Universal properties of lamellar systems under weak shear

Abstract:

We have observed that different lamellar phases (thermotropic, lyotropic of surfactants or blockcopolymers) share the same rheological properties \(\) = A(T)σ^m, m = 1.67±0.1, independently of their chemical nature, in a range of shear rates \(\), shear stresses σ, and temperatures T, where the flow is stationary. It is argued that the key phenomenon is the appearance of screw dislocations whose glide under an applied shear counterbalances plastically the applied vorticity, and stabilizes the layers, whose slip past each other is thus made more feasible. The theory, which makes use in other respects of the high-temperature creep model in solids, reproduces correctly the power law behavior and the values of A(T).