Determination of the viscoelastic behavior of sodium hyaluronate in phosphate buffered saline with rheo-mechanical and rheo-optical methods

Aqueous solutions of microbially produced sodium hyaluronate in phosphate buffered saline (pH=7.4, T=25 degrees C) were characterized with regard to their molecular parameters and viscoelastic behavior. The weight-average molar mass (M-W), z-average radius of gyration (R-G), and their distributions were determined using a hyphenated assembly of size exclusion chromatography, multi-angle light scattering, and a differential refractive index detector. Correlation of the obtained results with viscometric data enabled the establishment of [eta]-M and R-G-Mrelationships ([eta]=0.034M(W)(0.79); R-G=0.039M(W)(0.59)). Viscoelastic behavior was investigated by steady state shear experiments. The viscosity yield was determined for varying concentrations and molar masses using shear rates from 10(-3) to 10(3) s(-1). The elastic behavior in shear flow, represented by the first normal stress difference N-1, has been detected on one hand via rheo-mechanical experiments and on the other hand being correlated from the rheo-optical material functions flow birefringence Delta n(') and its orientation phi utilizing the stress-optical rule. This correlation enabled the extension of the measurement range toward lower absolute values of N-1 of more than two decades. The correlated values were in good agreement with the data obtained by rheo-mechanical measurements.