Nonuniversal critical behavior at the uniaxial-biaxial nematic phase transition in a lyotropic mixture

Measurements of the order-parameter critical exponent beta at the uniaxial-biaxial nematic phase transition in a lyotropic mixture are reported. They reveal a strong dependence of beta 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.