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The filler dispersion is an essential rubber compound characteristic. Traction, treadwear, and rolling resistance are affected by filler dispersion. The quantification of dispersion is a length scale phenomenon. The existing experimental tools, which are capable of measuring dispersion, for example transmission electron microscopy (TEM), mechanical scanning microscopy (MSM), optical microscopy, and reflectometry, have limitations and the information they provide may not probe the relevant scale length. The recent advance in instrumentation allows one to include electrical measurements in the arsenal of tools available to quantify the dispersion. This paper reviews the range of dispersion measurements and the correlation with compound dynamic properties is presented.

Inelastic neutron scattering experiments are powerful techniques for evaluating local molecular dynamics. These methods are especially sensitive to hydrogen atoms containing motions. An overview of these experimental techniques is presented. Neutron filter analyzer and time-of-flight spectroscopy methods are used to characterize the local dynamics of polymers in the presence and absence of fillers. Of particular interest is the comparison between bound rubber attached to the filler surface and the pure, unbound rubber. A commercial synthetic polyisoprene containing approximately 100% cis-1,4 isomers was compounded with three different carbon blacks: N299, G299 (graphitized N299), and N762. Soxhlet extraction on each of the samples was performed so that corresponding samples containing purely bound rubber with filler were obtained. The filter analyzer and time-of flight spectra show distinct differences between the bound and pure rubber as well as differences based on carbon black type. Correlation of the spectral differences to the type of carbon black and initial concentration of carbon black are discussed.

A high frequency viscoelasticity spectrometer, using the state-of-the-art ultrasonic technology, was constructed. The longitudinal and shear waves characteristics were measured in rubber compounds to obtain the attenuation coefficient, α, and sound velocity, v Preliminary results were obtained for a number of filled and unfilled polymers. The grade of carbon black used, filler loading, crosslinking density and filler dispersion were varied during the study. Temperature sweepS from −100°C to +60°C were also studied. It was found that the polymer type had a greater influence on α and v than did the grade of carbon black, loading or dispersion. The experimental data show that shear waves do not propagate in the rubbery state. Above the glass transition temperature, Tg, the longitudinal wave measurements could be sufficient to determine the high frequency dynamic properties of filled and unfilled polymers to characterize a tire tread compound. The temperature sweep measurements allowed the determination of the Tg of polymers at high frequency. It is proposed that the described method of measuring α and v be used as a laboratory tool for potential tire traction prediction.