Associating-polymer effects in a Hele-Shaw experiment

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Abstract
Pattern formation is studied by injecting water into a radial Hele-Shaw cell filled with an aqueous solution of hydrophobically terminated polyoxyethylene, which forms a reversible associating network in water. A crossover from fingering pattern to fracturing pattern is demonstrated as the injection rate exceeds a threshold value. The fingering-fracturing transition is sufficiently abrupt that no gradual crossover has been observed within our limits of experimental control, and it is found to be consistent with a Deborah-number scaling, except for homopolymers (where the hydrophobic end caps are replaced by hydroxyl groups) for which the fingering-fracturing transition was never observed.