(4kr) Harnessing Instabilities in Structured Materials for Enhanced Reaction Kinetics and Self-Assembly

Life is full of chaos, from turbulent weather patterns to unpredictable crowd decisions. Scientists typically seek to tame these disparate forms of chaos because they are considered undesirable. My work takes a different approach: I study how elasticity can inject chaotic dynamics into soft materials, with the goal of utilizing chaos to encode adaptive transport, enhance reaction kinetics, and pattern material self-assembly. I develop new visualization techniques to directly observe these microscale dynamics in complex, disordered, and 3D environments representative of applications. My work demonstrates how a range of chaotic and non-equilibrium dynamics can be harnessed to drive adaptive fluid transport, enhanced reaction kinetics, and self-assembly of life-like materials. Through this fundamental work, I aim to inform engineering design principles in environmental remediation, sustainable chemical processes, and biocellular health.

Harnessing elastic flow instabilities to enhance transport and reaction kinetics

A wide range of environmental, industrial, and energy processes rely on reactive transport in disordered 3D porous media, but laminar flow under strong geometric confinement (Re«1) imposes a fundamental limit on reagent transport. My dissertation work reports a novel technique to mimic turbulent-enhanced reactivity using dilute high molecular weight polymers, which induce an elastic flow instability. By directly visualizing the flow in transparent 3D porous media, I demonstrate that the flow exhibits chaotic spatiotemporal fluctuations reminiscent of inertial turbulence, despite the vanishingly small Reynolds number. My measurements enable us to quantitatively establish that the energy dissipated by unstable pore-scale fluctuations generates a macro-scale increase in the overall flow resistance, analogous to the turbulent dissipation in kinetic energy, resolving an over-50-year-old mystery in the field (Browne and Datta, Science Advances 2021). I further demonstrate how this flow resistance can be harnessed to design “smart” flows, that can adapt to heterogeneous environments to either homogenize or exacerbate flow partitioning (Browne et al. JFM 2023; U.S. patent application submitted 07/2023). Then, I demonstrate how these pore-scale velocity fluctuations can enhance the transport mixing by stretching and folding solute gradients exponentially in time—analogous to turbulent Batchelor mixing (Browne and Datta, under review; U.S. patent application submitted 07/2023). I observe a dramatic reduction in the required mixing length and improvement in the dispersion of concentration gradient, suggesting a cooperation between the elastic instability and the laminar chaotic advection inherent to the disordered 3D porous media. I show these two mixing mechanisms can be modeled with additive independent mixing rates, representing a dramatic conceptual simplification. I then extend these results to reactive mixing, accelerating a model reaction by 3× while simultaneously increasing throughput by 20×—circumventing the traditional trade-off between throughput and reactor length. My results thus provide the first demonstration, to our knowledge, that elastic flow instabilities can provide turbulent-like enhancements in chemical reaction rates, which can operate cooperatively with laminar chaotic advection in industrially-relevant geometries.

Harnessing liquid crystal condensation to pattern materials

My ongoing research explores how flow instabilities can influence transport in a very different context: during the phase separation of condensates. While condensation is well understood in the context of isotropic fluids, many biological condensates are formed from structured fluids, which can exhibit liquid crystallinity in isolation. My ongoing work demonstrates how some structured fluids can form dynamic condensate networks (Equal contribution: Morimitsu*, Browne*, et al. under review; arXiv 2403.01298). These networks are “living,” and can dynamically remodel themselves for hours. Microscopy, theory, and simulations help reveal how these networks are constructed by the growth of rapidly-elongating filaments, rather than spherical droplets, to relieve distortion of a simultaneously-forming internal smectic mesophase. As filaments densify, they collapse into bulged discs, lowering the elastic free energy. Additional distortion is relieved by retraction of filaments into the bulged discs, which are straightened under tension to form a ramified network. I demonstrate how the architecture of this network is mediated by the hydrodynamics of spontaneous flows induced by the anisotropic growth and retraction of filaments. Understanding and controlling these dynamics may provide new avenues to direct pattern formation or template materials.

Teaching Interests

The next generation of chemical engineers will play a key role in addressing global grand challenges in environmental remediation, sustainability, and health. As such, I am excited to contextualize the core curricula of chemical engineering within these modern grand challenges by integrating salient principles of transport, dynamics and networked systems across core courses. My research and teaching experience make me particularly well-suited to teach fluid dynamics, heat and mass transport, reaction engineering, and thermodynamics/statistical mechanics. I also hope to develop specialized courses in soft and active matter—providing a more nuanced appreciation for foundational physical concepts applied to complex, nonlinear, or non-equilibrium systems representative of many nascent industrial, environmental, and biomedical applications.

I have developed my pedagogical approach through extensive classroom experience. I have given 4 guest lectures, served as a teaching assistant for two courses (undergraduate and graduate), served as the primary instructor for a high school chemistry course, tutored 3 students, and taken a graduate course on pedagogy. Through this experience I have developed a Socratic teaching style that prioritizes student engagement with and ownership of their learning. This method has allowed me to maintain uniformly high performance across diverse student groups, even in virtual classrooms, while assessing and meeting the individual learning needs of each student. In the laboratory, I have directly advised six undergraduate students and one Ph.D. student, and mentored four Ph.D. students through reading groups and research workshops. By providing individualized mentorship, I have helped a diverse group of advisees from underrepresented backgrounds collectively co-author 5 publications, win 3 poster awards, and obtain 2 Ph.D. fellowships (NSF GRFP).

Background

I completed my B.S. in Chemical Engineering at Purdue University, where I worked with Prof. Stephen Beaudoin developing new techniques in the measurement of adhesive forces using atomic force microscopy, with the goal of informing the in-field detection of explosives and explosive-precursors, which I continued studying with Dr.’s Edward Sisco and Thomas Forbes at the National Institute of Standards and Technology. I then completed my Ph.D. at Princeton University (funded by NSF GRFP), where I worked in soft matter with Prof. Suit Datta studying viscoelastic and multiphase flow in porous media, percolation, and hydrogel dynamics. I am currently a postdoc at the University of Pennsylvania, working with Prof. Chinedum Osuji studying phase separation and formation of condensates in liquid crystal solutions.