Collaborative Research: Near-Surface Repulsion and Mixing- Limitations: Upscaling of Colloid Retention, Breakthrough, and Elution in Non-Uniform Media under Unfavorable Conditions

在环境条件（所谓的不利条件）下，排斥性的胶体-表面相互作用对胶体输运的深刻影响，使得在这些条件下多孔介质中胶体输运的定量预测迄今无法实现。一个主要的问题是，表面是否通常可以根据包含吸引异质畴的整体排斥表面来解释/分类？给定的大小和空间频率（表面覆盖）。具体来说，尚不清楚以这种方式表征表面是否允许在不利条件下预测多孔介质中的胶体输运。这种离散非均质模型预测（并且实验表明），由于弱引力相互作用，多孔介质颗粒周围流体中的一小部分胶体将在近地表流体中停留很长时间，这就提出了另一个基本问题：在不利条件下，胶体在近地表流体中的长停留时间如何影响达西尺度下的输运行为？需要什么样的放大策略来识别长近地表停留时间的影响？我们假设这些长时间的近表面停留时间会导致胶体在流体领域的不完全混合，需要记忆功能/多速率或相关随机漫步方法来升级。我们最近开发的带有异质域的机制模型捕获了不利条件下孔隙尺度上的胶体运输和保留行为。该模型将作为在不利条件下将预测扩大到达西尺度的平台。模型结果将与在撞击射流和多孔介质中胶体输运的实验结果进行比较，以确定一系列的胶体尺寸、溶液离子强度和流体速度。我们期望产生一个机制模型来预测在不利条件下胶体保留的程度和模式。该项目将在胶体输运的数值模型中表示不利表面，以便在多孔介质中提供胶体在输运过程中保留的机理预测。该机制模型的结果将用于探索胶体-表面相互作用对从孔隙到达西尺度的高级运输预测策略的影响。该项目将极大地提高我们在环境条件下预测胶体运输的能力，例如环境中的病原体运输，以及具有新代谢特性的细菌的靶向递送。

The profound influence of repulsive colloid-surface interactions on colloid transport under environmental conditions (so-called unfavorable conditions) has rendered quantitative prediction of colloid transport in porous media under these conditions unattainable to date. A major question is whether surfaces can generally be interpreted/categorized in terms of a bulk repulsive surface that includes attractive ?heterodomains? of given size and spatial frequency (surface coverage). Specifically, it is unknown whether characterizing surfaces in this way allows prediction of colloid transport in porous media under unfavorable conditions. This discrete heterogeneity model predicts (and experiments indicate) that a fraction of colloids in the fluid surrounding a porous media grain will spend long residence times in the near-surface fluid due to weak attractive interactions, which raises another fundamental question: how do the long residence times of colloids in the near-surface fluid under unfavorable conditions influence transport behavior at the Darcy scale? What scale-up strategies are needed to recognize the influence of long near-surface residence times? We posit that these long near-surface residence times yield incomplete mixing of colloids across the fluid domain, necessitating memory function/multirate or correlated random walk approaches to upscaling. Our recently-developed mechanistic model with heterodomains captures colloid transport and retention behavior at the pore scale under unfavorable conditions. This model will serve as the platform from which to scale up predictions to the Darcy scale under unfavorable conditions. The model results will be compared to experimental results for colloid transport in an impinging jet and in porous media for a range of colloid sizes, solution ionic strengths, and fluid velocities. We anticipate producing a mechanistic model that will predict the extent and mode of colloid retention under unfavorable conditions. This project will represent unfavorable surfaces in numerical models of colloid transport in order to provide mechanistic prediction of colloid retention during transport in porous media. The results of this mechanistic model will be used to explore the influence of colloid-surface interaction on strategies to upscale transport prediction from the pore to the Darcy scale. This project will greatly enhance our ability to predict colloid transport under environmental conditions, in contexts such as pathogen transport in the environment, and targeted delivery of bacteria with novel metabolic properties.