Influence of underlying local organisations in typical nematic phase of 6CHBT and induced nematic phase of bicomponent liquid crystalline systems 4DBT–12CB – a Fast Field Cycling NMR investigation

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry

“…It is known that OF modes are collective motions of viscoelastic nature and manifest as short-range and long-range orders in the isotropic and nematic phases, respectively. , The strength of OF modes is represented by A OF ∝ S 2 T (where S represents the orientational order parameter and T is the temperature). , As observed from the parametric dependence of A OF (see above), any decrease in S is outweighed by the corresponding increase in T , resulting in a declining tendency of A OF with a rise in T , and such observations were found elsewhere . It is worth remarking that such a functional behavior of A OF against temperature is equally valid in the hexagonal and lamellar phases (Tables and ).…”

“…Molecular mechanisms, which contribute to nuclear spin-relaxation in thermotropic mesogens, in particular, order fluctuations (OF), are well documented in the literature. , In the isotropic phase ( T > T NI , where T NI is the nematic–isotropic transition temperature) of thermotropic liquid crystals, the nuclear spin-relaxation is caused by local orientational fluctuations. However, the magnitude fluctuations in the nematic order parameter and director fluctuations due to the thermal energy ( k B T ) significantly contribute to spin-relaxation, just below T NI ( T – T NI ∼ 5 K) and well below T NI (pure nematic phase), respectively. , The modeling of nuclear spin-relaxation in lyotropics is accounted for OF modes (either short range or long range) which are typical for thermotropics, with a ω –p dependence of R 1OF , where the exponent is p ∼ 0.5, describes the validity of these modes …”

“…Hence, the frequency dependence of the relaxation rate due to order fluctuations ( R 1OF ) typical for nematics is given by , Here p ∼ 0.5 is the exponent typical for the signature of OF modes, while A O F denotes the relaxation amplitude.…”

Exploring Crystal-Phase Molecular Dynamics of the Low-Viscous Mesogen 6CHBT: A Combined FFC and High-Field NMR Relaxometry Investigation

“…These investigations unveiled that short-range nematic order fluctuations and order director fluctuations effectively influence the intramolecular dipolar interactions among nuclear spins ( 1 H– 1 H) in the isotropic and nematic phases, respectively . Furthermore, variable-temperature 1 H FFC NMR relaxometry analysis points out the correlation between molecular reorientations around the short axes and DF modes in the nematic phase of 6CHBT. , These studies enabled the extraction of the correlation times and amplitudes of molecular reorientations due to the short-range nematic order, director fluctuations, and the short axes, occurring on different time scales. , The static 1D 13 C and 2D proton-encoded local field (PELF) NMR experiments conducted in the nematic phase of 6CHBT monitored the trends of orientational order parameter vs temperature for various carbons from the knowledge of 13 C– 1 H dipolar couplings and 13 C chemical shifts . However, to the best of our knowledge, a detailed investigation concerning the dynamics of various molecular motions occurring on different time scales in the crystal phase of 6CHBT exhibited by elongated (rod-like) molecules is scanty.…”

“…In the -NCS family, 6CHBT is a low-viscosity and low-melting compound exhibiting a nematic phase over a wide range near room temperature and a crystal phase below 12 °C and is also often used as a base component of eutectic mixtures . The viscoelastic, structural, and physical properties of 6CHBT were documented elsewhere. − Our earlier 1 H FFC NMR and conventional relaxometry aided in probing molecular dynamics of isotropic and nematic phases of 6CHBT from the perspective of structure–dynamics correlation. , Nevertheless, there is a scope to probe the complex molecular dynamics in the crystal phase of 6CHBT, which is rarely found in the literature.…”