Meniscus formation in a capillary and the role of contact line friction

Abstract

We studied spontaneous formation of an internal meniscus by dipping glass capillaries of 25 μm to 350 μm radii into low volatile hexadecane and tributyl phosphate. X-ray phase contrast and high speed optical microscopy imaging were employed. We showed that the meniscus completes its formation when the liquid column is still shorter than the capillary radius. After that, the meniscus travels about ten capillary radii at a constant velocity. We demonstrated that the experimental observations can be explained by introducing a friction force linearly proportional to the meniscus velocity with a friction coefficient depending on the air/liquid/solid triplet. It was demonstrated that the friction coefficient does not depend on the capillary radius. Numerical solution of the force balance equation revealed four different uptake regimes that can be specified in a phase portrait. This phase portrait was found to be in good agreement with the experimental results and can be used as a guide for the design of thin porous absorbers.

Early regimes of water capillary flow in slit silica nanochannels

“…The axial velocity profiles are computed by implementing a static binning procedure using a bin size of 0.2 nm along the z-axis. 15,55,56,58 Moreover, the results indicate that the duration of the inviscid regime is height dependent. An example of the meniscus is shown in Fig.…”

“…Mathematically, the velocity A I is a singular point of the Bosanquet equation, obtained by applying boundary conditions as limits on the imbibition velocity and the position of the capillary front. [56][57][58] Moreover, in nano-confinement, the capillary filling speeds are typically high, 54,55,59 therefore incorrect values of the velocity in the initial inviscid regime may result in significant deviations for predicting flow rates in short nano-slits. Nevertheless, it leaves open questions about the physical sense of the initial conditions at the beginning of the liquid uptake.…”

Structural and physical determinants of the proboscis–sucking pump complex in the evolution of fluid-feeding insects

“…For example, if the galeae are linked together forming a food canal of diameter 17.3 μm, the moth will have to spend most of its energy moving fluid through the proboscis; the f -factor is f  = 2891. However, if the galeae are separated, the moth will not need to spend much energy on transporting fluid through the food canal; owing to capillarity, in a few milliseconds liquid will spontaneously fill the intergaleal gap up to the entrance of the cibarium 67 . High-speed X-ray imaging shows that a liquid meniscus, just after its formation at the edge of a capillary of 50 μm diameter, travels a distance of 250 μm in about 10 milliseconds 67 .…”

“…However, if the galeae are separated, the moth will not need to spend much energy on transporting fluid through the food canal; owing to capillarity, in a few milliseconds liquid will spontaneously fill the intergaleal gap up to the entrance of the cibarium 67 . High-speed X-ray imaging shows that a liquid meniscus, just after its formation at the edge of a capillary of 50 μm diameter, travels a distance of 250 μm in about 10 milliseconds 67 . Thus, capillary forces alone will ensure liquid delivery to the cibarial entrance, without involvement of the pump.…”

The dynamics of capillary-driven two-phase flow: The role of nanofluid structural forces

“…The optical technique [28,[51][52][53][54][55][56][57] is the most frequently used when monitoring the meniscus dynamics. A dye and tracer are used to increase the contrast and better visualize the meniscus movement.…”