A Mössbauer Study of a Sn-119 Bearing Solute in an Ordered Smectic Liquid Crystal, at 77°K

Abstract

An ordered solute “monocrystal” was obtained by dissolving 3.5-7.0% (by weight) of triethyltin palmitate (3EtSnPalm) into 4-n-hexoxybenzylidene-4′-n-propylaniline and cooling from 90°C to room temperature through the nematic and semectic A phases to the smectic H phase (T < 60°C) in a magnetic field of 9000 Gauss. The disc-shaped sample was then removed from the magnetic field and cooled to 77°K at which temperature the Mössbauer measurements were made. From the variation of the area ratio of the two quadrupole split Mössbauer absorption peaks as a function of the angle θ between the orienting magnetic fields and the γ-ray beam we have determined the sign of the axial electric field gradient (V_zz) at the tin site in 3EtSnPalm to be positive. Further, the theoretical fit to the data yielded the solute order parameter, S = 0.17 and the molecular contribution to the nuclear vibrational anisotropy for the tin atom in the 3EtSnPalm molecule, _M = - 0.8. An independent value of _M = -1.50 was obtained from the orientational dependence of the recoil-free fraction (as percent effect). The difference is attributed to the lattice contribution to the recoil-free fraction in the latter case. A field dependent study of the area ratio showed that the surface oriented the molecules perpendicular to the surface normal.