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Multiple dynamic regimes in a coarsening foam
Journal of Physics: Condensed Matter ( IF 2.7 ) Pub Date : 2020-10-14 , DOI: 10.1088/1361-648x/abb684
Fabio Giavazzi 1 , Veronique Trappe 2 , Roberto Cerbino 1
Affiliation  

Intermittent dynamics driven by internal stress imbalances in disordered systems is a fascinating yet poorly understood phenomenon. Here, we study it for a coarsening foam. By exploiting differential dynamic microscopy and particle tracking we determine the dynamical characteristics of the foam at different ages in reciprocal and direct space, respectively. At all wavevectors $q$ investigated, the intermediate scattering function exhibits a compressed exponential decay. However, the access to unprecedentedly small values of $q$ highlights the existence of two distinct regimes for the $q$-dependence of the foam relaxation rate $\Gamma (q)$. At high $q$, $\Gamma (q)\sim q$ consistent with directionally-persistent and intermittent bubble displacements. At low $q$, we find the surprising scaling $\Gamma (q) \sim q^{\delta}$, with $\delta=1.6 \pm 0.2$. The analysis of the bubble displacement distribution in real space reveals the existence of a displacement cut-off of the order of the bubble diameter. Introducing such cut-off length in an existing model, describing stress-driven dynamics in disordered systems, fully accounts for the observed behaviour in direct and reciprocal space.

中文翻译:

粗化泡沫中的多个动态状态

由无序系统中的内部应力失衡驱动的间歇性动力学是一种迷人但知之甚少的现象。在这里,我们研究了粗化泡沫。通过利用差分动态显微镜和粒子跟踪,我们分别确定了泡沫在互易空间和直接空间中不同年龄的动态特性。在研究的所有波矢量 $q$ 中,中间散射函数表现出压缩的指数衰减。然而,获得前所未有的小值 $q$ 突出了泡沫松弛率 $\Gamma (q)$ 的 $q$ 依赖性的两种不同机制的存在。在高 $q$ 处,$\Gamma (q)\sim q$ 与定向持续和间歇性气泡位移一致。在低 $q$ 时,我们发现令人惊讶的缩放 $\Gamma (q) \sim q^{\delta}$,$\delta=1.6 \pm 0.2$。对实际空间中气泡位移分布的分析揭示了气泡直径数量级的位移截断的存在。在现有模型中引入这样的截止长度,描述无序系统中的压力驱动动力学,完全解释了在直接和互易空间中观察到的行为。
更新日期:2020-10-14
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