Question

do you want paint is is a shear thinning or a shear thickening (dilatant) fluid?

Answer 1

Imagine a relatively dense suspension of microscopic particles, like paint or blood. The stronger the particles interact, the higher the viscosity of the fluid at the macro scale. Under high shear stress, the particles in the fluid will tend to organize in lubricated layers which will lower the overall viscosity. So for suspensions, shear thinning is a very common behavior.

Now imagine a polymer, with long, coiled chains. Under high shear stress, the chains will orient, again lowering the viscosity. This happens with most polymers. A shear thickening polymer would typically have very long, very entangled chains. Think about combing tangled hair slowly vs fast. Again, shear thinning seems to be the rule and thickening the exception.

When physicochemical interactions create bonds that are strong enough to resist breakage during shear, this mechanism would dominate and dilatant (shear-thickening) behavior is observed. In majority of the cases, the bonds thus formed are not strong enough and hence structural breakdown is what dominates, thereby depicting pseudoplastic (shear-thinning) behavior. This is the prime reason why dilatant (shear-thickening) fluids are so uncommon as compared to pseudoplastic (shear-thinning) fluids.

Hence paint is shear-thinning fluid .

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