Adapting Taylor Dispersion to Measure the Enhanced Diffusion Coefficient of Multispecies Electrolyte Solutions at the Microfluidic Scale*

Microfluidics applications in fields like biomedical engineering and chemistry have become increasingly prominent as they allow for rapid and precise studies, such as synthesizing compounds and separating mixtures. We developed an accessible and repeatable experimental method that adapts the Taylor Dispersion experiment to the microscale and used it to quantify the enhanced diffusivity of a passive single-species solute undergoing shear flow. Our protocol accurately measures the enhanced diffusivity and leverages it to compute the diffusion coefficient of single-species passive tracers while changing experimental parameters. We have since extended our experimental procedure to characterize the influence of multispecies electrolyte solutions on the enhanced diffusivity of the system. In these solutions, the electric current is carried by the dissolved ions. The electric field exerts significant body forces on the ions, affecting their fluxes and enhancing the diffusion coefficient. These interactions and consequent separation of ion species and their effects on each ion's enhanced diffusivity are observed and compared to theoretical predictions. Current challenges and potential future directions will be discussed.