Perfect Wetting Research Articles

The smallest nanodrop describable via macroscopic interfacial concepts: Testing classical heterogeneous nucleation theory with perfect wetting down to 3 nm

HypothesisThe smallest nanodrop tractable with macroscopic notions such as the interfacial energy could be determined by comparing heterogeneous nucleation observations and capillary theory predictions at decreasing drop diameters dp. AnalysisThis is done here for the condensation of n-butanol vapors on polyethylene glycol nano-globules (3 nm ≤ dp ≤ 9 nm). We use published activation probability measurements P(w,dp), where w is the accurately controlled saturation ratio of n-butanol vapor in a gas stream exiting a saturator. The maximal saturation ratio achieved in the nucleation region by cooling this gas-vapor stream in the apparatus of Gallar et al. satisfies Smax = Cw. The key unknown constant C and the preexponential term K governing the nucleation rate are determined by assuming that classical theory applies to the largest particles used. This yields P(Smax,dp) data, directly comparable with capillary theory with perfect wetting. FindingsExcellent agreement is found above 5 nm for the critical dependence Smax(dp) resulting from the constraint P(Smax,dp) = 0.5. The entire P(Smax,dp) curves also agree closely between 5 and 7 nm. Smaller particles depart only slightly from theory, even at dp = 3 nm. Capillary theory hence describes accurately the heterogeneous nucleation process above 3–5 nm, provides a reliable method to determine Smax, and yields experimentally the nucleation rate constant K.

Hydrophobic cotton fabric with 3-mercaptopropyltriethoxysilane/polyhedral oligomeric silsesquioxane/1-octadecanethiol modification for oil/water separation

A protocol to produce a silsesquioxane (POSS) with a long alkyl chain coating on natural cotton (CT) fabric is applied. The surface hydroxyl groups of cotton fabric are converted with 3-mercaptopropyltriethoxysilane (MPTES) to thiol groups. Then the POSS links to the thiol groups by thiol-ene click reactions triggered by UV irradiation to produce POSS-CT or grafted with 1-octadecanethiol (ODT) using one-pot or two-pot modification protocols to generate the ODT-POSS-CT fabrics. The POSS-CT is highly hydrophobic, could absorb 0.96 g hexane/g fabrics when competing with invaded water, and reach 1.12 hexane g/g fabrics when water was absorbed separately. The one-pot modification protocol yielded surfaces with almost constant water contact angle (144o) and perfect wetting by diiodomethane (0o), producing constant dispersive component (50.8 mJ/m2) and polar component (13.6 mJ/m2). The ODT-POSS-CT via two-pot modification leads to water contact angles >143o and diiodomethane contact angle of about 46o, with corresponding dispersive and polar components being 36.1 mJ/m2 and 9.4 mJ/m2, respectively. The complete grafting of ODT onto POSS yields a compact hydrophobic layer with reduced effective surface area for dispersive components, transferring the surface from hydrophobic to omniphobic for both water and diiodomethane.

Understanding and Engineering Interfacial Adhesion in Solid-State Batteries with Metallic Anodes.

High performance alkali metal anode solid-state batteries require solid/solid interfaces with fast ion transfer that are morphologically and chemically stable upon electrochemical cycling. Void formation at the alkali metal/solid-state electrolyte interface during alkali metal stripping is responsible for constriction resistances and hotspots that can facilitate dendrite propagation and failure. Both externally applied pressures (35-400 MPa) and temperatures above the melting point of the alkali metal have been shown to improve the interfacial contact with the solid electrolyte, preventing the formation of voids. However, the extreme pressure and temperature conditions required can be difficult to meet for commercial solid-state battery applications. In this review, we highlight the importance of interfacial adhesion or 'wetting' at alkali metal/solid electrolyte interfaces for achieving solid-state batteries that can withstand high current densities without cell failure. The intrinsically poor adhesion at metal/ceramic interfaces poses fundamental limitations on many inorganics solid-state electrolyte systems in the absence of applied pressure. Suppression of alkali metal voids can only be achieved for systems with high interfacial adhesion (i. e. 'perfect wetting') where the contact angle between the alkali metal and the solid-state electrolyte surface goes to θ=0°. We identify key strategies to improve interfacial adhesion and suppress void formation including the adoption of interlayers, alloy anodes and 3D scaffolds. Computational modeling techniques have been invaluable for understanding the structure, stability and adhesion of solid-state battery interfaces and we provide an overview of key techniques. Although focused on alkali metal solid-state batteries, the fundamental understanding of interfacial adhesion discussed in this review has broader applications across the field of chemistry and material science from corrosion to biomaterials development.

