A novel approach to the characterization of polar liquids. Part 2: binary mixtures.

Theoretical descriptions of solvent and solubility properties, important for a rational development of liquid dosage forms, have so far not proved completely satisfying. In this work, the modified Debye equation according to Leuenberger, which was introduced earlier for the description of polar and nonpolar pure liquids, is extended to liquid binary mixtures. Between 290.7 and 343.2 K, several binary aqueous systems were investigated. The values of (E(i)/E) (E(i)=internal electric field, E=external electric field), calculated by means of the modified Debye equation, were compared to the correlation factor g of the Kirkwood-Fröhlich equation, which describes the molecules' preference for either parallel or nonparallel alignment. The previously found correlation between /m/ of (E(i)/E)=m(1/T)+b (T=temperature) and the Hildebrand solubility parameter delta for pure liquids was investigated for binary mixtures. Furthermore, the applicability of percolation theory to the description of binary liquid mixtures was examined. This new approach allows the description of irregular solutions and provides a useful tool for a more rational design of liquid dosage forms.