Experimental determination of the cooperative length scale of a glass-forming liquid near the glass transition temperature

Photon correlation spectroscopy and dielectric relaxation are used to exami ne the molecular reorientation relaxation dynamics of a fragile glass-formi ng liquid Aroclor (a mixture of polychlorinated biphenyls), modified by the addition of low- and high-molecular-weight polyisoprene and polybutadiene as a function of temperature and polymer solute concentration. Concentratio n fluctuation contributes a temperature-dependent broadening of the relaxat ion spectrum of Aroclor. The rate of change of the Aroclor relaxation spect rum with temperature is more pronounced when the polymers added are of low molecular weight and exhibits a steplike decrease in the neighborhood of so me characteristic molecular weight. The radius of gyration of the polymer w ith this characteristic molecular weight is about 15 Angstrom, which determ ines the cooperative length scale L(T) of Aroclor to be approximately 30 An gstrom near and above the glass transition temperature. [S1063-651X(98)0181 1-X].