Effect of inertia on the dynamic contact angle in oscillating menisci

The contact angle between a gas–liquid interface and a solid surface is a function of the dynamic conditions of the contact line. Classic steady correlations link the contact angle to the contact line velocity. However, it is unclear whether they hold in the presence of inertia and the case of perfect wetting fluids. We analyze by means of experiments the shape of a liquid interface and the corresponding contact angle in accelerating conditions for two different fluids, that is, HFE7200 (perfect wetting) and demineralized water. The setup consists of a U-shaped quasi-capillary tube in which the liquid column oscillates in response to a pressure step on one of the two sides. We obtained the evolution of the interface shape from high-speed back-light visualization, fit interface models to the experimental data to estimate the contributions of all the governing forces, and perform measurements of the dynamic contact angle. We propose a new model to account for the impact of the interface acceleration on its shape, and we discuss the impact on the measurement of the transient contact angle. The new model allows us to perform dynamic contact angle measurements below 15°, which is challenging to obtain with traditional techniques. We show for the first time a dynamic characterization of the wetting behavior of HFE7200, and we compare the results with traditional hydrodynamic models.

Deposition of Co islands on Cu(111) and Cu–Al(111): A comparative study from DFT calculations

The growth behaviors, stability and magnetic moments of Co islands on Cu(111) surface and Cu–Al(111) alloy surface were compared by means of Density Functional Theory calculations. Similar to the case of Pb-precovered Cu(111), it was found that the diffusivity of Co adatom on Cu–Al(111) was lower than that on Cu(111), which could suppress the agglomeration of Co atoms on Cu–Al(111). Such behaviors could be explained by the different electronic structures of surface atoms of Cu(111) and Cu–Al(111). Co adatoms deposited on one monolayer Co island descending a Co edge step to substrate terrace via push-out/exchange mechanism is more favored than direct hopping on both surfaces, and push-out/exchange descent is more favorable on Cu–Al(111) than Cu(111) with similar “Schwoebel-Ehrlich” barrier and larger exothermic reaction energy. Island formation energies calculated suggest layer-by-layer growth mode is more favored for Co islands deposited on Cu–Al(111) covered with Co films than that on Cu(111). In agreement with experiments, layer-by-layer growth is identified for Co islands on Cu–Al(111), suggesting perfect wetting of Cu–Al(111) by Co. Our calculations show Al impurities in Cu(111) enhance the stability and magnetic moments of Co islands, which may shed light on Co/Cu–Al(111) being potential applications in magnetic hyperthermia treatments.

A 3nm-thick, quasi-single crystalline Cu layer with ultralow optoelectrical losses and exceptional durability

An ultrathin, highly crystalline, two-dimensional Cu layer is necessary for simultaneously achieving ultralow electrical and optical losses in transparent electrodes. However, perfect Cu wetting on heterogeneous oxide substrates has not yet been achieved. Herein, we report the Ge-mediated fabrication of an ultrathin, highly crystalline, complexly continuous Cu layer. The unique surfactant-like segregation of atomic Ge towards the outermost boundaries of the Cu geometries remarkably enhanced Cu wetting on the ZnO substrate. Numerical simulation indicated that the enhanced wetting can be attributed to the simultaneous decreases in the thermodynamic cohesive and formation energies at the surface and interface of the Cu nanostructures owing to Ge segregation. This enabled the fabrication of an ultrathin (∼3 nm), highly crystalline, two-dimensional Cu layer in a ZnO/Cu/ZnO configuration, which exhibited a record-low average optical loss at a near-bulk resistivity (8 × 10−8 Ω m) comparable to those of conventional Ag electrodes; it also showed exceptional durability in water, ozone, and high-temperature (up to 400 °C) environments. These unique features would ensure the development of highly reliable optoelectrical devices employing Cu superstructure-based transparent electrodes as inexpensive alternatives to Ag-based transparent electrodes.

