We have investigated the elastic and the optical properties of nematic and smectic side chain polymer liquid crystals at hypersonic frequencies. In contrast to classical liquid crystals, the polymer materials show a significant coupling between the static order parameter and the square of the elastic strain ε₃. The inverse shear stiffness constants do not diverge. All elastic constants behave continuously at the nematic-isotropic transition (Tₙᵢ). From certain optoacoustic properties and the refractive index functions, it follows that order-parameter fluctuations play no role at Tₙᵢ, but that the glass transition dominates the dynamic elastic properties at hypersonic frequencies.
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Krüger et al. (1988) studied this question.
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