Physicochemical processes under microfluidic conditions.

Abstract

Microfluidics is an interdisciplinary field of science and technology based on the manipulation of fluids in systems with channels generally less than 1 mm in thickness. Microfluidic devices allow the integration of complete analytical systems in reduced spaces and, in addition, new properties unique to small-scale flows are introduced. A fundamental characteristic of these systems is the predominance of viscous forces over inertial forces. Consequently, the typical chaotic and turbulent behavior of flows in the macroscopic world is replaced by an orderly fluid motion forming parallel layers - laminar flow - which hinders mixing processes. In these microsystems, diffusion becomes the main transport mechanism, whereas it is an inefficient phenomenon at larger scales. In this work, the predominant role of diffusion will be leveraged to develop an innovative methodology for determining diffusion coefficients using a microfluidic system, oriented to be implemented in teaching laboratories. This system will include an injection device recently acquired by the Universitat de Barcelona that is capable of propelling fluids through microchannels under pressure. In addition, it will be computer controlled and will be observed through a microscope equipped with an ultra high-speed camera. The diffusion coefficients of colored substances diffusing through two flows inside Y-shaped microchannels will be measured. To do so, concentration profiles along the channel will be extracted from the recorded images and diffusion times will be obtained from the flow velocity, which will be controlled by the aforementioned injection device. Additionally, by determining the diffusion coefficients, the Einstein-Stokes equation will be verified, studying the role of solute size and solvent viscosity.