Flow-induced structure change of CTAB/NaSal aqueous solutions in step planar elongation flow

摘要

Accurately controlled step planar elongation flow generated by a two-dimensional squeezing flow cell was applied to wormlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in water. Opaque regions were observed in the center plane and at the corners of the flow field during squeeze flow. The opaque region in the center plane is caused by planar elongation flow, resulting in elongation-induced structure (EIS), while the corner opaque regions are mainly induced by shear, generating shear-induced structure (SIS). SIS at the corners appeared earlier than EIS in the center plane in the squeezing process, but the strain required to generate EIS is considerably smaller than strain for SIS. In the case of high elongation rate and large strain, flow fluctuations appeared after EIS and SIS occurred. The appearance of both EIS and SIS are related to strain, the Weissenberg number, the Deborah number, and the concentration ratio of CTAB and NaSal in the solution but independent of the initial structure of the micelles in solution. (C) 2011 The Society of Rheology. [DOI: 10.1122/1.3528042]