Shear thinning of non-Brownian suspensions and its variation at different ambient conditions

TL;DR

This study examines how ambient humidity and particle surface roughness influence the shear-thinning behavior of oil-based suspensions over two years, revealing seasonal and surface property effects on flow behavior.

Contribution

It provides new insights into how environmental conditions and particle surface roughness affect the rheological properties of non-Brownian suspensions.

Findings

Humidity variations alter water droplet exchange and shear-thinning behavior.

Low surface roughness leads to free droplets and increased particle repulsion.

High surface roughness traps droplets, promoting attractive interactions and shear thinning.

Abstract

Immiscible contaminants are commonly involved in naturally occurring suspensions. The resulting variations of their flow behavior has rarely been evaluated. Here, we investigate the variation of the viscosity of the oil-based two-phase suspension over a period of two years, which is exposed to the ambient air at the production stage. We find that the air's absolute humidity, which strongly varies with the seasons, causes exchanges of water droplets with the suspension, substantially altering its shear-thinning behavior. Only in winter, when the humidity is low, is the latter close to that of ideal two-phase suspensions. Our measurements suggest that, when the surface roughness of the suspended solid particles is sufficiently low, immersed droplets remain in a free state, effectively increasing repulsion between particles, weakening shear thinning. In contrast, when the roughness is sufficiently high, immersed droplets become trapped on the particle surfaces, inducing an attractive particle interaction via water bridging, enhancing shear thinning.