Predicting the onset of discontinuous shear thickening in dense suspensions
In plain words
Some dense suspensions, such as cornstarch in water, become almost solid when stirred hard. The accepted explanation is that particles switch from slipping past each other to touching with friction, but the stress at which this happens cannot yet be predicted from particle properties.
Precise statement
In the frictional-contact picture of dense non-Brownian suspensions, stress converts lubricated contacts to frictional ones, lowering the jamming volume fraction from $\phi_J^0$ to $\phi_J^{\mu}$ and producing discontinuous shear thickening (DST) for $\phi$ between them. Predict the onset stress $\sigma*$ and the minimal DST volume fraction $\phi_{\mathrm{DST}}$ from particle surface chemistry, roughness, repulsive forces and rolling or sliding constraints, and test the predictions on real suspensions such as cornstarch and silica.
What would settle it
A model with independently measured interparticle force laws that predicts $\sigma*$ and $\phi_{\mathrm{DST}}$ for several suspensions within experimental error.
Status in the literature
Unverified note
The frictional-contact mechanism is widely accepted since the mid-2010s; quantitative prediction of $\sigma*$ and $\phi_{\mathrm{DST}}$ from particle-level properties is not available (2026).