A revolutionary discovery by Assistant Professor Peter Beltramo of the UMass Amherst Chemical Engineering (ChE) Department and his research team, published in the high-impact journal ACS Nano, will enable us to expand and improve upon our ability to develop ordered, two-dimensional materials for such important applications as solar cells, antireflective coatings, and biosensors.

To support this pioneering research, Beltramo has been awarded a significant, three-year grant of $381,851 from the National Science Foundation (NSF) for his proposal, titled “Cloaking Anisotropic Capillary Interactions Through Tunable Nanoscale Surface Topography.” 

This research was spurred by a collaboration among several researchers from UMass Amherst who have been working with Beltramo and have contributed to the paper in ACS Nano: Samuel Trevenen and Md Anisur Rahman of the ChE department; and Heather S.C. Hamilton, Alexander E. Ribbe, and Laura C. Bradley of the Department of Polymer Science and Engineering.

As Beltramo explains the back story of this research, “Colloidal particles (microscopic particles 1/100th the diameter of a human hair), adsorbed to the interface between two dissimilar fluids (like oil and water), have been extensively used as environmentally friendly alternatives to surfactants to stabilize emulsions (drops of oil in water, or vice versa) and as precursors for the development of two-dimensional materials for solar cells, antireflective coatings, and biosensors.”

According to Beltramo, “However, the material properties of colloidal interfacial monolayers are dictated by the particle shape, limiting our ability to use non-spherical particles that would expand and improve upon these applications.”

But now Beltramo and his research colleagues have made a critical discovery by showing that the interactions and material properties between particles at fluid interfaces can be controlled, independent of particle shape, by introducing surface roughness.

As Beltramo explains in his NSF abstract, “Novel materials, such as solar photovoltaics, antireflective coatings, synthetic membranes, and biosensors, may be engineered for improved performance through the nano- and micro-scale ordering of small particles.” He goes on to say that next-generation versions of these technologies will require well-ordered, two-dimensional structures that have direction-dependent organization.

“In this project,” says Beltramo, “we are investigating a new approach to creating such ordered assemblies of particles using stretched polymer spheres, termed ‘ellipsoids.’ Such particles irreversibly pin to air-water interfaces to conveniently create a two-dimensional layer; however, under normal conditions, strong attractive forces between the particles cause undesirable, aggregated, disorganized assemblies to form.”

But Beltramo thinks there may be a solution. The central hypothesis driving this work, he says, is that these “disorganized assemblies” can be avoided by engineering the interactions between the particles through novel particle synthesis techniques that give the particle surface a controlled degree of roughness.

As Beltramo notes, “The project will focus on how particle roughness can be manipulated to dictate the curvature of the fluid interface surrounding the particles and their interparticle forces which lead to their ultimate ordered assembly at the air-water interface.”   

As a direct result of the NSF grant, Beltramo and his colleagues have now described the first step towards these goals in their ACS Nano paper. As it turns out, their hypothesis was correct: roughness weakens the forces between polymer ellipsoids – and not trivially. The effect is orders of magnitude over large distances. Thanks to this “cloaking” of capillary attraction, the research team can now create stable, non-aggregated, particle interfaces. However, there are still many open questions about the mechanism that causes this discovery and how to translate it for applications.

By doing this fundamental science, Beltramo says he hopes his team will establish the foundation for developing two-dimensional materials applicable to a variety of fields, including plasmonics, solar cells, coatings, membranes, and biosensors.

Beltramo adds that “We’re extremely excited about the plethora of novel materials that could be enabled from the two-dimensional ordering of anisotropic colloids. In some of our first experiments towards making precursors towards these materials, we have had remarkable success, and there is still a wonderful parameter space to explore. We expect this approach will stimulate fruitful scientific contributions and collaborations in the future.”

Trevenen is a former Ph.D. student in the Beltramo group and currently works at GCP Applied Technologies in Wilmington, Massachusetts. Rahman is a current Ph.D. candidate in the Beltramo group. Hamilton is a former Ph.D. student in the Beltramo and Bradley groups.

Before coming to UMass Amherst, Beltramo earned his B.S. from the University of Pennsylvania, his Ph.D. from the University of Delaware, and he was a postdoctoral fellow at ETH Zurich. (August 2023)

Article posted in Research