RHEOLOGY OF LYOTROPIC LIQUID-CRYSTALS OF AEROSOL OT .2. HIGH-CONCENTRATION REGIME

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“ and G” are nearly independent of frequency (ω) and G′ is an order of magnitude greater than G’ in the range 10-2 to 102 s-1. Complex and dynamic viscosities decrease with frequency as ω-1. Steady shear measurements demonstrate a shear thinning behavior with η ∝ γ-1 but η does not tend to a Newtonian plateau at low shear rates. The measured material functions (G’, η*, and η) go through a minimum at around 50 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.