Thermodynamics of mixtures with strong negative deviations from Raoult’s law. XIII. Relative permittivities for (1-alkanol + cyclohexylamine) systems, and dielectric study of (1-alkanol + polar) compound (amine, amide or ether) mixtures

Abstract

Relative permittivities, εr, at 1MHz have been measured for (1-alkanol+cyclohexylamine) systems at T=(293.15 to 303.15)K and atmospheric pressure. The excess permittivity values, εrE, Kirkwood’s correlation factors, gK, and the excess values of this magnitude, gKE, have been also determined for these solutions and, using measurements available in the literature, for mixtures containing a number of 1-alkanols and n-propylamine, n-butylamine, aniline, N-methylaniline, pyridine, di-n-ethylamine, N,N-dimethylformamide, N,N-dimethylacetamide, di-n-propylether, di-n-butylether, 2,5,8,11,14-pentaoxapentadecane, or propanal. At ϕ1 (volume fraction)=0.5, εrE values of cyclohexylamine solutions change in the sequence: 1-propanol>1-butanol>1-heptanol<1-decanol and the symmetry of the εrE curves becomes skewed to higher ϕ1 values when the alcohol size increases. This seems to be a rather general behavior as is also encountered for many of the systems investigated. It can be explained in terms of the weaker and lower self-association of longer 1-alkanols. The analysis of gK data shows that cyclohexylamine solutions including shorter alcohols are more structured. In addition, mixtures with this cyclic amine are more structured than those containing a linear amine or aniline. The εrE(ϕ1) and gKE(ϕ1) curves of (1-alkanol+amine) mixtures show similar patterns. Thus, negative εrE values can be ascribed to the real mixture is less structured than the ideal solution; positive εrE values are due to the system is more structured than the ideal solution. We have also determined the orientational polarization and the corresponding excess values, PmE. The PmE and gKE functions have the same sign That is, negative values of such magnitudes suggest that the loss of structure of the real mixture compared with that of the ideal solution can be ascribed, at least in part, to a weakening of the orientational polarization.