It is known that structural heterogeneity induced by the distribution of the water and air phases creates complex flow patterns with a broad distribution of flow velocities, which in turn control key aspects of transport including arrival and residence times, dispersion and spatial distributions of dissolved salts and suspended colloidal particles. Stagnation zones serve as hot spots where colloidal particles can get entrapped, providing a challenging task in controlling their transport. Recent investigations in simple confined geometries suggest diffusiophoresis, the colloid migration driven by local salt gradients, to be an efficient mechanism to control colloidal migration. However, despite its potential, diffusiophoresis in complex porous media remains poorly understood. We use detailed numerical simulations to unravel the effects of diffusiophoresis occurring at pore-scale on the macroscopic dispersion of colloids in partially-saturated porous media with different water-saturation degrees. Diffusiophoresis can promote particle retention or removal, depending on the diffusiophoretic mobility. For fully-saturated media, the pore-scale dynamics due to diffusiophoresis are manifested in the long-time tailing of the breakthrough curves. For partially-saturated media as the degree of water-saturation decreases and flow heterogeneity increases, we observe accumulation and depletion effects in the colloid breakthrough curves which can be traced back to trapping and release in dead-end zones. Finally, our results suggest that colloid mobilisation and retention due to diffusiophoresis can be controlled by the flow rate of the injected salt solution.

中文翻译：

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胶体在部分饱和多孔介质中的扩散电泳


众所周知，由水和空气相分布引起的结构异质性会产生具有广泛流速分布的复杂流动模式，这反过来又控制了传输的关键方面，包括到达和停留时间、溶解盐和悬浮胶体颗粒的分散和空间分布。停滞区是胶体颗粒可能被截留的热点，为控制其传输提供了具有挑战性的任务。最近对简单受限几何形状的研究表明，扩散泳，由局部盐梯度驱动的胶体迁移，是控制胶体迁移的有效机制。然而，尽管具有潜力，但复杂多孔介质中的扩散电泳仍然知之甚少。我们使用详细的数值模拟来揭示孔隙尺度上发生的扩散泳对胶体在不同水饱和度的部分饱和多孔介质中的宏观分散的影响。扩散泳可以促进颗粒保留或去除，具体取决于扩散泳的迁移率。对于完全饱和的介质，由于扩散泳引起的孔隙尺度动力学表现为突破曲线的长期拖尾。对于部分饱和的介质，随着水饱和度的降低和流动非均质性的增加，我们在胶体突破曲线中观察到积累和消耗效应，这可以追溯到死胡同区的捕获和释放。最后，我们的结果表明，由于扩散泳引起的胶体动员和保留可以通过注入盐溶液的流速来控制。