Internal relaxation time in immersed particulate materials

TL;DR

This paper investigates the internal relaxation dynamics of immersed particulate materials during solid-liquid transition, highlighting a creep process driven by particle separation resisted by viscous forces, relevant to various soft matter systems.

Contribution

It introduces a model combining elastic, viscous, and steric interactions and demonstrates how internal relaxation governs creep time in immersed particulate materials.

Findings

Creep time depends on particle separation driven by stress and viscous friction.

Long creep phase precedes steady flow in the material.

Internal relaxation mechanism is key to understanding dynamics in soft matter systems.

Abstract

We study the dynamics of the solid to liquid transition for a model material made of elastic particles immersed in a viscous fluid. The interaction between particle surfaces includes their viscous lubrication, a sharp repulsion when they get closer than a tuned steric length and their elastic deflection induced by those two forces. We use Soft Dynamics to simulate the dynamics of this material when it experiences a step increase in the shear stress and a constant normal stress. We observe a long creep phase before a substantial flow eventually establishes. We find that the typical creep time relies on an internal relaxation process, namely the separation of two particles driven by the applied stress and resisted by the viscous friction. This mechanism should be relevant for granular pastes, living cells, emulsions and wet foams.