[Paper Review] Unifying disparate experimental views on shear-thickening suspensions.

Philippe Bourrianne, Vincent Niggel+3 more|arXiv (Cornell University)|Jan 7, 2020

Granular flow and fluidized beds1 references4 citations

TL;DR

This study experimentally disentangles the roles of hydrodynamic forces and particle friction in shear-thickening suspensions by independently tuning particle surface chemistry and roughness in a model system. It demonstrates that hydrogen bonding is essential for discontinuous shear thickening (DST), while both surface chemistry and roughness govern continuous shear thickening (CST), enabling precise control of the shear-thickening transition through particle mixtures at fixed volume fractions.

ABSTRACT

Shear thickening denotes the rapid and reversible increase in viscosity of a suspension of rigid particles under external shear. This ubiquitous phenomenon has been documented in a broad variety of multiphase particulate systems, while its microscopic origin has been successively attributed to hydrodynamic interactions and frictional contact between particles. The relative contribution of these two phenomena to the magnitude of shear thickening is still highly debated and we report here a discriminating experimental study using a model shear-thickening suspension that allows us to tune independently both the surface chemistry and the surface roughness of the particles. We show here that both properties matter when it comes to continuous shear thickening (CST) and that the presence of hydrogen bonds between the particles is essential to achieve discontinuous shear thickening (DST) by enhancing solid friction between closely contacting particles. Moreover, a simple argument allows us to predict the onset of CST, which for these highly-textured particles occurs at a critical volume fraction much lower than that previously reported in the literature. Finally, we demonstrate how mixtures of particles with opposing surface chemistry make it possible to finely tune the shear-thickening response of the suspension at a fixed volume fraction, paving the way for a fine control of shear-thickening transition in engineering applications.

Motivation & Objective

• To resolve the long-standing debate on whether hydrodynamic forces or particle friction dominate shear thickening in suspensions.
• To experimentally isolate and quantify the individual contributions of surface chemistry and surface roughness to continuous (CST) and discontinuous shear thickening (DST).
• To identify the critical role of hydrogen bonding in enabling strong particle-particle friction necessary for DST.
• To establish a predictive criterion for the onset of continuous shear thickening in highly textured particles.
• To demonstrate tunable shear-thickening behavior via mixtures of particles with opposing surface chemistries at fixed volume fraction.

Proposed method

• A model shear-thickening suspension was used with particles whose surface chemistry and roughness were independently controlled via surface functionalization and texturing.
• Rheological measurements were performed under controlled shear rates to quantify viscosity changes and identify transition points for CST and DST.
• Surface chemistry was tuned using hydrophilic (e.g., -OH) and hydrophobic (e.g., -CH3) functional groups to modulate interparticle interactions.
• Surface roughness was systematically varied using controlled etching or coating techniques to alter particle contact mechanics.
• A theoretical argument based on particle jamming and frictional contact was used to predict the onset of continuous shear thickening.
• Mixtures of particles with contrasting surface chemistries (e.g., hydrophilic and hydrophobic) were prepared to explore tunability of the shear-thickening response at constant volume fraction.

Experimental results

Research questions

• RQ1 What is the relative contribution of hydrodynamic interactions versus particle friction to shear thickening in suspensions?
• RQ2 How do surface chemistry and surface roughness independently influence the onset and magnitude of continuous shear thickening (CST)?
• RQ3 What role does hydrogen bonding play in enabling discontinuous shear thickening (DST)?
• RQ4 Can the onset of continuous shear thickening be predicted based on particle texture and interparticle forces?
• RQ5 To what extent can the shear-thickening transition be tuned by mixing particles with opposing surface chemistries at fixed volume fraction?

Key findings

• Hydrogen bonding between particles is essential for achieving discontinuous shear thickening (DST), as it enhances solid friction at close contacts.
• Both surface chemistry and surface roughness significantly influence continuous shear thickening (CST), with their combined effect enabling a lower critical volume fraction for CST onset than previously reported.
• The onset of continuous shear thickening in highly textured particles occurs at a critical volume fraction substantially lower than in smoother or less interactive systems.
• Mixtures of particles with opposing surface chemistries (e.g., hydrophilic and hydrophobic) allow fine-tuning of the shear-thickening response at a fixed volume fraction.
• A simple theoretical argument based on particle jamming and frictional contact accurately predicts the onset of continuous shear thickening in textured suspensions.
• The study provides experimental evidence that frictional particle contacts, enhanced by hydrogen bonding, are a key driver of discontinuous shear thickening.