Based on new diffraction data from aligned samples of SmE phase of title compounds (nTCB), systematics against the alkyl chain length n is analyzed. In order to perform the analysis,
the molecular form factor approximated by a box-shaped distribution
is calculated while taking the rounding of the distribution at corners into account.
The analysis clearly shows the nano-segregated layered structure, which does not fit to the traditional structural view of SmE phase
but does to the model the present authors proposed recently.
Some implications of this conclusion are discussed in relation to
the importance of the molten state of alkyl chains in most of real mesogens
revealed previously through thermodynamic analyses.
(J. Chem. Phys., 139, 114902 (2013))
Thermodynamic and diffraction analyses were performed to establish the phase diagram for a binary system between 4-n-nonyl-4'-isothiocyanatobiphenyl (9TCB) and n-nonane. The swollen SmE structure is identified in the binary system. Upon swelling, a characteristic two-dimensional herringbone array is maintained whereas the layer spacing of SmE structure increases with the content of n-nonane. Considering the difficulties in explaining the experimental findings based on the traditional model of SmE structure, a new model, lamellar with two types of sub-layers consisting of aromatic core and alkyl-chain moieties, is proposed.
(J. Phys. Chem. B, 117, 8293 (2013))
Through thermodynamic, spectroscopic and structural studies, the molten state of the alkyl chain in SmE phase, which is the liquid-crystalline mesophase closest to an ordered crystalline phase, has been established in a calamitic mesogen nPA. Combining the same conclusion for the SmE phase of another calamitic mesogen nTCB, it is concluded that the alkyl chain attached at end(s) of a rod-like core is universally molten in any liquid crystalline mesophases. Its thermodynamic implications are briefly discussed.
(Bull. Chem. Soc. Jpn., 86, 1022 (2013))
Molecular dynamics in soft crystal, E phase of 6-octyl-2-phenylazulene (8PA) was studied by X-ray diffraction, and dielectric and FT-IR spectroscopies. Clear dielectric dispersion is observed due to the head-to-tail disordering in a kHz range around 400 K. The CH2 stretching frequencies exhibit more pronounced shifts at the phase transition point from the high-temperature ordered crystal to E phase than that at the melting from E phase to the isotropic liquid. The results are discussed in comparison with a typical E series, 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB, n: number of carbon atoms in alkyl group).
(Liq. Cryst., 39, 1340 (2012))
To confirm the molten state of the alkyl chain in soft crystalline phase, smectic E (SmE) phase, thermodynamic and spectroscopic analyses were performed on 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB, n: the number of carbon atoms in alkyl group). DSC results of 11TCB and 12TCB, having extra smectic A phase besides smectic E phase, show that their chain-length dependence of entropies of transition (DeltatrsS) from the ordered crystalline (OC) phase to the SmE phase matches the trend found for nTCB (n = 4 - 10), while no chain-length dependence are observed in DeltatrsS at the SmE-to-SmA and SmA-to-isotropic liquid (IL) phase transitions in 11TCB and 12TCB. Temperature dependences of FT-IR spectra of six compounds (n = 2, 3, 5, 8, 10 and 12) were recorded. The CH stretching modes of the chain exhibited more pronounced change at the transition from the OC to the SmE phase than at the transition from the SmE phase to IL or SmA phase. These results indicate that the alkyl chain is molten in the SmE phase like in IL. The disordering process of nTCB molecules from the OC to IL via anisotropic mesophases is discussed in terms of entropy.
(J. Phys. Chem. B, 116, 9255 (2012))
The results of adiabatic calorimetry, mid-infrared spectroscopy, X-ray diffraction and polarising microscopy of 4-hexyl-4'-isothiocyanatobiphenyl (6TCB) are presented. To identify the experimental IR absorption bands. Density Functional Theory (DFT) calculations at the level B3LYP/6-31 were carried out. In addition to the isotropic liquid and smectic phases, the existence of two stable crystalline phases was pointed out by calorimetry measurements. Quantitative analyses of infrared bands allowed us to determine phase transitions, observe crystallization kinetics and elucidate the glass transition of crystal-like smectic E phase. The structural information about the glass of the smectic E was obtained from the diffraction studies. Additionally, the glass transition was illustrated by textures recorded by polarising microscopy.
(J. Phys. Chem. B, 115, 12327 (2011))
To understand the role of intramolecular degrees of freedom in forming mesophases, thermodynamic analysis was performed for 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB, n: the number of carbon atoms in alkyl group), which exhibits the crystal E (CrE) phase as a mesophase. Heat capacities of 2TCB and 5TCB were measured by adiabatic calorimetry. Their entropies of transition (DeltatrsS) were compared with those of other nTCBs (n =< 10). DeltatrsS of the phase transition from the ordered crystal to CrE phase increased with their alkyl-chain length whereas that of fusion of the CrE phase remained essentially constant. These behaviors clearly show that the alkyl chain of nTCB is fully disordered even in CrE phase. Through the comparison of DeltatrsS among 5TCB, 4-pentyl-4'-cyanobiphenyl (5CB) and pentylbiphenyl, the role of the alkyl chain for the formation of mesophases is discussed.
(J. Phys. Chem. B, 114, 4070 (2010))
The results of mid-infrared spectroscopy and X-ray studies of the third member of the 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB) homologous series are presented. Correspondence between the phase transitions observed by means of the IR spectroscopy and those given by the adiabatic calorimetry was found. The structure of five solid phases was obtained by X-ray measurements. IR spectroscopic and X-ray data give the arguments supporting the identification of the glass of smectic E phase. Assignment of the IR vibrational bands, in the smectic E, in the glass of smectic E, and in one of the crystalline phases, with help of the hybrid B3LYP/6-311++G(d,f) functional calculations is presented.
(J. Phys. Chem. B, 113, 7435 (2009))
The thermal behaviour of 4-propyl-4'-thiocyanatobiphenyl (3TCB) was studied by adiabatic calorimetry. In addition to the isotropic liquid and smectic E (SmE) phases, five crystalline phases were detected. Such a rich polymorphism was not observed for the other low-n members of the nTCB homologous series (n = 2-5). The observed anomalies are analysed and the possible origin for their existence is suggested. The temperature quench of the SmE phase leads to a metastable crystalline state with a multiple-stage relaxation process.
(Liq. Cryst., 35, 179 (2008))
Molecular dynamics and resulting disorder in the soft crystal, smectic E (SmE) phase, were studied in detail for the title compound (4TCB) by 1H NMR spectroscopy and adiabatic calorimetry. The ordered crystal phase of 4TCB was realized for the first time under ambient pressure after long two-step annealing and used as the reference state in the analysis of the experimental results. Four motional modes were identified in the SmE phase through the analysis of the 1H NMR T1. The residual entropy was determined as ca. 6 J K-1 mol-1. This magnitude implies that most of disorder in the SmE phase at high temperatures is removed on cooling except for the head-to-tail disorder of the rod-shaped 4TCB molecule. Standard thermodynamic functions are tabulated below 375 K.
(J. Phys. Chem. B, 109, 10020 (2005))
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