MATHEMATICAL MODEL FOR DETERMINE OF THE MESH BUBBLE POINT PORE DIAMETER

The article presents mathematical models for determining the bubble point diameter of the pores of meshes with micron sizes square cells of plain and full twill weaving. Analyzed are mathematical models developed by a number of researchers to determine the bubble point pore diameter of the meshes and their point pore pressure. The analysis of the mathematical models showed that they were developed on the basis of a number of assumptions that, to varying degrees, take into account the spatial shape of the mesh cells and the physicochemical processes when the free surface through the mesh. This undoubtedly affects the accuracy of analytical calculations that are based on the use of these models. In the presented work, mathematical models have been developed that take into account the complex spatial shape of the wires from which the mesh is made. Mathematical models have been developed for plain and twill weaving meshes. When developing mathematical models, it was assumed that the free surface is formed on a hole with elliptical edges. In this case, it is assumed that the points of contact of the free surface of a plain weave mesh correspond to the most distant points of the projection of the mesh cell. For full twill meshes, taking into account the structure of their weaving, it is assumed that the free surface is formed on two adjacent cells. The influence of the contact angle between the mesh surface and the working fluid was taken into account by analyzing the spatial shape of the mesh wires. The developed models make it possible to take into account the effect of liquids with a contact angle from zero to 90 degrees. Simplified mathematical models of the meshes have also been developed for the case of perfect wetting of the mesh surface with a liquid, when the contact angle is zero. The obtained mathematical models can be used in the design of capillary phase separators of liquid acquisition devices in zero gravity of spacecraft, as well as in the calculation of capillary devices of various technical systems, such as heat exchangers, gas-liquid mixers, chemical reactors, bubble filters, etc.

Wetting transition and phase separation on flat substrates and in porous structures.

In contrast to the wetting phenomenon of pure substance phase, we here concentrate on the wetting behavior of immiscible fluids with two components via numerical simulations. We investigate the energetic contribution, the wall energy and the surface excess energy, to the wetting behavior of liquid solutions varying with temperature. This investigation is in accordance with Cahn's wetting transition theory, where the surface composition plays a vital role. By analyzing the energetic contributions, we reveal two different physical mechanisms of complete wetting: (i) surface tension driven complete wetting, where the wetting microstructure is achieved via the outward spreading of the triple junction, and (ii) diffusion induced complete wetting, where the wetting film is achieved through a direct deposition of the solute on the substrate. The former one is consistent with the classic theory of Young's law, and the latter one is an alternative mechanism. To indicate the broad multiplicity of the microstructural arrangements, we take porous structures to exemplarily elucidate the formation of alternative perfect wetting structures. Differing from the wetting on a flat substrate, we show that the surface composition varying with temperature leads to a distinct wetting phenomenon in porous structures. The present findings provide an alternative interpretation for complete wetting and are expected to be exploited for designing more effectively and efficiently superhydrophilic structures.

A novel experimental method for investigating secondary wetting

ABSTRACT This paper proposes a novel and simple technique to study secondary wetting for bimetallic systems characterised by almost perfect primary wetting. The main principle is to promote complete dissociation between primary and secondary wettings, avoiding the use of the conventional sessile drop technique and its variants. For the first time, evidence is thus obtained that secondary wetting occurs in aluminium alloys.

Wetting Transition in a Molten Metal and Solid Substrate System in High Magnetic Fields

Wetting transitions between molten metals and different solid substrates were investigated using the sessile drop method to evaluate the possibilities of regulating wettability by high magnetic fields (HMFs) during wetting. For most wetting counterparts, the molten-metal droplet outline showed an apparent change because of the influence of HMFs. Contact angles that were measured with HMFs decreased compared with contact angles that were measured without HMFs. The temperature and magnetic-flux density had an evident but more complicated effect on the wetting transition. For reactive wetting systems, the effect of HMFs on changes of element distributions at the metal/substrate interface may lead to a variety of wetting transitions. For non-reactive wetting systems, solidified metal droplets can move from the solid substrates after wetting. No detailed and comprehensive explanations on HMF wetting-transition mechanisms exist, and further work is required. This study contributes to perfect wetting mechanisms and theories and provides a scientific approach to control wettability.

Measuring surface energy of carbon nanotubes using modified washburn method

In this study, the Washburn method and Owens and Wendt model were used to estimate the surface energy of an industrial grade multiwalled carbon nanotube (MWCNT) having a carbon purity of 90%. Identical MWCNT beds were prepared and tested using seven different solvents covering wide range of surface tensions and polarities. The solvents were water, diiodomethane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), toluene, chloroform, and n-hexane. DMF showed the highest affinity towards the MWCNT. Therefore, it was used to determine the packing constant of the MWCNT beds assuming perfect wetting between the MWCNT and DMF. The contact angles between the solvents and MWCNT were fitted using the Owens and Wendt model to calculate the dispersive and polar components of the MWCNT surface energy. The test results showed that the surface energy of the 90% carbon pure MWCNT is with dispersive and polar components of and respectively.

