A nematic gap in mixtures of smectics A1 and Ad

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Abstract
The effect is tested of the smectic layer spacing ratio, r, on the phase diagram for the binary systems consisting of 80CB (smectic Ad) and one of the twelve compounds of the 5-n-alkyl-2-(4'-isothiocyanatophenyl) dioxane-1,3 homologous series (DBT compounds-smectics A1) has been studied The stability of the smectic phase in the mixture decreases with increasing r, and for r >> 1.4 a nematic gap separating the smectics A1 and Ad is observed The density, viscosity and scattering of X-rays as a function of temperature are measured and the enthalpy of the phase transitions is determined for the binary system 80CB-4DBT. The nematic phase reveals in the nematic gap a viscosity and structure characteristic for typical nematics. The binary system increases its molar volume as a result of mixing and assumes a maximum in the concentration range x8OCB < 0.2