(2gb) Bridging Dissimilar Materials through Dynamic Bonds

Hierarchical assemblies of dissimilar materials are plentiful in nature, leading to exceptional properties that are a constant source of inspiration for a broad range of materials-focused research. However, a major issue in reproducing the natural composites lies at the interface between dissimilar materials. Generally, interfaces between materials are areas of stress concentration and low domain connectivity, leading to failure under load. While some promising photopatterning approaches have been developed, the resulting materials are formed using irreversible bonds, which prohibits reprocessing. Incorporating dynamic bonds into such systems should simultaneously allow for forming direct linkages between dissimilar material domains and enable stress relaxation / reprocessibility. My proposed research program is divided into three themes focused on employing such dynamic bonds: 1) Development of new light-sensitive dynamic bonding motifs and networks, 2) Reconfigurable, stimuli-responsive polymer architectures and morphologies, and 3) Dynamic-bond mediated composites from commodity plastic waste.

Research Interests: The proposed research program will leverage expertise in organic synthesis, photophysical chemistry, and precision polymer design alongside an extensive suite of materials characterization techniques. The interdisciplinary nature of the proposed work will actively encourage students to develop strong scientific communication skills and will serve as a broad platform for collaborative studies.

Aim 1. Development of new light-sensitive dynamic bonding motifs and networks: Light is a powerful and highly tunable stimulus to manipulate chemistry, with ready access to changes in wavelength and intensity as well as the benefit of spatiotemporal control. However, a majority of polymeric materials generated through light-driven chemistry (photocuring) have static bonds, generally forming non-reprocessible parts. This aim seeks to develop new photoactive dynamic bonding motifs, where light can be used to orthogonally control the exchange characteristics of the underlying material. Synthetic targets focus on analogues to hydrazone, hemi-indigo, azobenzene, and diarylethene switches whose conformation/sterics/electronics can be reversibly modified through exposure to light. Projects in this aim will use traditional organic chemistry approaches/characterization methods alongside real-time photochemical measurements such as pump-probe UV-vis and LED-coupled NMR to develop next-generation dynamic bonds and networks.

Aim 2. Reconfigurable, stimuli-responsive polymer architectures and morphologies: Dynamic exchange has been thoroughly leveraged to synthesize a suite of interesting materials with controllable stress relaxation and self-healing properties. However, bond exchange (particularly low energy / temperature reactions) are prone to creep, eventually leading to loss of form under extended load times. While this creep can be leveraged in certain applications (pressure sensitive adhesives for instance), it generally limits the application scope of dynamic networks. However, creep can be mitigated through the formation of microphase separated materials (thermoplastic elastomers), and external control over the morphology of phase separation would allow for user-defined and spatially controlled relaxation kinetics. To this end, this aim seeks to develop stimuli-responsive polymer architectures, which can lead to spatially controlled morphologies. Projects focused in this aim will use controlled polymerization techniques and precise polymer modification (end groups, junctions) to insert dynamic bonds at critical positions to impact polymer architecture. Initial polymers will be composed of well-understood polymer pairs (PS/PMMA), but future works will investigate systems with high degrees of conformational asymmetry, giving access to richer phase diagrams (such as Frank-Kasper phases).

Aim 3. Dynamic Immiscible Polymer Composites: The interface between dissimilar (immiscible) plastics often leads to macrophase separation and unfavorable interactions leading to loss of desirable properties, which has (in part) hamstrung our ability to recycle polymeric materials, leading to a disastrous accumulation of plastic waste globally. By stabilizing the domains, the size of phase separated domains can be shrunk dramatically, and properties can recover. By employing a combination of complimentary-functional particles and short stabilizing polymers, stabilized composite materials with enhanced mechanical properties could be produced. Projects will focus on the optimization of dynamic chemistries and particle loading to target interfaces / optimize mechanical properties for known immiscible blends, eventually extending to relevant commodity plastic blends (PE/PP, PS/PVC, as well as complex mixtures simulating real-world waste makeup). Projects focused in this aim will cover particle synthesis / functionalization in conjunction with a variety of casting / compounding strategies for forming composites from immiscible polymer blends. Additionally, electron microscopy will be thoroughly leveraged to understand plastic/particle localization.

Teaching Interests: I am eager and well-prepared to teach a range of topics, including undergraduate level core courses covering physical and organic chemistry, materials science, and select chemical engineering core courses, but would be most excited to continue instructing polymer-centric courses. During my graduate career, I gained significant exposure to teaching polymer science (TA, upper-level undergraduate level), which allowed me to quickly identify aspects of polymer science that first time learners may find challenging. I expanded this experience during my postdoc, taking on the role of co-instructor for the Introduction to Polymer Science course (8 lectures, graduate student polymer core). Lecturing, working with the TA, and writing the midterm were effective experiences in developing my pedagogy. When instructing graduate students, I made sure to put emphasis on how various concepts and equations are used day-today in polymer research (helping students apply class material to their own projects). I have received (largely) positive feedback from my students, which I attribute to my experience in polymer-centric outreach programs, where I have already done the hard work in making the overall concepts digestible for nonspecialist audiences. In my independent career, I hope to develop highly applied graduate-level courses, namely: Logical Approaches to Precision Polymers as well as Effective Scientific Communication (focusing on presentation skills).