Colloidal Transport, Self-Assembly, and Deposition in Evaporating Droplets

从厨房餐桌上的饮料痕迹到家用汽车车窗上的盐渍，我们都熟悉这些困扰我们家和车辆的污渍。然而，这种残基既不是随机的，也不是均匀的，它们经常以圆形斑点的形式出现，中心明亮，边缘黑暗。对这一现象的仔细检查表明，颗粒在边缘的积累是由液滴内部的流体流动促进的，而液滴内部的流体又是由液体由于蒸发而离开液滴的自由表面而驱动的。除了与日常生活相关外，蒸发驱动的溶质沉积为组装复杂的微型结构提供了一种简单、廉价的方法。该方法还可用作法医分析、疾病检查和生物检测的诊断工具。该奖项的目标是研究悬浮在蒸发胶体液滴中的颗粒的运动，并将胶体的传输与液滴干燥时最终停留的位置联系起来。计划中的研究与一系列教育活动相结合，包括对代表性不足的初中生和高中生的推广，对不同社区大学和研究生的指导，以及课程开发。该奖项旨在调查干燥胶体固着液滴中非挥发性颗粒的传输和聚集，最终目的是了解各种沉积模式背后的机制。具体地说，高保真的数值模拟和理论分析将被用来研究(I)液-气界面在蒸发自组装过程中的作用，(Ii)形状和多分散性对溶质传输和沉积的影响，以及(Iii)粒子传输和沉积对液滴几何形状和屏蔽效应的敏感性。这一奖项的发现将缩小我们目前的知识和对蒸发诱导的颗粒运输、自组装和沉积的基本理解之间的差距，这些颗粒最初悬浮在简单液体的无座液滴中。他们还将为沉积图案建立一个基于物理的变革性制度图，作为调整系统参数的工程指导方针，以便为各种高科技应用得出所需的自组装结构。该地图还可以用作诊断工具，用于精确确定悬浮颗粒的性质及其与自身、与液-气界面以及与基质的相互作用的性质。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

From beverage marks on the kitchen table to salt deposits on windows of the family car, we are all familiar with these stains that plague our homes and vehicles. However, such residues are not in random nor uniform patterns, and they often appear as circular spots with a bright center and a dark rim. A closer inspection of this phenomenon reveals that the accumulation of the particles at the edge is facilitated by the fluid flow inside the droplet, which is, in turn, driven by the liquid leaving the free surface of the drop due to evaporation. Apart from its everyday relevance, the evaporation-driven deposition of solutes offers a simple, inexpensive method for assembling complex miniature structures. This method can also be used as a diagnostic tool for forensic analysis, disease examination, and biodetection. The goal of this award is to examine the motion of particles suspended in evaporating colloidal droplets that rest on a substrate, and to link the transport of the colloids to where they finally reside when the droplet is desiccated. The planned studies are coupled with a range of educational activities that involve outreach to underrepresented middle and high school students, mentorship of diverse community college and graduate students, and curriculum development.This award aims to investigate the transport and aggregation of nonvolatile particles in drying colloidal sessile drops with the ultimate goal of understanding the mechanisms underlying various deposition patterns. Specifically, high-fidelity numerical simulations and theoretical analyses will be used to study the (i) role of the liquid-gas interface in the evolution of the evaporative self-assembly process, (ii) impact of shape and polydispersity on transport and deposition of solutes, and (iii) sensitivity of particle transport and deposition to droplet geometry and shielding effect. The findings of this award will narrow the gap in our current knowledge and fundamental understanding of the evaporation-induced transport, self-assembly, and deposition of particles initially suspended in a sessile drop of a simple liquid. They will also establish a transformative physics-based regime map for deposition patterns that can serve as an engineering guideline for tailoring the system parameters in order to elicit the desired self-assembled structure for a variety of high-tech applications. The map can also be utilized as a diagnostic tool for pinpointing the properties of the suspended particles and the nature of their interactions with themselves, with the liquid-gas interface, and with the substrate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.