Wetting of surfaces and grain boundaries in cemented carbides and the effect from local chemistry

Wettability is an important factor in the sintering of cemented carbides. We study wetting of surfaces and grain boundaries in WC–Co och WC–Ni cemented carbides using density functional theory (DFT). Based on experimental observations of WC grain orientations in cemented carbides, relevant model interfaces are created. The local chemical composition at the interfaces is taken into account by substitution of interface atoms, and the effect of temperature is evaluated based on a companion study of temperature dependent interface energies in cemented carbides.The results indicate that the wettability of Ni and Co on WC surfaces are similar. Furthermore, the wettability of Co on the commonly occurring basal WC surface is better in W-rich materials compared to C-rich materials. At liquid phase sintering temperatures we get perfect wetting in W-rich materials, while only partial wetting in C-rich materials, which is in agreement with recent experiments on wetting in WC–Co cemented carbides.The segregation of binder phase atoms to WC/WC grain boundaries stabilize grain boundaries and make them more resistance against infiltration (wetting) by binder phase. We find that the amount of dissolved binder atoms in essentially all studied WC/WC grain boundaries are of half a monolayer proportion, which is in agreement with experimental studies. Further, in WC–Co there is a stronger resistance against grain boundary infiltration compared to WC–Ni. We find that the continuous skeleton of WC grains seen after sintering and which is crucial for the superior mechanical strength of the material exists already during liquid phase sintering.

Low temperature pressureless “immediate sintering” of a novel nanostructured WC/Co/NiCrSiB-alloy cemented carbide

A novel nanostructured cemented carbide formed from WC-5%Co-20%Ni-based brazing alloy is described. During sintering, the Ni-brazing alloy is infiltrated into a green compact of WC-5%Co at 1050–1100°C for 2–60min. Perfect wetting behavior and a zero contact angle are achieved after only 40 s. Relative densities of 98.5% and 100% and microhardness values of above 1500HV1 and 1800HV1 are obtained after 2 and 30min, respectively. A change in mean particle size of 550–650nm in the precursor to a bimodal distribution of 350–400nm and 10–20nm is explained by a solution/reprecipitation mechanism.

Contact angle mechanical influence in wet granular soils

We investigate the macroscopic mechanical influence of the local liquid–solid contact angle that governs the fluid distribution in granular soils under unsaturated conditions. To this end, a discrete element method (DEM)-based implementation that accommodates for any contact angle is proposed and applied to an idealized granular material in the pendular regime. The DEM model includes resultant capillary forces as well as a comprehensive description of the capillary bridges (volume, surface, orientation tensor) by solving the Laplace–Young equation in a general case, instead of using any unnecessary phenomenological relation. Macroscale mechanical simulations for different constant contact angle values reveal that granular assemblies are less sensitive to unsaturated conditions for higher contact angles, which is in line with the contact angle influence at the microscopic capillary bridge scale. The contribution of the fluid mixture to the total stresses of the wet soil, the so-called capillary stresses, indeed decreases according to the contact angle. Thus, the increase in apparent shear strength due to unsaturated conditions is reduced for higher contact angles. As such, the classical assumption of perfect wetting (zero contact angle) appears to be non-conservative.

Wetting and spontaneous infiltration: the case study of TaC/(Au, Al and Cu) compared to TiC/Cu

Spontaneous infiltration of molten metals in to ceramic skeletons, in the course MMCs' production, is related to improved wetting of the ceramic by metals. TiC is considered a "metal-like" carbide and is supposed to be wetted well by metals through metallic bonding mechanism. Nevertheless, TiC/Cu exhibit an unusual behavior since spontaneous infiltration of molten Cu takes place, while TiC is partially wetted by Cu (θ=90°).In this work we studied the relation between wetting and spontaneous infiltration in the TaC/Au, Al and Cu systems. TaC is also considered a "metal-like" carbide and indeed no chemical interaction was observed at the interfaces of the studied systems.Sessile drop experiments showed almost perfect wetting in the three system but spontaneous infiltration occurred only in the first two (e.g. TaC/Au or Al). Thermodynamic calculation shows the difference between the systems which also has its' influence on the mechanical properties of the MMCs'. Further calculation clarifies the difference between TaC/Cu and TiC/Cu infiltration behavior, but is unable to explain the wetting results differences.Correlation between wetting and spontaneous infiltration in some cases is not straight forward and more studies and calculations on the atomistic level should be done in order to clarify this matter.

A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy.

First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

Preparation of a smooth GaN–Gallium solid–liquid interface

We discuss the preparation of an atomically flat solid–liquid interface between solid gallium nitride and liquid gallium using in situ surface X-ray diffraction to probe the interface roughness. For the creation of this interface it is necessary to start the experiment with liquid gallium which first etches into the solid at a temperature of 823K in a nitrogen free ambient. After this rigorous cleaning procedure there is perfect wetting between solid and liquid. The roughness created due to the fast etching of the solid has to be repaired at a nitrogen pressure of 10–20bar and a temperature around 1150K. The (2,1) crystal truncation rod data are excellently described by a surface model having 0±0.1Å roughness, which indicates a successful repair. The lateral length scale on which the roughness is determined has a lower limit of 750±50Å.

