(6ls) Understanding the hierarchy of structure, dynamics, and interactions in soft matter

In soft matter systems, the structure, dynamics, and interactions between foundational building blocks lead to complex material responses. Engineers have exploited the interplay of these properties to design materials with similar compositions but with drastically different properties, such as processable polymer composites that are as strong as metal or swollen polymer gels whose elasticity controls the expression and fate of stem cells. The knowledge and understanding generated by studying synthetic soft materials – emulsions and foams, polymer melts and solutions, liquid crystals, etc. – also translates into understanding the behavior of biological soft materials such as cells and tissues. Better understanding of these complex biological materials will lead to the development of synthetic analogues to greatly benefit biomedical research and the development of therapeutics and diagnostics. Fundamental control of how soft matter components structure, move, and interact in a hierarchical fashion from the nano- to micro- to macroscale is critical to develop materials that respond to environmental stimuli and serve as biological mimics.

My research uses a combination of complementary techniques to characterize the behavior and the consequences of that behavior in soft matter systems from molecular to bulk time and length scales. During my Ph.D., I investigated how the dynamics of tracer particles couple to the structure and relaxations in complex, heterogeneous materials to improve the processing of composite materials and efficacy of targeted drug delivery methods. My work identified that nanoparticles diffuse orders of magnitude faster than expected when they are comparably sized to characteristic length scales in the material. For my postdoctoral research, I characterized the mechanics of dense gels of cellulose nanofibrils using bulk rheology. At high concentrations, the fibrils form physical networks whose yielding behavior bifurcates around a critical stress during aging as segmental fluctuations rebuild a percolating network. This work provides fundamental insight into the yielding of amorphous materials to aid the design of sustainable inks for additive manufacturing and of hydrogels for tissue engineering applications. Throughout my doctoral and postdoctoral experience, I identified the physics that underly material properties using static and dynamic scattering methods to drive drastic changes in the bulk material response characterized with bulk rheology. This bottom-up approach builds a comprehensive understanding of the hierarchical physical interplay that underlies soft materials.

As a faculty member, I will continue to focus on investigating and exploiting the interplay between structure, dynamics, and interparticle interactions on the nano- to macroscopic length and time scales and exploit these mechanisms to design the following:

• soft matter systems that undergo self-sustained periodic responses under a constant environmental stimulus
• facile and scalable methods to separate and purify mixtures of nanoparticles, and
• synthetic mimics of biological tissues.

Each of these projects focuses on critical open questions facing soft matter physics and achieving these goals will directly benefit applications ranging from energy storage, additive manufacturing, soft robotics, and tissue engineering.

To fund my research group, I will actively pursue funding resources from governmental agencies, private, non-profit groups, and industry. During my doctoral and postdoctoral research, I gained experience developing and writing successful proposals to acquire x-ray and neutron beamtime resources at multiple national labs as well as contributing to multiple funding proposals. The aim of my research overlaps with the goals of the Materials Genome Initiative and of many funding agencies, including NSF, ACS PRF, DOE, and DARPA, to which I will submit grant applications. Additionally, I aim to collaborate with potential industrial partners such as Unilever, Proctor & Gamble, and ExxonMobil due to my focus and expertise in soft matter materials and processing conditions.

Teaching Interests

I see beauty in the ability of chemical engineers to distill problems into simple, useful models. For example, biological cells are amazingly complex objects with multiple functions that interact with and respond to their surroundings. As chemical engineers, we can look at a cell and see a chemical reactor in miniature, with multiple inputs of raw materials and energy, internal reactions, control loops, and product outputs. Although the analogy of a cell as a reactor ignores much of the biological complexity, it distills the problem into a tractable and useful model that allows engineers to exploit the biological specificity of a cell to commercially produce valuable products such as insulin and monoclonal antibodies. With strong fundamentals and experience identifying and developing connections, students should be able to quickly master problems such as these even if they do not have specific training on how E. coli produces insulin. As an educator, I aim to focus on fundamental theories and critical thinking to inspire students to make connections between disparate fields and develop independent and creative solutions. Students should graduate as chemical engineers with the ability and self-confidence to jump into new disciplines, breakdown problems into basic building blocks, develop a solution, and justify their decisions without needing specific experience on those exact problems.

My training as a chemical engineer has prepared me to teach any of the core chemical engineering courses in the undergraduate curriculum. I am particularly interested in teaching classes relating to transport phenomena, such as heat and mass transfer or fluid dynamics, which will bring my research into the classroom. On a graduate level, I am interested in teaching advanced transport phenomena but also electives focusing on soft matter and polymer physics. My vision for a soft matter graduate elective course would focus on colloidal dynamics and structure, surface forces, and techniques to measure and characterize these phenomena on multiple length scales, with specific focus on scattering and rheological methods. For a polymer course, I would want to build a strong foundation of thermodynamic driving forces and how polymers relax and structure over different time and length scales.

Selected Publications (17 total, 8 first author)

For more information, please visit: http://www.ryanps.info

Poling-Skutvik, R.; Slim, A. H.; Narayanan, S.; Conrad, J. C.; Krishnamoorti, R. Soft interactions modify the diffusive dynamics of polymer-grafted nanoparticles in solutions of free polymer. ACS Macro Lett. 2019, 8, 917-922.

Poling-Skutvik, R.; Roberts, R. C.; Slim, A. H.; Narayanan, S.; Krishnamoorti, R.; Palmer, J. C.; Conrad, J. C. Structure dominates localization of tracers within aging nanoparticle glasses. J. Phys. Chem. Lett. 2019, 10, 1784-1789.

Poling-Skutvik, R.; Lee, J.; Narayanan, S.; Krishnamoorti, R.; Conrad, J. C. Tunable assembly of gold nanorods in polymer solutions to generate controlled nanostructured materials. ACS Appl. Nano Mater. 2018, 1 (2), 877–885.

Poling-Skutvik, R.; Olafson, K. N.; Narayanan, S.; Stingaciu, L.; Faraone, A.; Conrad, J. C.; Krishnamoorti, R. Confined dynamics of grafted polymer chains in solutions of linear polymer. Macromolecules 2017, 50 (18), 7372–7379

Poling-Skutvik, R.; Mongcopa, K. I. S.; Faraone, A.; Narayanan, S.; Conrad, J. C.; Krishnamoorti, R. Structure and dynamics of interacting nanoparticles in semidilute polymer solutions. Macromolecules 2016, 49 (17), 6568–6577.

Poling-Skutvik, R.; Krishnamoorti, R.; Conrad, J. C. Size-dependent dynamics of nanoparticles in unentangled polyelectrolyte solutions. ACS Macro Lett. 2015, 4 (10), 1169–1173.