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Most of the current highly polar rod-shaped molecules that form ferroelectric nematic (NF) phase do so only at elevated temperatures and multicomponent mixtures are generally needed to obtain a broad and room temperature range NF phase. In this work, we describe the synthesis, phase characterization and measurement of various physical properties of a new ferroelectric nematic compound 4-[(4-nitrophenoxy)carbonyl]phenyl 2-isopropoxy-4-methoxybenzoate (RT11165). The molecular structure of RT11165 with a 2-isopropoxy group differs only by a substitution of the 2-methoxy group found in the prototype ferroelectric nematic material 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). This small structure change produces a rather dramatic change in phase behavior leading to an NF phase from 63 °C down to room temperature. Below about 45°C the rotational viscosity of RT11165 increases critically and the temperature dependence indicates a glass transition at ~19°C. The transparent and polar glassy state of RT11165, which should be also piezoelectric, is a good candidate for energy storage, piezoecatalysis, data storage and other applications.
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Precision adiabatic scanning calorimetry of a nematic – ferroelectric nematic phase transition
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-N-F) in the liquid crystal molecule 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). The N-N-F was found to be very weakly first order with a latent heat Delta h = 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 N-F phase. In both phases the power-law analysis of c(p)(T) resulted in a critical exponent alpha = 0.50 +/- 0.05 and amplitude ratio A(NF)/A(N) = 0.42 +/- 0.03. The very small latent heat and the value of alpha indicate that the N-N-F transition is close to a tricritical point. This is confirmed by a value of the order parameter exponent beta approximate to 0.25, recently obtained from electric polarisation measurements. Invoking two-scale-factor universality, it follows from the low value of A(NF)/A(N) ratio that the size of the critical fluctuations is much larger in the N-F phase than in the N phase.
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- PAR ID:
- 10312365
- Date Published:
- Journal Name:
- Liquid Crystals
- ISSN:
- 0267-8292
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Six members of the 1,ω-bis(4-cyanobiphenyl-4′-yl) alkanes are reported and referred to as CBnCB in which n = 1, 15, 16, 17, 19 and 20 and indicates the number of methylene units in the spacer separating the two cyanobiphenyl units. The behaviour of CB3CB is revisited. The temperature dependence of the refractive indices, optical birefringence, and dielectric permittivities measured in the nematic, N, phase for selected homologues are reported. The dimers with n ≥ 15 showed an enantiotropic N phase, and for the odd members the twist-bend nematic, NTB, phase was observed. CB3CB shows a direct NTB-isotropic, I, transition whereas for CB1CB a virtual NTB-I transition is found. The temperature dependence of the bend elastic constant, K33, measured in the oblique helicoidal cholesteric state formed by mixtures of CBnCB with a chiral additive S811, shows strong non-monotonous behaviour with a deep minimum near the transition point to the NTB phase. The minimum value of K_33 decreases as n increases. The long even members of the CBnCB series show similar values of TNI to their odd-membered counterparts but their estimated values of TNTBN are considerably lower. This is attributed to molecular shape and its effect on K33.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1080/02678292.2021.2007550
