidal glasses, and compared them with the current soft particle gels.
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