RELAXATION MECHANISMS IN A BENZYL-CHLORIDE TOLUENE GLASS

Using frequency-dependent dielectric susceptibility, we have studied three different types of relaxation phenomena, namely primary (a), secondary (b), and conductivity (c) relaxation, in a sample of 25 vol % benzyl chloride in toluene. The measurment covers ten decades of frequency: 10(-3) < v < 10(7) Hz. The conductivity relaxation which is due to mobile ionic impurities in the sample has characteristics similar to those of the primary relaxation. Using the universal scaling curve for the primary relaxation response in glasses, we can separate the primary and secondary relaxations which overlap in frequency. The shape of the secondary relaxation is log-normal in the frequency domain and corresponds to a Gaussian distribution of energy barriers. The relaxation time for this process can be fitted by an Arrhenius form. Extrapolating the data to higher temperatures, we find that it crosses the primary-relaxation curve. We compare a set of similar molecular liquids and conclude that the secondary relaxation is mainly due to the rotation of a subgroup in the benzyl chloride molecule. We also report a measurement of the nonlinear dielectric response. There is no evidence of a divergent nonlinear susceptibility as the glass transition is approached.