Biology subjects

Tokihiro, J. C.

Publications and source records attributed to Tokihiro, J. C..

2 recordsLinked to original sources

bioRxiv2023

On the dynamic contact angle of capillary-driven microflows in open channels

The true value of the contact angle between a liquid and a solid is a thorny problem in capillary microfluidics. The Lucas-Washburn-Rideal (LWR) law assumes a constant contact angle during fluid penetration. However, recent experimental studies have shown lower liquid velocities than predicted by the LWR equation, which are attributed to a velocity-dependent dynamic contact angle that is larger than its static value. Inspection of fluid penetration in closed channels has confirmed that a dynamic angle is needed in the LWR equation. In this work, the dynamic contact angle in an open channel configuration is investigated using experimental data obtained with a range of liquids, aqueous and organic, and a PMMA substrate. We demonstrate that a dynamic contact angle must be used to explain the early stages of fluid penetration, i.e., at the start of the viscous regime, when flow velocities are sufficiently high. Moreover, the open channel configuration, with its free surface, enhances the effect of the dynamic contact angle, making its inclusion even more important. We found that for the liquids in our study, the molecular-kinetic theory (MKT) is the most accurate in predicting the effect of the dynamic contact angle on liquid penetration in open channels.

bioengineering↗

bioRxiv2022

Enhanced capillary pumping using open-channel capillary trees with integrated paper pads

The search for efficient capillary pumping has led to two main directions for investigation: first, assembly of capillary channels to provide high capillary pressures, and second, imbibition in absorbing fibers or paper pads. In the case of open microfluidics (i.e., channels where the top boundary of the fluid is in contact with air instead of a solid wall), the coupling between capillary channels and paper pads unites the two approaches and provides enhanced capillary pumping. In this work, we investigate the coupling of capillary trees-- networks of channels mimicking the branches of a tree--with paper pads placed at the extremities of the channels, mimicking the small capillary networks of leaves. It is shown that high velocities and flow rates (7 mm/s or 13.1 {micro}L/s) for more than 30 seconds using 50% (v/v) isopropyl alcohol, which has a 3-fold increase in viscosity in comparison to water; 6.5 mm/s or 12.1 {micro}L/s for more than 55 seconds with pentanol, which has an 3.75-fold increase in viscosity in comparison to water; >3.5 mm/s or 6.5 {micro}L/s for more than 150 seconds with nonanol, which has an 11-fold increase in viscosity in comparison to water) can be reached in the root channel, enabling higher sustained flow rates than that of capillary trees alone.

bioengineering↗