Viscous fingering to fracturing transition in shear thickening fluid

We experimentally investigate the interplay of viscous fingering and fracturing in a radial Hele-Shaw cell displacing a non-Newtonian (shear-thickening) fluid. We have used cornstarch suspension of different weight fractions (39-48% w/w dispersed in water-CsCl solution) and the rheology of the suspension exhibit shear thickening behavior beyond a shear rate of 1s^-1. We observe the transition from viscous fingering to dendritic fracturing morphology, beyond a critical weight fraction of cornstarch suspension. We analyze the plot of the fraction of injected phase to displaced phase as a function of injected volume for different weight fractions of cornstarch suspension. Moreover, the flow rate of the invading fluid (air or turpentine oil) also affects the viscous fingering and fracturing patterns. The width of the finger decreases with the flow rate of invading fluid and widens with injected volume due to the reduced local shear rate beyond a critical size. The width of the dendritic fracturing decreases with the flow rate of invading fluid, but increases with the injected volume.