Method for Determining the Viscoelastic Properties of Dilute Polymer Solutions at Audio-Frequencies

A sensitive instrument for the measurement of the viscoelastic properties of dilute polymer solutions is described. It makes use of torsion pendulums with resonant frequencies in the range between 200 cps and 2300 cps. The test liquid is contained in a hollow oscillating disk. The shearing stress which is exerted at the liquid-metal interface alters the frequency and rate of decay of the free oscillations of the pendulum. By means of an optical system, the oscillations of the pendulum are caused to modulate the light striking the cathode of a phototube. The frequency and the rate of decay of the resulting alternating voltage are measured electronically. The operation of the instrument and the factors affecting the precision of measurement are analyzed.