Positron lifetimes in five phases of BEA

Research paper by W. W. Walker, E. L. Mueller

Indexed on: 01 Feb '74Published on: 01 Feb '74Published in: Applied Physics A


Positron lifetimes have been measured as a function of temperature in 4-butyloxybenzal-4′-ethylaniline (BEA). BEA has been previously reported to have two liquidcrystalline phases (smectic and nematic) with transition temperatures as follows: solid → smectic, 40.5° C; smectic → nematic, 51.0° C; and nematic → isotropic liquid, 65.5° C. Positron life time spectra were resolved into two components, with the shorter component τ1 remaining approximately constant in all phases, and τ2 exhibiting reversible changes at all of the above transitions. In addition, an irreversible discontinuity in the τ2 lifetime was observed in the vicinity of 28° C, indicating the presence of a new phase (phase X) of BEA. The τ2 andI2 values obtained for the various phases of BEA are: solid (1.25 nsec, 7.1%), phase X (1.97 nsec, 26.2%), smectic (2.36 nsec, 23.6%), nematic (2.72 nsec, 28.3%), and isotropic liquid (2.69 nsec, 29.8%).