Light‐Scattering Measurements of Structural Relaxation in Glass by Digital Correlation Spectroscopy

Digital clipped auto correlation spectroscopy was used to investigate the kinetic features of thermodynamic fluctuation processes which relax on time scales from 10 −6 to 10 2 s. The autocorrelation function associated with structural relaxation in Na 2 O· K 2/ O·6SiO 2 , glass was determined in the annealing region. The results indicate a nonexponential correlation function that can be fitted with the decay function exp ‐ ( t /τ β ) β , where β and τ β are adjustable parameters. The parameter β which characterizes the deviation from a simple exponential, was essentially constant (β= 0.57 ± 0.02) from 468 ° to 550 ° C. The characteristic time constant, τ β ranged from 1.35 × 10 −2 to 6.30 s. The computed average relaxation times were compared with shear viscosity data reported for a similar glass; both the temperature dependence and the magnitude agreed well with the predictions of viscoelastic theory.