Spontaneous Imbibition in Paper-Based Microfluidic Devices: Experiments and Numerical Simulations

Abstract

Microfluidic paper-based analytical devices (μPADs) have quickly been an excellent choice for point-of-care diagnostic platforms ever since they appeared. Because capillary force is the main driving force for the transport of analytes in μPADs, low spontaneous imbibition rates may limit the detection sensitivity. Therefore, quantitative understanding of internal spontaneous capillary flow progress is requisite for designing sensitive and accurate μPADs. In this work, experimental and numerical studies have been performed to investigate the capillary flow in a typical filter paper. We use light-transmitting imaging technology to study wetting saturation changes in the paper. Our experimental results show an obvious transition of a saturated wetting front into an unsaturated wetting front as the imbibition proceeds. We find that the single-phase Darcy model considerably overestimates the temporal wetting penetration depths. Alternatively, we use the Richards equation together with the two-phase flow material properties that are obtained from the image-based pore-network modeling of the filter paper. Moreover, we have considered a dynamic term in the capillary pressure due to strong wetting dynamics in spontaneous imbibition. As a result, the numerical predictions of spontaneous imbibition in the paper are significantly improved. Our studies provide insights into the development of a quantitative spontaneous imbibition model for μPADs applications.

Spontaneous Imbibition in Nanomatrix–Fracture of Low Permeability Using Multiscale Nanofluidic Chips

“…The correlation coefficient values ( R 2 > 0.999) exhibit exceptional strength, indicating compliance with the power law described by the Lucas–Washburn equation. , Moreover, given the Bond number ( Bo ) in this study is considerably less than 1, we can justify the neglect of gravitational effects . Subsequently, based on the two-phase model derived from Darcy’s law, the observations made within the porous medium are expected to conform to the following formula. ,, Here, K represents the permeability, m 2 ; Φ denotes the porosity (see the Supporting Information for details); μ represents the viscosity of the wetting phase, mPa·s; and Δ P represents the capillary pressure. The calculation formula for the capillary pressure is given in Formula .…”

“…The capillary force exerts a dominant influence in the early stages. However, a balance is reached between the two forces at a later stage, causing the stabilization of the imbibition rate …”

“…19 Subsequently, based on the two-phase model derived from Darcy's law, the observations made within the porous medium are expected to conform to the following formula. 27,35,47 i k j j j j y…”

“…However, a balance is reached between the two forces at a later stage, causing the stabilization of the imbibition rate. 47 Effect of Heterogeneous Nanomatrix Structures (Geometry M 2 ). To deeply investigate the impact of the intricate nanomatrix structure on the imbibition behavior, we conducted experiments performing eight different oils (C8− C10, C12, C14−C16, and crude oil) within the heterogeneous nanomatrix (Geometry M 2 ) and compared the results with those in Geometry M 1 .…”

Paper based microfluidic devices: a review of fabrication techniques and applications

“…For building sensitive and precise PADs, a quantitative understanding of internal spontaneous capillary flow progression is necessary. Wang et al [ 126 ] examined the capillary flow in a porous substrate both experimentally and numerically. The authors computationally analyzed the experimental data in order to enhance the prediction of spontaneous imbibition.…”