Dynamic shear rheometer and method

An improvement in the method 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 is coupled with opposed plates, one of the opposed plates is oscillated angularly relative to the other of the opposed plates, 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 within a predetermined range of torque and angular displacement for determining the rheological properties, the improvement comprising:

• selectively coupling a first contact surface on one of the opposed plates 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 one of the different temperatures;
• and
• selectively coupling a second contact surface on said one of the opposed plates with the test specimen by effecting relative movement between the second contact surface and the test specimen in a direction essentially normal to said angular displacement to establish a second contact area between said one of the opposed plates and the test specimen when the test specimen is at another of the different temperatures;
• 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 at each of said one and said another of the different temperatures fall within the predetermined range.

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, the apparatus comprising:

• a cup having a reservoir for receiving the test specimen;
• a disk opposed to the cup and having a first contact surface for being coupled with the test specimen in the reservoir of the cup to couple the disk with the cup when the test specimen is at one of the different temperatures, and a second contact surface confronting the reservoir in the cup for being coupled with the test specimen in the reservoir of the cup to couple the disk with the cup when the test specimen is at another of the different temperatures;
• moving means for causing relative angular oscillation between the disk and the cup about an axis when the disk is coupled with the cup through the test specimen so as to induce relative angular displacement between the disk and the cup about the axis, and a torque associated with the relative angular displacement;
• measuring means for measuring the relative angular displacement between the disk and the cup and for measuring the torque associated with the relative angular displacement within a predetermined range for determining the rheological properties of the test specimen;
• and
• selective coupling means for selectively coupling the first contact surface with the test specimen to establish a first contact area between the disk and the test specimen when the test specimen is at said one of the different temperatures and is coupled with the cup, said selective coupling means including further means for effecting relative movement between the second contact surface and the test specimen in a direction essentially normal to said angular displacement to selectively couple the second contact surface with the test specimen to establish a second contact area between the disk and the test specimen when the test specimen is at said another of the different temperatures and is coupled with the cup;
• 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.