Lubrication-Induced Newtonianization Enables Passive Transport of Non-Newtonian materials

TL;DR

This paper demonstrates that boundary lubrication can suppress the nonlinear rheology of non-Newtonian materials, enabling their transport as if they were Newtonian fluids, with significant practical implications.

Contribution

It introduces the concept of lubrication-induced Newtonianization, showing how shear localization in thin lubricating layers simplifies complex material flow behavior.

Findings

Lubrication localizes shear, suppressing nonlinear rheology.

Transport becomes primarily controlled by geometry and lubrication layer.

Passive gravity-driven flow is significantly enhanced under lubrication.

Abstract

Non Newtonian flows are typically governed by intrinsic bulk rheology, which imposes strong constraints on transport through confined geometries. Here, we show that stable boundary lubrication can fundamentally alter this behavior by localizing shear within a thin, low-viscosity interfacial layer. As a result, the nonlinear rheological response of a broad class of complex materials, including yield-stress, shear-dependent, and thixotropic materials, is strongly suppressed during flow. Using analytical solutions of Stokes flow and numerical simulations, we demonstrate that lubrication-induced shear localization leads to an apparent Newtonianization of transport, in which the macroscopic flow response becomes primarily controlled by the lubricating layer and geometric confinement rather than the intrinsic material properties. In this regime, materials that would otherwise require large pressure gradients can be transported at substantially lower driving forces. Notably, this boundary-dominated transport enables gravity-driven passive flow with orders-of-magnitude enhancement in throughput compared to rigid-wall conduits. These results establish lubrication as a powerful mechanism for tuning and simplifying complex fluid transport, with implications for biological systems, soft and jammed materials, and energy-efficient fluids.