Ca. Garcia-franco et Dw. Mead, Rheological and molecular characterization of linear backbone flexible polymers with the Cole-Cole model relaxation spectrum, RHEOL ACT, 38(1), 1999, pp. 34-47
The empirical Cole-Cole distribution is an analytical three parameter model
of the relaxation spectra that provides accurate fits to experimental dyna
mic viscosity data for many systems of commercial linear backbone flexible
polymers. We demonstrate that for disparate systems of polyethylenes, the t
hree Cole-Cole model parameters have simple power law relationships to mome
nts of the molecular weight distribution enabling direct molecular interpre
tation of the mechanical relaxation spectrum. A simple relationship between
the Cole-Cole distribution and the Cross model for the non-linear flow cur
ve can be deduced utilizing the empirical Cox-Merz rule. Accurately represe
nting the linear viscoelastic material functions with empirical analytical
relaxation spectra containing relatively few fitting parameters that can be
readily interpreted is a major advance in polymer characterization. The th
ree Cole-Cole parameters effectively replace single point material characte
rizations such as melt flow index. Development of higher resolution polymer
characterization methods is imperative with the advent of metallocene cata
lyst technology, which enables the molecular weight and backbone architectu
re to be carefully controlled.