RHEOLOGICAL AND RHEOOPTICAL CHARACTERIZATION OF SHEAR-INDUCED STRUCTURE FORMATION IN A NONIONIC DRAG-REDUCING SURFACTANT SOLUTION

We know of only a few rheological studies of nonionic surfactant solut ions, and these did not show clear evidence of shear-induced structure s (SIS) formation. This paper reports, however, some rheological and r heo-optical results for nonionic surfactant solutions at different con centrations and temperatures that do show clear evidence of such SIS f ormation. For example, in a 0.3% SPE 95285 solution at 5 degrees C, th e shear viscosity, N-1, and flow birefringence start from a low level and takes tens of seconds to grow to a high plateau region upon the ap plication of a 100 s(-1) shear. The re-application of the same shear a fter rest following a preshear indicates that the effect of the shear persists for a very long time (hundreds of seconds). These transient f low results resemble those exhibited by cationic surfactants or associ ating polymer solutions. The time needed for the viscosity and N-1 to reach plateau values generally decrease with increasing shear rate and temperature. At moderate shear rates, the N-1 and viscosity decrease monotonically with increasing temperature, whereas at low shear rate t he viscosity increases with temperature up to the cloud point, and the n decreases. The steady state N-1 and viscosity levels increase with t he surfactant concentration. Both the transient and steady state behav ior appear rather insensitive to the addition of contaminants. (C) 199 7 The Society of Rheology.