Oscillatory Spreading and Surface Instability of a Non-Newtonian Fluid under Compression

TL;DR

This paper investigates the unique oscillatory spreading and surface instability of non-Newtonian starch solutions under compression, revealing behaviors distinct from Newtonian fluids and modeling them with a visco-elastic approach.

Contribution

It introduces a visco-elastic model using generalized calculus to explain the oscillatory surface behavior of non-Newtonian fluids under compression.

Findings

Surface contact area oscillates under load.

Viscous fingering instability develops at the periphery.

Model replicates qualitative oscillatory strain behavior.

Abstract

Starch solutions, which are strongly non-Newtonian, show a surface instability, when subjected to a load. A droplet of the fluid is sandwiched between two glass plates and a weight varying from 1 to 5 kgs. is placed on the top plate. The area of contact between the fluid and plate increases in an oscillatory manner, unlike Newtonian fluids in a similar situation. The periphery moreover, develops a viscous fingering like instability, which is not expected under compression. We attempt to model the non-Newtonian nature of the fluid through a visco-elastic model incorporating generalized calculus. This is shown to exhibit a qualitatively similar oscillatory variation in the surface strain.