RESUMEN
When capillary flow occurs in a uniform porous medium, the depth of penetration is known to increase as the square root of time. However, we demonstrate in this study that the depth of penetration in multi-section porous layers with variation in width and height against the flow time is modified from this diffusive-like response, and liquids can pass through porous systems more readily in one direction than the other. We show here in a model and an experiment that the flow time for a negative gradient of cross-sectional widths is smaller than that for a positive gradient at the given total height of porous layers. The effect of width and height of local layers on capillary flow is quantitatively analyzed, and optimal parameters are obtained to facilitate the fastest flow.
Asunto(s)
Modelos Teóricos , PorosidadRESUMEN
We perform molecular dynamics simulations to demonstrate that when a nanodroplet is confined inside a carbon nanotube (CNT), unidirectional motion can be created by a nonzero surface energy gradient. It is found that the water nanodroplet moves along the direction of increasing surface energy. The transportation efficiency of the water nanodroplet is found to be dependent on the surface energy gradient; environmental temperature; and the flexibility, diameter, and defectiveness of the CNT. It is shown that higher surface energy gradient, the smaller diameter of the CNT, and fewer defects promote higher transportation efficiency. However, when the temperature is too high or too low, the water transport across the CNT is impeded. Except for the initial stage at the relatively low environmental temperature, higher flexibility of the CNT wall reduces the transportation efficiency. It is also found that the hydrogen bonds of water molecules play a role in the dynamic acceleration process with a wavelike feature. The present work provides insight for the development of CNT devices for applications such as drug delivery, nanopumps, chemical process control, and molecular medicine.
