Drying dynamics of a charged colloidal dispersion in a confined drop
Drying dynamics of a charged colloidal dispersion in a confined drop
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DOI：
10.1103/physrevfluids.1.084201
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发表时间：
2016-12-12
影响因子：
2.7
通讯作者：
Salmon, Jean-Baptiste
中科院分区：
文献类型：
--
作者：
Loussert, Charles;Bouchaudy, Anne;Salmon, Jean-Baptiste
我们进行了彻底的调查，在一个封闭的几何形状的带电胶体分散液滴的干燥动力学。我们开发了一种基于拉曼显微光谱的原始方法，以测量空间分辨的胶体浓度分布在干燥过程中的下降。这些测量导致在很宽的浓度范围内的分散体的集体扩散系数的估计。集体扩散系数是一个数量级以上的斯托克斯-爱因斯坦估计，显示的重要性的静电相互作用的浓度梯度的弛豫。与此同时，我们还在液滴干燥期间对嵌入分散体中的示踪剂进行荧光成像，这揭示了两种不同的状态。在早期阶段，浓度梯度沿着下降导致浮力诱导的流动。引人注目的是，这些流动并不影响产生它们的胶体浓度梯度，因为质量传递仍然由扩散主导。在较长的时间尺度上，示踪剂轨迹揭示了准均匀干燥的凝胶的形成。对于这样的凝胶，我们表明使用线性多孔弹性模型的干燥动力学仍然是由相同的传输方程描述的液体分散体。然而，集体扩散系数遵循修改的广义斯托克斯-爱因斯坦关系，如在由Style和Peppin [Style和Peppin，在干燥胶体悬浮液中的结壳形成，Proc.R. A 467，174（2011）]。
We perform a thorough investigation of the drying dynamics of a charged colloidal dispersion drop in a confined geometry. We develop an original methodology based on Raman microspectroscopy to measure spatially resolved colloids concentration profiles during the drying of the drop. These measurements lead to estimates of the collective diffusion coefficient of the dispersion over a wide range of concentration. The collective diffusion coefficient is one order of magnitude higher than the Stokes-Einstein estimate, showing the importance of the electrostatic interactions for the relaxation of concentration gradients. At the same time, we also perform fluorescence imaging of tracers embedded within the dispersion during the drying of the drop, which reveals two distinct regimes. At early stages, concentration gradients along the drop lead to buoyancy-induced flows. Strikingly, these flows do not influence the colloidal concentration gradients that generate them, as the mass transport remains dominated by diffusion. At longer time scales, the tracer trajectories reveal the formation of a gel that dries quasihomogeneously. For such a gel, we show using linear poroelastic modeling that the drying dynamics is still described by the same transport equations as for the liquid dispersion. However, the collective diffusion coefficient follows a modified generalized Stokes-Einstein relation, as also demonstrated in the context of unidirectional consolidation by Style and Peppin [Style and Peppin, Crust formation in drying colloidal suspensions, Proc. R. Soc. A 467, 174 (2011)].