The Use of Liquid Crystals in Mössbauer Studies and the Use of the Mössbauer Effect in Liquid Crystal Studies

Abstract

An ordered solute ‘monocrystal’ can be obtained by dissolving iron or tin bearing molecules into the liquid crystalline material 4-n-hexoxybenzylidene-4’-n-propylaniline (HBPA) and cooling from 90°C to room temperature through the nematic and smectic A phases to the smectic H phase (T≤60°C) in a magnetic field of 9000 gauss. The smectic H structure persists to 77°K and therefore allows the observation of the quadrupole interaction as a function of the angle θ between the aligning field and the gamma direction. In particular, from the θ dependence of the area ratio (A_π/A_σ) of the quadrupole split doublet both the sign of V_zz and the value of the molecular contribution (at 77°K) to the nuclear vibrational anisotropy (ε_M) have been determined for the triethyltinpalmitate molecule. Furthermore, the 6 dependence of the recoil free fraction (f) yielded the lattice contribution to the vibrational anisotropy. The above information was obtained by making use of the known ordering properties of liquid crystals in the theoretical fits to the Mössbauer data. In addition, the temperature dependence of f for a 0.2% solution of diacetylferrocene in HBPA has been observed for both the supercooled smectic H phase and the crystal phase in the range 100°–300°K. The data show that the crystal obeys the Debye model and that the smectic H structure is much less rigid and deviates significantly from the Debye prediction above 150°K.

This research has been supported in part by the National Science Foundation under Grant #GH-34164X.