ERI: Incipient contact dynamics of viscoelastic drops

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。在液滴通过气体接触固体表面之前，液滴和表面之间的气体必须被置换。如果置换不完全，一些气体可能以小气泡的形式夹带在液滴内。这一过程已被广泛地研究用于常见的系统，如水滴在空气中运动，影响各种固体表面。这个ERI奖的重点是当液滴含有聚合物添加剂时，接触动力学是如何变化的。载聚合物液滴对固体表面的影响与许多应用有关，包括生物打印、农药配方和载病原体的呼吸道液滴在表面的沉积。聚合物添加剂对液滴下空气位移的影响将采用实验和理论相结合的方法进行研究。一种最先进的流变仪和一种高速光学技术，可以跟踪纳米级液滴的接触方式，将用于评估含有商业相关聚合物（如聚乙烯氧化物）的液滴中的空气夹带。该项目的结果将为必须控制空气夹带以确保各种应用中产品质量的工程从业人员提供有用的信息。研究生和本科生将参与研究，研究成果将纳入本科和研究生课程。该项目将与贝勒校园的梅伯恩博物馆合作，加强现有的推广工作，旨在向所有年龄段的学生和公众传播科学。在喷墨印刷和各种涂布过程中，空气夹带是一个常见的工业问题。尽管空气夹带的基本流体力学已经引起了广泛的兴趣，但这个问题仍然具有挑战性，因为它跨越了时空动力学的数量级。揭示液滴早期接触的努力主要集中在由牛顿液体组成的液滴上，尽管重要的应用涉及聚合物液滴。为了填补这一知识空白，该ERI项目将利用实验和理论分析纳米到毫米尺度的动力学，以揭示聚合物负载液滴的接触途径。研究包括三个任务：(1)研究聚合物添加剂对空气夹带现象的影响；(2)表征了液滴扩散过程中夹带气膜造成的能量损失；(3)分析控制携气机理的策略。聚合物浓度对空气夹带的影响以及剪切变薄和弹性的作用将使用高速全内反射显微镜和流变测量相结合的方法进行研究。该项目将开发新的实验工具来评估聚合物负载液滴的粘弹性，这将有助于研究界面现象和多相流体力学。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Before a droplet moving through a gas can contact a solid surface, the gas between the droplet and surface must be displaced. If the displacement is incomplete, some of the gas may be entrained as small bubbles inside the drop. This process has been studied extensively for common systems such as water droplets moving through air that impact various kinds of solid surfaces. This ERI award focuses on how the contact dynamics change when the liquid drop contains polymer additives. The impact of polymer-laden drops on solid surfaces is relevant to many applications including bioprinting, pesticide formulation, and the deposition of pathogen-laden respiratory droplets on surfaces. The influence of polymer additives on air displacement underneath droplets will be examined using a combination of experiments and theory. A state-of-the-art rheometer and a high-speed optical technique that can track the approach of droplets nanometers from contact will be used to assess the air entrainment in droplets containing commercially-relevant polymers such as polyethylene oxide. Results from the project will provide useful information to engineering practioners who must control air entrainment to ensure product quality in various applications. Graduate and undergraduate students will participate in the research, and research results will be incorporated into undergraduate and graduate courses. The project will partner with the Mayborn Musuem on the Baylor campus to enhance existing outreach efforts aimed at communicating science to students of all ages and the general public.Air entrainment is a common industrial problem in inkjet printing and various coating processes. Although the fundamental hydrodynamics underlying air entrainment has generated broad interest, the problem remains challenging because it spans orders of magnitude in spatiotemporal dynamics. Efforts to uncover the incipient contact of droplets have focused mainly on droplets composed of Newtonian liquids even though important applications involve polymeric drops. In order to fill this knowledge gap, this ERI project will analyze nanometer- to millimeter-scale dynamics using experiments and theory to uncover the contact routes for polymer-laden drops. The research comprises three tasks: (1) investigate the influence of polymer additives on air entrainment phenomena; (2) characterize the energy loss caused by the entrained air film during droplet spreading; and (3) analyze strategies to control the air entrainment mechanism. The influence of polymer concentration on air entrainment and the roles of shear thinning and elasticity will be investigated using a combination of high-speed total internal reflection microscopy and rheometric measurements. The project will develop new experimental tools for assessing the viscoelasticity of polymer-laden droplets, which will benefit researchers studying interfacial phenomena and multiphase fluid mechanics.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.