Universidad de Concepción Facultad de Ingeniería

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Wagemann Herrera Enrique Ignacio

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Sobre Wagemann Herrera Enrique Ignacio

Ingeniero Civil Químico – UdeC

Doctor en Ciencias de la Ingeniería con mención en Ingeniería Química –UdeC

Publicaciones

On the Wetting Translucency of Hexagonal Boron Nitride (2020), When a liquid drop sits on an atomically thin layer of a 2D van der Waals (vdW) solid (like graphene) supported by a hydrophilic material, it is possible that the drop demonstrates an equilibrium contact angle that is influenced by this underlying hydrophilic material and hence is different from that observed on the bulk 2D material (e.g., graphite) surface. Such a behavior is known as the wetting translucency effect. While the wetting translucency effect of graphene has been extensively studied, the wetting translucency of hexagonal boron nitride (hBN) remains largely unexplored despite significant similarities in structural properties between these materials. In this study, we probe the wetting translucency of hBN. For this purpose, we conduct molecular dynamics simulations of water droplets and water films on hBN layers supported on a gold-like hydrophilic substrate. Our results show that for a substrate coated by monolayer hBN (“coated substrate”), depending on the contact distance between underlying substrate and hBN, an increase in the hydrophilicity of the underlying surface causes a monotonic increase in the overall adhesion energy between water and the coated substrate and a monotonic decrease in the contact angle of a drop on the coated substrate. For an increasing number of stacked hBN layers, the wettability of coated substrate becomes independent of the wettability of the underlying solid. Accordingly, our results confirm a distinct wetting translucency nature of hBN very similar to that observed in graphene. https://doi.org/10.1039/D0CP00200C

Wettability of Nanostructured Hexagonal Boron Nitride Surfaces: Molecular Dynamics Insights on the Effect of Wetting Anisotropy (2020), Nanostructured van der Waals (vdW) layered materials hold great potential for achieving smart surfaces with controllable wettability. Inspired by this possibility, we conduct Molecular Dynamics (MD) simulations of the wetting of nanostructured hexagonal boron nitride (hBN) surfaces. The nanostructure consists of periodically placed nanopillars made of hBN nanoribbons. We demonstrate that the polarity effect of the nanoribbon edges triggers wetting anisotropy of the nanoribbons: the vertical edges of the nanoribbons demonstrate a different wetting behavior as compared to the flat surfaces of the nanoribbons. Depending on the nature of the edge of the nanoribbon (armchair or zigzag), these vertical edges can be more hydrophilic for the zigzag edges or more hydrophobic for the armchair edges than the flat part. Such differences ensure that the nanostructured hBN surfaces become more hydrophilic (hydrophobic) as compared to the flat non-nanostructured hBN surfaces for cases where the edges of the nanoribbon are more hydrophilic (hydrophobic) than the flat part. Overall, the present study develops a most remarkable design space where by introducing nanopillars/nanoribbons on hBN and by merely changing the nature of the edges of these nanopillars, one can ensure atomistically thin coating of hBN with a wide range of wettability. https://doi.org/10.1039/C9CP06708F

Water Flow in Silica Nanopores Coated by Carbon Nanotubes from a Wetting Translucency Perspective (2019), Nearly frictionless water transport makes carbon nanotubes promising materials for use as conduits in nanofluidic applications. Here, we conduct molecular dynamics simulations of water flow within amorphous silica nanopores coated by a (39,39) single-walled carbon nanotube (SWCNT). Our atomistic models describe the interaction between water and pore walls based on two possible scenarios, translucency and opacity to wetting of a SWCNT. Simulation results indicate that the SWCNT coating enhances water flow through silica pores ca. 10 times compared to predictions from the classical Hagen–Poiseuille relation. By varying the strength of the water–pore interaction, we study the relationship between surface wettability and hydrodynamic slippage. We observe an increase in the slip length for higher values of water contact angle. Moreover, cases with SWCNT opacity and translucency to wetting display a substantial difference in the computed slippage, showing that the water contact angle is not the only factor that determines the slip boundary condition under nanoconfinement. We attribute this disparity to the corrugation of the potential energy landscape at the inner pore wall. The present study provides a theoretical framework for the use of carbon nanotube-based coatings in designing more efficient nanofluidic conduits. https://doi.org/10.1021/acs.jpcc.9b05294

Effect of an external electric field on capillary filling of water in hydrophilic silica (2018), https://doi.org/10.1039/c8cp03186j

Slip divergence of water flow in graphene nanochannels: The role of chirality (2017), Graphene has attracted considerable attention due to its characteristics as a 2D material and its fascinating properties, providing a potential building block for nanofabrication. In nanochannels the solid–liquid interface plays a non-negligible role in determining the fluid dynamics. Therefore, for an optimal design of nanofluidic devices, a comprehensive understanding of the slippage in a water flow confined between graphene walls is important. In nanoconfinement, experimental and computational studies have found the slip length to increase nonlinearly when the shear rate is larger than a critical value. Here, by conducting molecular dynamics simulations, we study the influence of the graphene crystallographic orientation on the slip boundary conditions inside a nanoslit channel. The flow in channels with heights of 2.0, 2.4 and 2.8 nm is driven parallel to the zig-zag and arm-chair crystallographic directions. We extract flow rates, velocity profiles, slip velocities and slip lengths. The slip velocity displays a linear relationship to the shear stress up to a critical value, which is not size dependent. Moreover, the slip length is found to be shear stress dependent above a critical shear stress value of 0.4 MPa. Furthermore, our results indicate that after this critical shear stress is reached, the flow rates are significantly influenced (up to 10%) by the particular orientation of the graphene topology. https://doi.org/10.1039/C6CP07755B

Wall embedded electrodes to modify electroosmotic flow in silica nanoslits (2015), Electroosmotic flow in a silica slit channel with nonuniform surface charge density is investigated. In nanoconfinement, the electrical double layer occupies a non-negligible fraction of the system. Therefore, modifying the charge density on specific locations on the channel wall surface allows effective manipulation of the electroosmotic flow rates. In the present study, extensive (160 ns) nonequilibrium molecular dynamics simulations are conducted to investigate the ability of controlling the electroosmotic flow control in a nanoslit by patterning the surface potential. The mechanism to modify the surface charge consists of a set of charged electrodes embedded within one of the channel walls. The presence of the embedded electrodes results in the redistribution of ions in the electrolyte solution and in the alteration of the electroosmotic flow throughout the nanochannel. Indeed, the results reveal significant changes in the electroosmotic driving force and velocity profiles including local flow reversal. This study provides physical insight into the direct manipulation of the electrokinetic flow in nanoslits. https://doi.org/10.1039/C5CP05785J

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