Dielectric studies of molecular motions in glassy and liquid nicotine

The dielectric permittivity and loss spectra of glassy and liquid states of nicotine have been measured over the frequency range 10(-2)-10(9) Hz. The relaxation spectra are similar to common small molecular glass-forming substances, showing the structural alpha-relaxation and its precursor, the Johari-Goldstein beta-relaxation. The alpha-relaxation is well described by the Fourier transform of the Kohlrausch-Williams-Watts stretched exponential function with an approximately constant stretch exponent that is equal to 0.70 as the glass transition temperature is approached. The dielectric alpha-relaxation time measured over 11 orders of magnitude cannot be described by a single Vogel-Fulcher-Tamman-Hesse equation. The most probable Johari-Goldstein beta-relaxation time determined from the dielectric spectra is in good agreement with the primitive relaxation time of the coupling model calculated from parameters of the structural a-relaxation. The shape of the dielectric spectra of nicotine is compared with that of other glass-formers having about the same stretch exponent, and they are shown to be nearly isomorphic. The results indicate that the molecular dynamics of nicotine conform to the general pattern found in other glass-formers, and the presence of the universal Johari-Goldstein secondary relaxation, which plays a role in the crystallization of amorphous pharmaceuticals.