The surface free energy components of clay-organic complexes were determined to assess to what extent an organic adsorbate modified the surface properties of the mineral, insofar as the stability of soil aggregates is concerned. Adsorption isotherms for two synthetic, humic acid-like polymers were determined on a Ca-montmorillonite. From contact-angle measurements performed on dry surfaces, the surface free energy properties of the clay-organic complexes were determined using the two-liquid-phases method (water and hydrocarbons). This method allows both the dispersive and nondispersive components of the solid surface free energy, γDS and γPS, to be determined. The results show that a very small amount of polymer (1% by weight) adsorbed on the external surfaces of the montmorillonite decreased markedly the surface free energy components of the clay: γDS decreased from 75 to 28 mJ/m2 for polycondensate catechol (PC) and from 75 to 30 mJ/m2 for polycondensate catechol triglycine (PCT), whereas γPS ranged from 35 to 16 mJ/m2 (PC) and from 35 to 17 mJ/m2 (PCT). Although their chemical compositions were different, both polymers similarly modified γDS and γPS. Increasing the amount of polymer adsorbed (from 1% to 3.5% by weight) affected mostly γPS, which became as low as 5 mJ/m2; meanwhile, γDS decreased from 30 to 23 mJ/m2. Possibly, the molecular orientation of the adsorbate changed in the process of dehydration. Following adsorption of synthetic humic acid-like polymers, dry Ca-montmorillonite complexes displayed γS values < 50 mJ/m2, which were consistent with the solid-water contact angles measured in air.

The influence of adsorbed H+, Na+, K+, Ca2+, Mg2+, Ba2+, and Al3+ ions on the wettability of a kaolinite surface was determined from contact angles, which were measured in kaolinite-water drop-air (saturated water vapor) and kaolinite-diiodomethane drop-air systems. From the results and using a modified Young equation, the dispersion and nondispersion components of the free energy of the kaolinite hydrated surface were determined. The dispersion component of all the tested samples was between 32.8 and 38.9 mJ/m2, but the nondispersion component changed almost linearly from 53 to 95.9 mJ/m2 with the change of the entropy of hydration of the adsorbed ions, except for K+ and Ba2+. The latter ions were exceptions, probably due to their large ionic radii.

A reservoir rock is a porous geological formation in contact with 2 liquids, brine and oil. An improved knowledge of rock wettability is of primary importance to estimate the amount of crude oil in underground resources. The petroleum industries have observed that wettability contrasts in sedimentary reservoir rocks are largely correlated to the presence of clays, illite and/or kaolinite in the rocks’ intergranular space.

More precisely, the grain surfaces of illite show a preference for brine. Kaolinite preferentially adsorbs oil, which imparts its hydrophobic characteristics to the mineral surface. Using X-ray absorption spectroscopy (XAS) and Fourier transform infrared (FTIR) spectroscopy, we studied the adsorption process of asphaltenes in the presence of water at the microscopic level. We demonstrate experimentally that the wettability contrasts observed in kaolinite and illite are related to structural differences between these 2 clays, and we show the role of the grain surface hydroxyls. With clay materials, the purity of the samples is the most important limitation of the quantitative use of extended X-ray absorption fine structure (EXAFS).

The effect of humic acid (HA) adsorption on the hydrophilicity of two different montmorillonite samples (Na-montmorillonite, NaMt, and a Na-fluorinated Na-montmorillonite, FNaMt, or ‘Rassoul’) was investigated. The changes in the wettability of clays were discussed in terms of the non-electrostatic free energy of interaction between the clay particles immersed in aqueous humic acid solutions (ΔG121), using the van Oss-Chaudhury-Good (vOCG) model. The surface free energy components (both non-polar or Lifshitz-van der Waals, and polar or acid-base) of clays were obtained from contact angle measurements, after adsorption of humic acid, at acid or basic pH, in 10−2 M NaCl solutions. It was found that: (1) at acid pH, a progressive decrease in the hydrophilic character of both clays was observed when the humic acid concentration was increased; (2) at basic pH, the hydrophilic character of both samples studied increased with HA concentration; (3) the effect of humic acid adsorption on the wettability of model edge surfaces of the laminar montmorillonite particles was estimated from a parallel study on silica and alumina surfaces, and only a slight decrease in the hydrophilicity was observed, whatever the pH of the liquid media. The ζ potentials of both clays in the absence and presence of humic acid were determined and the linkage between ζ potential and the electron-donor character of the materials is discussed.

Organo-clays are of interest in the modification of anion transport properties in engineered barriers. In the present study, surface charge and wettability were assessed for tracking changes in the effective diffusion coefficient (Deff) by the formation or suppression of bound H2O layers on the external surfaces of clays. Bentonite samples modified with three different organic cations in amounts of 0 to 400% of the cation exchange capacity were used. Diffusive transport was determined in H2O→D2O exchange experiments in a newly constructed cell adapted to the attenuated total reflectance (ATR) accessory of a Fourier-transform infrared (FTIR) spectrometer at two different dry bulk densities and various degrees of water saturation.

