Partial Wetting Research Articles

Ground heave movement evaluation in shallow foundations for expansive soils in Tunja, Colombia

A current challenge in unsaturated soil mechanics is the need to estimate ground heave and associated shallow foundation movements in expansive soils due to water content changes. Such estimation should be simple for geotechnical engineering practitioners and provide reliable foundation designs through quantifying the risk associated with the ground heave. The difficulties in generalizing a method are related to several variables influencing the expansive behavior, including the initial and final stress state condition, soil mineralogical composition, ground wetting depth, soil wetting degree, and geotechnical profile comprising soil strata thickness and groundwater condition. In this research, the evaluation of heave movements for the expansive soils located in the north-east of Tunja (Colombia) is performed through surrogate path (SPM), water content, and consolidation theory-based methods. Initial and final suction profiles were defined to quantify the wetting strains developed at each scenario of partial wetting. The sensitivity of the SPM to the estimated or measured value of constant volume swelling pressure was corroborated. The higher deformations that the soil profile would be able to develop when subjected to a progressive wetting were obtained along with the remaining heave capacity of the soil profile. Finally, concluding remarks and recommendations associated with the practicality and applicability of the methods are presented.

Study of Active Janus Particles in the Presence of an Engineered Oil-Water Interface.

We present a systematic study of motion of Pt@SiO2 Janus particles at a liquid-liquid interface. A special microfluidic trap is used for creating such an interface. The increased surface energy of the large surface results in partial wetting of the substrate, leaving patches of oil on the glass surface. This allows us to directly compare the motion at the two interfaces, i.e., oil-water and solid-water interface within the same setting, guaranteeing identical conditions in terms of additional parameters. The propulsion behavior of Janus particles is found to be quantitatively similar at both surfaces. The interplay of reaction product absorption by oil, slip locking by surfactant, microscale friction, lubrication efficiency, and potential Marangoni effect controls the resemblance of motion characteristics at the two interfaces. Additionally, we also observed guidance effect on the Janus particles by the pinning line of oil patches, similar to solid side walls.

Long-time evolution of interfacial structure of partial wetting

When a solid plate is withdrawn from a partially wetting liquid, a liquid layer dewets the moving substrate. High-speed imaging reveals alternating thin and thick regions in the entrained layer in the transverse direction at steady state. This paper systematically compares this situation to the reversed process, forced wetting, where a solid entrains an air layer along its surface as it is pushed into a liquid. To quantify the absolute thickness of these steady-state structures precisely, I have developed an optical technique, taking advantage of the angle dependence of interference, combined with a method based on a maximum likelihood estimation. The data show that the thicknesses of both regions of the film scale with the capillary number, Ca. In addition, a new region is observed during onset which differs from the behavior predicted by previous models.

Spontaneous Capillary Imbibition of Water and Nonaqueous Liquids into Dry Quarry Limestones

Rates of spontaneous imbibition of water and nonaqueous liquids into dry limestones have been measured at 25 °C. Thirteen English and French limestones were used, with eight liquids (water, decane, dodecane, sec-butanol, iso-propanol, tetrahydrofuran, perfluorodimethylcyclohexane, ethanediol). For the nonaqueous liquids, the measured sorptivity generally scales as (surface-tension/viscosity)^{1/2} (here called F-scaling). Water sorptivities deviate from F-scaling, indicating partial wetting. A wetting coefficient (wetting index) is derived. Data show that there is little difference in the Hirschwald saturation coefficient measured with the different liquids, although there is a large variation between stones. Results suggest that physicochemical alteration of exposed pore surfaces strongly (and unpredictably) influences the capillary absorption of water by limestones.

Experimental study of dynamic contact angles in liquid-liquid microfluidic plug flow with partial wetting

Partial wetting of walls by immiscible liquids in microfluidic flows is a crucial parameter for heat and mass transfer applications. Dynamic contact angles, which characterize wettability, are studied experimentally for different liquid-liquid sets in microchannels with 200×400 μm and 120×240 μm cross-sections. An appropriate algorithm is chosen for meniscus shape approximation. Cox-Voinov law is found to predict correctly advancing contact angles in liquid-liquid flow. The generalized version of Cox-Voinov law is proposed for the liquid sets with different physical properties. Based on experimental data, new dependences of receding contact angle on contact line velocity are provided for the systems with concave and convex rear meniscus of a plug.

