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When the rotational viscometer measures the viscosity of the sample liquid, the difference between Newtonian fluid and non-Newtonian fluid:

1. Newtonian and non-Newtonian fluids:

Newtonian fluid is a low-viscosity fluid that is easily deformed after being subjected to force, and the shear stress is proportional to the deformation rate. According to Newton's theory, the viscosity of fluids is constant. Most pure liquids such as water and alcohol, light oils, low molecular compound solutions, and gases flowing at low speeds are Newtonian fluids; Newtonian fluid viscosity: shear Shear force/shear rate = constant value; the shear stress required for non-Newtonian fluid flow varies with the flow rate, and solutions of polymers, suspensions, emulsions and surfactants generally fall into this category.

Non-Newtonian fluid viscosity: shear force/shear rate ≠ constant value; that is, viscosity is a variable; common factors that cause its change are shear rate, time, etc.

2. Rheological curve:

In fact, most fluids are non-Newtonian and the material will change with shear rate or time. Therefore, the viscosity value measured under certain conditions is not the same, the measured viscosity value is a curve rather than a constant constant.

The curve of a Newtonian fluid: Shear force/shear rate = tanα is a constant; the viscosity curve of non-Newtonian fluids is roughly divided into two categories, one is shear thickening, the other is shear thinning; shear thinning refers to It is that the viscosity decreases with the increase of shear rate, the more sheared the material, the thinner it is, and the opposite of shear thickening.