Measurement of Translational Diffusivity by Microchannel Multiphase Flow

Abstract

A method is proposed for the rapid measurement of translational diffusion coefficient by employing the unique multiphase flow of perfectly miscible incompressible fluids in microchannels. The molecule of interest is injected, as a bolus or continuously, into the middle phase of a three phase flow system. Subsequently, the phase or stream is depleted of molecule by diffusion into the adjacent streams through the common interface. By monitoring the elution profile of the molecule, one may obtain estimates of the diffusion coefficient under fixed experimental conditions. Transport of molecule in the microchannel is described by a transient convection-diffusion-dispersion model. Analytical and numerical solutions are provided to illustrate the change of elution profile with stream velocity and other design parameters. The diffusion coefficient is estimated from a graphical plot. It is shown that diffusion coefficient may be measured without prior knowledge of dispersion. Experimental data is presented for the proteins, fibrinogen and insulin. A number of advantages over the T-sensor and Taylor-Aris methods are highlighted.