Solid-State Compounding for Recycling of Sawdust Waste into Green Packaging Composites

The present study explores solid-state cryomilling for the compounding of green composites. Herein, wood plastic composites (WPCs) composed of sawdust (SD) and poly(ε-caprolactone) (PCL) with various compositions were prepared. Two compounding techniques, namely, extrusion and cryomilling, were utilized to prepare WPC raw material pellets and powders, respectively, for comparison purposes. Flat pressing was further utilized to prepare WPC films for testing. Morphological, structural, thermal, mechanical, and surface wettability properties were investigated. Results indicate the advantages of cryomilling in producing WPCs. Scanning electron microscopy (SEM) along with optical micrographs revealed well ground SD particles and uniform distribution in the PCL matrix. Tensile strength and elongation at break of the composites declined with increasing SD content, however, the modulus of elasticity significantly increased. Water contact angles averaged less than 90°, implying partial wetting. Visual observations and thermo-gravimetric analysis (TGA) indicated thermal stability of composites during processing. In conclusion, PCL/SD WPC is a potential candidate to replace conventional plastics for packaging applications. This would also provide a much better utilization of the currently undervalued wood waste resources.

A dual-layer, nanofibrous styrene-acrylonitrile membrane with hydrophobic/hydrophilic composite structure for treating the hot dyeing effluent by direct contact membrane distillation

A robust, nanofibrous membrane with dual-layer composite structure and remarkable features has been developed in this work. The new membrane is based on the affordable styrene-acrylonitrile (SAN) polymer and a commercial hydrophilic nonwoven for the support layer. This can help to step forward the industrialization of the direct contact membrane distillation (DCMD) process for treating the hot dyeing effluent in the textile industry. The modified electrospinning with a gas-jet surrounding the Taylor cone was used for fabricating the membrane samples. Using the gas-assisted electrospinning, a nanofibrous nonwoven structure embedded with micro-cups and micro-spheres can be achieved in a one-step, gas-assisted electrospinning. The hydrophilic substrate was used for enhancing the permeate flux of the resultant composite membrane. The fabricated membrane showed remarkable features in comparison with a commercial polytetrafluoroethylene (PTFE) membrane, including high surface hydrophobicity (≥148°), higher porosity (≥81%), and smaller tortuosity factor (1.71). The unique properties of the membrane with the best performance provided a promising permeate flux (28.31 kg.m−2.h−1) and contaminant rejection (RCOD: 98.15%) compared to the commercial membrane (flux: 18.50 kg.m−2.h−1 and RCOD: 97.10%), without considerable pore wetting. However, the new membrane possessed lower liquid entry pressure (LEP) owing to its higher porosity, larger maximum pore size (0.76 μm), and thinner structure (150 μm). Results indicated that the decline in the permeate flux was mainly caused by the cake layer formation on the surface of the membrane rather than the partial pore wetting during the long-term operation for 48 h. Therefore, the newly developed nanofibrous SAN membrane with hydrophobic/hydrophilic composite structure is a promising, robust candidate for DCMD application in the textile wastewater treatment.

One-step to synthesize multilevel structured ZnO films with exceptional wettability

A facile one-step synthesis approach was developed to prepare ZnO films with multilevel structures composed of microclusters and nanohairs. The hierarchically structured ZnO films demonstrate peculiar wettability—superhydrophobicity but with high normal adhesion. The very high aspect-ratio of ZnO nanohairs minimizes the area of the (002) high potential surface which is the preferential growth direction. Microclusters of ZnO ensure the sufficient short-distance interactions for the normal adhesion, while the overall ZnO platforms with unique geometrical configuration and chemical composition provide the bulk scale conformity necessary for superhydrophobicity and high adhesion for rough or contoured surfaces. The superhydrophobicity of the ZnO nanohair films can be explained with the Cassie impregnating model or partial wetting model. Thanks to its purity as an inorganic material, the superhydrophobic ZnO films exhibit outstanding durability.

