Plastic rearrangements in colloidal gels investigated by LAOS and LS-Echo
Plastic rearrangements in colloidal gels investigated by LAOS and LS-Echo
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DOI：
10.1122/1.4872059
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发表时间：
2014-09-01
影响因子：
3.3
通讯作者：
Petekidis, G.
中科院分区：
文献类型：
--
作者：
Laurati, M.;Egelhaaf, S. U.;Petekidis, G.
我们使用流变学和光散射回波 (LS-Echo) 研究了中等体积分数的胶体聚合物凝胶的屈服行为，这些凝胶受到大幅振荡剪切的影响。特别关注应力响应的非和谐贡献以及塑性重排的特征时间尺度和程度。在接近 1% 的小应变幅度 gamma(0) 下已经观察到屈服，其中互连簇的网络开始破裂，并且首先观察到不可逆的粒子重排。然而，只有在应变幅度相当大时，gamma(0) >= 100%，网络才会完全破坏，小簇或单个颗粒才会流动。这种复杂的屈服行为反映在不同的循环屈服状态中，这些状态是从对应力的非简谐贡献的分析中提取出来的。在键断裂开始的应变幅度范围内，观察到循环内应变硬化和剪切增稠，其中应变硬化可能是由剪切诱导形成更致密的团簇引起的。当网络被破坏时，随着应变幅度的增加，观察到循环内剪切稀化，但仍然伴随着应变硬化。弹性和粘性非线性贡献都随着应变幅度的增加而减少，表明系统的渐进流化，与 LS-Echo 中观察到的更快的塑性重排一致。小应变下的初始屈服存在两种不同的频率相关机制：在小到中等振荡频率下，第一屈服应变随着频率的增加而增加，而在大频率下则减少。这可能与键断裂的时间尺度有关，即小频率下的布朗扩散时间和大频率下振荡频率的倒数。 (C) 2014 年流变学会。
We investigate the yielding behavior of colloid-polymer gels with intermediate volume fraction, which are subjected to large amplitude oscillatory shear, using rheology and light scattering echo (LS-Echo). Particular attention is given to the anharmonic contributions to the stress response and the characteristic timescale and extent of plastic rearrangements. Yielding is already observed at small strain amplitudes gamma(0) approximate to 1%, where the network of interconnected clusters starts to break up and irreversible particle rearrangements are first observed. However, only at considerably larger strain amplitudes, gamma(0) >= 100%, the network is completely disrupted and small clusters or individual particles flow. This complex yielding behavior is reflected in different regimes of in-cycle yielding, which were extracted from the analysis of the anharmonic contributions to the stress. In the range of strain amplitudes where bond breaking starts, in-cycle strain hardening and shear thickening are observed, with the strain hardening possibly caused by the shear-induced formation of more compact clusters. When the network is broken down, in-cycle shear thinning is observed with increasing strain amplitude, but still together with strain hardening. Both, the elastic and viscous nonlinear contributions, decrease with increasing strain amplitude, indicating the progressive fluidization of the system, consistent with the faster plastic rearrangements observed in LS-Echo. Two-distinct frequency-dependent regimes for the initial yielding at small strains are present: At small to moderate oscillation frequencies, the first yield strain increases with increasing frequency, while it decreases at large frequencies. This might be associated with the timescale for bond breaking, namely, the Brownian diffusion time at small frequencies and the inverse of the oscillation frequency at large frequencies. (C) 2014 The Society of Rheology.