Dynamic shear rheometer and method

An improvement in an apparatus for measuring rheological properties of a viscoelastic test specimen at different temperatures, at which different temperatures the viscoelastic properties exhibit a relatively wide difference, wherein the test specimen is placed between and coupled with opposed plates, one of the opposed plates is oscillated angularly relative to the other of the opposed plates, about an axis, and the angular displacement of one of the plates relative to the other of the plates and the torque associated with the relative angular displacement are measured by measuring means within a predetermined range of measurement of torque and angular displacement for determining the rheological properties, the improvement comprising:

• a first contact surface on one of the opposed plates for being coupled with the test specimen when the test specimen is at one of the different temperatures;
• a second contact surface on said one of the opposed plates for being coupled with the test specimen when the test specimen is at another of the different temperatures;
• the first and second contact surfaces extending radially along the said one of the opposed plates, the first contact surface being spaced axially from the second contact surface;
• and
• selective coupling means for selectively coupling the first contact surface with the test specimen to establish a first contact area between said one of the opposed plates and the test specimen when the test specimen is at said one of the different temperatures and is coupled with the other of the opposed plates, and for selectively coupling the second contact surface with the test specimen to establish a second contact area between said one of the opposed plates and the test specimen when the test specimen is at said another of the different temperatures and is coupled with the other of the opposed plates, the selective coupling means including means for effecting selective relative axial movement between said one of the opposed plates and the test specimen to establish said first and second contact areas;
• the first contact surface lying in a first plane and the second contact surface lying in a second plane spaced from the first plane;
• and
• the first contact area being different in area from the second contact area such that, by virtue of the difference in area between the first and second contact areas, the torque and the relative angular displacement measured by the measuring means at each of said one and said another of the different temperatures fall within the predetermined range.