British Society meeting focuses on rheology.

The principles and applications of rheology were the focus of the November meeting of the British Society. Andrew Walton, of Malvern Instruments, discussed the product range of his company. He noted that rheology instruments were added when Malvern Instruments acquired Bohlin in 2003.

Mr. Walton defined basic rheology terms, including shear stress deformation, shear rate, viscous flow, and shear viscosity. Using graphs and rheograms, he described flow behaviors such as Newtonian, pseudoplastic, dilatant, shear thinning, and shear thickening. These mathematical models were then related to specific coatings-related examples using silicone oil, paint, and plastisols. It was noted that the shear rates for different coatings applications can give an indication of how a coating will behave. However, a rheometer provides a more accurate picture since some viscometers may measure in too narrow a range, he said. For example, a brushing paint was measured by a viscometer which covered the mid-range, but this did not highlight the area in which the brush marks would appear. A rheometer gave a more complete picture.

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Mr. Walton then discussed thixotropy. He detailed the variations that occur when using a rheometer hysteresis loop to indicate thixotropic behavior, compared with a rheometer using a three-speed step technique.

He concluded his presentation with a discussion on viscoelasticity, frequency sweep, creep and recovery tests.