Mössbauer studies of DNF and FMA in a smectic B liquid crystal

Abstract

The FE-57 Mössbauer effect (ME) was used to study two solutions 0.4 wt% of ferrocenyl-4′-methoxyaniline (FMA) in the liquid crystalline material 4-n-butoxybenzylidene-4′-n-octylaniline (40.8) and 0.4 wt% of 1,1′-dinonanoyl-ferrocence in 40.8. The ME parameters were determined for the temperature range 40-300 K in the crystalline solid phase and 40–220 K in the cold smectic B phase of 40.8 for both samples. The ‘cold smectic B’ is defined as the smectic B glass and the supercooled smectic B phase. For T < 60 K the DNF-40.8 system exhibited a ME spectrum that was composed of two quadrupole split doublets. This four-line spectrum was observed for both the crystal phase and the smectic B glass phase of the DNF-40.8 system. The FMA-40.8 system exhibited a single quadrupole doublet. The In (recoil-free intensity f) versus T data exhibited linear Debye behaviour for the solid phase over the entire temperature range. The cold smectic In f versus T data also exhibited Debye behaviour for this system. The smectic B glass gave a Mössbauer-Debye temperature (θ_lc) about 23 K lower than the crystalline phase for the FMA-40.8 system and about 25 K for the DNF-40.8 system. The intermolecular contribution to the vibrational ellipsoid (ε_L) declined linearly with increasing temperature for both systems.