ASSOCIATING-POLYMER EFFECTS IN A HELE-SHAW EXPERIMENT

Pattern formation is studied by injecting water into a radial Hele-Sha w cell filled with an aqueous solution of hydrophobically terminated p olyoxyethylene, which forms a reversible associating network in water. A crossover from fingering pattern to fracturing pattern is demonstra ted as the injection rate exceeds a threshold value. The fingering-fra cturing transition is sufficiently abrupt that no gradual crossover ha s been observed within our limits of experimental control, and it is f ound to be consistent with a Deborah-number scaling, except for homopo lymers (where the hydrophobic end caps are replaced by hydroxyl groups ) for which the fingering-fracturing transition was never observed.