Abstract
The cholesteric mesophase of poly(γ-benzyl L-gultamate) in concentrated solutions of helicogenic solvents was investigated by the laser-light scattering technique. The observed, elastic scattering intensity distributions are theoretically explained in terms of the cholesteric domains embedded in an optically active medium. Analysis of the scattering patterns provides information on the identity period and sense of the cholesteric twisting.
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This is possible since the “cholesteric scattering” depends only on the spatial orientation correlation of the optical axes, while the “rodlike scattering” depends as well on the density correlation owing to the effect of optical activity of the medium, (thus the sense of distortion of the “rodlike scattering pattern” should also depend on p).
The distortion of the patterns also arises from a macroscopic orientation of the cholesteric domains as pointed out in ref 6. One can distinguish two kinds of distortions, at least, in principle. If the distortion purely arises from the effect of form optical rotation, the pattern under given polarization condition is unchanged with the rotation of the sample around the incident beam axis, while if the distortion arises from the macroscopic orientation, the pattern changes with the rotation due to the effect of birefringence on the scattering distribution.19–21 Moreover, if the distortion dominantly arises from the macroscopic orientation, the Hv pattern should be identical to the VH pattern, while if the distortion arises from the optical activity, the Hv pattern is not identical to, but related to the VH pattern by eq 2.
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If the orientation of the cholesteric domains significantly contributes to the distortion of the pattern, the determination of the sense of the cholesteric twisting is somewhat obscured.
In a real system, a given cholesteric domain is surrounded by other cholesteric domains, so that there may be no isotropic phase as assumed in our model. Thus, the surrounding medium is generally anisotropic, having polarizabilities αs1 and αs2 parallel and perpendicular to their optical axes. In this treatment we assume the medium has an average polarizability αs=(αs1+αs2)/2. This assumption is good for our systems in which scattering dominantly arises from anisotropy fluctuations (or orientation fluctuations) rather than from density fluctuations caused by difference in the average polarizabilities between the cholesteric domain and the surrounding medium.
It should be noted that at small scattering angles, j0(πT(1–cos θ′)/λ)→1 unless T is extraordinarily large compared with L and D.
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Hashimoto, T., Ebisu, S., Inaba, N. et al. Supramolecular Structure of Polypeptides in Concentrated Solutions and Films. II. Small-Angle Light Scattering from Cholesteric Mesophase. Polym J 13, 701–713 (1981). https://doi.org/10.1295/polymj.13.701
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DOI: https://doi.org/10.1295/polymj.13.701