Two-component systems of isomorphous orientationally disordered crystals. Part 2 - Thermodynamic analysis

A thermodynamic analysis was made of a set of two-component systems display ing isomorphous orientationally disordered phases (ODIC). The pure compound s are molecular materials belonging to the series (CH3)(4-n1)C(CH2OH)(n1) ( n(1) = 1, 2, 3), (NO2)(CH3)(3-n2)C(CH2OH)(n2) (n(2) = 0, 1) and (NH2)(CH3)( 3-n3)C(CH2OH)(n3) (n(3) =2, 3). The Equal Gibbs Curve method was used in or der to determine the Gibbs excess energy of the orientationally disordered mixed crystals. The excess Gibbs energies of the disordered phases obtained from the disordered-liquid equilibria were used on the analysis of the low -temperature ordered-disordered equilibria. This excess property was correl ated for the mentioned chemically coherent group of materials (neopentane d erivatives)studied in this work, with a crystallographic parameter, the pac king coefficient, which accounts for the steric factors and intermolecular interactions in the disordered mixed crystals.