Suspensions of small ultra-soft colloids remain liquids in overcrowded conditions

TL;DR

This study shows that small ultra-soft colloids remain liquid-like even at high concentrations due to their high compressibility, unlike other soft glass-formers which tend to arrest.

Contribution

It provides experimental evidence that ultra-soft colloids do not undergo dynamic arrest in crowded conditions, highlighting their unique relaxation and flow properties.

Findings

No dynamic arrest observed in concentrated suspensions

Zero-shear viscosity grows weakly with packing fraction

Ultra-soft colloids remain diffusive even in overcrowded states

Abstract

Concentrated suspensions of small ultra-soft colloids (ultra-low crosslinked microgels) are investigated with scattering and steady shear rheology to capture their equilibrium dynamics. The suspensions lack dynamic arrest, although the slow relaxation time $\tau_2$ follows exponential growth with increasing generalized packing fraction, $\zeta$. The zero-shear viscosity grows weakly with $\zeta$, and never diverges in contrast to other soft glass formers, e.g.~star-polymers, microgels, green particles. Their high compressibility allows these ultra-soft spheres to diffuse even in overcrowded environments.