CPOS Seminar: Microrheology of Kinetically Evolving Systems
Speaker: Caidric Gupit, PhD - Department of Mechanical Engineering, University of California Santa Barbara
Abstract: Monitoring kinetic processes is critical in understanding and thus optimizing the process itself for materials development and sustainability. These processes include polymerization, degradation, and phase separation which were monitored using a recently developed passive probe microrheology technique based on differential dynamic microscopy (DDM). In this work, we demonstrated this technique as a facile, low-cost, and high-throughput means to track kinetic processes using the measured viscosity.
This technique was applied to N-N-dimethylacrylamide undergoing reversible addition-fragmentation chain-transfer (RAFT) polymerization where the results were validated against conventional size-exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy measurements. A simple and intuitive workflow based on a single-point Mark-Houwink analysis was used to estimate an apparent viscosity from SEC and NMR data and, equivalently, an apparent molecular weight from DDM microrheology data. Good quantitative agreement was observed between the measured and apparent viscosities and molecular weights, demonstrating the ease and reliability of this technique in tracking changes in the molecular weight through the measured viscosity.
In a similar way, DDM microrheology was also applied to poly(methyl methacrylate) undergoing photo-assisted depolymerization, a pressure-sensitive adhesive analogue based on polylipoate undergoing reductive degradation, and a water-soluble derivative of cellulose, carboxymethylcellulose, undergoing enzymatic degradation. The extent of degradation was evaluated across various formulations at different molecular weights, compositions, and degradation conditions, highlighting the efficiency and high-throughput capability of DDM microrheology in screening sample degradation and potentially enabling closed-loop recycling of polymer materials. Lastly, this technique was applied to dispersions of reflectin protein undergoing liquid-liquid phase separation where the viscosity data is expected to construct the phase diagram with time- and cost-efficiency.
Taken together, the results in this work demonstrate that DDM microrheology can sensitively monitor various kinetic processes through the solution viscosity as an attractive alternative to conventional methods.
Bio: Caidric received his Ph.D. degree at the University of Tokyo, Japan under the guidance of Prof. Mitsuhiro Shibayama and Prof. Xiang Li, where he worked on correlating the structure and mechanical properties of soft materials using scattering and mechanical measurements. He is currently a postdoctoral researcher in the groups of Prof. Matthew Helgeson and Prof. Megan Valentine at the University of California, Santa Barbara, working on the development of microrheological methods to study dynamically evolving soft materials such as polymer solutions, networks, and stimuli-responsive materials.
