SHEAR-INDUCED HEXAGONAL ORDERING OBSERVED IN AN IONIC VISCOELASTIC FLUID IN FLOW PAST A SURFACE

We present the first clear evidence of a shear induced hexagonal phase in a polyionic fluid in flow past a plane quartz surface. The dilute surfactant solution studied is viscoelastic due to the formation and e ntanglement of highly extended charged threadlike micelles many thousa nds of A long, which arc known to align along the flow direction under shear. Small-angle neutron diffraction data show that in the high she ar region within a few tens of microns of the surface these micelles n ot only align, but form a remarkably well ordered hexagonal array sepa rated by 370 angstrom, 8 times their 46 angstrom diameter.