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

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

This Particles on Curved Interfaces: Geometry, Mechanics, and Self Assembly The 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.