The Physical Properties of an Ester/Biphenyl Mixture Exhibiting an Injected Smectic Phase

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Abstract
Measurements are reported of the phase-coexistence temperatures, transition enthalpies, refractive indices and electric permittivities of a series of mixtures of 4-n -pentyl 4′cyanobiphenyl (component 1) and 4 n-pentylphenyl 4 n'-pentyloxybenzoate (component 2). The temperature composition phase diagram shows the presence of an injected smectic phase, and the nature of this phase together with its effect on the adjacent nematic phase is discussed in the light of the measured physical properties. The results suggest that the injected smectic A to nematic transition is second order (or very weakly first order) for mole-fractions of component 1 greater than 0.55, but at lower mole-fractions the nature of the transition alters to become more characteristic of a first order phase change. In the nematic phase above the injected smectic, the orientational order is reduced, as evidenced by enthalpy measurements, refractive indices and electric permittivities. Using a recent adaptation of mean field theory, the component order parameters in the mixture have been calculated, and hence values predicted for the optical and dielectric anisotropies. There is reasonable agreement between the theoretical and experimental results provided that an empirical scaling procedure is adopted for the component order parameters in the mixture. Finally the presence of coexisting phases in the phase diagram is considered, and implications for the structure of the injected smectic phase are discussed.