Yield Stress Fluids Solidifying in Capillary Imbibition

When subjected to an external stress that exceeds the yield stress ($\sigma_\mathrm{Y}$), yield stress fluids (YSFs) undergo a solid-to-liquid transition. Despite the extensive studies, there has been limited attention to the process of liquid-to-solid transition. This work examines the solidification of YSFs through capillary imbibition, easily observed in the processes of wetting, coating, spreading, and wicking. During gradual deceleration of the capillary rise, YSFs display an unexpected flowing behavior, even when subjected to stresses below the $\sigma_\mathrm{Y}$. We propose a model with numerical solutions based on rheological properties of YSFs and slip to capture this unusual, yet universal behavior.