Investigation of the glass transition in polymers under the aspect of mode coupling predictions

Abstract

A review of recent neutron scattering experiments on polybutadiene to study the glass transition is given. Coherent and incoherent scattering data are compared and tested against mode coupling predictions made for simple liquids near the glass transition. Given the complexity of a polymer, a reasonable qualitative agreement is found. A two-step relaxation process is identified, where the slower alpha (α)-relaxation shows scaling and stretching. A critical temperature, T c, was extrapolated from both literature viscosity data and the measured non-ergodicity parameter. The formfactors for both relaxation components show characteristic Q-dependences either in phase or in anti-phase with the static structure factor. The susceptibility spectra show on the high frequency side a peak interpreted as beta (β) resonance. A minimum is formed due to a slight increase at the low frequency side, ascribed to the α-relaxation. Quantitative agreement is found for the square-root dependence of the non-ergodicity parameter below T c.