Dielectric and X-ray Studies of Eleventh and Twelfth Members of Two Isothiocyanato Mesogenic Compounds

Abstract

Results of the dielectric and X-ray studies of the long-alkyl-chain members (n = 11, 12) of two homologous series: nBT (4-n-alkyl--4 -isothiocyanato-biphenyl) and nCHBT (4-trans-4 -n-alkyl-cyclohexyl--isothiocyanato-benzene) in their liquid crystalline phases are presented. These compounds exhibit different polymorphisms: the nematic phase for nCHBTs and the smectic E and smectic A phases for nBTs. The dielectric measurements were performed in a wide frequency range of 1 kHz-3 GHz. The layer thickness in the smectic E and smectic A phases and the orthorhombic unit cell parameters of the smectic E phase were determined using the small angle X-ray diffraction method. In the smectic E phase the layer-thickness-to-molecular-length ratios are found to be close to 1. The corresponding ratios observed for the smectic A phase of nBTs are considerably higher (≈ 1.24), which indicates that an alternating head-to-tail arrangement of molecules in the layers is favored. The rotational dynamics of molecules in the smectic E phases is discussed in relation to their packing in a unit cell.

Volumetric, dielectric, calorimetric and X-ray studies of smectogenic 10PBO8 at atmospheric and elevated pressures

“…However, as seen in the right inset to Figure 7(a), there is a small splitting of this peak, which increases slightly on lowering temperature. Because this splitting is significantly smaller than observed for typical SmE phases [28][29][30][31], its presence in 10PBO8 may reflect interlayer ordering of the molecules [32].…”

“…X-Ray diffraction patterns, obtained by the method in [29,30], are displayed in Figure 7. In the SmC phase a sharp peak (001) close to the incident beam and a broad maximum around 2θ ≈ 20…”

Reassessment of structure of smectic phases: Nano-segregation in smectic E phase in 4-n-alkyl-4′-isothiocyanato-1,1′-biphenyls

“…1, because a binary system between n-nonane and 4-n-alkyl-4 -isothiocyanato-1,1biphenyl (abbreviated as nTCB with n being the number of carbon atoms in the alkyl chain, shown in Fig. 2 for n = 4), on which the largest number of studies has been reported as a representative of SmE mesogens, 3,7,8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] exhibits a swollen SmE phase in a continuous range of composition. 29 Only the c, the cell constant parallel to the molecular long axis in average, exhibits a notable increase in swelling while retaining the three-dimensional periodicity.…”

Thermodynamic analysis of the low frequency relaxation time in the smectic A and C phases of a liquid crystal

“…X-ray studies indicate that the distance between the centers of molecules in smectic phases are approximately 30%-40% of their lengths on average. [1][2][3] External pressure reduces the intermolecular distances and thus must influence considerably the dynamical characteristics of molecules in LC phases. Dielectric relaxation is well suited to study the dynamical properties of dipolar molecules in LC phases subjected to elevated pressures, [4][5][6] especially the low frequency relaxation time ʈ characterizing the flipflop motions of elongated molecules in a given LC phase.…”