Determination to 2 kbar of the Nematic-Isotropic and Melting Transitions in p-Azoxyanisole

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Abstract
Differential thermal analysis to 2 kbar of zone-refined p-azoxyanisole in hydrostatic apparatus has corroborated the results of Hulett and of Robbcrecht at lower pressures—initial slopes ≲ 48 deg kbar−1 for the nematic-isotropic transition and ≲ 31–32 deg kbar−1 for the melting curve—and also established that the curvatures, -d2 T trans/dp 2, are ∼ 5 deg kbar−2 for the liquid transition and >O tor the melting curve. At transition temperatures above ∼ 2 kbar, irreversible effects are encountered. A self-consistent discussion, using 1 bar data, is given for the thermodynamics of the nematic-isotropic transition in p-azoxyanisolc and the implications of this discussion have been pursued for p-azoxyphenetole and other di-n-azoxy-benzcnes.