(4cg) Multi-Scale Design and Processing of Soft Materials for Sustainability

Achieving contemporary sustainability goals for plastics circularity and clean energy storage requires multi-scale understanding of structure–processing–property relationships to guide soft materials design. Material performance is dictated by processing, where improper materials processing results in adverse effects including irreversible polymer chain scission in plastics and disruption of delicate microstructures. Despite this known interplay of microstructure and bulk properties, few characterization techniques provide a unified understanding that bridges molecular behaviors to macroscopic properties during processing. Rheology is critical to establishing structure–processing–property relationships in soft materials by providing bulk stress responses to different imposed flows. However, common rheological methods focus on idealized flow protocols, which provide limited information for soft materials that experience complex processing. Additionally, many rheological measurements assume materials deform uniformly and remain compositionally homogeneous during processing. Augmenting conventional rheological measurements with complementary techniques such as single-molecule fluorescence microscopy, flow visualization, small-angle scattering, spectroscopy, and dielectric measurements will provide powerful insights to material dynamics spanning molecular to macroscopic length scales. In my lab, we will combine in situ characterization tools with expertise in the design of reversible polymer networks, synthesis of polymers with complex architectures, and assembly of polymer nanocomposites to unify our understanding of soft materials processing for sustainability. In support of this vision, research in my lab will pursue three thrusts:

• Re-processable dynamic covalent polymer networks for plastics circularity
• Flow dynamics of mixed architecture polymeric liquids for enhanced polymer processing
• Complex fluid structuring and rheo-electric properties of polymer-colloid mixtures for clean energy storage

As a faculty member, I will build upon my graduate training in experimental nonlinear rheology and constitutive modeling of entangled polymer liquids and my postdoctoral work on the molecular design of polymers with complex architectures to engineer soft materials for sustainability.

Research Experience

Molecular engineering of architecturally complex polymers for sustainability and human health, Department of Chemical Engineering, Stanford University (advised by Danielle J. Mai)

As an Arnold O. Beckman Postdoctoral Fellow, my research focuses on the molecular-level design of architecturally complex polymers. In one project, I aim to circumvent single-use plastic waste by engineering reversible polymeric materials. I leverage end-functionalized multi-arm star polymers for photochemically recyclable 3D printing. As part of this work, I designed a photo-rheology setup which allows for dynamic rheological characterization during light irradiation with wavelengths that trigger either “printing” or “erasure”. By preparing star polymers of different molecular weights and numbers of arms per star, I discovered that fewer arms per star results in slower printing speeds, but faster erasure compared to star polymers with more arms. In using these well-defined polymers, I have advanced molecular design rules for polymer resins in sustainable 3D printing applications. In another project, I seek to understand how the “bottlebrush” shape of biopolymers (e.g., lubricin and mucin) results in the superior (bio)lubrication observed within the human body. To do this, I have developed a hybrid biosynthetic approach that combines “graft to” and “graft from” strategies used by synthetic polymer chemists to create bottlebrush polymers. This hybrid approach enables the preparation of model bottlebrush DNA polymers with precise backbone/side chain lengths and side chain grafting densities for direct single-molecule visualization in lubrication flows using fluorescence microscopy.

Flow-concentration coupling of entangled polymer liquids, Department of Chemical Engineering, UC Santa Barbara (advised by Matthew E. Helgeson and L. Gary Leal)

My dissertation resolved a longstanding disagreement between the flow behavior of chemically disparate entangled polymer solutions. In completing this work, I developed an expertise in the flow-based processing of polymers. Understanding the flow behavior of polymer liquids is critical to engineering processing operations that ensure material uniformity while reducing energetic demands. Entangled polymers are highly viscoelastic materials that exhibit shear rate dependent viscosities, which can vary by orders of magnitude depending on the applied shear rate. These changes to fluid viscosity are connected to a flow-induced fluid microstructure that standard rheological measurements alone cannot measure. To study the coupling of microstructure and rheology, I developed rheo-optical methods to quantify the polymer concentration and flow fields, complementing standard rheological measurements. My work resulted in the first experimental measurements that confirmed a theoretically predicted flow instability, which arises from a coupling of flow to concentration. I discovered that strong departures from a uniform velocity profile develop across sheared entangled polymer solutions and coincide with macroscopic changes to the polymer concentration profile. These advanced rheo-optical measurements revealed that macroscopic changes to polymer concentration develop in flow and underscored the importance of accounting for concentration heterogeneities in sheared polymeric liquids. This implied need to account for concentration heterogeneities represents a paradigm shift in the development of constitutive models and multi-faceted characterization methods for complex fluids. Taken together, future constitutive models and characterization techniques must account for nonuniform flows and composition heterogeneities to accurately design polymer processing operations.

