Molecular Dynamics and Residual Entropy in the Soft Crystal, SmE Phase, of 4-Butyl-4‘-isothiocyano-1,1‘-biphenyl

Ishimaru, Shin’ichi; Saito, Kazuya; Ikeuchi, Satoaki; Massalska-Arodź, Maria; Witko, W.

doi:10.1021/jp0501244

Cited by 24 publications

(28 citation statements)

References 21 publications

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“…The model can be regarded as an anisotropic analog of "plastic crystal," 2 which usually has cubic or rhombic symmetry. The residual entropy determined calorimetrically 3 is compatible with the model. It is also widely accepted 4, 5 that the excellent electrical property (high hole/electron mobility) of SmE compounds reported previously 6 are based on this high degree of structural order.…”

Section: Introductionsupporting

confidence: 73%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Saito

Miyazawa

Fujiwara

et al. 2013

The Journal of Chemical Physics

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Based on new diffraction data from aligned samples of smectic E (SmE) phase of 4-n-alkyl-4'-isothiocyanato-1,1'-biphenyls, 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 fit 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.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

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

Saito

Miyazawa

Fujiwara

et al. 2013

The Journal of Chemical Physics

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“…1 Indeed, residual entropy determined experimentally is compatible with this structural view. 4 Despite its structure similar to crystals, both of thermodynamic (the most macroscopic) and spectroscopic (microscopic) analyses reached the same conclusion of the molten state of the chain in SmE phase, even if the compound passes the SmA phase before the melting to IL. The present authors reported that two members (n = 8 and 16) of 6-alkyl-2-phenylazulene (nPA, n being the number of carbon atoms in the alkyl group as show in Figure 1b) have SmE phase as a mesophase.…”

Section: ¹1mentioning

confidence: 78%

“…4 Despite its Figure 1. Molecular structures of (a) 4-alkyl-4¤-isothiocyanatobiphenyl (nTCB), (b) 6-alkyl-2-phenylazulene (nPA), and (c) 2-(4-alkylphenyl)indene.…”

mentioning

confidence: 99%

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Adachi

Saitoh

Yamamura

et al. 2013

Bulletin of the Chemical Society of Japan

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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 molten in any liquid-crystalline mesophase. The thermodynamic implications are briefly discussed.Organic molecules are arranged with positional and orientational orders in crystals. When the crystal melts directly into an isotropic liquid (IL), these orders are lost simultaneously at the fusion. If these orders are lost step by step, the molecule forms a mesophase like liquid crystal (LC). Traditional classification of LCs 1 does not take into account the intramolecular degrees of freedom. Many actual mesogens have, however, intramolecular degrees of freedom in addition to those of rigid particles. It is at a glance unclear why this classification is useful in the real world. As a source of such intramolecular motional degrees of freedom, the conformational degrees of freedom of an alkyl group (or chain) is the most important because most mesogenic molecules have a molecular structure of corechain or chaincorechain, where "core" means a rigid part like a biphenyl moiety. The fact that n-alkanes, the molecules of which are just of a chain, do not exhibit liquidcrystalline mesophases implies the molecules are conformationally melted (disordered) in IL. This is really the case as evidenced by the linear increase of the entropy of fusion with a slope of ca. 10 J K ¹1 (mol of CH 2 ) ¹1, which is compatible with the threefold disorder around a CC bond. It is then natural to imagine the chain part of mesogens is also conformationally melted in their IL states. A question when the chain part melts arises, accordingly.The present authors 2,3 have previously demonstrated that the alkyl chain is already molten in smectic E (SmE) phase almost equally to those in IL in 4-alkyl-4¤-isothiocyanatobiphenyl (abbreviated as nTCB or nBT with n being the number of carbon atoms in the alkyl chain, Figure 1a) even though the SmE phase is the LC mesophase closest to a crystalline phase. 1In SmE phase, molecules are arranged in layered structure with orthorhombic symmetry. The SmE phase has no fluidity accordingly, though the layered structure is similar to the smectic A (SmA) structure. The orientational order of the molecules is partially lost in SmE phase. Namely, the molecule reorients itself around the short and the long axes, resulting in no distinction between head and tail, and front or rear faces. This is why the phase is often classified as a soft crystal (crystal E or CrE phase).1 Indeed, residual entropy determined experimentally is compatible with this structural view. 4 Despite its Figure 1. Molecular structures of (a) 4-alkyl-4¤-isothiocyanatobiphenyl (nTCB), (b) 6-alkyl-2-phenylazulene (nPA), and (c) 2-(4-alkylphenyl)indene.

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“…They reported the correlation between the series of maxima and minima in the  3 dependence on temperature and activation of different intra-and intermolecular motions for quenched 6OCB and other nematic LCs. The supercooled SmE phase of 4TCB does not exhibit such maxima and minima in the  3 dependence although activation of different modes of molecular motions also takes place with rising temperature [36]. The character of the I 3 dependence on temperature indicates thermal activation of the sites where o-Ps is formed and it can be explained within two-state model of glass transition assuming that Ps can be formed in liquid-like domains in the sample [37,38].…”

Section: Positron Annihilation In Liquid Crystalsmentioning

confidence: 93%

Positron annihilation in liquid crystals

Dryzek

Juszyńska-Gałązka

2015

Nukleonika

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Abstract. Positron annihilation studies of liquid crystals are reviewed with particular reference to thermotropic liquid crystals with rod-like molecules. The studies of compounds exhibiting smectic A or smectic E phases indicate that local arrangement of dipole molecules play an important role because high electron density at the end group of molecules can infl uence substantially formation and annihilation of positronium. The obtained ortho-positronium lifetimes in these phases can be explained by antiparallel pairing of molecules in case of the smectic A phase or a structure with a nanosegregation of alkyl chains and others parts of molecules into sublayers and liquid-like state of alkyl chains in case of the smectic E phase.

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Molecular Dynamics and Residual Entropy in the Soft Crystal, SmE Phase, of 4-Butyl-4‘-isothiocyano-1,1‘-biphenyl

Cited by 24 publications

References 21 publications

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

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

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Positron annihilation in liquid crystals

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