Ultralong polymers in dilute solution have been known since the 1940s to significantly modify turbulent flow, a phenomenon called drag reduction, but these long covalent chains suffer from bond scission under stress. As a result of degradation and the complexity of turbulence, the mechanism of how long chains impact flow is still not well understood. To imitate ultralong polymers and study the interaction between chains and turbulence, we use long end-associative polymers with hydrogen-bonding end-groups that link in solution at low concentrations to form multi-million molecular weight supramolecules (megasupramolecules). These megasupramolecules can stretch to microns in length, while reversibly breaking and reforming in flow conditions, and can be designed to target different length and energy scales in turbulence. Changing the backbone length of the associative units adjusts the reach of the megasupramolecules, both in the coiled and stretched states. Changing the association strength by choosing alternate functional groups adjusts the stress the megasupramolecule will withstand before disassociating. The action of the molecules on the flow is observed through particle imaging velocimetry, a technique for determining detailed velocity profiles and fluctuations, with increased reproducibility due to the ability of the megasupramolecules to reversibly associative instead of permanently degrading. Using these megasupramolecules as probes explores suppression of different turbulence modes as a route to understand both how drag reduction occurs in polymer solutions and how turbulence can be characterized and manipulated.

Megasupramolecules as molecular probes of turbulence

253rd National Meeting (2017)

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