Nucleation modalities in poly(lactide), poly(butylene succinate), and poly(ε‐caprolactone) ternary blends with partial wetting morphology

Ternary biodegradable polymer blends of poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and poly(ε-caprolactone) (PCL) with the composition 45/10/45 wt% and exhibiting partial-wetting morphology were prepared. In this morphology, the minor phase is present as self-assembled droplets at the co-continuous interface of the other two major phases. The crystallization of the components in the various blends was thoroughly investigated. Differential scanning calorimetry highlighted minor differences in the overall kinetics of a given component in the ternary blend, with respect to the neat polymer. On the other hand, several unusual nucleation mechanisms could be studied by polarized optical microscopy (PLOM). With reference to the major phases, PLA spherulites displayed surface-induced nucleation from the interface with molten PBS or PCL droplets. On lowering the crystallization temperature, the PBS phase effectively nucleated at the interface with previously crystallized PLA domains, forming a transcrystalline morphology. Concerning the minor phase, weak partial-wetting PBS droplets displayed a droplet-to-droplet percolation of the nucleation events. Strongly partial-wetting PCL droplets were confined between previously crystallized PLA and PBS co-continuous phases and, instead, solidified as isolated domains randomly in space. This work provides further insights in the relationship between morphology and crystallization in immiscible ternary blends.

Wettability and capillary effects: Dynamics of pinch-off in unconstricted straight capillary tubes.

We study the interfacial evolution of immiscible two-phase flow within a capillary tube in the partial wetting regime using direct numerical simulation. We investigate the flow patterns resulting from the displacement of a more viscous fluid by a less viscous one under a wide range of wettability conditions. We find that beyond a wettability dependent critical capillary number, a uniform displacement by a less viscous fluid can transition into a growing finger that eventually breaks up into discrete blobs by a series of pinch-off events for both wetting and nonwetting contact angles. This study validates previous experimental observations of pinch-off for wetting contact angles and extends those to nonwetting contact angles. We find that the blob length increases with the capillary number. We observe that the time between consecutive pinch-off events decreases with the capillary number and is greater for more wetting conditions in the displaced phase. We further show that the blob separation distance as a function of the difference between the inlet velocity and the contact line speed collapses into two monotonically decreasing curves for wetting and nonwetting contact angles. For the phase separation in the form of pinch-off, this work provides a quantitative study of the emerging length and timescales and their dependence on the wettability conditions, capillary effects, and viscous forces.

Study of wetting of the animal retinas by Water and organic liquids and its Implications for ophthalmology

Interfacial properties of the animal retinas are reported. Wetting of the retina-retinal pigment epithelium-choroid-sclera tissues of cow, sheep, and pig eyes by water, silicone and castor oil was explored experimentally. Both water and silicone oils demonstrated complete wetting of the retina, regardless of the viscosity of the silicone oil, whereas the castor oil demonstrated a partial wetting regime. Similar wetting regimes were observed for sheep, cow and pig retinas. The intact surface of animal retina was found to be both hydrophilic and oleophilic. Wetting experiments with double sandwich oil/water layers were performed. Water demonstrated stronger affinity to the retina than silicone and castor oils, and eventually replaced the oils at the liquid/retina interface. We conclude that aqueous solutions continuously secreted in the living eye may displace silicone oil from the retinal surface and contribute to retinal re-detachment. Study of dynamics of wetting of the animal retina by water and organic oils is reported. The exponent describing the dynamics of spreading of the castor oil is lower than that predicted by the Tanner law. Castor oil may provide more effective tamponade than silicone oil.

