pseudoplastiskt

Pseudoplastiskt, also known as pseudoplastic or shear-thinning, refers to a rheological behavior observed in certain fluids and semi-solids wherein viscosity decreases with increasing shear rate. This means that these materials become less viscous and more fluid-like when subjected to higher forces or movement, and revert to a more viscous state when the shear force is reduced.

This property contrasts with Newtonian fluids, which maintain a constant viscosity regardless of applied shear, and with dilatant or shear-thickening fluids, which exhibit increased viscosity under shear stress. Pseudoplastic behavior is common in various natural and synthetic substances, including blood, ketchup, paint, blood, and certain polymers.

The phenomenon arises primarily from the alignment and disentanglement of particles, polymers, or other internal structures within the fluid under shear. As shear rate increases, these structures tend to rotate or align in the direction of flow, resulting in decreased internal resistance and lower viscosity. When shear is reduced, the internal structures repolymerize or reorient randomly, restoring higher viscosity.

Understanding pseudoplastic behavior is important in industries such as pharmaceuticals, food processing, cosmetics, and materials engineering. It influences the formulation and application of products requiring ease of spreading or pumping while maintaining stability during storage.

To quantify pseudoplasticity, rheologists often use flow curves and models such as the Power Law model, which describes viscosity as a function of shear rate. This behavior facilitates the design of products and processes that leverage shear-thinning properties for improved performance and handling.