(2ew) Transport in Complex Fluids for Applications in Sustainable Energy and Health

I envision building a research group that will focus on advancing the understanding of transport processes in systems with complex fluids across a wide range of industries and natural processes. The goal is to leverage this knowledge to design materials for sustainable energy storage and chemical synthesis, biological and biomedical applications, and consumer care products. A diverse set of research experiences in experimental, computational, and theoretical complex fluids related to particle-laden flows, electrochemical systems, and biological systems places me at a unique advantage to address the following transport challenges.

Suspension electrolytes are a class of complex fluids in which conductive or redox-active particles of sizes ranging from a few hundreds of nanometers to a few microns are suspended in a solvent. These are emerging as a potential alternative to porous electrodes in developing large-scale electrochemical systems for sustainable energy storage (flow batteries) and chemical synthesis. These flowing suspension electrolytes, in addition to allowing for independent scaling of power and energy density, have the advantage of reconfigurable electrode microstructures, extremely high surface areas, tunable charge and mass transport profiles and regenerable materials. In addition, they offer new reactor and process design opportunities. However, to realize efficient electrochemical systems with suspension electrolytes, we need to solve key challenges related to charge transport coupled with mass transport, electrochemistry and rheology in these suspensions especially under various flowing conditions. Continuous particles networks in the flowing suspension electrolytes facilitate charge transport but they continuously break and reform. We seek to develop tools to simulate these dynamic networks and develop models to predict the charge transport for various material sets and operating conditions relevant to practical electrochemical systems.

Protein suspensions are another class of complex fluids consisting of proteins of sizes ranging from a few tens to a few hundreds of nanometers suspended in solvents. Protein suspensions provide key functions in biological systems and are a significant part of the therapeutic drug industry. For example, the aggregation of Amyloid and tau proteins in and around brain cells is thought to be the cause of Alzheimer’s disease. The presence of defective CFTC regulator protein leads to formation of a thick sticky mucus (suspension of mucin proteins) in the airways of the lungs causing cystic fibrosis disease. Developing effective treatment methods requires knowledge of transport mechanisms for drug particles across such protein suspensions to reach the target cells. On the other hand, engineering high dose therapeutic drugs such as monoclonal antibody suspensions with rheology suitable for intravenous injection is an ongoing challenge. Dynamics of these protein suspensions can be simulated using molecular dynamics (MD) up to nanosecond timescales with severe limitation on the number of proteins that can be simulated. This limits the exploration of macroscopic rheology and transport properties of protein suspensions using simulation techniques and necessitates the development of additional simulation tools that can capture long time transport in these materials.

In conclusion, my research group will develop new particle-based simulation tools to address transport challenges related to suspension electrolytes and protein suspensions. We will combine simulations, theory and simple experiments to develop macroscopic transport models for these materials and collaborate with electrochemists and biophysicists from academia and industry to design materials and systems for electrochemical and biological applications.

Research experience

Through graduate and postdoctoral research, I developed expertise in experimental, theoretical and computational complex fluids with applications in diverse areas.

Graduate research:

Advisors: Jeffrey Morris and Sanjoy Banerjee, City College of New York.

My graduate research focused on understanding the inertial flow behavior of non-Brownian suspensions using experiments and theory. Motivation for this work arose from lack of fundamental understanding and accurate transport models necessary to design pumping and mixing systems for industry. I designed and built Taylor-Couette experimental flow setup, used flow visualization and particle tracking techniques and linear stability theory. I systematically studied the effect of size and concentration (up to 30%) of particles in a neutrally buoyant non-Brownian suspension on the inertial flow transitions and flow structures when the suspension is sheared in a Taylor-Couette setup. I discovered that the presence of particles in suspension under inertia leads to key deviations from a Newtonian fluid behavior: particles destabilize the flow, particles amplify non-axisymmetric disturbances, and with decreasing particle size suspension behavior moves towards that of a Newtonian fluid. These observations led me to hypothesize that the anomalous flow behavior may be explained by additional stresses arising from the non-linear interaction of finite-sized perturbations caused by the non-uniformly distributed particles in the flow structures.

