Localized relaxation in a glass and the minimum in its orientational polarization contribution

The dielectric permittivity and loss spectra of the glassy state of 5-methyl-2-hexanol obtained by quenching it from the liquid state has been studied. In one experiment, the spectra were studied at different temperatures as the quenched sample was heated at 0.1 K/min from 105.3 to 160.5 K. In the second experiment, the quenched sample was heated from 77 to 131.6 K and kept at that temperature for 14.6 ks. The relaxation rate, f m ,b , the dielectric relaxation strength, Deb , and the distribution of relaxation time parameters, a and b, for the Johari–Goldstein process were determined. The parameter b was found to be equal to 1 and independent of both the temperature and time, Deb initially decreased on increasing the temperature, reached a minimum value at ;145.6 K, and then increased. The plot of f m ,b against the reciprocal temperature decreased in slope and at ;140 K became linear. This indicates that f m ,b increases on structural relaxation. In the course of the annealing at 131.6 K, Deb of the quenched sample decreased with time, approaching a plateau value. It is described by an equation, Deb(t)5Deb(t→`)1@Deb(t50)2Deb(t →`)#exp@2(t/t)#, where t is the time, and t ~53.5 ks! is the characteristic time. It is pointed out that contrary to the earlier finding, o-terphenyl shows a b relaxation in the equilibrium liquid state. A consideration of dielectric permittivity arising from small-angle motions of all molecules, which has been suggested as an alternative mechanism for the localized motions seen as b relaxation, indicates that this mechanism is inconsistent with the known increase in the equilibrium permittivity on cooling. © 2002 American Institute of Physics. @DOI: 10.1063/1.1485960#