Abstract
It is necessary to understand and predict the behavior of continuous nanoflow, especially inside the nanochannel with uneven wettability. Because the properties of fluid confined in the nanochannel are different from the macroscopic fluid, molecular level understanding is critical for future applications. In this work, a series of molecular dynamics simulations were executed to investigate the effect of the wettability gradient on the continuous nanofluid. In the simulations, different osmotic pressures were applied to make the water transport through different nanochannels. Simulation data was analyzed to obtain water flow rate, shear viscosity, capillary force, density distributions along the height directions of channel and apparent friction factor. Results show that the uneven wettability has a significant effect on the transportation of confined water only under the proper applied osmotic pressure and the height of channel. Under the appropriate conditions, the uneven wettability has a promotion on the transportation of water when it is at the exit of channel. When the uneven wettability locates in the entrance and middle of the channel, the uneven wettability will hinder the transportation of water. Especially, it is worth mentioning that there is a special phenomenon when the height of the nanochannel becomes 0.8 nm. Depending on the applied osmotic pressure, the uneven wettability has a double-sided effect on the confined fluid inside the channel with H = 0.8 nm. Our work may contribute to the design of nanochannels.
Highlights
We focus on the effect of the wettability gradient and the position of the wettability gradient on nanofluidic behaviors by using molecular dynamics simulations
It is demonstrated that the effect of the wettability gradient on the transportation of water inside the nanochannel depends on the appropriate combination of the applied osmotic pressure and the height of channel
The presence of wettability gradient will promote the transportation efficiency of water inside nanochannel when the position of wettability gradient is at exit of channel
Summary
The liquid-solid interaction has often been used to tune and control the micro/nano-fluid to develop different flow fashions.[24,25]. Ritos et al reported that the flow enhancement depends on the tube’s geometric characteristics and the liquid-solid interaction by investigating the flows in nanotubes of different materials and lengths.[26] Bakli found that it is possible to switch the surface characteristics of hydrophobic nanochannels from slippery to sticky in tunable hydrophobic nanochannels.[27] Kou et al showed that water nanodroplets confined inside carbon nanotubes can unidirectionally move by means of a surface energy gradient.[28] Moskowitz et al studied that the water fill and transport through a simple model of functionalized carbon nanotubes.[29] It is thought that the uneven wettability will affect the flow properties under certain conditions. It is necessary to make a systematic understanding about the effect of the uneven wettability and the driving force on the transportation of water inside nanochannel. Due to the unique properties of the grapheme like high specific surface area and good chemical stability, the graphene stacked channel will hopefully become an exciting material with immense application in micro/nano manufacturing techniques.[31,32] In this paper, we focus on the effect of the wettability gradient and the position of the wettability gradient on nanofluidic behaviors by using molecular dynamics simulations
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