Collect. Czech. Chem. Commun. 1987, 52, 1235-1245

Evaluation of polydispersity index Mw/Mn by quasielastic light scattering

Petr Štěpánek, Zdeněk Tuzar and Čestmír Koňák

Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6


The response of quasielastic light scattering to the polydispersity of scattering objects has been investigated. A new method of the polydispersity index determination has been suggested, suitable for the range 1.02 ⪬ Mw/Mn ⪬ 2.0 and consisting in the measurement of the dependence of the apparent decay time on the correlator sampling time. The polydispersity index can be determined by comparing these dependences with the theoretical ones obtained using correlation curves simulated for various values of the polydispersity index, assuming lognormal and Schulz-Zimm distributions of molecular weights. The test measurements on polystyrene standards having molecular weights in the range 9 103 – 20.6 106 give polydispersity index values Mw/Mn that are in a good agreement with those given by the manufacturer. The polydispersity index for polystyrene having the molecular weight Mw = 20.6 106 thus determined was Mw/Mn = 1.35.