Studies of critical behaviour at the nematic to smectic A phase transition in C6 and C7 binary mixture system

Abstract

The nematic (N) to smectic A (SmA) phase transitions in binary mixtures of the 6th (D6AOB) and 7th (D7AOB) members of alkylazoxybenzene series have been studied using high-precision calorimetry at 10, 20, 30, 50, 75 and 100 wt% of D7AOB concentrations. The temperature range of the nematic phase on six binary mixtures was wide, and it was dependent on the concentration of D7AOB and the ratio of transition temperatures TNA/TNI changes from 0.889 for 10 wt% D7AOB to 0.951 for 100 wt% D7AOB. The ratio of specific-heat amplitudes above and below the nematic to smectic (NA) transition, A+/A−, remains ∼1.0. The value of specific-heat exponent, α, changes from 0.1 to 0.4, implying variations from three-dimensional Ising type behaviour to mean field tricritical type behaviour, respectively, when the concentration of D7AOB increased from 10 wt% to 100 wt%.

Calorimetric study of the nematic to smectic-Aphase transition in octylcyanobiphenyl-hexane binary mixtures

“…The N-SmA transition is also a model phase transition for the study of confinement and disorder effects such as in mixtures with silica aerosil [3][4][5], or embedded in an aerogel [6,7] and controlled porous glass [8][9][10]. The phase transition behavior is also sensitive to an applied external electric and magnetic field [11,12] as well as with LC+LC mixtures [13][14][15][16][17].…”