Computational and Statistical Physics

I started my career in physics as a Ph.D. student at Georgetown University, working with Prof. Emanuela Del Gado. There I became interested in computational and statistical physics, applying advanced mathematics to the study of physical systems. I ended up in the world of soft matter physics–an interdisciplinary field bringing together aspects of statistical physics, chemistry, engineering, and more. My dissertation was focused on the study of cement, which is a surprisingly unique and complex material. I worked on projects related to understanding hydration in the presence of chemical gradients and explaining the electrostatic origins of cement cohesion. Each of these involved developing new mathematical models, translating them into large-scale computer simulations, and analyzing data from those simulations to derive physical insights.

After defending in the midst of a pandemic in 2020, I became a postdoctoral researcher at NIST (National Institute of Standards and Technology). There I built models to study large-scale suspensions: investigating particle ordering under shear and the microstructural origin of discontinuous shear thickening. I received an NRC fellowship for my independent research proposal to build a modeling framework for additive manufacturing (AM) with cement/concrete, and quickly expanded to working on ceramic AM as well.

Below are links to my Google Scholar Profile and access to all my published papers.

Modeling particle suspensions: from microstructure to rheology

At NIST, I developed a modeling framework that enabled simulations of suspensions with 10-100x more particles than previously studied. The scale of the simulations I performed allowed me to make new discoveries about the microstructure that underlies the rheological properties of suspensions. In a set of Journal of Rheology papers, I discuss two very different types of microstructure associated with two very different types of rheological phenomena.

The first dealt with ordering of frictionless particles and shear thinning. The above snapshots show that large domains of crystal-like ordering can emerge in sheared suspensions with stiff particles and no friction, due to mainly an entropic effect as those crystalline regions can be more densely packed. It's an interesting regime where order emerges in a very rapidly moving and unstable system!

The second paper dealt with the case of frictional particles and rigidity percolation within shear thickening suspensions. Discontinuous shear thickening (DST) is the counter-intuitive phenomenon by which a suspension becomes more solid-like the harder you push it. Perhaps you've been introduced to a common example as a kid: Oobleck, corn starch mixed with water, becomes a very weird slime-like substance that is often used in school experiments. There are also many practical applications, from vibration control and damping to body armor and protection.

While scientists have determined this arises due to particle friction, the microstructural origin of this phenomenon has remained a mystery for decades. In particular, we would expect some kind of large scale structural changes within the suspension that lead to the physical properties changing, but nothing like this has been observed despite decades of extensive research. My recent work identifies, for the first time, a microstructural unit which does exhibit suspension-spanning structure exactly at the onset of DST.

The relevant microstructural unit is what I called a constrained particle: one with enough neighbors (i.e. particles in contact with it) to restrict it's motion along all degrees of freedom. The snapshots above show the contact network between these constrained particles, in a 58% volume fraction suspension. The two images are from the same suspensions, sheared at the same rate, but with different instantaneous stresses. The stress fluctuations within the suspension correspond precisely to the percolation of these particles! Additionally, if we vary the shear rate and do a statistical percolation analysis, the critical rate corresponding to this percolation is exactly the rate of onset for DST.

The physics behind cement: from electrostatics to gels