Nonuniversal Critical Behavior at the Uniaxial-Biaxial Nematic Phase Transition in a Lyotropic Mixture

Measurements of the order-parameter critical exponent β at the uniaxial-biaxial nematic phase transition in a lyotropic mixture are reported. They reveal a strong dependence of β on the concentration of the mixture compounds with two distinct intervals of values separated by a discontinuity. This nonuniversal behavior is interpreted as the result of three different contributions, which express the micellar biaxiality and the distribution of the micellar population with respect to biaxiality and volume.