Dielectric behavior of long-chain molecules in the solid state

The dielectric constants of pure samples of four normal long-chain bromides and four normal long-chain alcohols were measured as a function of temperature at 0.25, 0.5,5.0, 50 and, in one case, at 525 kc. to obtain information on the relationship between the molecular structure of solids and their dielectric properties. Long-chain molecules present the interesting possibility of rotation about the long molecular axis, in the solid state. If the rotating molecules contain dipoles, orientation polarization, and hence a high dielectric constant corresponding to rotation should be observed below the freezing point. This effect was observed in n-C22H⁴⁵Br and n-C14H29OH, and n-C18H37OH. The dielectric constants of these compounds in the rotator phase were shown to be consistent with that expected for rotation about-the long molecular axes of all the molecules. Similar freedom of molecular rotation was not shown by the dielectric constants of n-C12H25OH, n-C12H25Br, n-C16H33Br and n-C18H37Br in the solid state. All the molecules with rotation in the solid phase showed a transition temperature where the dielectric constant dropped sharply indicating that much of the molecular rotation had disappeared. These dielectric transitions coincided with thermal transitions as observed by cooling curves.