Rheology of complex fluids by particle image velocimetry in microchannels
Résumé
The rheology of complex fluids has been the subject of attention for decades, partly in relation to its relevance for many processing or commercial applications.1 Recent studies have pointed out that many reported nonlinear behaviors may be related to the heterogeneous nature of the flow, which can adopt various forms, from simple steady “shear banding”2 to more complex spatiotemporal organizations.3 This has triggered the development of experimental methods to probe flow and structural heterogeneities (birefringence,4 NMR,5 neutrons,6 light scattering,7 and ultrasound8), as well as theoretical effort.
In this letter we propose a complementary experimental method to access directly relevant information in this context. We flow the fluid in transparent microchannels of controlled geometry and measure in a spatially resolved way the motion of tracers embedded in that fluid. The resulting velocity profiles allow us to measure directly the nonlinear rheology of such fluids, with simultaneous information as to the occurrence of heterogeneities or wall slip. After a presentation of our setup (Fig. 1) and experimental procedure, we demonstrate here the power of our method by quantifying the bulk nonlinear rheology of model shear-thinning polymer solutions. We then comment on the observation of wall slip and point out perspectives for studies of more complex fluids.