Eur. Phys. J. E (2012) 35: 54
https://doi.org/10.1140/epje/i2012-12054-5

Regular Article

Evidence from adiabatic scanning calorimetry for the Halperin-Lubensky-Ma effect at the N-SmA phase transitions in mixtures of 7OCB+heptane with an injected SmA phase

¹ Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001, Leuven, Belgium
² Condensed Matter Physics Department, Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
³ Department of Physics, University of Athens, 15784, Athens, Greece

^* e-mail: chandrashekharpatitripathi@gmail.com
^** e-mail: jan.thoen@fys.kuleuven.be

Received: 30 March 2012
Revised: 5 June 2012
Accepted: 11 June 2012
Published online: 6 July 2012

Abstract

The high-resolution adiabatic scanning calorimetric technique has been used to investigate the nematic-smectic A transition (N-SmA in binary mixtures of the non-smectogenic liquid crystal heptyloxycyanobiphenyl (7OCB) and heptane, exhibiting a so-called injected smectic A phase. With the exception of a mixture with the lowest heptane mole fraction for which only an upper limit of 0.2 ± 0.2 J kg⁻¹ for a possible latent heat could be obtained, for all other mixtures finite latent heats were obtained. The mole fraction dependence of the latent heat could be well fitted with a crossover function consistent with a mean-field free energy expression with a non-zero cubic term arising from the Halperin-Lubensky-Ma (HLM) coupling between the SmA order parameter and the orientational director fluctuations. The mole fraction dependence of the heat capacity effective critical exponents is similar to that observed in mixtures of the two liquid crystals octyloxycyanobiphenyl (8OCB) and nonylcyanobiphenyl (9OCB). The thermal behavior observed along the N-SmA phase transition line yields further strong evidence for the HLM coupling effect.