First Winter Lunch and Learn: Professor Danielle Mai
SPC is lucky to be joined by Professor Danielle Mai from the Department of Chemical Engineering, presenting on the Stretching Dynamics of Topologically Complex Polymers. Sign up for the Lunch and Learn on Monday, February 10th from 12 pm to 1 pm.
Molecular-scale polymer connectivity, or topology, dictates the structure and function of polymeric materials from self-healing hydrogels to separation membranes to flexible electronics. Topologically complex polymers exhibit particularly useful properties in extensional flow, such as the stabilization of blown films by branched polymers or the toughening of self-healing gels by entanglements. Recent progress in the synthesis of structurally defined polymers has provided new opportunities to investigate how molecular-scale phenomena give rise to the emergent behavior of topologically complex polymers. In this talk, I will present two biopolymer systems that enable the precise design, synthesis, and molecular-scale characterization of topologically complex polymers.
First, we directly observe polymer chain dynamics at the molecular level using single-molecule fluorescence microscopy. Although the vast majority of single polymer studies have focused on linear or circular DNA molecules, we developed a method to generate DNA-based comb polymers as model branched polymers. We applied a molecular rheology approach and precision microfluidics to perform “hydrodynamic trapping” of single DNA combs in planar extensional flow. Here, observations of detailed intramolecular interactions and topology-controlled dynamics revealed the impact of local topological constraints on global molecular behavior.
Second, we investigate the role of entanglement on the mechanics of associative protein hydrogels. Physically crosslinked, entangled polymers have emerged as self-healing and stretchable materials with remarkable toughness and extensibility. Such materials have been produced by several distinct chemical approaches, which suggests that these enhanced mechanical properties result from molecular-scale topology. We compare well-defined unentangled and entangled protein hydrogels by measuring uniaxial strain-induced structural changes with in situ small-angle X-ray scattering and in situ polarized optical microscopy. Here, rate-dependent, anisotropic optical responses indicate the critical roles of topological constraints on the high toughness and elongation of entangled physical gels.