Thread Content
Science popularization: The difference between viscosity units “centiStokes” and “centipoise”. People often ask about centiStokes (centi- means one percent). St: Stoles, which is the unit used for indicating bubble viscosity tubes and flow cups from the BYK company that we represent; and Poise, which is the unit used for rotary viscometers from the BROOKFIELD company that we represent. These are units of viscosity measured under two different conditions. CST is the smallest unit for dynamic viscosity, while cP is the smallest unit for static viscosity. Dynamic viscosity is a measure of the internal friction force that arises when a liquid flows under the effect of gravity; it is expressed as the ratio of a liquid’s static viscosity to its density at the same temperature, and in the International System of Units it is denoted in mm2/s. Dynamic viscosity represents a measure of the internal friction force when a liquid flows under certain shear stress; it is equal to the ratio of the shear stress applied to the flowing liquid to its shear rate. In the International System of Units, it is expressed in Pa•s, while in common usage it is denoted by cP. 1cP = 10-3Pa•s. Absolute viscosity = dynamic viscosity × density. Density = mass per unit volume. 1 Poise = 1 Stole × g/ml. CPS represents melt viscosity; the unit for dynamic viscosity is st, while the unit for absolute viscosity is centipoise (cp) or millipascal-second. Both CPS and cp are units of centipoise. Unit conversion table for dynamic viscosity (source: Global Polyurethane Network)