An instrument for precise measurement of viscoelastic properties of low viscosity dilute macromolecular solutions at frequencies from 20 to 500 kHz

A high‐frequency torsional rod apparatus (HFTRA) has been developed for measurements of moderately high‐frequency viscoelastic properties of dilute, low viscosity polymer solutions. It employs a long cylindrically shaped resonating element driven by an X‐cut (torsional mode) quartz piezoelectric crystal. Up to 11 different normal modes are employed, resulting in 11 discrete frequencies, ranging from approximately 20 to 500 kHz. Measurements are made in free decay; a key feature of the apparatus is the method for high precision measurements of damping coefficients and eigenfrequencies. The instrument is suitable for liquids with 0.003P<‖η*‖<5P and η’≥1.33η‘. Typically, η’ has a relative uncertainty of ±2% or less, with the relative uncertainty for η‘ being about 4% for liquids with η‘ greater than 0.01P. Values of η’ obtained in the HFTRA for low viscosity liquids with small η‘ show excellent agreement with the known steady flow viscosities. Measurements of the viscoelastic properties of polymer solutions ...