
MSE Seminar: Peter Beltramo (UMass Amherst)
Using surface roughness to manipulate interfacial colloidal interactions, dynamics, and assembly
Soft matter interfaces are ubiquitous across diverse technologies ranging from pharmaceuticals to chemical formulations. The presence of surfactant molecules or colloidal particles at fluid interfaces gives the interface distinct properties in response to flow, deformation, and external fields that must be measured, understood, and manipulated for desired functionalities. In this talk, we discuss the disparate ways in which particle surface roughness on spheres and ellipsoids impacts the interfacial pinning, capillary interactions, and mechanics of particle monolayers. We use a seeded emulsion polymerization technique to produce polystyrene microspheres and microellipsoids with controlled surface topography. By monitoring the dynamics of two particles approaching one another, we find that concave rough ellipsoids exhibit a strikingly shorter-range capillary interaction potential than smooth ellipsoids. Interferometry measurements of the fluid deformation surrounding a single particle quantitatively confirm the decrease in capillary interaction energy and point to roughness-induced changes to interfacial pinning as the mechanism for reduced attraction. This results in a capillary cloaking effect, where rough ellipsoids are interfacially invisible to one another at separations where their smooth counterparts would normally strongly attract. We further explore how controlling particle roughness on both spheres and ellipsoids dictates the interfacial mechanics and microstructural assembly of particle monolayers. In particular, the reduction in interparticle capillary attraction between rough ellipsoids minimizes the propensity for kinetically arrested particle aggregation, allowing the assembly of close-packed, anisotropic, ordered particle monolayers. These results have profound implications on the design and tunability of Pickering emulsions, foams, and the development of anisotropically ordered 2D materials.
Bio:
Peter Beltramo is an assistant professor in the Department of Chemical Engineering at UMass Amherst. He earned a B.S. in chemical engineering from the University of Pennsylvania in 2009 and a Ph.D. in chemical engineering from the University of Delaware in 2014, where he studied the electrokinetics and self-assembly of colloidal suspensions. Before starting at UMass Amherst in 2018, he completed a postdoc in soft materials at ETH Zurich. At UMass, his lab studies interfacial soft matter in contexts ranging from membrane biophysics and biomimetic materials to particle stabilized emulsions and ordered 2D materials. His recent recognitions include the NSF CAREER Award, ACS-PRF Doctoral New Investigator Award, and a Lilly Teaching Fellowship at UMass Amherst.