Equilibrium and Dynamics of Polymer-Grafted Nanoparticles at Fluid Interfaces

1332836 PI：Tilton聚合物刷是聚合物链的一种命名，每个聚合物链的一端固定在表面上，而其余的链从表面延伸到溶剂中。该小组先前的NSF支持的研究开发了聚合物刷修饰的纳米颗粒，它们是水包油或油包水乳液的非常有效的稳定剂。这些纳米颗粒刷稳定乳液数月至超过一年，而没有乳液液滴聚结或宏观油和水相分离。最重要的是，他们这样做，而只需要两个数量级的纳米粒子的浓度低于通常所需的常规颗粒用于稳定乳液。所提出的研究的目标是确定负责纳米粒子刷的独特乳化效率的基本界面现象。目前对颗粒稳定的Pickering乳液的理解主要涉及长期稳定性的起源，但它还不能解释为什么具有不同物理化学性质的颗粒产生具有非常相似的长期稳定性的乳液，但显示出截然不同的乳化效率，也就是说，为什么它们首先需要截然不同的浓度来产生稳定的乳液。这需要对纳米颗粒吸附到油/水界面时的界面性质进行基本研究。指导这项研究的主要假设是，那些在最低表面浓度下产生最强界面张力降低和界面弹性的纳米粒子刷将是最有效的乳化剂。通过可控自由基聚合，合成了一系列具有明确组成和结构的纳米刷。 对于每个纳米颗粒刷，将在油/水界面处测量表面状态方程（界面张力与吸附颗粒表面浓度之间的关系）、界面摩擦弹性和扩散动力学，并将其与乳化效率相关联。纳米粒子刷是一类新型的表面活性材料。通常，这种材料被设计成操纵不相容材料之间的界面，以使它们更相容。例如，他们将油和水混合成乳液，在药物或个人护理产品中提供活性成分。这项研究是变革性的，因为它专注于为什么纳米粒子刷是非常有效的乳化剂的根本原因，以及更广泛的基本理解，它将提供化学结构如何控制这类新的表面活性材料的界面行为。这些知识将使超低乳化剂浓度的高稳定性乳液产品成为可能。除了有效使用原材料的好处外，这也保证了没有高效和高效乳化剂的新产品是不可行的。 一种可能性是清洁燃烧的柴油燃料乳液，其满足严格的稳定性要求而没有过量的添加剂。技术劳动力发展的更广泛的影响是由化学工程和化学博士的跨学科研究教育提供。和本科生。来自代表性不足群体的匹兹堡中学生将接受密切相关的、以发现为基础的科学项目的指导，这些项目教学生如何利用科学理解来做出预测？在这种情况下涉及不同种类材料的界面张力降低和乳化性能。 与高中化学学生的研讨会访问将介绍化学相关的职业生涯的全方位，以鼓励在他们过渡到大学的STEM途径保留。这是由CBET（化学，生物，环境和运输）工程部门的颗粒和多相过程和界面过程和热力学计划共同资助。

1332836PI: TiltonA polymer brush is a descriptively named monolayer of polymer chains, each of which is anchored by one end to a surface, while the rest of the chain stretches away from the surface into a solvent. Prior NSF-supported research by this group developed polymer brush-decorated nanoparticles that were extremely efficient stabilizers of oil-in-water or water-in-oil emulsions. These nanoparticle brushes stabilized emulsions for several months to well over a year without emulsion droplet coalescence or macroscopic oil and water phase separation. Most importantly, they did so while only requiring nanoparticle concentrations that were two orders of magnitude lower than are generally required for conventional particles used to stabilize emulsions. The goal of the proposed research is to determine the fundamental interfacial phenomena responsible for the unique emulsifying efficiency of nanoparticle brushes. Current understanding of particle-stabilized Pickering emulsions mainly concerns the origins of long-term stability, but it cannot yet explain why particles with different physico-chemical properties produce emulsions with quite similar long-term stability yet display vastly different emulsifying efficiencies, that is, why they require vastly different concentrations to produce a stable emulsion in the first place. This requires fundamental investigation of the interfacial properties of the nanoparticles when they adsorb to the oil/water interface. The main hypothesis guiding this research is that those nanoparticle brushes that produce the strongest interfacial tension reduction and interfacial elasticity at the lowest surface concentration will be the most efficient emulsifiers. A series of nanoparticle brushes with well-defined compositions and architectures will be synthesized by controlled radical polymerization. For each nanoparticle brush, the surface equation of state (the relationship between interfacial tension and the adsorbed particle surface concentration), interfacial dilatational elasticity, and diffusional dynamics will be measured at the oil/water interface and correlated with emulsifying efficiency. Nanoparticle brushes are a new class of surface active material. Typically, such materials are designed to manipulate the interface between incompatible materials to make them more compatible. For example, they mix oil and water in emulsions that deliver active ingredients in pharmaceuticals or personal care products. This research is transformative for its focus on the fundamental reasons why nanoparticle brushes are extremely efficient emulsifiers and for the broader fundamental understanding it will provide for how chemical structure controls the interfacial behavior of this new class of surface active materials. This knowledge will enable high stability emulsion products with ultra-low emulsifier concentrations. Besides the benefit of efficient raw materials usage, this also promises new products that are infeasible without emulsifiers that are both highly effective and highly efficient. One possibility is a clean-burning diesel fuel emulsion that meets stringent stability requirements without excessive additives. Broader impact for technology workforce development is delivered by the interdisciplinary research education of Chemical Engineering and Chemistry Ph.D. and undergraduate students. Pittsburgh middle school students from under-represented groups will be mentored in closely-related, discovery-based science projects that teach students how they can use scientific understanding to make predictions ? in this case concerning interfacial tension reduction and emulsification performance of different kinds of materials. Seminar visits with high school chemistry students will introduce the full spectrum of chemistry-related careers to encourage retention in the STEM pathway as they transition to college.This reasearch is jointly funded by the Particulate and Multiphase Processes and Interfacial Processes and Thermodynamics Programs in the CBET (Chemical, Biological, Environmental and Transport) division in Engineering.