Particles on Curved Liquid Interfaces: Geometry, Mechanics, and Self-Assembly

曲面界面上的粒子：几何、力学和自组装在人造系统和生物世界中，类固体粒子在软界面上的吸附是普遍存在的。这些现象的多功能性范围从皮克林乳剂滴被密集的胶体悬浮液覆盖，到驻留在细胞膜上的蛋白质。了解颗粒与界面之间的相互作用以及颗粒之间的相互作用力对于开发有效的自组装方法和控制颗粒负载乳状液的稳定性至关重要。各种物理机制被认为会影响这些相互作用，从表面张力和接触线固定到静电和范德华力。如果粒子被吸附在弯曲的界面上，它们的力学也可能受到表面几何形状的显著影响。这些几何效应还没有被详细讨论，本提案的目的是开始对它们进行系统的研究。聚焦于简单而非平凡的几何，我们提出了旨在阐明曲面上粒子力学的普遍方面的实验和理论研究。智力优势：(i)我们将研究固体粒子与曲面的结合能仅取决于吸附粒子附近的局部界面曲率的条件。（ii）我们将研究几何诱导的弯曲界面上几个粒子之间的相互作用。我们将开发一套实验来测试曲率相关的相互作用。特别是，我们将探讨这些力是否可以作为吸附粒子之间经常存在的令人费解的长距离吸引力的基础。（iii）我们将描述吸附颗粒在非平衡表面流动下的行为。我们将讨论允许比较几何诱导力和与非平衡流动相关的粘性应力的流动几何。（iv）我们将讨论与吸附颗粒的密集悬浮液的行为有关的基本问题。特别是，我们将探讨许多吸附颗粒的存在是否会影响弯曲界面的稳定性，以及致密悬浮液中吸附颗粒之间相互作用的性质。广泛影响：(i)拟议的研究将为一名研究生和一名或多名本科生提供各种实验和分析方法的培训，并有机会在同一项目中结合这两种观点。（ii）两位PI都在领导一些教育项目，面向马萨诸塞大学阿默斯特分校和其他地方的研究生和本科生。该提案的一个新组成部分是为地区高中学生和教师开发外展计划，这将传授软物质物理学正在进行的研究的意识，兴奋和积极接触。将强调来自低收入和代表性不足社区的学生和教师的参与。（iii）了解几何诱导力的基本原理将产生革命性的结果，可用于探索定向组装颗粒的新方法，以及控制，颗粒稳定（皮克林）乳化。（iv）最后，该提案试图通过关注简单（轴对称）界面和固体（球形）粒子来探索最基本的几何诱导效应。所提出的研究结果将刺激一系列卓有成效的研究，这些研究将解决更复杂系统中几何诱导相互作用的表现，这些系统以柔性粒子（如蛋白质）、其他类型的表面（如弯曲模量）以及复杂的表面几何形状和粒子形状为特征。

This Particles on Curved Interfaces: Geometry, Mechanics, and Self AssemblyThe adsorption of solid like particles on soft interfaces is ubiquitous in man-made systems as well as in the biological world. The versatility of these phenomena range from Pickering emulsions drops that are covered by a dense colloidal suspension, to proteins that reside on cellular membranes. Understanding the interactions between particles and interfaces and the mutual forces between particles themselves is crucial for developing effective self assembly methods and for controlling the stability of particle laden emulsions. A variety of physical mechanisms are believed to affect these interactions, from surface tension and contact line pinning to electrostatics and van-der-Waals forces. If particles are adsorbed on a curved interface, their mechanics may also be significantly influenced by the surface geometry. Such geometry induced effects have not been addressed in detail, and the purpose of this proposal is to commence their systematic study. Focusing on simple yet nontrivial geometries, we propose experimental and theoretical studies aimed at illuminating universal aspects of the mechanics of particles on curved surfaces.Intellectual Merit:(i) We will study the conditions under which the binding energy of solid particles to curved surfaces depends only on the local interfacial curvatures near the adsorbed particle.(ii) We will study the geometry induced interactions among a few particles on a curved interface. We will develop a set of experiments to test the curvature dependent interactions. In particular, we will explore whether such forces can underlie the puzzling long range attraction that often exists between adsorbed particles.(iii) We will characterize the behavior of adsorbed particles under nonequilibrium surface flows. We will address flow geometries that allow comparison between geometryinduced forces and the viscous stresses associated with nonequilibrium flow.(iv) We will address basic problems related to the behavior of a dense suspension of adsorbed particles. In particular, we will explore whether the presence of many adsorbed particles can affect the stability of curved interfaces, and what is the nature of interactions between adsorbed particles in dense suspension.Broad Impact:(i) The proposed research will provide training for a graduate student and one or more undergraduate students in a variety of experimental and analytic methods, and the opportunity to combine both perspectives within the same project.(ii) Both PI's are leading a number of educational projects, intended for graduate and undergraduate students in UMass Amherst and elsewhere. A new component of the proposal is the development of outreach programs for regional high school students and teachers, which will impart awareness, excitement, and active exposure to ongoing research in soft matter physics. An emphasis will be given to participation of students and teachers from low income and underrepresented communities.(iii) Understanding the basic principles underlying geometry induced forces will yield transformative results, that could be used to exploring new approaches to directed assembly of particles, and to controlled, particle stabilized (Pickering) emulsification.(iv) Finally, the proposal seeks to explore the most basic geometry induced effects by focusing on simple (axially symmetric) interfaces and solid (spherical) particles. The results of the proposed studies will spur a fruitful line of research that will address the manifestations of geometry induced interactions in more complicated systems, characterized by flexible particles (e.g., proteins), other types of surfaces (e.g., with bending modulus), and complicated surface geometries and particle shapes.