Development of a Combinatorial Rheometer for Polymer Formulations
H J. Walls, Robert F. Berg, Kathryn L. Beers, Eric J. Amis
Finding the best formulation for a new application, or fine-tuning an existing formulation to meet various customer needs, requires extensive sample preparation and testing. Our goal is to make this exploration more efficient for the property of viscosity, or more generally, viscoelasticity (complex viscosity). We have developed a device that simultaneously measures the mechanical response of four small fluid samples. Each sample cell contains an oscillating rotor. An oscillating magnetic field drives the rotors by coupling to a permanent magnet imbedded in each rotor. A CCD (charge-coupled device) camera records the oscillations. Image analysis yields the amplitude and phase of each rotor s angular displacement relative to the amplitude and phase of the applied magnetic field. We present measurements of three fluids of known viscosity and compare them to the model of the viscometer. Preliminary results with a fourth, viscoelastic fluid demonstrate qualitatively different behavior.