Characterization of intermediate wetting states on micro-grooves by water droplet contact line

The wetting state of a water droplet remarkably affecting its sliding behavior is characterized by the droplet boundary contact line. This paper presents experimental studies of the apparent contact angle against droplet deposition time, as well as contact angle hysteresis, and compares the results with the Wenzel and Cassie–Baxter models. Observations indicate that different intermediate wetting phenomena exist. The sliding performance of a droplet under intermediate wetting states is also investigated. It is found that the droplet does not slide under partial wetting but slides when the side walls of the grooves have been wetted by part of the droplet. Further, that droplets under different wetting states on surfaces with varied groove spacing and widths, under the same groove spacing to width ratio, present altered sliding performance before rolling off from the micro-grooves in a parallel direction. This study broadens the characterization method of intermediate wetting states, which determines the condition of anisotropic sliding on micro-grooves. The findings have great potential for application to artificial self-cleaning surfaces.

Ag nanoparticle decorated Sb2O3 thin film: synthesis, characterizations and application

The property modifications in a thin film when its surface undergoes a nanoparticle decoration process in addition to its surface nanostructuring are investigated this paper. In specific, it describes the property modifications of antimony trioxide and its annealed variant, when their surface is decorated with Ag nanoparticles. Along with the modifications brought to the thin films, the morphology variations or agglomeration effects happening to Ag nanoparticles through/after this decoration process is also discussed here. We observe a mutual tuning of morphology as well as properties of thin film and nanoparticles. A fractal like cluster formation of Ag nanoparticle on the surface of nanostructured Sb2O3 thin film was witnessed. Whereas on the surfaces of Sb2O3 (annealed) thin film and glass plate, clustering of Ag nanoparticle is found to be different. On annealed Sb2O3 thin film surface, instead of forming fractal clusters most of the Ag nanoparticles fill in the voids between the thorns like structure of the film. The surface modification highly influences the optical absorption as well as the hydrophilicity of antimony trioxide samples. Due to the introduction of Ag nanoparticle, the absorption of Sb2O3 thin film in the visible region increased. All the synthesized films have roughness coefficient >1 and all are hydrophilic in nature. Nano structured Sb2O3 thin film is extremely hydrophilic and they become hydrophilic due to the introduction of Ag nanoparticle. The filling of Ag nanoparticles in the voids between the thorn structures might have prevented the water droplet penetration into these voids. Consequently, a partial wetting occurs on the film surface. High SERS efficiency factor (EF) and good reproducibility of Ag/Sb2O3/Glass make it a good candidate for SERS application.

A modeling study on the effects of pH and partial wetting on the removal of ammonia nitrogen from wastewater by membrane contactors

Abstract A one-dimensional mass transfer model, which includes two vital parameters on the performance of the membrane contactors for the ammonia nitrogen removal from wastewater, namely wastewater pH and membrane partial wetting, was developed. The degree of membrane wetting was estimated as a function of wastewater velocity and included in the determination of the overall mass transfer coefficient based on the resistance-in-series model. A modified Henry’s law constant was employed to take into account the effect of pH on the mass transfer. The calculated overall mass transfer coefficients based on the proposed model fitted well with experimental results in various ranges of wastewater inlet pH and velocities. The contribution analysis of resistance in each phase to the overall mass transfer resistances showed that the wastewater phase was still the dominant phase, although the partial wetting was included in the consideration. Comparing with the carbon dioxide and methane desorption, the membrane phase resistance of the ammonia desorption was much more significant to the mass transfer. The determination of the membrane area required to remove the dissolved ammonia revealed that the area was greatly influenced by the wastewater inlet pH. The K OV along the length of membrane module was gradually decreased due to the NH3 desorption. Thus, the membrane area could be significantly much lower when the wastewater pH was adjusted to the initial value in between the membrane modules connected in the series.

