1. Precision adiabatic scanning calorimetry of a nematic – ferroelectric nematic phase transition.
- Author
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Thoen, Jan, Korblova, Eva, Walba, David M., Clark, Noel A., and Glorieux, Christ
- Subjects
PHASE transitions ,SPECIFIC heat capacity ,NEMATIC liquid crystals ,LATENT heat ,ELECTRIC measurements ,CALORIMETRY - Abstract
In high-resolution adiabatic scanning calorimetry (ASC) experiments, data for the temperature dependence of the specific enthalpy, h(T), and of the specific heat capacity, c
p (T), are simultaneously obtained, from which the order of the phase transition and critical behaviour can be evaluated. ASC was applied to study the nematic to ferroelectric nematic phase transition (N–NF ) in the liquid crystal molecule 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). The N–NF was found to be very weakly first order with a latent heat Δh = 0.115 ± 0.005 J/g. The pretransitional specific heat capacity behaviour is substantially larger in the high-temperature N phase than in the low-temperature NF phase. In both phases the power-law analysis of cp (T) resulted in a critical exponent α = 0.50 ± 0.05 and amplitude ratio ANF /AN = 0.42 ± 0.03. The very small latent heat and the value of α indicate that the N–NF transition is close to a tricritical point. This is confirmed by a value of the order parameter exponent β ≈ 0.25, recently obtained from electric polarisation measurements. Invoking two-scale-factor universality, it follows from the low value of ANF /AN ratio that the size of the critical fluctuations is much larger in the NF phase than in the N phase. [ABSTRACT FROM AUTHOR]- Published
- 2022
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