Wicking dynamics of two-ply channels in porous medium-based microfluidic devices

Abstract

In the advancement of paper-based microfluidic devices, it is reported that the two-ply channel transports fluid noticeably faster than traditional single-ply channels. In this work, the capillary flows in two-ply channels, consisting of a gap of width w between two porous sheets with porosity ε and thickness d, are investigated through many-body dissipative particle dynamics simulations. The advancing meniscus varies with position, characterized by the penetration lengths in the gap (Lg), the porous sheet (Lp), and the maximum value (Lmax). Lmax is always located within the porous sheet but near the gap. The time evolution of the penetration lengths can be described by Washburn's expression, L2 = (S)t, and the imbibition rates Sp, Sg, and Smax depend on ε, d, and w, differing from each other. Two distinct imbibition characteristics are identified: Sg > Sp for low porosities and Sg < Sp for high porosities. Both Sg and Sp decrease with d but increase with w. As ε increases, a minimum of Smax occurs due to the synergistic competition between Sp and Sg. Compared to the single-ply channel, which consists of a single porous sheet, the imbibition rate of the two-ply channel is significantly enhanced by at least four times due to side-imbibition from the gap (acting as a reservoir) toward the porous sheet.