Dielectric studies of molecular motions in glassy and liquid nicotine

Abstract

The dielectric permittivity and loss spectra of glassy and liquidstates of nicotine have been measured over the frequency range10−2–109 Hz.The relaxation spectra are similar to common small molecular glass-forming substances, showing thestructural α-relaxation and its precursor, the Johari–Goldsteinβ-relaxation.The α-relaxation is well described by the Fourier transform of the Kohlrausch–Williams–Wattsstretched exponential function with an approximately constant stretch exponent that isequal to 0.70 as the glass transition temperature is approached. The dielectricα-relaxation time measured over 11 orders of magnitude cannot be described by a singleVogel–Fulcher–Tamman–Hesse equation. The most probable Johari–Goldsteinβ-relaxation time determined from the dielectric spectra is in good agreement with the primitiverelaxation time of the coupling model calculated from parameters of the structuralα-relaxation. The shape of the dielectric spectra of nicotine is compared with that of otherglass-formers having about the same stretch exponent, and they are shown to be nearlyisomorphic. The results indicate that the molecular dynamics of nicotine conform to thegeneral pattern found in other glass-formers, and the presence of the universalJohari–Goldstein secondary relaxation, which plays a role in the crystallization ofamorphous pharmaceuticals.