Superfast water transport discovered in graphitic nanoconduits, including carbon nanotubes and graphene nanochannels, implicates crucial applications in separation processes and energy conversion. Yet lack of complete understanding at the single-conduit level limits development of new carbon nanofluidic structures and devices with desired transport properties for practical applications. Here, we show that the hydraulic resistance and slippage of single graphene nanochannels can be accurately determined using capillary flow and a novel hybrid nanochannel design without estimating the capillary pressure. Our results reveal that the slip length of graphene in the graphene nanochannels is around 16 nm, albeit with a large variation from 0 to 200 nm regardless of the channel height. We corroborate this finding with molecular dynamics simulation results, which indicate that this wide distribution of the slip length is due to the surface charge of graphene as well as the interaction between graphene and its silica substrate.

Fast water transport in graphene nanofluidic channels

Capillary evaporation in nanoscale conduits is an efficient heat/mass transfer strategy that has been widely utilized by both nature and mankind. Despite its broad impact, the ultimate transport limits of capillary evaporation in nanoscale conduits, governed by the evaporation/condensation kinetics at the liquid–vapor interface, have remained poorly understood. Here we report experimental study of the kinetic limits of water capillary evaporation in two dimensional nanochannels using a novel hybrid channel design. Our results show that the kinetic-limited evaporation fluxes break down the limits predicated by the classical Hertz–Knudsen equation by an order of magnitude, reaching values up to 37.5 mm/s with corresponding heat fluxes up to 8500 W/cm2. The measured evaporation flux increases with decreasing channel height and relative humidity but decreases as the channel temperature decreases. Our findings have implications for further understanding evaporation at the nanoscale and developing capillary eva...

Exploring Ultimate Water Capillary Evaporation in Nanoscale Conduits.

A novel method to calculate the solid-liquid contact angle is introduced in this study. Using the 3D configuration of a liquid droplet on a solid surface, this method calculates the contact angle along the contact line and provides an angular distribution. Although this method uses the 3D configuration of liquid droplets, it does not require the calculation of the 3D density profile to identify the boundaries of the droplet. This decreases the computational cost of the contact angle calculation greatly. Moreover, no presumption about the shape of the liquid droplet is needed when using the method introduced in this study. Using this method, the relationship between the size and the contact angle of water nano-droplets on a graphite substrate was studied. It is shown that the contact angle generally decreases by increasing the size of the nano-droplet. The microscopic contact angle of 83.0° was obtained for water on graphite which is in a good agreement with previous experimental and numerical studies. Neg...

Wetting at the nanoscale: A molecular dynamics study.

Hypothesis The wetting behaviour is a key property of a porous medium that controls hydraulic conductivity in multiphase flow. While many porous materials, such as hydrocarbon reservoir rocks, are initially wetted by the aqueous phase, surface active components within the non-wetting phase can alter the wetting state of the solid. Close to the saturation endpoints wetting phase fluid films of nanometre thickness impact the wetting alteration process. The properties of these films depend on the chemical characteristics of the system. Here we demonstrate that surface texture can be equally important and introduce a novel workflow to characterize the wetting state of a porous medium. Experiments We investigated the formation of fluid films along a rock surface imaged with atomic force microscopy using ζ-potential measurements and a computational model for drainage. The results were compared to spontaneous imbibition test to link sub-pore-scale and core-scale wetting characteristics of the rock. Findings The results show a dependency between surface coverage by oil, which controls the wetting alteration, and the macroscopic wetting response. The surface-area coverage is dependent on the capillary pressure applied during primary drainage. Close to the saturation endpoint, where the change in saturation was minor, the oil-solid contact changed more than 80%.

https://biblio.ugent.be/publication/8636472/file/8678799.pdf

Relationship between wetting and capillary pressure in a crude oil/brine/rock system: From nano-scale to core-scale

Slippery liquid infused porous surfaces (SLIPS) have recently gained a lot of attention because of their wide range of applications We recently showed that SLIPS with most of their surface depleted of lubricant, as little lubricant as 002 ± 001 μL cm–1, were effective against marine biofouling Characterization of the depletion and configuration of the immobilized liquid layer on SLIPS is crucial to optimizing their performance Previous attempts at mapping lubricant thickness have been diffraction limited or indirectly measured thickness Here, we use atomic force microscopy meniscus force measurements to directly map lubricant thickness with nanoscale resolution on wrinkled surfaces made from Teflon and poly(4-vinylpyridine) (P4VP) Using this method, we show that SLIPS are easily depleted and are effectively heterogeneous surfaces, where the majority of the surface is a thick lubricating layer stabilized by capillary forces and part nanothin layer stabilized long-range intermolecular forces We foun

Mapping Depletion of Lubricant Films on Antibiofouling Wrinkled Slippery Surfaces

Direct measurement of the contact angle of water droplet on quartz in a reservoir rock with atomic force microscopy

There remain significant gaps in our ability to predict dewetting and wetting despite the extensive study over the past century. An important reason is the absence of nanoscopic knowledge about the processes near the moving contact line. This experimental study for the first time obtained the liquid morphology within 10 nm of the contact line, which was receding at low speed (U < 50 nm/s). The results put an end to long-standing debate about the microscopic contact angle, which turned out to be varying with the speed as opposed to the constant-angle assumption that has been frequently employed in modeling. Moreover, a residual film of nanometer thickness ubiquitously remained on the solid after the receding contact line passed. This microscopic residual film modified the solid surface and thus made dewetting far from a simple reverse of wetting. A complete scenario for dewetting and coating is provided.

Nanoscale View of Dewetting and Coating on Partially Wetted Solids

Nanoscopic morphology of equilibrium thin water film near the contact line

The air micro- and nanobubbles on a silicon wafer surface, generated by ethanol–water exchange method in THF solution, are found with anomalous small contact angles on the gas side due to the pinni...

Effect of Micro- and Nanobubbles on the Crystallizationof THF Hydrate Based on theObservation by Atomic Force Microscopy

The crystallization process of a droplet of tetrahydrofuran (THF) solution on a silicon wafer is studied based on the in situ observation with a high-resolution atomic force microscope. On the basi...

Yajun Deng

Papers

Direct measurement of the contact angle of water droplet on quartz in a reservoir rock with atomic force microscopy

Nanoscale View of Dewetting and Coating on Partially Wetted Solids

Nanoscopic morphology of equilibrium thin water film near the contact line

Effect of Micro- and Nanobubbles on the Crystallizationof THF Hydrate Based on theObservation by Atomic Force Microscopy

Study of THF Hydrate Crystallization Based on In Situ Observation with Atomic Force Microscopy