Mass transport characteristics of diffusioosmosis: Potential applications for liquid phase transportation and separation

Abstract

This study is to investigate the transport of neutral analytes being dispersed in a diffusioosmotic flow. Along this line, an accurate approximate formula is derived for the locally developed velocity distribution, considering a relatively thin electrical double layer (EDL) thickness and a small concentration gradient along the channel, based on which analytical solutions are presented for the Taylor dispersion of the analytes. To track the hydrodynamic dispersion of the analytes from the time of injection, a full numerical method is also developed that models the diffusioosmotic flow in its most general form and estimates the effective diffusivity from statistical computations. Despite the fact that the two approaches considered have basic differences, both in the assumptions and in measuring the dispersion coefficient, the analytical and numerical results agree well with a maximum error of about 10% which is much smaller for thin EDLs. We demonstrate that the hydrodynamic dispersion in the diffusioosmotic flow may get even smaller than that of electroosmosis under certain conditions; accordingly, diffusioosmosis is of potential applications in lab-on-a-chip devices where minimum solute dispersion is sought. Moreover, the results that are corresponding to the centroid and time-evolution of the injected analytes reveal that diffusioosmosis can be employed for the separation of uncharged samples.