Effect of nonmesogenic impurities on the order of the nematic to smectic-A phase transition in liquid crystals.
By means of adiabatic scanning calorimetry, we have studied the effect of the nonmesogenic solutes cyclohexane (CH) and biphenyl (BP) on the nematic-smectic-A phase transition in the liquid crystal octylcyanobiphenyl (8CB). For all concentrations of BP studied, the transition remains second-order. For 8CB+CH, however, crossover from second-order to first-order is observed at a tricritical point of the mole fraction x of CH around 0.0460. The difference between the two systems and the crossover is explained in terms of a mean-field free energy density expression including coupling terms of x with the nematic and smectic-A order parameters.
Denolf
Katleen
K
Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium.
Van Roie
Bert
B
Glorieux
Christ
C
Thoen
Jan
J
D001713:Biphenyl Compounds / Q000737:chemistry; D002151:Calorimetry / Q000379:methods*; D002627:Chemistry, Physical / Q000379:methods*; D003510:Cyclohexanes / Q000737:chemistry; D006358:Hot Temperature; D050866:Liquid Crystals; D008956:Models, Chemical; D015233:Models, Statistical; D009570:Nitriles / Q000737:chemistry; D044367:Phase Transition; D013696:Temperature; D013816:Thermodynamics
D001713:Biphenyl Compounds; D003510:Cyclohexanes; D009570:Nitriles; C495061:4'-octyl-4-cyanobiphenyl; C010574:biphenyl; C506365:Cyclohexane