Jabbari-Farouji S, Atakhorrami M, Mizuno D, Eiser E, Wegdam G H, Mackintosh F C, Bonn Daniel, Schmidt C F
van der Waals-Zeeman Institut, Universiteit van Amsterdam, 1018XE Amsterdam, The Netherlands.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Dec;78(6 Pt 1):061402. doi: 10.1103/PhysRevE.78.061402. Epub 2008 Dec 11.
We report measurements of the frequency-dependent shear moduli of aging colloidal systems that evolve from a purely low-viscosity liquid to a predominantly elastic glass or gel. Using microrheology, we measure the local complex shear modulus G;{*}(omega) over a very wide range of frequencies (from 1Hzto100kHz ). The combined use of one- and two-particle microrheology allows us to differentiate between colloidal glasses and gels-the glass is homogenous, whereas the colloidal gel shows a considerable degree of heterogeneity on length scales larger than 0.5microm . Despite this characteristic difference, both systems exhibit similar rheological behaviors which evolve in time with aging, showing a crossover from a single-power-law frequency dependence of the viscoelastic modulus to a sum of two power laws. The crossover occurs at a time t_{0} , which defines a mechanical transition point. We found that the data acquired during the aging of different samples can be collapsed onto a single master curve by scaling the aging time with t_{0} . This raises questions about the prior interpretation of two power laws in terms of a superposition of an elastic network embedded in a viscoelastic background.
我们报告了对老化胶体系统频率相关剪切模量的测量，该系统从纯低粘度液体演变为主要为弹性玻璃或凝胶。使用微观流变学，我们在非常宽的频率范围（从1Hz到100kHz）内测量了局部复剪切模量G*(ω)。单粒子和双粒子微观流变学的联合使用使我们能够区分胶体玻璃和凝胶——玻璃是均匀的，而胶体凝胶在大于0.5微米的长度尺度上表现出相当程度的不均匀性。尽管存在这种特征差异，但两个系统都表现出相似的流变行为，随着老化时间而演变，显示出从粘弹性模量的单幂律频率依赖性到两个幂律之和的转变。转变发生在时间t₀，它定义了一个力学转变点。我们发现，通过用t₀对老化时间进行缩放，不同样品老化过程中获取的数据可以合并到一条单一的主曲线上。这就对之前关于两个幂律是由嵌入粘弹性背景中的弹性网络叠加来解释的观点提出了质疑。
