Boosting migration of large particles by solute contrasts
Boosting migration of large particles by solute contrasts
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DOI：
10.1038/nmat2254
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发表时间：
2008-10-01
期刊：
影响因子：
41.2
通讯作者：
Bocquet, L.
中科院分区：
文献类型：
--
作者：
Abecassis, B.;Cottin-Bizonne, C.;Bocquet, L.
布朗扩散是从物理学、化学到生物学的各种领域中的一个关键概念（1）。扩散输运控制着各种各样的情况，如生物学和化学中的反应扩散过程（2-4）、布朗棘轮过程（5-7）、微流体装置中的分散（8，9），甚至是海洋混合背景下的双扩散不稳定性和盐指现象（10）。虽然这些例子跨越了很宽的长度尺度范围，但扩散传输对于较大的颗粒变得越来越低效。例如，在微流体中的应用通常求助于涉及外部源的替代驱动方法来诱导和控制迁移。在这里，我们通过实验证明了大颗粒的强烈增强的迁移，通过将它们的动力学奴役于快速载体物种（稀盐）来实现。潜在的快速盐扩散导致大颗粒的明显的扩散样动力学，这比它们的自然“裸”扩散快两个数量级。此外，可以根据需要实现颗粒集合体的扩散和聚焦。一个模型的描述显示出显着的定量协议与所有测量数据。这个过程的应用说明在微流体过滤和浓缩操作，以及与标准的流体动力学聚焦。从更广泛的角度来看，这一机制可以影响范围广泛的尺度和现象，从生物迁移到海洋环境中沉积物和污染物的扩散。
Brownian diffusion is a keystone concept in a large variety of domains, from physics, chemistry to biology(1). Diffusive transport controls situations as diverse as reaction-diffusion processes in biology and chemistry(2-4), Brownian ratchet processes(5-7), dispersion in microfluidic devices(8,9) or even double-diffusive instability and salt-fingering phenomena in the context of ocean mixing(10). Although these examples span a broad range of length scales, diffusive transport becomes increasingly inefficient for larger particles. Applications, for example, in microfluidics, usually have recourse to alternative driving methods involving external sources to induce and control migration. Here, we demonstrate experimentally a strongly enhanced migration of large particles, achieved by slaving their dynamics to that of a fast carrier species, a dilute salt. The underlying fast salt diffusion leads to an apparent diffusive-like dynamics of the large particles, which is up to two orders of magnitude faster than their natural 'bare' diffusion. Moreover both spreading and focusing of the particle assembly can be achieved on demand. A model description shows a remarkable quantitative agreement with all measured data. Applications of this process are illustrated in microfluidics for filtering and concentrating operations, as well as in conjunction with standard hydrodynamic focusing. In a wider perspective, this mechanism can affect a broad range of scales and phenomena, from biological transport to the dispersion of sediments and pollutants in oceanographic situations.