Smectic-C-Alpha(*)-Smectic-C-* Phase Transition And Critical Point In Binary Mixtures

We have investigated the smectic-C-alpha(*)-smectic-C-* (SmC alpha*-SmC*) transition in a series of binary mixtures with resonant x-ray diffraction, differential optical reflectivity, and heat capacity measurements. Results show that the phases are separated by a first-order transition that ends at a critical point. We report the observation of such a critical point. We have proposed the appropriate order parameter and obtained values of two critical exponents associated with this transition. The values of the critical exponents suggest that long-range interactions are present in the SmC alpha*-SmC* critical region.