Role of interparticle attraction in the yielding response of microgel suspensions
Role of interparticle attraction in the yielding response of microgel suspensions
复制标题
DOI：
10.1039/c3sm50209k
复制
发表时间：
2013-05
期刊：
影响因子：
3.4
通讯作者：
Z. Shao;A. Negi;C. Osuji
中科院分区：
文献类型：
--
作者：
Z. Shao;A. Negi;C. Osuji
我们使用流变学测量来检查微凝胶系统的屈服行为，其范围从软堵塞的玻璃状悬浮液（由粒子间排斥主导）到由吸引相互作用产生的胶体凝胶。在排斥条件下，悬架表现出典型的软玻璃屈服响应，其中剪切损失模量在从弹性到粘性行为的交叉过程中随着应变的增加而呈现单峰。相比之下，在完全吸引条件下，胶体凝胶表现出更复杂的屈服，在屈服应变附近有两个明显的损失模量峰。很明显，凝胶最初是由网络破裂产生的，然后是剪切引起的致密化，导致致密团簇的形成。我们发现损耗模量的第二个峰与这些密集簇随后的破裂一致。我们定量地绘制了从简单的玻璃屈服到更复杂的凝胶响应的稳定进展，通过峰位置、幅度和频率依赖关系的演变来增加吸引力强度。值得注意的是，随着吸引力强度的增加，网络变得更加脆弱和空间异质性，峰值位置也会出现分歧。峰值位置的频率依赖性很小，但第二个屈服峰的振幅显示出非单调依赖性，其最大值在5 rad s−1附近。时间分辨测量和减小的应变扫描突出了网络破裂和簇破裂过程的可逆性的显著差异。相应地，凝胶的线性粘弹性特性强烈依赖于机械历史，而玻璃则没有这种依赖。
We use rheological measurements to examine the yielding behavior of a microgel system spanning the range from soft jammed glassy suspensions dominated by inter-particle repulsion to colloidal gels produced by attractive interactions. Under repulsive conditions, the suspensions display a prototypical soft glassy yielding response in which the shear loss modulus exhibits a single peak on increasing strain during the crossover from elastic to viscous behavior. By contrast, under fully attractive conditions the colloidal gel displays a more complex yielding, with two distinct peaks in the loss modulus in the vicinity of the yield strain. It is apparent that the gels yield initially by network rupture, followed by shear induced densification which leads to the formation of compact clusters. We show that the second peak in the loss modulus is consistent with the subsequent breakup of these dense clusters. We quantitatively map the steady progression from simple glassy yielding to the more complex gel response on increasing attraction strength by the evolution of peak locations, magnitudes and frequency dependencies. Notably, the peak locations diverge as the network becomes more fragile and spatially heterogeneous with increasing attraction strength. There is little frequency dependence in the peak positions, but the amplitude of the second yielding peak shows a non-monotonic dependence with a maximum near 5 rad s−1. Time-resolved measurements and decreasing strain sweeps highlight pronounced differences in the reversibility of the network rupture and cluster breakup processes. Correspondingly, the linear viscoelastic properties of the gel are strongly dependent on mechanical history whereas the glass exhibits no such dependence.