A Brief Description of Pseudoplastic Fluids and Expansive Fluids

Pseudoplastic fluid

If a fluid can flow after a force is applied, but the shear stress is not proportional to the shear rate, generally the shear rate increases more than the shear stress, and the line segment is a smooth curve convex to the shear stress axis. Fluids are called pseudoplastic fluids—or shear-thinning fluids.

Pseudoplastic flow is a classification of heterogeneous flows that are similar to the case of plastic fluids at moderate to higher shear rates and to Newtonian fluids at low shear rates.

Generally speaking, this kind of fluid can flow well when it is stirred or sheared, but once the fluid structure is damaged, it will not recover, that is to say, this phenomenon is irreversible.

Cooked starch paste, fiber solutions, emulsions and many other polymer solutions belong to this category of fluids.

There are quite a few inks that also have the properties of a pseudoplastic fluid.

dilatant fluid

If a fluid increases its flow resistance when it is sheared, that is, the apparent viscosity increases when the shear stress increases, generally the shear rate increases less than the shear injection force, and the line segment is concave to the shear stress axis. Smooth curves, such fluids are called dilatant fluids—or shear-thickening fluids.

Dilatant fluids can be viewed as the opposite of pseudoplastic fluids.

The dilatant fluid needs to meet two conditions: (1) the concentration of the dispersed phase needs to be large, and (2) the particles in the dispersed phase need to be dispersed, not flocculated.

Dilatation occurs when particles in a fluid cannot move quickly enough and tend to "cluster" together, forming a rigid structure from the outside.

This dilatation phenomenon can often be observed when kneading dough at home, that is, it becomes harder when kneaded Dispersions of deflocculated particles with a high content of suspended solids, such as 45-50% uncooked starch slurry, fall into this category.

It can be imagined that when the content of solid components (pigments, fillers, etc.) in the ink is very high.