ISSN:
1435-1528
Keywords:
Key words Surfactant solution
;
salt concentration
;
shear-induced structure
;
Cox-Merz rule
;
small-angle light scattering
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract We investigate the effect of excess salt and simple shear on the dynamics and structure of semidilute aqueous solutions of cetyltrimethylammonium bromide and sodium salicylate. Small-amplitude oscillatory rheological measurements suggest a structural evolution from an entangled to a multi-connected network as the salt concentration is increased. Steady-shear measurements, however, show a significant departure from the Cox-Merz rule. At low salt concentrations, this departure occurs at high shear rates with η*∝ω–0.92±0.08 and η∝˙γ–0.51±0.06 and is attributed to the formation of large shear-induced structures. The critical shear rate ˙γ c at which the Cox-Merz rule fails approximates the inverse of the terminal relaxation time, τ. At high salt concentrations, however, the departure occurs at both low and high shear rates and is attributed to the formation of a multi-connected network. Small-angle light scattering (SALS) under shear was used to probe the mesoscopic structure and revealed novel scattering patterns exhibiting two-fold symmetry at low salt concentration and four-fold symmetry at high salt concentration. The SALS patterns were in qualitative agreement with the formation of large scale anisotropic structures at high shear rates and a multi-connected network at high salt concentrations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00366719
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