Rheology of Lyotropic Liquid Crystals of Aerosol OT: II. High Concentration Regime

✍ Scribed by Oscar Robles-Vásquez; Sergio Corona-Galván; J.Felix A. Soltero; Jorge E. Puig; Silvana B. Tripodi; Enrique Vallés; Octavio Manero

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 345 KB
• Volume: 160
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1993.1368

✦ Synopsis

Dynamic and steady-shear rheological measurements of the AOT/water lamellar liquid crystalline phase are reported as a function of surfactant concentration. Dynamical measurements indicate that the AOT/water lamellar phase behaves as a weak gel; i.e., both the elastic and the loss moduli, (G^{\prime}) and (G^{\prime \prime}), are nearly independent of frequency ((\omega)) and (G^{\prime}) is an order of magnitude greater than (G^{\prime \prime}) in the range (10^{-2}) to (10^{2} \mathrm{~s}^{-1}). Complex and dynamic viscosities decrease with frequency as (\omega^{-1}). Steady shear measurements demonstrate a shear thinning behavior with (\eta \propto \dot{\gamma}^{-1}) but (\eta) does not tend to a Newtonian plateau at low shear rates. The measured material functions (\left(G^{\prime}, \eta^{*}\right.), and (\left.\eta\right)) go through a minimum at around (50 \mathrm{wt} %) AOT. This minimum is explained in terms of attractive and repulsive colloidal forces in the bilayers and in terms of interactions among the liquid crystalline microdomains. ⑲93 Academic Press, Inc.