Separation of nematic and smectic-A potential effects on solute ordering in a series of binary 6OCB–8OCB mixtures

Abstract

1H NMR and optical microscopy have been used to study four solutes dissolved in samples of a binary mixture of 4-n-hexyloxy-4′-cyanobiphenyl (6OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) that are close to the region of the phase diagram where the smectic-A (SmA) and re-entrant nematic (RN) phases exist. Optical microscopy clearly indicates that one of the four studied samples shows the phase sequence of isotropic–nematic–SmA–RN. The derived solute order parameters were interpreted by means of two Maier–Saupe mechanisms in conjunction with the Kobayashi–McMillan theory in the case of the SmA phase. The novel feature of this study is that the nematic potential is extrapolated from the nematic to the SmA phase based on concentrations of the 6OCB–8OCB mixtures. The derived smectic order parameters for each of the studied solutes clearly show a maximum absolute magnitude near the centre of the SmA temperature range. The different partitioning of these solutes in the binary mixture is also discussed.

Recent NMR Studies of Thermotropic Liquid Crystals

“…[343]. This method of extrapolation of G(i) for each solute(s) (where possible) was deemed safer than the extrapolation of MSMS model parameters as a function of temperature [348]. Since the G parameters obtained for each solute that describe the nematic potential were essentially identical for all four samples when all the mixtures are in the N phase, a reasonable ansatz was made, that is, in the SmA phase of the two samples with a SmA phase the nematic mean-fields G(1) and G(2) for each solute in the phase could take the ones without SmA phase at the same temperature.…”

“…Note that τ 0 is distinct for each solute in a particular LC solvent. The smectic order parameters τ s of several solutes have been easily evaluated once the smectic potential is known [348].…”

NMR of solutes in nematic and smectic A liquid crystals: the anisotropic intermolecular potential

“…Figure displays an example NMR spectrum obtained from one of the samples . The complicated NMR spectra (a superposition of spectra from all five solutes; Figure ) that are then obtained are readily analyzed using a covariance matrix adaptation evolutionary strategy (CMA‐ES) .…”

“… 1 H NMR spectra of five codissolved solutes in a sample of 27 wt.% 6OCB/73 wt.% 8OCB in the N phase (sample 4 of Burnell et al …”

Order and Conformation of Biphenyl in Cyanobiphenyl Liquid Crystals: A Combined Atomistic Molecular Dynamics and 1H NMR Study

“…Simulated dipolar couplings could in fact serve as a useful starting point for the spectral fitting algorithm in cases that would be otherwise impossible to solve in a reasonable timeframe. However, given the importance of the problem, proposals to indirectly obtain positional information with the help of mean-field [23,24] or density functional theory [25,26] have been put forward to this effect. the nature of the dominant orientational interactions) [15][16][17][18][19][20][21] and a few attempts have recently been published.…”