Thermal and mechanical analysis of LN2 jet impinging on rock surface

The transient cooling of rock surface by liquid nitrogen (LN2) jet was experimentally studied in this article. Experimental conditions cover a range of 1.4–2.4 MPa for jet pressure and 3–5 cm for stand-off distance. The nozzle diameter was fixed at 1 mm and the rock specimen was a circular plate, with diameter of 16 cm and thickness of 2 cm. The temperature curves at different radial locations in rock were measured during LN2 jet impingement. Based on these data we mapped the complete heat flux across the rock surface and attained the three dimensional temperature field within the rock. Thermal stresses inside the rock were further computed according to the experimentally determined temperature field. It is shown that the partial wetting of rock surface by LN2 jet created sharp thermal gradients in both radial and vertical directions. The induced thermal stress was in tensile state and the spatial range of thermal stress is consistent with the wetted region by LN2. The propagation speed of wetting front increases with increasing jet pressure and decreasing stand-off distance. Under the present experimental conditions, the maximum heat flux of LN2 jet was around 2.4 × 105 W/m2. The maximum tensile stress on rock surface was calculated to be ~5 MPa, which could potentially damage the rock structure and deteriorate rock’s strength.

When does Wenzel's extension of Young's equation for the contact angle of droplets apply? A density functional study.

The contact angle of a liquid droplet on a surface under partial wetting conditions differs for a nanoscopically rough or periodically corrugated surface from its value for a perfectly flat surface. Wenzel's relation attributes this difference simply to the geometric magnification of the surface area (by a factor rw), but the validity of this idea is controversial. We elucidate this problem by model calculations for a sinusoidal corrugation of the form zwall(y) = Δ cos(2πy/λ), for a potential of short range σw acting from the wall on the fluid particles. When the vapor phase is an ideal gas, the change in the wall-vapor surface tension can be computed exactly, and corrections to Wenzel's equation are typically of the order σwΔ/λ2. For fixed rw and fixed σw, the approach to Wenzel's result with increasing λ may be nonmonotonic and this limit often is only reached for λ/σw > 30. For a non-additive binary mixture, density functional theory is used to work out the density profiles of both coexisting phases for planar and corrugated walls as well as the corresponding surface tensions. Again, deviations from Wenzel's results of similar magnitude as in the above ideal gas case are predicted. Finally, a crudely simplified description based on the interface Hamiltonian concept is used to interpret the corresponding simulation results along similar lines. Wenzel's approach is found to generally hold when λ/σw ≫ 1 and Δ/λ < 1 and under conditions avoiding proximity of wetting or filling transitions.

Dynamic Wetting of Molten Polymers on Cellulosic Substrates: Model Prediction for Total and Partial Wetting

This work consists in an experimental investigation of forced dynamic wetting of molten polymers on cellulosic substrates and an estimation of models describing this dynamic. A previous work of Pucci et al. (Pucci et al. 2018) showed that for totally wetting liquids (as paraffin oils), temperature-induced variations in dynamic wetting are included into the capillary number (Ca) and then a master curve of dynamic contact angle (θd) as a function of Ca can be obtained. The hydrodynamic theory (HDT) correctly describes the dynamic wetting for Ca > 2 · 10−3. For lower Ca, a change in the dynamic wetting behavior was observed. Here, partially wetting liquids (polyethylene glycols, a.k.a. PEGs) at different molecular weight (Mn) were used at temperatures above their melting point to investigate the dynamic wetting behavior on cellulosic substrates for a large range of Ca. It was found that the dynamic curves of θd vs. Ca depend on Mn. Moreover, the HDT correctly describes the experimental measurements for Ca > 2 · 10−3. Below this threshold the dynamic contact angle decreases towards the static one. A linear correlation between parameters obtained fitting the HDT and the molecular weight of polymer was found. The prediction of dynamic wetting for low Ca (Ca < 2 · 10−3) with the molecular kinetic theory (MKT) was also evaluated and discussed.