All organo-clay combinations showed changes in surface charge after the addition of organic cations, from a negative value of 99 mmolc/kg for the original bentonite to a maximum positive value of 230.5 mmolc/kg for hexadecylpyridinium (HDPy)-montmorillonite. The positive charge resulted from adsorption of the organic cation in excess of the CEC. Hydrophobic surface properties with contact angles >90° were obtained for HDPy-montmorillonite samples with monolayers of organic cations on the external surfaces only. Here, where hydrophobicity suppressed the formation of bound H2O layers, the largest Deff o f 2.7×10−10 m2/s was observed in the high dry bulk density range (1.0–1.5 g/cm3) under water-saturated conditions. In the low dry bulk density range (0.6–0.9 g/cm3) this effect was weakened significantly because, with increasing pore size, the effect of bound H2O layers was reduced. In the high dry bulk density range at partial water saturation (40%), diffusive transport was hindered by the small water volume. Previous work found that, in the high dry bulk density range and water-saturated state, Deff was 2.4×10−11 m2/s for the original bentonite. Deff for all hydrophilic organo-clay samples was ⩽2.1×10−11 m2/s, somewhat less than for the hydrophobic sample. In hydrophilic organo-clay samples, retardation factors that retard the value for Deff, up toa magnitude of 0.5, include an increase in dry bulk density and a decrease in water saturation. In the water-saturated state at high dry bulk densities, hydrophobic surface properties suppressing the formation of bound H2O layers can increase Deff by one order of magnitude.

We report on enhanced mechanical, tribological, and surface-wettability characteristics of polymeric films dispersed with inorganic fullerene (IF)-type tungsten disulfide (WS2) nanoparticles derived through a two-step hydrothermal route. Imaging through transmission electron microscopy suggests the occurrence of polyhedral cage-like structures with a visibly nonspherical hollow ranging 55–75 nm. The mechanical stability of IF-type WS2 dispersed in polyvinyl alcohol (PVA) gets improved with increasing nano-inclusions, and upto 6 wt% loading. As compared with nanosheets, the IF-WS2 in PVA at the critical loading offers nearly 28.6, 33.6, and 42% respective improvements as regards, breaking stress, elongation at break, and toughness. Moreover, Stribeck curves in the mixed lubricating regime have revealed a nearly ∼80% reduction of coefficient of friction (COF) due to inclusion of IF-type WS2 in PVA. In the hydrodynamic region, the COF is drastically lowered from a typical value of 0.55 to 0.15 at the maximal sliding velocity with nanoparticle loading and despite the fact that the tribo feature gives a rising trend for a particular curve. Furthermore, exhibiting a progressive increase in water contact angle, a clear transition from the hydrophilic (∼64°) to hydrophobic (∼107°) surface of the nanocomposite films has been witnessed after inclusion of nano IF-WS2. An increased hydrophobicity and lowered surface adhesion and COF values along with marginal drop in surface energy are ensured in the investigated specimens. Investigation of responsive tribological and wetting–dewetting transition would find scope not only in coating and textile industry but also in smart miniaturized components.

An array of nano-scale protrusions, called the nipple array, is found on the body surface of various invertebrates, and this structure is believed to decrease light reflectance and water wettability on the surface in the terrestrial environment. However, its potential functions have not been well studied in aquatic environments. Clavelina spp. are colonial ascidians that have the nipple array on their integumentary matrix (i.e. tunic). We examined the physical properties on the surface of the tunic of C. cyclus and C. obesa, such as hardness, wettability and refractive indices, to evaluate the functional importance of this structure. The tunic cuticle of both species was covered with the nipple array, and the cuticle of C. cyclus was bent into folds forming parallel plications. The Clavelina tunic was very soft and had high bubble- and oil-repellency. The refractive-index deviation between the tunic and seawater was 0.07–0.095 for 589-nm light (D-line). Rigorous coupled wave analysis (RCWA) showed that the nipple array slightly reduced reflectance on the surface and the parallel plications reduced the reflectance still more. The nanoimprinted plates imitating the parallel plications have higher bubble repellency and lower reflectance than the flat plates. These findings support the functional importance of the plications as well as the nipple array.

In some metazoans, the body surface is entirely or partly covered with an array of nipples about 100 nm or less in height. This structure, a nipple array, is sometimes called the moth-eye structure because it serves as an anti-reflection property on the compound eyes of a night moth. The nipple array is supposed to be a multifunctional structure since this structure occurs in various species across different taxa. Here, we hypothesize that the nipple array may prevent the settlement of epibionts that are often a nuisance and potentially cause serious problems for the host. Using a synthetic film that imitates the nipple array, we tested the substrate selection within ascidian larval settlement. The results indicate that the nipple array has anti-fouling properties, since more larvae settled on the flat surface than the nipple array (P < 0.01, paired t-test). The present results demonstrated that the nipple array potentially serves an anti-fouling function on the body surface, which should be important especially for sessile organisms.

