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The dielectric absorption at five microwave frequencies of solutions of the monohalobenzenes, nitrobenzene and benzonitrile in p-xylene at 15 and 60°C has been examined. Solutions of nitrobenzene in cyclohexane and carbontetrachloride at 25 and 15°C respectively, and also benzonitrile in cyclohexane at 15"C, have also been studied. All solutions of the halobenzenes may be characterized by a dielectric absorption contribution from one Debye term 1 and are in harmony with the Perrin theory2 None of the systems showed high-frequency absorption of the type reported by Poley 3 for the liquid halobenzenes. Some benzonitrile and nitrobenzene systems have definite distribution coefficients which may be resolved into contributions from two relaxation processes, one associated with molecular re-orientation and a longer relaxation time related to the presence of some form of polar aggregate.

The dielectric absorption at five n~icrowave frequencies of solutions of seven rigid polar molecules in nonpolar solvents has been examined as also has cyclohexanone. Furan, pyridine, and thiophene have their dipole moments along the major axis and their dielectric absorption should be characterized by a single relaxation time. Unlike the n~onohalobenzenes, camphor, pentamethylene sulfide, tetrahydropyran, and s-trioxan, however, furan, pyridine, and thiophene have non-zero distribution coefficients at 25 "C, whereas for pyridine at 50 "C and cyclohexanone at 25 "C the value is zero. The non-zero distribution coefficients are to be related to either weak solute-solute or solute-solvent interactions, resulting in the polar molecule experiencing a variety of local environn~ents. The observed relaxation times of furan, pyridine, and thiophene are comparable with those of other rigid molecules of similar shape and size. For such cases, even though the distribution parameters are not zero, it is not feasible to analyze the dielectric data into contributions from more than one relaxation process.

A microwave procedure of improved accuracy has been employed to study the dielectric absorption at 25°C of liquid toluene, ethylbenzene, isopropylbenzene, t-butylbenzene and their solutions in cyclohexane. Solutions of toluene in cyclohexane have been examined at 15,40 and 60°C and also toluene in carbon tetrachloride at 25°C. All systems have definite distribution coefficients * and all are characterized by an absorption that may be analyzed into two relaxation times, one associated with molecular re-orientation and a shorter relaxation time. Possible explanations for the latter are considered.* The distribution coefficient is the Cole-Cole 9 parameter a, which is zero for a system with one relaxation time and can take values between 0 and 1. Its deviation from zero is an indication of the distribution of the relaxation times.

Articles you may be interested in Dielectric functions of bulk 4H and 6H SiC and spectroscopic ellipsometry studies of thin SiC films on SiThe dielectric absorption of benzocyclobutene, 2-bromonaphthalene, o-dichlorobenzene, m-dichlorobenzene, indane, 1-methylnaphthalene, 2-methylnaphthalene, tetralin, o-xylene, and m-xylene in cyclohexane solution has been examined. All the dielectric data were analyzed in terms of a Cole-Cole distribution, and where appropriate, the data were further analyzed into contributions from two relaxation times. Tetralin at 15° and 25°C showed a nonzero distribution coefficient (a); at 50°C its a was zero and this was also the case for benzocyclobutene, indane, o-dichlorobenzene, and m-dichlorobenzene at 25°C. A short relaxation time process, together with that of molecular reorientation, contributes to the dielectric absorption of the methyl-substituted compounds and may also be present in the benzocyclobutene, indane, and tetralin solutions. The short relaxation time for the aromatic hydrocarbons may be accounted for by an intermolecular relaxation process.