Viscoelastic Measurement in High Frequency Range with New Rheometer Based on Mechanical Impedance Analysis.

A new rheometer measuring viscoelasticity of liquids at high frequencies with a surface loading method was constructed and applied to a waterborne polymer. An impedance head that could simultaneously detect force and acceleration was employed in this rheometer. A small glass plate was attached to a vibrator through the impedance head. The mechanical impedance of liquids was evaluated from difference between the transfer functions for the two cases, one with the plate being immersed in the sample and the other with the plate in the air. Then, the storage and loss moduli were calculated from the mechanical impedance as functions of frequency in the range of 102 to 104 rad s-1. As a calibration, the moduli data for a solution of polystyrene in diethylphthalate obtained with this rheometer were compared with those with a conventional rheometer. Agreement of the two sets of data indicated a good performance of the new rheometer. Viscoelasticity of aqueous solution of associating polymer was determined at frequencies 103-104 rad s-1 with this rheometer and at 10-1-103 rad s-1 with a conventional rheometer. This associating polymer solution was found to possess single relaxation viscoelasticity.