Molecular dynamics of a discotic liquid crystal investigated by a combination of dielectric relaxation and specific heat spectroscopy

Abstract

International audienceThe molecular dynamics of the discotic liquid crystal pyrene-1,3,6,8-tetracarboxylic tetra(2-ethylhexyl)ester is studied by dielectric relaxation and specific heat spectroscopy. Dielectric spectroscopy shows 3 processes: a β-relaxation at low temperatures and an α-relaxation in the temperature range of the mesophases followed by conductivity. The dielectric α-relaxation is assigned to a restricted glassy dynamics in the plastic crystal as well as in the liquid crystalline phase. The obtained different Vogel-Fulcher-Tammann laws (different Vogel temperatures and fragility) are related to the different restrictions of the dipolar fluctuations in the corresponding phases. By means of specific heat spectroscopy glassy dynamics is also detected in the plastic crystalline phase but with quite a different temperature dependence of the relaxation times. This is discussed considering the different probes involved and how they are influenced by the structure. In the frame of the fluctuation approach a correlation length of glassy dynamics is calculated to 0.78 nm which corresponds to the core-core distance estimated by X-ray scattering

High-resolution dielectric study reveals pore-size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores

“…This implies that the dipolar relaxation corresponds to the so-called quasi-static limit, τ ≪ (2πf ) −1 , where τ is the corresponding relaxation time. This is in agreement with recent dielectric studies on bulk Py4CEH [53,59], where the Arrhenius plot (see Fig. 4 of Ref.…”

“…These processes are not in the focus of this study. At higher frequencies, particularly close to the upper limit of the frequency window of the frequency response analyzer (f 10 6 Hz) the dielectric losses of confined DLC Py4CEH are comparable to the experimental resolution used here [59]. Because of the KramersKronig relationship between dielectric loss and real part of the permittivity, the real part, ε ′ (f ), can be considered frequency-independent.…”

“…4 of Ref. [59]) at the temperature region relevant here (from 310-370 K) give relaxation frequencies, f r = (2πτ ) −1 , in the range between 30 and 500 MHz. Our measurements have been performed at a constant frequency of 200 kHz.…”

From monomers to self-assembled monolayers: the evolution of molecular mobility with structural confinements

“…[46][47][48][49][50][51][52] It can also be valuable when studying structural transitions within highlyordered liquid and plastic crystals. [53][54][55] Data analysis Fig. 1a shows the dielectric loss (3 00 ) of OTS monomers as a function of frequency and temperature in a 3D representation.…”

Dielectric properties of three liquid crystal polymers

“…Liquid crystal polymers (LCPs) are very attractive for industrial applications due to their outstanding mechanical properties, chemical stability, and high processability [1][2][3]. Many LCPs have been developed since the 1980s and have achieved practical applications in various fields such as high-speed electronic devices, circuit boards, and high-strength fibers [3][4][5][6][7].…”