(4ce) Electromagnetic Fields to Drive Assembly and Transport in Colloidal Soft Materials

Colloidal particles are powerful building blocks for functional soft materials, providing a means to tune macroscopic properties through synthetic control of individual colloids. Such materials are highly sought for use in optoelectronic devices, consumer products, and biomedical applications. Traditional examples involve passive particles; particle interactions are innate, and dynamics are constrained by relaxation to thermodynamic equilibrium. Driving particles using external electromagnetic (EM) fields breaks these constraints and allows a rich array of assembled states and transport mechanisms. Perhaps most promising is the ability to vary these fields in time and space, allowing us to modulate properties on-the-fly and drive materials out of equilibrium. My proposed research aims to leverage electromagnetic fields to design and control functional colloidal materials, using computational and theoretical methods to carry out the investigations. While EM phenomena are notoriously hard to incorporate into colloidal models because they involve long-ranged and many-bodied interactions, I have built up a suite of rapid numerical tools throughout my graduate and postdoctoral studies to simulate colloids in EM fields. I will employ these tools for three initial research areas, each involving a different mode of electromagnetic transport.

Collective transport of electric-field-driven colloids in electrolytes. Colloids dispersed in electrolytes translate, rotate, and produce flows when exposed to an electric field. The dynamics of a particle are highly coupled not only to the surrounding ionic double layer but also to the motion and ionic structure of other particles. These many-bodied effects lead to remarkable emergent dynamics in experiments, but most computational studies have focused on decoupled systems and fail to describe these observations. To address this shortcoming, I will investigate the collective transport properties of colloid-electrolyte mixtures driven by (time-varying) electric fields, focusing on the coupling between ionic structure and particle dynamics. Understanding how electrolytes and fields dictate particle transport, we can invert this paradigm and use colloids to control effective electrolyte properties, e.g., in batteries and fuel cells.

Enhanced magnetophoresis through porous media in time-varying fields. Paramagnetic nanoparticles (NPs) can be directed using magnetic fields to deliver molecular cargo for targeted therapeutics. Often, target sites (e.g., tumor cells) are surrounded by dense porous tissue, and NP aggregation hinders mobility through the small pores. Experiments have demonstrated that time-varying fields break apart aggregates and greatly enhance the flux of cargo. While these proof-of-concept experiments are promising, we do not have the fundamental understanding needed to quantitatively predict this transport process. I will investigate time-varying magnetophoresis through model porous media using dynamic simulations. In particular, we will examine how different modes of time-variation enhance NP transport through various pore morphologies. Beyond biological materials, the principles developed here apply to magnetophoretic transport in other porous media like membranes and hydrogels.

Inverse design of self-assembled plasmonic materials. Certain nanoparticles, like inorganic nanocrystals, are plasmonic and interact strongly with particular resonant frequencies of EM waves. Strong plasmonic coupling between NPs results in structure-dependent effective properties, and experiments have shown that structures assembled from plasmonic NPs are promising for use as photovoltaics and electrocatalysts. However, a major challenge to realizing these possibilities is the enormous number of physical parameters and structures to screen, even for computationally accelerated approaches. I propose to couple self-assembly simulations and optical calculations with methods of numerical optimization to formulate plasmonic material design as an inverse problem. That is, we specify a target plasmonic response and use optimization routines to identify the tunable parameters that yield assembled materials with the desired behavior. This builds on inverse methods from statistical mechanics effective for design of target structures and will ultimately reduce the time and cost needed to produce plasmonic materials.

Teaching, Mentoring, and DEI Interests

Not all parts of a faculty position are enjoyable, but teaching and mentoring are aspects that I am excited about. Teaching and mentoring have been a valued part of my academic career so far; I have been a teaching assistant for three different courses at the undergraduate and graduate levels and have mentored five undergraduate researchers in the lab. I’ve even been recognized for these endeavors through several awards, including the MIT School of Engineering Graduate Student Award for Extraordinary Teaching and Mentoring and the MIT Department of Chemical Engineering Outstanding Graduate Teaching Assistant Award. Through these experiences, I have converged on a set of core principles that I value as an educator and hope to infuse into the courses I teach, including:

• Positivity: An uplifting, optimistic environment where students are as excited about science as I am.
• Inclusivity: Everyone is safe, valued, and welcome in the classroom. Diversity in identity and in thinking are encouraged.
• Student Well-Being: Physical and mental health are highly valued. I aim for reasonable workloads and strive to be understanding, accommodating, and flexible to students’ needs.
• Patience: All students have different academic backgrounds and learning speeds, and I aim to be sensitive and patient to these variations.

I am particularly excited about teaching thermodynamics and statistical mechanics, numerical methods, transport, and fluid mechanics, though I am equipped to teach any course in the core chemical engineering curriculum. I am also eager to develop elective courses delving further into applied mathematics as well as creating computational modules to augment existing courses -- for example, a molecular simulation module for thermodynamics or a module on numerical differential equations for fluid mechanics/transport. Finally, I am interested in creating alternative resources for students beyond lectures, textbooks, and notes, such as short videos on particularly tough topics, a resource students found helpful during my teaching assistantships.

Beyond education at the university level, I am also invested in educating younger students as well as promoting diversity, equity, and inclusion in STEM. I’ve had wonderful opportunities in these areas through my role as Outreach Chair in the Materials Research, Science, and Education Center (MRSEC) at UT Austin, where I lead the MRSEC’s Outreach Committee. We’ve focused around: 1) bolstering science education for K-12 students from communities/identities underrepresented in science, 2) improving accessibility of K-12 science education, especially for students and teachers with limited financial and time resources, and 3) engaging MRSEC students, postdocs, staff, and faculty to incorporate outreach into their regular work habits. MRSEC Outreach has organized numerous, easy-to-get-involved-in avenues, including participating in events bolstering women in STEM, partnering with Austin schools to develop science activities for visually impaired students, creating classroom lab kits available for no-charge rental, and filming virtual demos easily accessible online. Additionally, through MRSEC’s “Research Experience for Teachers” program, I worked with an Austin school teacher to design science curriculum for elementary grade students.

These experiences have influenced my planned approach to DEI and mentoring as a professor. In addition to organizational-level initiatives like committees and programs (in which I am interested in participating), I have seen how developing good habits, many small things done consistently every day, week, and month, can lead to a supportive, inclusive culture that is pervasive throughout an organization. Creating this kind of supportive culture is an important goal for my own research lab, and I have identified several core values that I will promote to accomplish this goal, including:

• Positivity: An uplifting, optimistic lab environment that values all members and their physical and mental well-being.
• Collaboration: Members are encouraged to work together and feel safe and supported to do so. Ideas and work are critiqued in a positive, constructive way. After all, we are a team solving tough problems together.
• Inclusivity: My lab promotes diversity in members’ identities as well as in their research backgrounds and approaches.
• Accessibility: We strive to make our work easily available to many people. Strategies include developing open access code, organizing clear data sets for data sharing, and disseminating illustrative videos and graphics.
• Transparency: Clearly communicate all my expectations of the students as well as what the students expect of myself as the PI.

A crucial first step is to create a lab manual which will lay out a clear plan to promoting these core values and will provide a useful reference for current and prospective members. This is something I want to create collaboratively with my group and continually refine over time. I am eager to begin developing these ideas and learn many new ones to create a supportive, inclusive lab culture.