(2co) Towards Rational Design of Structured Soft Earth Materials | AIChE

(2co) Towards Rational Design of Structured Soft Earth Materials


Pradeep, S. - Presenter, North Carolina State University
Research Interests

Overview: Building on my extensive research training in the fields of transport mechanics, materials chemistry, and soft matter physics, I propose to develop a new research theme in Chemical Engineering focused on fluid-mediated soft earth materials. The proposed research area will focus on developing novel model soft earth materials and experiments that yield fundamental insights into establishing engineering frameworks addressing challenges in climate change, developing eco-friendly plastic alternatives, and improve manufacturing in space.

Background: Earth’s surface is composed of diverse set of fluid-particulate mixtures that dictate geophysical flows and drive geomorphological changes that shape our landscapes. The fluid-particulate mixtures are characterized by complexities such as particle size polydispersity, shape, softness, and size-dependent interactions between its constituent particles. In addition, the earth’s surface also hosts several additional soft materials – such as polymers, bacteria etc. – which on interaction with fluid-particulate mixtures modify their mechanical and transport properties, thus by adding more complexity to the existing earth suspensions. One can ask a fundamental question: how do the constituent materials in an earth suspension mixture contribute to its mechanical and flow properties?

Two ways to quantify the dissipation mechanics in systems that exhibit collective behavior - such as earth suspensions - are performed by characterizing rheological and tribological properties of the system. There is a growing need to connect the fields of suspension rheology and wet granular matter tribology – with model soft earth materials – to engineer earth matter, such as mud, for desired applications. Investigating contributions from various dissipation modes in tandem allows the exploration of material processing windows that can be tuned for various end applications. My independent research group will develop model experimental systems that mimic hierarchical length scales and complex interactions observed in earth materials. We will design and assemble novel instrumentation tools that characterize system mechanics - macroscopically combining rheology and tribology, and microscopically using new optical tools - which will provide design principles to engineer fluid-particulate systems that mimic the soft earth materials.

Postdoctoral Research: Geophysical Suspension Flow Mechanics (University of Pennsylvania, Mentors: Prof. Doug Jerolmack and Prof. Paulo Arratia)

My current research work focuses on elucidating the flow mechanics of geophysical flows through the framework established for dense granular rheology. The main challenge in geophysical flows is extending the current rheological models – established for ideal, homogenous mixtures – toward explaining the flow properties of natural heterogenous suspension mixtures. For instance, debris flows – which are dense sedimenting suspensions formed after heavy rainfall – are traditionally difficult to explain using conventional rheological models. As climate change effects intensifies, precise models are needed to predict such events. Our study samples collected from the Montecito mudslides (Santa Barbara, CA) showed self-similar flow curves that collapsed to a simple Bingham-type flow model. The work enabled rethinking debris-flows as simple viscoplastic fluids, and this approach will help model and predict hazard potentials associated with similar flows in the future. At present I am working on extending frictional jamming framework to understand the failure of subaqueous dunes.

Doctoral Research: Rough Colloidal Suspension Rheology (North Carolina State University, Advisor: Prof. Lilian Hsiao)

During my graduate work, I focused on decoupling the effects of surface roughness on the flow mechanics in dense colloidal suspensions. Constrained rotational degree of freedom in rough particle suspensions introduced interesting flow properties in the dense suspension regime. At near-equilibrium low shear conditions, a thousand-fold increase in the rough suspension viscoelastic moduli was observed. Using arguments from kinetic trapping models, mode-coupling description of glassy dynamics, and scaling theories for lubrication films, we were able to explain the enhanced hydrodynamic interactions between surface asperities as a probable reason for the observed increase in moduli. On the other end of the flow curve – at high shear rates - rough suspensions exhibited stronger shear thickening effects compared to model smooth suspensions. Using an in-house assembled confocal rheometer, characterization of the contact microstructures enabled one of the first experimental observation of 3D contact chains during the shear thickening process. This subsequently led to an understanding that the restriction to spatial rearrangement of particles as the reason for stronger shear thickening observed in rough suspensions. The work enabled generation of dense suspension design framework based on a universal shear thickening scaling for suspensions as a function of its jamming distance.

Teaching, Mentoring & DEI Interests

Throughout my graduate studies I was involved in teaching both undergraduate and graduate level courses. I have served as teaching assistant in diverse classrooms and course environments – with class-sizes ranging from 20 to 200 students and settings ranging from laboratory experiments to hybrid lectures. During my doctoral studies, I underwent intense training in academic pedagogy earning “Teaching and Communications Certificate” from NC State University. During my postdoc at Penn, I helped develop a new undergraduate course titled “Engineering in the environment” aimed at linking transport principles and concepts from soft matter physics that guide geomorphological changes in the environment. Given my experience and research interests, I will be interested in teaching the following courses - fluid mechanics, transport phenomena, thermodynamics, and statistical mechanics. Furthermore, I will be interested in developing a new graduate level course (suited for junior/senior level undergraduates) that aims at introducing principles from soft matter physics to engineer soft materials for desired applications. During my graduate and postdoctoral work, I have mentored six undergraduate students through their research training. I was always interested in mentoring young minds where I constantly ask them to be curious about the things around them and cultivated a work atmosphere where they value diversity, equity, and inclusion. I believe that my experience with DEI-focused mentoring will help create a future research group which will strive to create an inclusive and respectful atmosphere for everyone.