Determination of the Hindered Rotation Degree of Chiral Molecules Around Their Long Molecular Axes in the Sc* Phase of 4-(2‘-Methylbutyl)-4‘-n-Octylbiphenyl-4-Carboxylate

Abstract

Chiral 4-(2“-methylbutyl)-phenyl-4‘-octylbiphenyl-4-carboxylate (CE8) has been studied by dielectric, densytometric, refractic and X-ray measurements. On the basis of these measurements the effective value of the molecular dipole moment (μ), the angle between the vector of the molecular dipole moment and the long axis of molecule (γ) as well as the transverse (α₁) and longitudinal (α₁) molecular polarizabilities have been calculated⁸. In addition the sign and the magnitude of spontaneous polarization (P_s), the tilt angle (6) and the helical pitch (λ) have been measured for the same liquid crystal CE8. Knowing the molecular parameters μ, γ, α, α₁ and Θ from the experiment and the molecular structure from computer investigation, the spontaneous polarization P_s has been calculated as the vector sum of the components of molecular dipole moments μ perpendicular to the tilt direction. To do it the rotational potential given by B.Zeks² has been used. According to this approximation the measured spontaneous polarization P_s is induced by hindered rotation of the molecules around their long axes and is expressed by molecular parameters μ, γ, α₁, α₁, tilt angle Θ and the hindered rotation parameter η The hindered rotation parameter for CE8 shows that dipolar ordering in this smectic C* phase is rather weak in the comparison with the strong orientational order of long molecular axes of the same phase.