Yoshiko Uematsu

Polypeptide liquid crystals

The recent studies on the structure and properties of polypeptide liquid crystals, which are formed in solution as well as in the solid state, are reviewed in this article. Especially the cholesteric pitch and the cholesteric sense (right-handed or left-handed), which are characteristic factors of cholesteric liquid crystals, are discussed in detail in relation to the effects of temperature, concentration, and solvent. Further cholesteric liquid crystalline structure retained in cast films and thermotropic mesomorphic state in some copolypeptides are also discussed.

Cholesteric Structure of Lyotropic Poly (γ-benzyl L-glutamate) Liquid Crystals

Abstract The cholesteric liquid crystals formed by poly(γ-benzyl L-glutamate) (PBLG) in various solvents exhibit a cholesteric sense inversion when the temperature or the solvent composition is changed. The sense inversion in 1,2,3-trichloropropane and in m-cresol occurs from right to left-handed via an untwisted nematic state with increasing temperature. The helical twisting power (reciprocal of the cholesteric half-pitch) in mixtures of these two solvents shows a quadratic dependence on the solvent composition, accompanied by a two-fold sense inversion (right → left → right) at low temperatures.The measurements of the twisting power are also reported for PBLG in a series of alkylcholorieds in order to establish the role of solvent. In solvents with low dielectric constants PBLG forms the right-handed cholesteric sructure while it changes to the left-handed one when the dielectric constant is increased beyond a critical value of ca. 9. The increase in temperature enhances the left-handed twisting power i...

Piezoelectric Characteristics of Polymer Film Oriented under a Strong Magnetic Field

The possibility has been indicated that polymers with helical chirality, such as poly-γ-benzyl-L-glutamate (PBLG) and poly-L-lactic acid (PLLA), exhibit a large shear piezoelectric constant. To attempt the realization of a PBLG membrane with a large piezoelectric constant, we fabricated the PBLG membrane oriented by magnetic field force. Concretely, the PBLG membranes were casted from 1,2-dichloroethane solution with various PBLG concentrations under the magnetic field generation equipment incorporating a superconducting magnet. First, the orientation of the chain molecules of the PBLG membranes obtained was observed macroscopically by means of a polarizing microscope (POM). The orientation of the chain molecules of the PBLG membranes was recognized for the case of casting from the PBLG 1,2-dichloroethane solution in the liquid crystal state. Also, from X-ray photograph measurements, it was found that the orientation direction of the chain molecules of PBLG was perpendicular to the magnetic field direction. We then measured the shear piezoelectric constant d14 of the oriented PBLG membranes. With increasing the strength of the applied magnetic field in the casting process for the film preparation, d14* of the PBLG membranes obtained increases. Finally, a large piezoelectric constant of 26 pC/N was found in the PBLG membrane. It is assumed that d14* is not saturated even at the magnetic field of 10 T.

Structure and mobility of poly (γ-n-alkyl-L-glutamate)s in the solid and liquid crystalline states as studied by NMR spectroscopy

Abstract 13 C CP/MAS NMR and pulse 1 H NMR experiments were carried out for poly(γ- n -alkyl-L-glutamate)s (PALGs) in which the number of carbon atoms of the alkyl side-chains was either odd or even, in order to elucidate the conformation, crystal structure and dynamics of the polymers. From these results, it is found that the main-chain takes an γ-helix conformation irrespective of the alkyl side-chain length. However, n -alkyl side-chains crystallize with an all-trans zigzag conformation for PALGs when the number of carbon atoms in the n -alkyl side-chains is more than 14. Further, from the pulse 1 H NMR results, it is found that the 1 H spin—spin relaxation time ( T 2 ) of the side-chains increases abruptly with an increase in temperature for PALGs with a carbon number of more than 10, which is evidence for the solvent-like nature of the side-chains in the liquid crystalline phase.

