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The temperature dependence of the birefringence and magnetic field induced effects were studied on thin films of mixtures of potassium laurate, 1-decanol, and D2O. The selected mixtures have a small biaxial nematic range between two uniaxial nematics. The biaxial–uniaxial nematic phase transitions are second order and have critical properties that deviate from mean field behavior. Values of critical exponents were determined for the order parameter in the biaxial phase at the lower temperature transition to the uniaxial nematic phase Nd, and for the susceptibility exponents on both sides of this transition. The experiment gives β=0.37 or β=0.35, depending on the method of evaluation, γ=1.33 and γ′=0.81. The values for β and γ agree within error limits with the theoretical values of the x, y model but γ′ deviates.

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