Selected Publications

• M. C. Burroughs, et al., “Photochemically reversible star polymer networks as a platform for circular materials engineering”, (2024), in prep.
• Zhou, B. M. Wirtz, T. H. Schloemer, M. C. Burroughs, et al., “Spatially controlled UV light generation at depth by upconversion micelles”, Advanced Materials, 35, 2301563 (2023).
• M. C. Burroughs, et al., “Gelation dynamics during photocrosslinking of polymer nanocomposite hydrogels”, ACS Polymers Au, 3, 217–227, (2023).
• M. C. Burroughs, et al., “Flow-concentration coupling determines features of nonhomogeneous flow and shear banding in entangled polymer solutions”, Journal of Rheology, 67, 219–239, (2023).
• M. C. Burroughs, et al., “Flow-induced concentration nonuniformity and shear banding in entangled polymer solutions”, Physical Review Letters, 126, 207801, (2021).
• M. C. Burroughs, et al., “Coupled non-homogeneous flows and flow-enhanced concentration fluctuations during startup shear of entangled polymer solutions”, Physical Review Fluids, 5, 043301, (2020).
• P. Cheng, M. C. Burroughs, et al., “Distinguishing shear thinning from shear banding in flows with a stress gradient”, Rheologica Acta, 56, 1007–1032, (2017).
• M. C. Burroughs*, S. M. Bhaway*, et al., “Cooperative Assembly of Metal Nitrate and Citric Acid with Block Copolymers: Role of Carbonate Conversion Temperature on the Mesostructure of Ordered Porous Oxides”, Journal of Physical Chemistry C, 22, 12138–12148, (2015). *indicates co-first author

Selected Awards

• Arnold O. Beckman Postdoctoral Fellowship in the Chemical Sciences (2022 – 2025)
• Invited Postdoc Competition Winner, Georgia Tech Student Polymer Network (2023)
• University of Washington, Distinguished Young Scholars Seminar Speaker (2023)
• ACS Polymeric Materials Science and Engineering Future Faculty Scholar (2023)
• Stanford Bio-X Travel Award (2023)
• APS Future Investigator Travel (FIT) Award (2023)
• NSF Graduate Research Fellowship, Honorable Mention (2016, 2017)
• Senior Award for Scholarly Achievement, NC State University Department of Chemical and Biomolecular Engineering (2015)

Teaching Interests

Given my educational background in chemical engineering, I am excited and qualified to teach all chemical engineering core courses. I especially look forward to teaching transport phenomena, material and energy balances, and thermodynamics. Beyond these courses, I am interested in developing two new elective courses: (i) a consumer products formulations course that introduces students to engineering industrially relevant properties in soft matter, and (ii) a rheology course focused on measurement techniques and characterization of soft materials.

My role as an educator extends beyond the classroom into the research lab. I am committed to training researchers from all career stages and backgrounds in an interdisciplinary research environment focused on polymer science and engineering. In fulfillment of this vision, projects in my group will utilize concepts from chemical engineering, materials science, physics, and chemistry.

Teaching Experience

During graduate school, I served as a teaching assistant for three chemical engineering courses including:

• Senior Unit Operations Lab (ChE 180)
• Material and Energy Balances (ChE 10)
• Graduate Transport Phenomena II (ChE 220B)

Each of these experiences afforded me opportunities to grow as an educator. In addition to TA duties, I guest lectured for several ChE 10 classes. I also worked with John Wiley & Sons to develop and proofread a solutions manual for the 4^th edition of “Elementary Principles of Chemical Processes” by Felder, Rousseau, and Bullard.

Service

I am committed to fostering a diverse, equitable, and inclusive environment in the classroom, research lab, and broader scientific community. This commitment has guided my continued participation in service and outreach activities for over a decade. At UC Santa Barbara, I co-founded the Graduate Student Association for the Chemical Engineering department, which organized social and professional development activities for students. In graduate school, I chaired the planning of our department’s 12^th annual Amgen-Clorox Graduate Student Symposium. At UC Santa Barbara and Stanford, I lead a weekly seminar series for researchers and faculty in the chemical sciences to build on-campus community, provide scientific communication training opportunities, and catalyze interdisciplinary research activity. Since graduate school, I remain engaged in K-12 outreach at local elementary, middle, and high schools. I am a firm believer in the importance of early exposure to STEM in the recruitment of future students from diverse backgrounds and identities. As a faculty member, I will continue to engage in service and outreach activities on lab, university, and scientific community levels.