title: Calorimetric study of the effect of bent-shaped dopant molecules on the critical behavior at the nematic-smectic-Ad phase transition.
abstract: We report results of calorimetric studies for the binary mixture of rodlike host n-alkyloxy-cyanobiphenyl (nOCB, n=8,9) and bent-shaped guest 1,3-phenylene-bis[4-(3-methylbenzoyloxy)]-4'-n-dodecylbiphenyl-4'-carboxylate (BC12). The effect of bent-shaped dopant molecules on the critical behavior associated with the nematic-smectic-A(d) phase transition has been studied in detail. The transition temperature for the nematic-smectic-A(d) phase sharply decreases as the increase of the mole fraction of the dopant concentration (denoted X for the BC12/9OCB mixture and Y for the BC12/8OCB mixture). The dependence of the critical exponent α on X and Y is well explained in terms of the McMillan ratio. A nearly tricritical exponent has been obtained for the X=0.01 mixture. X=0.02-0.03 mixtures, pure 8OCB, and Y=0.01-0.03 mixtures exhibit nonuniversal behaviors with effective exponents lying between the 3D-XY and tricritical exponents. The heat capacity anomaly for Y=0.05 has been well described with the 3D-XY exponent. The critical amplitude ratio A(-)/A(+) is close to 1 and insensitive to the dopant concentration. No Fisher renormalization of the critical exponent has been observed even for nearly tricritical compositions, which indicates the smallness of the concentration plays a decisive role rather than the steepness of the N-SmA(d) phase boundary.
authors.affiliation: Department of Physics, Tokyo Institute of Technology, O-okayama, Meguro, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Sasaki
authors.forename: K
authors.initials: K
authors.lastname: Ema
authors.forename: K V
authors.initials: KV
authors.lastname: Le
authors.forename: H
authors.initials: H
authors.lastname: Takezoe
authors.forename: S
authors.initials: S
authors.lastname: Dhara
authors.forename: B K
authors.initials: BK
authors.lastname: Sadashiva