Mass transfer characteristics of a continuously operated hollow-fiber membrane contactor and stripper unit for CO2 capture

Mass transfer performance of a polypropylene hollow-fiber membrane contactor as part of a continuously operated CO2 capture unit with amino acid salt (potassium glycinate) absorbent and vacuum solvent regeneration was studied. The effects of key operating parameters on the absorption mass transfer characteristics were explored. Without vacuum stripping, absorption rate was found to be limited by low CO2 desorption efficiency from the loaded absorbent solution in the stripping unit, resulting in high solvent CO2 loadings and limited chemical absorption rates. Introduction of vacuum stripping greatly improved desorption performance, resulting in improved steady-state absorption performance. The overall mass transfer coefficient increased at higher stripping temperatures and lower vacuum pressures in the range of 60−80 °C and 300−800 mbar (abs). The overall mass transfer coefficient increased with increasing liquid flow rate, and the highest value reached was 1.8 ∙ 10−4 m s-1. The individual mass transfer coefficients in absorption were calculated based on mass transfer correlations and experimental data, including estimation of the enhancement factor for chemical absorption. The overall mass transfer resistance was found to be dominated by the liquid-side resistance, at almost 90 % of the total resistance. The estimated membrane mass transfer coefficient was low compared to a theoretical value assuming non-wetted operation, suggesting potential partial wetting of the membrane. Stable performance of the unit and the membrane contactor was demonstrated during a stability test with over 30 h of operation.

Induced Polarization in Molecular Dynamics Simulations of the 5-HT3 Receptor Channel.

Ion channel proteins form water-filled nanoscale pores within lipid bilayers, and their properties are dependent on the complex behavior of water in a nanoconfined environment. Using a simplified model of the pore of the 5-HT3 receptor (5HT3R) which restrains the backbone structure to that of the parent channel protein from which it is derived, we compare additive with polarizable models in describing the behavior of water in nanopores. Molecular dynamics simulations were performed with four conformations of the channel: two closed state structures, an intermediate state, and an open state, each embedded in a phosphatidylcholine bilayer. Water density profiles revealed that for all water models, the closed and intermediate states exhibited strong dewetting within the central hydrophobic gate region of the pore. However, the open state conformation exhibited varying degrees of hydration, ranging from partial wetting for the TIP4P/2005 water model to complete wetting for the polarizable AMOEBA14 model. Water dipole moments calculated using polarizable force fields also revealed that water molecules remaining within dewetted sections of the pore resemble gas phase water. Free energy profiles for Na+ and for Cl– ions within the open state pore revealed more rugged energy landscapes using polarizable force fields, and the hydration number profiles of these ions were also sensitive to induced polarization resulting in a substantive reduction of the number of waters within the first hydration shell of Cl– while it permeates the pore. These results demonstrate that induced polarization can influence the complex behavior of water and ions within nanoscale pores and provides important new insights into their chemical properties.

Nucleation of Poly(lactide) Partially Wet Droplets in Ternary Blends with Poly(butylene succinate) and Poly(ε-caprolactone).

This work presents the first investigation on the crystallization behavior of partially wet droplets in immiscible ternary blends. Poly(lactide), poly(ε-caprolactone), and poly(butylene succinate) (PLA, PCL, and PBS, respectively) were melt blended in a 10/45/45 weight ratio to produce a “partial wetting” morphology with droplets of the PLA minor phase located at the interface between the other two major components. The crystallization process of the higher melting PLA droplets was studied by polarized light optical microscopy, while the other components remain in the molten state. We found that neighboring partially wet droplets nucleate in close sequence. This is unexpected since partially wet droplets display points of three-phase contact and, hence, should not touch each other. Moreover, the onset of poly(lactide) crystallization is frequently observed at the interface with molten PCL or PBS, with a significant preference for the former polymer. The observed sequential droplet-to-droplet crystallization is attributed to the weak partial wetting behavior of the PCL/PLA/PBS ternary system. In fact, the contact between the interfacially confined droplets during crystallization due to their mobility can lead to a transition from a partial to a completely wet state, with the formation of thin continuous layers bridging larger partially wet droplets. This allows crystallization to spread sequentially between neighboring domains. Using a simple heterogeneous nucleation model, it is shown that the nucleation of PLA on either PCL or PBS melts is energetically feasible. This study establishes a clear relationship between the unique partial wetting morphology of ternary blends and the nucleation of the minor component, paving the way to the understanding and control of crystallization in multiphasic polymer blends for advanced applications.