Application of Generalized Van Der Waals Theory of Homologous Nematogens — Part 1: Trans-4-Ethoxy-4’-N-Alkanoyloxyazobenzenes
In the generalized van der Waals theory (GVDW) of Cotter, nematogens are viewed as rigid spherocylinders moving in a mean field potential given by V(θ) = -λovo0ρ-λ2vo ρ ηP2(cos θ) where λo and λ2 are potential parameters independent of temperature. Employing the equation of state developed by Cotter, values of λo, λ2, and the order parameter are calculated for a homologous series of trans-4-ethoxy-4’-alkanoyloxyazobenezenes from observed volume and temperature data. Calculated λo values were found to be 3 to 5 times those calculated from heat of vaporization estimates. In calculating the temperature dependence of the order parameter, the λ2 values were found to vary markedly with temperature. In addition, calculated values of the order parameter were generally about one-half to one-third of the experimentally measured values.
KeywordsWidth Ratio Potential Parameter Molecular Volume Helmholtz Free Energy Nematic Phase
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