The use of acetone to enhance the infiltration of HA nanoparticles into a demineralized dentin collagen matrix

ObjectivesThis study investigates the role of acetone, as a carrier for nano-hydroxyapatite (nano-HA) in solution, to enhance the infiltration of fully demineralized dentin with HA nanoparticles (NPs). MethodsDentin specimens were fully demineralized and subsequently infiltrated with two types of water-based nano-HA solutions (one containing acetone and one without). Characterization of the dentin surfaces and nano-HA particles was performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface wettability and infiltration capacity of the nano-HA solutions were quantified by means of contact angle measurements and energy dispersive X-ray spectroscopy (EDS), respectively. Contact angle measurements were taken at baseline and repeated at regular intervals to assess the effect of acetone. The P and Ca levels of infiltrated dentin specimens were measured and compared to sound dentin and non-infiltrated controls. ResultsThe presence of acetone resulted in an eight-fold decrease in the contact angles of the nano-HA solutions recorded on the surface of demineralized dentin compared to nano-HA solutions without acetone (one-way ANOVA, p<0.05). Perfect wetting of the demineralized dentin surface was achieved 5min after the application of the nano-HA solution containing acetone. Infiltration of demineralized dentin with the nano-HA solution containing acetone restored the lost mineral content by 50%, whereas the mean mineralization values for P and Ca in dentin treated with the acetone-free nano-HA solution were less than 6%. SignificanceAcetone was shown to act as a vehicle to enhance the capacity to infiltrate demineralized dentin with HA NPs. The successful infiltration of dentin collagen with HA NPs provides a suitable scaffold, whereby the infiltrated HA NPs have the potential to act as seeds that may initiate heterogenous mineral growth when exposed to an appropriate mineral-rich environment.

Growth process of nanosized aluminum thin films by pulsed laser deposition for fluorescence enhancement

Pulsed laser deposition was used to deposit aluminum thin films of various thicknesses (tAl) ranging from 5 to 40 nm and to investigate their growth process when they are deposited onto SiO2 and Y2O3. Atomic force microscopy and x-ray reflectivity measurements show that the structure of the Al films are related to the wettability properties of the underlaying layer. Onto SiO2, ultra-smooth layers of aluminum are obtained, due to a perfect wetting of SiO2 by Al. In contrast when deposited onto Y2O3, percolated Al layers are observed with apparent pore size decreasing from 200 to 82 nm as is increased from 5 to 40 nm, respectively. This particular morphology is related to partial dewetting of Al on Y2O3. These two different growth mechanisms of aluminum depend therefore on the surface properties of SiO2 and Y2O3. The plasmon resonance of such Al nanostructures in the UV region was then analyzed by studying the coupling between Eu3+ rare earth emitters and Al.

LEIS and XPS investigation into the growth of cerium and cerium dioxide on Cu(111)

The controlled growth of Ce and CeO2 on Cu(111) was investigated applying low energy ion scattering spectroscopy (LEIS) and X-ray photoelectron spectroscopy (XPS). Previous LEIS studies on metallic and oxidised cerium deposits using other metallic substrates reported serious difficulties related to the neutralization of noble gas ions. For this reason, special attention was paid here to reveal possible matrix effects for the neutralization ("neutralization effects"), which would severely hinder quantitative evaluation of the LEIS data. The adsorption of O2 on Cu(111) induced no neutralization effects either with He(+) or Ne(+). Similarly, no neutralization effects were identified using He(+) upon the deposition of metallic Ce on Cu(111), but it arises for the Ce peak monitored with Ne(+). The initial growth of Ce is two dimensional up to ΘCe ∼ 0.5 ML, while almost complete coverage of Cu(111) is achieved at ΘCe = 2 ML. CeO2(111) was deposited evaporating Ce in a background of O2 at a sample temperature of 523 K. No neutralization effects were observed either with He(+) or Ne(+). In harmony with literature data, the growth mode is three dimensional. Here it was demonstrated that the continuity of the film, which could be efficiently checked by LEIS, is influenced by the applied oxygen pressure in the range of 5 × 10(-7)-3 × 10(-6) mbar. At pO2 = 3 × 10(-6) mbar the film was not completely closed even at relatively large coverages (16 ML), and a significant part of copper atoms were oxidized to Cu(1+). Deposition of CeO2 at pO2 = 5 × 10(-7) mbar was characterized by a nearly perfect wetting, with metallic copper atoms at the interface, and with a slightly more reduced ceria layer.