A Mössbauer Temperature Study of 1,1′-diacetylferrocene in the Liquid Crystal, N-(P-hexyloxybenzylidene)-P-toluidine

Abstract

The Fe-57 Mössbauer Effect was used to study a solution (0.2% by Weight) of 1,1′-diacetylferrocene (DAF) in the liquid crystalline material p-n-hexyloxy-benzylidene-p-toluidine (HBT). The DAF contained enriched Fe-57. The Mössbauer Effect parameters were determined for the temperature range 100–300K in the crystalline solid phase and 100–200K in the cold smectic ß phase of HBT. Here “cold” means the smectic glass and the supercoded smectic phase. The Ln recoil-free intensity (f) vs T data exhibited linear Debye behavior for the solid phase over the entire temperature range. The low temperature (T < 190) portion of the cold smectic Inf vs T data also exhibited Debye behavior, and the smectic glass gave a Mössbauer-Debye temperature (θ _lc ) about 30 K. lower than the crystalline phase. The smectic glass-super cooled smectic transition was determined to be T_g = 190 K from the deviation of the Inf vs T data from linear behavior. Above T_g , the deviation from linear Debye behavior followed a (T-Tg)² dependence. The smectic B glass yielded an order parameter of S = 0.06 for DAF molecules at 100 K. Rotational and transitional diffusion were not observed for the cold smectic B phase.

Key Words:

• Mössbauer Effect
• liquid crystal
• diacetylferrocene