Thermodynamics and molecular ordering of carbonate‐type dimer liquid crystals with emphasis on the geometrical characteristics of the linking group

Abe, Akihiro; Furuya, Hidemine; Nam, Su Yong; Okamoto, Satoshi

doi:10.1002/actp.1995.010460606

Cited by 20 publications

(27 citation statements)

References 28 publications

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“…The observed values of ΔS NI /R are shown for X ¼ carbonate (CBC-n), ether (CBA-n), and ester linkages (CB-n) in Fig. 3 [14]. In accordance with Roviello and Sirigu's finding [5], the carbonate linkage is undoubtedly the origin of the less pronounced oscillation of the dimer [7].…”

Section: Influence Of Bond Angle Restrictions and Rotationalsupporting

confidence: 83%

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Nematic Conformation of Chain Molecules Predominating in the Ordered Mesophase

Abe

2013

Hierarchical Macromolecular Structures: 60 Years After the Staudinger Nobel Prize II

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The physical picture of the nematic conformation has been discussed on the basis of the rotational isomeric state analysis for segmented liquid-crystal (LC)-forming molecules, comprising mesogenic units on both sides of a flexible spacer. The disorientation angles (θ) of the two terminal mesogenic units are calculated for given spatial configurations of the spacer. The observed odd-even character of the thermodynamic quantities at the nematic (N)-isotropic (I) phase transition T NI ¼ ΔH NI /ΔS NI has been interpreted in terms of the profiles of the calculated distribution curves P(θ) À θ. Combined use of rotational isomeric state and 2 H NMR techniques has led to an estimate of the conformer fraction in the nematic state. The transition entropies derived on this basis are favorably compared with the constant-volume transition entropies obtained from the pressure-volume-temperature measurement. The observed V-T relation indicates that the expansivity of the nematic LC phase is higher relative to that of the isotropic melt. It has been pointed out that the nematic conformation might possibly gain extra stability from the free volume effect in the LC state. These considerations offer an explanation why amazingly long flexible chain segments can be accommodated in the nematic fluid.

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Section: Influence Of Bond Angle Restrictions and Rotationalsupporting

confidence: 83%

“…(1) (note that Z C ¼ 1 for the crystalline state). In fact, the analysis was carried out for representative samples of the carbonate and ether series [13,14,31,32]. The results obtained for CBC-5 and CBC-6, and CBA-9 and CBA-10 (see Fig.…”

mentioning

confidence: 99%

Nematic Conformation of Chain Molecules Predominating in the Ordered Mesophase

Abe

2013

Hierarchical Macromolecular Structures: 60 Years After the Staudinger Nobel Prize II

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“…This is best illustrated by comparing the properties of three series of dimers containing cyanobiphenyl as the mesogenic group and attached to the spacer via an ether link [18], a carbonate group [16,53] or a methylene link [16,54]:…”

Section: Classification Of Liquid Crystal Dimersmentioning

confidence: 99%

“…8. The dependence of the nematic-isotropic transition temperature, T NI , on the total number of atoms, n, in the spacer for the cyanobiphenyl dimers linked via ether (s) [18], alkyl (d) [16] and carbonate groups (j) [16,53] Fig. 9.…”

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confidence: 99%

Liquid Crystal Dimers

1999

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A liquid crystal dimer is composed of molecules containing two conventional mesogenic groups linked via a¯exible spacer. These materials show quite different behaviour to conventional low molar mass liquid crystals and in particular their transitional behaviour exhibits a dramatic dependence on the length and parity of the¯exible spacer. In this review a comprehensive overview of the relationships between molecular structure and liquid crystallinity in dimers is provided. This includes a description of the novel modulated and intercalated smectic phases exhibited by dimers.

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“…20 In conclusion, the physical principle underlying the helix-helix transition observed in various states should be basically identical. 21 …”

Section: Discussionmentioning

confidence: 99%

Reversible Screw-Sense Inversion of α-Helical Poly(β-phenethyl aspartate) in the Solid State

Okamoto

Furuya

Watanabe

et al. 1996

Polym J

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ABSTRACT:A racemic mixture (PPDLA) comprising an equal amount of optical antipodes, Poly(/J-phenethyl L-aspartate) (PPLA)+Poly(p-phenethyl o-aspartate) (PPDA), was found to exhibit a moderately sharp and reversible transition at around 200°C. A combined use of X-ray and CP/MAS NMR methods revealed that the transition involves an interconversion of the screw-sense between the right-and left-handed IX-helical molecules. The backbone conformation and the molecular packing (tetragonal) were found to remain nearly identical before and after the transition. The transition mechanism previously deduced in the liquid-crystalline state seems to be consistent with experimental observations in the solid state. On the other hand, PPLA alone is known to transform from the right-handed IX-helix to the left-handed n-helix at around 130°C: the crystallographic form concurrently changes from a tetragonal to a rectangular and eventually to a hexagonal arrangement at about 200°C. The difference between PPDLA and PPLA systems is discussed.KEY WORDS Poly(P-phenethyl aspartate) / Racemic Mixture / Solid-State Phase Transition / HelixSense Inversion/ X-Ray Measurement/ CP/MAS NMR / 13 C NMR Chemical Shifts/ It is well known that poly(L-aspartic acid) esters +NH-CH-yO+,;-CH2COORform an ()(-helix in either the right-handed or left-handed screw sense depending on the chemical structure of the ester group (R). While poly(L-aspartic acid ester) with R = benzyl 1 or methyl 2 forms the left-handed ()(-helix in chloroform, the right-handed arrangement is more popular among polymers having longer alkyl side chains such as R=ethyl 2 or phenethyl 3 group. Reversal of the helical sense in copolymer systems such as those comprising R 1 = nitrobenzyl and R 2 = benzyl residues has been studied by Goodman et al. in l 960's. 4 More recently, Uematsu and his collaborators have investigated the helix-sense inversion characteristic of poly(/J-phenethyl L-aspartate) (PPLA), where R = -CH 2 CH 2 c/>. According to Sasaki et al., 5 PPLA exhibits an irreversible helix-sense inversion from the righthanded ()(-helix to the left-handed n-helix in the solid state at an elevated temperature. Toriumi et al. 6 have observed a transition from the right-handed to the lefthanded ()(-helix in chloroform by addition of a small amount of denaturant acid, dichloroacetic acid. These observations suggest that the energy difference between the two alternative helical forms is relatively small. 7 In our previous studies on PPLA, 8 -10 we have found that the transition between the two ()(-helical forms takes place reversibly in solution as a function of temperature. The transition was observed in the isotropic solution as well as in the anisotropic liquid-crystalline state within certain temperature range (80-90°C). In these measurements, various NMR techniques were employed to follow the transition.In this study, we report a helix-helix transition observed for a racemic mixture comprising an equal amount of PPLA and PPDA (hereafter designated as PPDLA) in the solid state. In ...

show abstract

Thermodynamics and molecular ordering of carbonate‐type dimer liquid crystals with emphasis on the geometrical characteristics of the linking group

Cited by 20 publications

References 28 publications

Nematic Conformation of Chain Molecules Predominating in the Ordered Mesophase

Nematic Conformation of Chain Molecules Predominating in the Ordered Mesophase

Liquid Crystal Dimers

Reversible Screw-Sense Inversion of α-Helical Poly(β-phenethyl aspartate) in the Solid State

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