Department Seminar: Julie Kornfield
Ultralong polymers (weight-average molecular weight Mw ≥ 5000 kg/mol) exhibit striking effects on fluid dynamics even at low concentration. For example, at 100 ppm,they can control mist and reduce turbulent drag, thanks to their ability to store energy as they stretch, such that the fluid as a whole resists elongation. Unfortunately, ultralong backbones undergo chain scission during routine handling because hydrodynamic tension builds up along the backbone to a level that breaks covalent bonds; this “shear degradation” continues until the their aluable effects are lost (Mw < 1000 kg/mol). After 9/11, we took a fresh look at polymers for mist control in the hope of discovering a polymer that might make it impossible to use a jumbo jet to bring down a skyscraper. For use in fuel, the polymer would need to be effective at very low concentration. Prior literature showed that self-assembly of end-associative polymers creates supramolecules that break and reassociate reversibly, but formation of ultra-long supramolecules at low concentration had never been achieved. Statistical mechanics showed us how to design polymers that self-assemble into “megasupramolecules” (≥5000 kg/mol) at low concentration (≤0.3%wt). Theoretical treatment of the distribution of individual subunits—end-functional polymers—among cyclic and linear supramolecules predicts that megasupramolecules can format at low total polymer concentration if, and only if, the backbones are long (>400 kg/mol) and end-association strength is optimal. Viscometry and scattering measurements of long telechelic polymers having polycyclooctadiene backbones and acid or amine end groups verify the formation of megasupramolecules. They inhibit misting (the cause of fuel fireballs) and reduce drag in the same manner as ultralong covalent polymers. With individual building blocks short enough to avoid hydrodynamic chain scission (weight-average molecular weights of 400 to 1000 kg/mol) and reversible linkages that protect covalent bonds, overcoming the obstacles of shear degradation and engine incompatibility. Megasupramolecules confer a variety of benefits beyond mist control and are currently being evaluated for commercialization.
Julia A. Kornfield, Professor of Chemical Engineering at the California Institute of Technology (Caltech), is an expert in polymer science, particularly how polymers influence and are influenced by flow. She has applied small angle neutron and x-ray scattering to diverse systems, including end-associative polymers for aviation safety and security (Wei et al., Science 2015), flow-induced crystallization of polymers (e.g., Science 2007) and the effects of flow on polymer self-assembly (e.g., Science 1997). Since she joined the Caltech faculty in 1990, Kornfield has received the Dillon Medal of the American Physical Society and been elected Fellow of the American Physical Society and the American Association for the Advancement of Science, among other honors. She holds 27 patents and is a co-founder of Calhoun Vision, which uses polymers developed at Caltech to customize vision by noninvasively optimizing a lens after it is implanted into a patients’ eye. Thus, her work spans from fundamental research on the molecular basis of polymer structure and properties, to commercialization of polymers that improve health and safety.