X‐Ray Diffraction Studies on the Phase‐Transformational Behavior of a Smectic Liquid‐Crystalline Elastomer Composed of Chiral Mesogens

Structural changes through successive phase transformations of a chiral smectic liquid-crystalline elastomer are investigated by X-ray scattering technique. In uniaxially deformed elastomers, the smectic layer seemingly tilts even in the SmA phase, in which an in-plane chevron structure formed in the tilted smectic phase. On the basis of an analysis of the layer reflection peaks, the layer correlation length in the tilted smectic phases is shorter than that in the non-tilted SmA phase, though smectic layers in the tilted smectic phases are better ordered than those in SmA.

Collective fluctuation in chiral smectic phases of main‐chain liquid crystalline polymers

We have investigated the collective fluctuation in the chiral smectic phases of main‐chain polyesters having a mesogenic p,p′‐dibenzoate unit via dielectric and dynamic electrooptical measurements. A relaxation due to the Goldstone mode was observed at several tens of Hz in the chiral smectic C (SmC*) phase in both measurements, where another relaxation associated with the soft mode was also confirmed around the SmA–SmC* phase transition temperature. Although the mesogens are linked together in a main‐chain liquid crystalline polymer, the observed soft mode is associated with the tilt fluctuation of the average direction of the mesogens.

Banded Texture Induced by an Electric Field in Lyotropic Liquid Crystals

Abstract Using polarization microscopy, the formation of transient banded textures in a liquid crystalline solution of poly(γ-benzyl L-glutamate), PBLG, that had applied in-plane DC and AC electric fields was investigated. Striped bands perpendicular to the direction of the electric field were observed under an applied electric field. The images depended on time and were recorded by video camera and then analyzed. The dynamics of director-reorientation was followed by the measurement of the optical transmittance of a sample between crossed polarizers. A reproducible optical response to a low frequency square wave was observed. The dependencies of the band spacing and the reorientation rate of director on the field strength were quantitatively investigated.

Dielectric Behavior in Chiral Smectic Phases of Main-Chain Polyesters

Abstract We have investigated the SmA-SmC* phase transition of main-chain polyesters having a mesogenic p,p′-bibenzoate unit by means of the dielectric and electrooptic measurements. In the SmC* phase, a relaxation due to the Goldstone mode was observed at several 10 Hz. In addition, we recognized the other relaxation exhibiting softening behavior around the SmA-SmC* phase transition temperature.

Electrostatic Field-Induced Transformation in the Homeotropically Aligned Liquid Crystalline Polymer

Abstract For the liquid crystalline(LC) solution of Poly(γ-benzyl L-glutamate),(PBLG),/1,1,2-trichioroethane, which gives a nematic texture aligned homeotropically at a glass surface, the effect of DC field applied perpendicularly to the director in a homeotropic texture was investigated by microscopic optical measurements. An increase of the DC field above a threshold generates some planar texture at the negative electrode and the texture develops with a distinct boundary between the homeotropic and the planar ones. After the field direction was inverted, the boundary begins to move backward into the electrode, and at the same time, the planar texture to develop slowly from the another electrode. Under a fixed strength of the field, the ratio of the homeotropic and the planar areas is kept constant during transforming process after an inversion and the value depends on the field strength. The phenomenon may be qualitatively associated with the balance between some electrostatic interaction of the polar t...

13C-NMR Studies on Fluctuation of Rod-Like Molecules in Solution: Molecular Dynamics in a Polar Solvent of CDCl3

To investigate the molecular dynamics of rod-like molecules in solution, 13C-NMR measurements of a liquid crystalline material (4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate: MHPOBC) with a CDCl3 solvent are carried out. When MHPOBC leaves the solution and deposits as crystals, peak broadening, which may result from a slowing down of molecular motion, occurs simultaneously. In addition, the correlation time τc of the corresponding molecular motion is estimated to be approximately 10−8 s by the spin-lattice relaxation time T1 measurements.