Pretransitional scaling close to a double critical point in a potassium laurate, 1-decanol, and heavy water lyotropic liquid crystal.

Light scattering measurements were done close to the double critical point of the isotropic boundary of the lyotropic liquid crystal potassium laurate, 1-decanol, and heavy water. From scaling analysis we find susceptibility and correlation length exponents that are clearly higher than the mean-field values usually found in other studies on this and similar systems. In order to recover mean-field analysis, we use a parabolic version of the Landau-de Gennes free energy in account of the convex nature of the phase diagram. We also observe pretransitional characteristic domain sizes greater than the correlation length. Furthermore, we show that the transition goes into a new two-phase coexistence region, between the convex tips of pure isotropic and discotic nematic boundaries.