MOSSBAUER TEMPERATURE STUDY OF A COLD NEMATIC LIQUID-CRYSTAL - NEMATIC GLASS SUPERCOOLED NEMATIC

A 0.2% (by weight) solution of 1,1'-diacetylferrocene (DAF) in n-(p-methoxybenzylidene)-p-butylaniline (MBBA) was prepared and studied with the Fe-57 Mössbauer effect. The Mössbauer parameters were observed for the temperature range 110-300 K. The recoil-free fraction (f) data showed that the MBBA crystal phase exhibited Debye behavior for the entire temperature range with a Mössbauer-Debye temperature (θL) of 70 K. The lower temperature data for the cold nematic also gave a linear lnf vs T plot with θL= 47 K for the MBBA glass. The θL for the nematic glass was indepentent of molecular orientation. The nematic glass-supercooled nematic transition was determined to be Tg= 181 K from the deviation of the lnf vs T curve from linear behavior. The nematic glass provided a nonvanishing temperature independent contribution to the Fe-57 vibrational ellipsoil (εL). Above 180 K εL became temperature dependent. Line broadening and a reduction of the quadrupole splitting were observed for the supercooled nematic with increasing temperature in the range 220-240 K. We interpret these results in terms of a model for rotational diffusion of the DAF molecule in the MBBA supercooled nematic. The rotational diffusion appears to occur without simultaneous translational diffusion. © 1979 American Institute of Physics.