Adsorption in Confined Films

许多常见的产品是由悬浮在液体中的颗粒集合组成的。例子包括油漆、食品和化妆品。这些产品的一个重要特征是，颗粒保持在特定的排列中，而不是聚集或从悬浮液中分离。保持颗粒的正确排列可能是具有挑战性的，特别是对于保质期较长的产品。保持所需的粒子排列的关键方面是控制粒子几乎彼此接触的小间隙中发生的事情。这个项目利用了我们最近在能力方面的发展，为这些小差距提供了明确的例子。该项目研究了分子如何吸附到缝隙中，以及缝隙大小对吸附的影响。这种分子吸附对于控制差距是随时间缩小还是扩大至关重要，从而控制消费品是否保持最有用的排列。这个项目的研究将被整合到本科生和研究生的教学项目中，并将提供教育工具来激励高中生，特别是那些在STEM领域未被充分代表的学生，继续进行科学和工程研究。离子、表面活性剂、聚合物和颗粒的吸附是决定薄膜中胶体分散稳定性的关键因素，因此是许多工程过程的核心。单一界面的吸附已经得到了很好的研究，但与胶体稳定直接相关的量是在两个界面之间的薄膜中的吸附。这在以前的工作中很少被测量到。开发了一种新的技术来测量纳米级薄膜中两个固体之间的物种数量。这项技术将被用来测量关键区域的吸附，在这些区域，基于泊松-玻尔兹曼理论的简单模拟预计将失败，例如在浓溶液、多价离子、表面活性剂和颗粒中。这项技术有三个要素：(1)在两个连续厚度梯度为1200 nm的固体之间制备坚固的薄膜；(2)用干涉法测量薄膜厚度；(3)根据荧光发射的强度测量吸附分子的量。预期的结果是：(1)准确测量薄膜中的物种数量；(2)评估常用模型的有效性；(3)洞察薄膜在各种应用中的稳定性；以及(4)在垂直于平面薄膜的方向上测量荧光团浓度分布的方法的一些发展。我们将把这项工作整合到“弗吉尼亚理工大学的计算机与技术”(C-Tech2)项目中，这是一个为期两周的暑期项目，每年有120所女子高中参加实践活动，以帮助培养和保持对科学和工程的兴趣。这项工作还将为一名研究生提供光学、微制造、建模和显微镜领域的跨学科培训。本科生将致力于这个项目，目的是激励他们继续在工程学或科学方面的研究生学习。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。

Many commonplace products are composed of collections of particles suspended in liquid. Examples include paints, food products and cosmetics. An important feature of these products is that the particles remain in particular arrangements, rather than aggregating or separating from the suspending liquid. Maintaining the proper arrangement of the particles can be challenging, especially for products with long shelf lives. The key aspect of maintaining the desired arrangement of particles is to control what happens in the small gaps where the particles almost touch each other. This project takes advantage of a recent development in our ability to make well-defined examples of these small gaps. The project examines how molecules adsorb into the gaps, and how the adsorption is affected by the gap size. This molecular adsorption is critical to controlling whether the gaps close or widen with time, and thus whether consumer products maintain the most useful arrangement. The research in this project will be integrated into programs that teach undergraduate and graduate students, and will provide educational tools to inspire high school students, especially those underrepresented in STEM fields, to continue in science and engineering studies.Adsorption of ions, surfactants, polymers, and particles is a key factor in determining the stability of colloidal dispersions in thin wetting films, and thus is central to many engineering processes. Adsorption at single interfaces has been well studied, but the directly relevant quantity for colloid stabilization is adsorption in a thin film between two interfaces. This has only rarely been measured in prior work. A new technique has been developed to measure the amount of a species in nanometer-scale films between two solids. This technique will be used to measure adsorption in critical regimes where simple modeling based on Poisson-Boltzmann theory is expected to fail, such as in concentrated solutions, multivalent ions, surfactants, and particles. The technique has three elements: (1) fabrication of a robust thin film between two solids with a continuous gradient of thicknesses in the range of 1?200 nm; (2) measurement of film thickness by interferometry; and (3) measurement of the amount of adsorbed molecules from the intensity of fluorescence emission. The expected outcomes are: (1) accurate measurements of amounts of species in thin films; (2) assessment of the validity of common models; (3) insight into the stabilization of films in various applications; and (4) some development of the method to measure the profile of fluorophore concentration in the direction normal to a planar film. We will integrate this work into the "Computers and Technology at Virginia Tech" (C-Tech2), which is an annual two-week summer program for 120 female high school to participate in hands-on activities to help develop and sustain interest in science and engineering. The work will also provide interdisciplinary training for a graduate student in the fields of optics, microfabrication, modelling, and microscopy. Undergraduates will work on the project, with the aim of inspiring them to pursue graduate study in engineering or science.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.