Influences of viscoelasticity and streaming potential on surface reaction kinetics in microreactors

Most biofluids examined in Lab-on-a-Chip (LOC) devices show a non-linear rheological behavior. Moreover, due to the very small sizes of the ducts encountered in different components of LOCs, like microreactors and micromixers, the pressure-driven liquid flow in these devices is prone to the streaming potential effects that tend to retard the fluid flow. The present study deals with investigating the influences of the streaming potential and a non-linear rheology of the carrier fluid on mass transport and surface reactions in heterogeneous microreactors. To this end, the PTT viscoelastic model is used to predict the non-linear behavior of the fluid. The governing equations are solved in a dimensionless form utilizing the finite-difference method for a non-uniform grid. The results show that the streaming potential effects are pronounced by increasing the ionic strength of the electrolyte and thickening the electric double layer. Upon magnifying these effects, the fluid velocity and, accordingly, the speed of analyte transfer to the downstream are lowered, thereby reducing the surface reaction rates. The streaming potential effects are so severe that may lead to 100% increase in the saturation time at limiting conditions. Although the elasticity effects decrease the saturation time by increasing the fluid velocity near the wall, they are less important as compared to the streaming potential effects.