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We study the role of underlying substrates on interfacial heat transfer within supported graphene nanochannels. Due to graphene's translucency, the underlying substrate, apart from its known hydrodynamic impact on fluid flow, also influences heat transport. We introduce the term "thermal translucency" to describe this phenomenon in the context of interfacial heat transfer. Our findings reveal that the Kapitza resistance, R K , is dependent on the specific underlying substrate. The specific underlying substrate alters the water-graphene interface potential landscape due to graphene's translucency, leading to a breakdown in the inverse relationship between interfacial water density peaks and R K values, typically observed at water-graphene and water-graphite interfaces. Remarkably, higher interfacial water density peaks correlate with more ordered energy patterns, not necessarily tied to more hydrophilic substrates as the literature commonly suggests for lower R K values. The insights provided have implications for controlling and tuning thermal transport and heat storage in nanofluidic devices.

Accurate control of fluid transport in nanoscale structures is key to enable the design of foreseeable nanofluidic devices with applications in many fields such as chip cooling, energy conversion, drug delivery and medical diagnosis. Here, inspired by the experimental observation of intrinsic thermal ripples in graphene and by recent advances in the manipulation of 2D nanomaterials, we introduce a graphene-based thermal nanopump which produces controlled and continuous liquid flow in nanoslit channels. We investigate the performance of this thermal nanopump employing large scale molecular dynamics simulations. Upon systematically imposing thermal gradients, a net water flow towards the low-temperature zone is observed, achieving flow velocities up to 4 m s -1 . We observe that water flow rates increase monotonically due to larger ripple fluctuations on the graphene layers as higher thermal gradients are applied. Moreover, we find that the out-of-plane flexural phonons in graphene are responsible for flow generation wherein lower frequency phonon branches are activated with higher imposed thermal gradients. Furthermore, by modifying the wettability of the channel walls, an increase of 50% in the water flow rates is observed, showing that the efficiency of the proposed thermal pump can be enhanced by tuning the channel wall hydrophobicity. Our results indicate that thermal gradients can be employed to drive continuous water flow in graphene nanoslit channels with potential applications in nanofluidic devices.

A molecular dynamics simulation study is conducted to investigate the capability of the pristine graphdiyne nanosheet for nitrate ion separation from water. The removal of nitrate ion contaminants from water is of critical importance as it represents an environmental hazard. The graphdiyne is a carbon-based membrane with pore density of 2.4 × 10 18 pores/m 2 and incircle radius of 2.8 Å. We show that the efficient water flow is accurately controlled through fine regulation of the exerted hydrostatic pressure. The high water permeability of 6.19 L.Day -1 cm -2 MPa -1 with 100% nitrate ions rejection suggests that the graphdiyne can perform as a suitable membrane for nitrate separation. The potential of mean force analysis of the single water molecule and nitrate ion indicated the free energy barriers for nitrate of about 4 times higher than that of water molecules. The results reveal the weak interaction of the water molecules and the membrane which aid to high water flux., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

A comprehensive understanding of fluid dynamics of dilute electrolyte solutions in nanoconfinement is essential to develop more efficient nanofluidic devices. In nanoconduits, the electrical double layer can occupy a considerable part of the channel cross-section, therefore the transport properties of a nanoconfined electrolyte solution can be altered by interfacial phenomena such as the charge inversion (CI). CI is an electrokinetic effect that has been associated with the presence of hydrated multivalent cations in nanoconfinement. Here, all-atom molecular dynamics simulations are employed to study the structure and dynamics of aqueous multivalent electrolyte solutions within slit-shaped silica channels. All simulations are conducted for more than 100 ns to capture the equilibrium ion distribution, the interfacial hydrodynamic properties, and to reveal the influence of CI on nanoconfined fluid transport. The electrolyte solutions consist of water as solvent, chloride as co-ion and different counter-ions, i.e. , sodium, magnesium and aluminum. We find that the interfacial viscosity is related to the concentration and valence of the counter-ions in the solution. Our results suggest that higher CI is correlated to the presence of a layer of fluid with augmented viscosity adjacent to the channel wall. As the thickness of this interfacial high-viscosity fluid increases, lower flow rates are measured whereas higher interfacial viscosities and friction coefficients are computed.

The extreme liquid transport properties of carbon nanotubes present new opportunities for surpassing conventional technologies in water filtration and purification. We demonstrate that carbon nanotubes with wettability surface patterns act as nanopumps for the ultrafast transport of picoliter water droplets without requiring externally imposed pressure gradients. Large-scale molecular dynamics simulations evidence unprecedented speeds and accelerations on the order of 10 10 g of droplet propulsion caused by interfacial energy gradients. This phenomenon is persistent for nanotubes of varying sizes, stepwise pattern configurations, and initial conditions. We present a scaling law for water transport as a function of wettability gradients through simple models for the droplet dynamic contact angle and friction coefficient. Our results show that patterned nanotubes are energy-efficient nanopumps offering a realistic path toward ultrafast water nanofiltration and precision drug delivery.