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Comparatively Speaking: Types of Flow Behavior
By: Anthony J. O'Lenick Jr., Siltech LLC, and Kelly Dobos, Kao Corp.
Posted: June 8, 2010
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Viscosity can also increase with shear forces like shaking or mixing and then lower to the original value in what is described as rheopectic behavior, but this type of behavior also is rare. Both thixoptrophy and rheopexy can occur with other types of flow behavior and the initial viscosity may not be fully recovered.
Another important rheological value is the yield point. Some fluids behave like solids at rest but flow like liquids and decrease in viscosity once the yield value or yield point is exceeded. Fluids with high yield points can easily suspend particles like mica or pigments in cosmetic preparations.
By considering these types of fluid behavior, the cosmetic formulator can design the desired rheological properties of cosmetic formulations through choice of ingredients and processing conditions, as well as learning to troubleshoot product failures.