Sn-119 Mössbauer effect study of two Sn-bearing liquid crystalline materials

Abstract

A 119Sn Mössbauer, lattice dynamic orientational study, at 77 K, of the smectic B glass phase of the Sn-bearing liquid crystals (LC) p-(11-trimethyltin)undecyloxy-benzilidene-p′-n- butylaniline (Sn-UBBA) and p-(11-trimethyltin)undecyloxy-benzilidene- p′-octylaniline) (Sn-UBOA), and solutions of these liquid crystals in LC of similar structure which do not contain Sn as part of their molecules, is presented. The Sn-bearing liquid crystals were designed and synthesized specifically for this study and their synthesis is described. The samples were aligned by cooling from the melt in the presence of a magnetic field. For the samples of Sn-UBBA and Sn-UBOA, the experimental linewidth appears to depend on the orientational angle ϑ. This is explained as due to the non-negligible sample thickness and the rff versus ϑ variation. These ϑ dependencies were used to extract the absolute fractions for various orientations of Sn-UBBA and then the corresponding Debye temperatures ΘD(ϑ). For the other samples the lattice contribution to the nuclear vibration anisotropy εL was found. A comparison of these parameters suggests that the alignment found in the solutions is similar to the pure LC. Further,the existence of a nematic phase is not important in the alignment of smectics via cooling from the melt in the presence of a magnetic field. The effect of the aligning field intensity on the quality of the alignment is discussed. The ϑ dependence of the apparent line position for pure Sn-UBBA and Sn-UBOA is explained as due to the presence of a weak unresolved doublet, probably induced by the anisotropic enviornment of the Sn nuclei in the LC.

Moessbauer spectroscopy

“…Kandpal and Bhide (151) used diacetyl ferrocene as a Mossbauer probe to study molecular diffusion in nematic liquid crystals at low temperature. Several smectic liquid crystals containing tin in the crystalline matrix have been studied at 77 K by Ktorides et al (169). Effects of the alignment angle on the 119Sn recoilless fraction are reported.…”