Megasupramolecules take to water

Ultralong linear polymers at low concentration profoundly alter the behavior of low viscosity liquids in flows that involve elongation---yet leave the shear viscosity and interfacial tension nearly unchanged. The advent of dripping-on-substrate extensional rheometry (DoSER) represents a major contribution to characterizing these low shear viscosity solutions. One of the key features of ultralong polymers is their susceptibility to irreversible degradation in extensional flow: DoSER proved to be a fast measurement that quantitatively correlates with molecular weight determined by gel permeation chromatography (GPC) for the present systems (long, flexible polymers with 30,000 or more backbone atoms at c/c* of 0.2 to 2 in an inertio-capillary solvent with Ohnesorge number Oh << 1). To overcome irreversible chain scission, we examine long end-associative polymers that can link into ultralong supramolecules, “megasupramolecules.” Individual molecules of 860kg/mol polyacrylamide (PAM) are long, yet their aqueous solutions resist chain scission. Installing terpyridine groups at each end allows them to assemble pairwise by metal-ligand interactions. In strong flows, these pairs dissociate before the force reaches levels that break covalent bonds. DoSER sensitively detects supramolecules, showing that a 0.1%wt solution of 860k terpy-PAM with Ni²⁺ 1:2 terpy behaves like a 0.1%wt 5.5M PAM homopolymer, hence the name megasupramolecules.