Postdoctoral research:

Advisors: Eric Shaqfeh, Stanford University; James Swan and Fikile Brushett, Massachusetts Institute of Technology

In my postdoctoral research, I employed computational simulation techniques and theory to investigate particulate flows. Colloids in many real world applications have rough surfaces (eg: carbon black). Accurate constitutive models that describe these colloidal materials are necessary to design practical applications with these materials. For my first project, I seek to understand the effect of particle roughness on the microstructure and rheology of colloidal gels of moderate concentrations. I developed a pair-wise model for hydrodynamically interacting rough particles and integrated with the Stokesian dynamics simulations to simulate gels of rough particles. I found that with increase in particle roughness resulted in less-densely packed clusters and more uniform material. For the second project, as part of the effort to understand charge transport across sheared suspensions of conductive particles for electrochemical applications, I developed a coarse grained model for the charge diffusivity using kinetic Monte Carlo based charge hopping approach across the microstructure. The sheared suspension microstructures are generated using Stokesian dynamics simulations. The computed charge diffusivity agreed reasonably well with the experimental measurements (performed by collaborators) for various moderate suspension concentrations. The results are published in PNAS. As a parallel effort in this project, I integrated macroscopic rheological, mass transport, conductivity models for suspensions with the porous electrode theory and developed a one dimensional model for a redox flow battery with suspension electrolyte to test the performance tradeoffs. This computationally inexpensive model allows for predicting cell performance as a function of wide range of material sets and operating conditions and thereby helping with identifying experimental directions.

The objective of my third project was to understand how microparticles (dust or aerosols embedded with viruses) travel through and deposit in the human airways and to assess the consequent negative health effects. I employed computational fluid dynamics simulations coupled with point particles with stokes drag to compute the flow of air-particle mixture though airways of humans and rhesus monkeys.

Teaching interests

I am passionate about teaching in an engaging and effective way with the help of visualizations and real-life examples while encouraging curiosity and critical thinking. I strive to create inclusive and respectful environments suitable for a diverse set of students to flourish. As a faculty, I am happy to teach any of the fundamental chemical engineering courses both at the undergraduate and graduate level. I am particularly interested in designing and teaching courses related to complex fluids, fluid dynamics, heat and mass transfer, chemical engineering thermodynamics, and numerical methods.

I have thoroughly enjoyed my teaching experiences at all levels of chemical engineering including in academia as well as in industry. During my Ph.D., I served as a teaching assistant for two undergraduate level thermodynamics courses and one graduate level mass transport course. I particularly enjoyed recitations, where I had the opportunity to deconstruct the complexity of a problem and devise easily accessible approaches to solve problems. I also learned effective ways of preparing course material and delivering content when I got the opportunity to give two lectures on the reaction equilibria for the undergraduate thermodynamics course and one lecture on linear stability analysis for a graduate level fluid particle systems course. In addition, during my work in the nuclear industry, I gave a week long short course on computational methods related to fluid flow and heat transfer to the new batch of engineers as part of their training.

Publications

• Madhu V. Majji, James W. Swan, “A new hydrodynamics based method to quantify inter-particle friction and rheology of suspensions of rough particles.”, Physical Review Fluids, submitted. Preprint arXiv:2203.06300
• Han Lin, Madhu V. Majji, Noah Cho, John R. Zeeman, James W. Swan, Jeffrey J. Richards, “Quantifying the Hydrodynamic Contribution to Electrical Transport in Non-Brownian Suspensions”, Proceedings of the National Academy of Sciences (2022), accepted for publication.
• Baroudi, Lina, Madhu V. Majji, and Jeffrey F. Morris, "Effect of inertial migration of particles on flow transitions of a suspension Taylor-Couette flow." Physical Review Fluids5, no. 11 (2020): 114303.
• Taylor S. Geisler, Madhu V. Majji, Jana S. Kesavan, V. J. Alstadt, Eric S. G. Shaqfeh, G. Iaccarino, “Simulation of microparticle inhalation in rhesus monkey airways”, Physical Review Fluids, 4, 083101, 2019.
• Madhu V. Majji, Sanjoy Banerjee, and Jeffrey F. Morris, ”Inertial flow transitions of a suspension in Taylor–Couette geometry”, Journal of Fluid Mechanics, 835, pp.936-969, 2018.
• Madhu V. Majji, and Jeffrey F. Morris, “Inertial migration of particles in Taylor-Couette flows”, Physics of Fluids, 30(3), p.033303, 2018.