Megasupramolecules as molecular probes of turbulence

Abstract

Ultralong polymers in dil. soln. have been known since the 1940s to significantly modify turbulent flow, a phenomenon called drag redn., but these long covalent chains suffer from bond scission under stress. As a result of degrdn. 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 soln. at low concns. to form multi-million mol. wt. supramols. (megasupramols.). These megasupramols. 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 megasupramols., both in the coiled and stretched states. Changing the assocn. strength by choosing alternate functional groups adjusts the stress the megasupramol. will withstand before disassocg. The action of the mols. on the flow is obsd. through particle imaging velocimetry, a technique for detg. detailed velocity profiles and fluctuations, with increased reproducibility due to the ability of the megasupramols. to reversibly associative instead of permanently degrading. Using these megasupramols. as probes explores suppression of different turbulence modes as a route to understand both how drag redn. occurs in polymer solns. and how turbulence can be characterized and manipulated.