Positron lifetimes in five phases of BEA

Abstract

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 andI ₂ 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%).