Electrochemical treatments, such as electropolishing on titanium alloys, are used to promote the formation of nanostructured surfaces, which can contribute to the bone regeneration process. However, sterilization methods can change the superficial and physicochemical properties of the biomaterials. The objective of this work was to evaluate the effect of three sterilization methods (air plasma, ethanol + PBS, and autoclave sterilizations) on nanostructured Ti6Al4V surfaces properties obtained by electrochemical treatment. These methods, especially the first two, have been widely used in literature, yet few studies in the literature highlight the changes on the surface of the samples. The nanostructures were obtained by electropolishing in a H2SO4/HF/glycerine solution, at 25 V and at 7 °C for 4 min. Samples were characterized by atomic force microscopy (AFM), profilometry, and wettability. Samples were seeded with hESC-MPs, and the cell number was measured. The air plasma sterilization did not promote changes in nanometric morphology and roughness of the Ti6Al4V nanostructured samples. Unlike air plasma sterilization, the ethanol + PBS and the autoclave sterilizations, which strongly affected the nanostructured surface morphology and properties, and, consequently, the cellular viability after 7 days of contact with human embryonic stem cell-derived mesenchymal progenitors (hESC-MPs).

The anion adsorption capability of clays can be improved significantly by modification with certain organic cations. However, surface properties and the microstructure of the clay might change and limit the use of organo-clays in barrier systems. In this study an experimental setup is introduced which allows the rapid determination of effective diffusion coefficients (Deff) for H2O in clay samples. H2O→D2O exchange experiments on hexadecyl-pyridinium (HDPy)-montmorillonite samples were performed in a diffusion cell attached to the ATR unit of a Fourier-transform infrared spectrometer. The mean Deff for H2O in a D2O-saturated original montmorillonite is 2.44 × 10–11 m2/s in the bulk density range of 1.1–1.8 g/cm3. Hydrophobic surfaces increase the diffusivity only at high bulk densities in the saturated state. The mean Deff is lower when HDPy is applied in amounts ⩾80% of the cation exchange capacity in comparison with the original sample. At a saturation degree of the pores of 40%, Deff for all samples is one order of magnitude less than in the saturated state. Results on Deff obtained by ATR-FTIR spectroscopy are in good agreement with through-diffusion studies.

Hybrid material based on halloysite nanotubes (HNTs) and sodium perfluorooctanoate (NaPF8) was used as a consolidant for paper treatment. The consolidation efficiency was determined by thermogravimetry as well as by paper grammage determination. Morphological analysis of the treated paper was performed by means of scanning electron microscopy while the effect of modified HNTs on the thermal behaviour of the cellulose fibres was investigated by differential scanning calorimetry which determined the combustion enthalpy of the paper.Water contact angle measurements were performed to study the paper wettability. The physico-chemical properties investigated (mesoscopic structure, thermal stability and wettability) of the treated paper were correlated successfully with the consolidation loading and, consequently, to the affinity between the fluorinated modified HNTs and the fibrous cellulose structure. This study proposes a new green protocol for paper consolidation based on natural tubular nanoparticles with a flame retardant effect.

The amorphous carbon thin films were deposited by the ion beam sputtering deposition technique on Ni–Cu alloy substrates. The effect of sputtering ion beam energy on wettabillity, surface, and structural properties of thin films was examined. The sputtering ion beam energy was varied over a wide range from 2 to 5 keV. Raman spectra showed that the values of ID/IG ratio and the ‘G’ peak position have a reduction trend by increasing the argon ion beam energy while the surface roughness increased due to the resputtering effect. The wettability and surface energy of a-C carbon films were studied by contact angle measurements in relation to structure and topography. The deposited films showed a relatively high water contact angle (CA) that decreases from 87° to 75°. The X-ray photoelectron spectroscopy showed that the value of sp3/sp2 bond content of a-C thin films deposited with the highest argon ion beam energy of 5 keV was about 0.8. Furthermore, the optical band gap followed similar trends of the structural properties.

Two related aspects of nano-droplet condensation and droplets coalescence are studied for droplets on self-supported thin water films. The experiments are conducted in the environmental scanning electron microscope using wet scanning transmission electron microscopy. Favorable condensation sites are examined and in-situ position-controlled condensation experiments are conducted. The interaction among condensed multi-droplets as well as between a single droplet and the underneath nano-thick water film are dynamically examined with 10nm lateral resolution. The droplet round shape is reshaped to flat-like facets in-between droplets of 30-230 nm separation. Dynamic imaging of a few minutes duration shows a delayed coalescence effect, being explained by increased droplet-droplet electrostatic interaction relative to van der Waals interaction.

A thermal lattice Boltzmann method (LBM) for two-phase fluid flows in nucleate pool boiling process is proposed. In the present method, a new function for heat transfer is introduced to the isothermal LBM for two-phase immiscible fluids with large density differences. The calculated temperature is substituted into the pressure tensor, which is used for the calculation of an order parameter representing two phases so that bubbles can be formed by nucleate boiling. By using this method, two-dimensional simulations of nucleate pool boiling by a heat source on a solid wall are carried out with the boundary condition for a constant heat flux. The flow characteristics and temperature distribution in the nucleate pool boiling process are obtained. It is seen that a bubble nucleation is formed at first and then the bubble grows and leaves the wall, finally going up with deformation by the buoyant effect. In addition, the effects of the gravity and the surface wettability on the bubble diameter at departure are numerically investigated. The calculated results are in qualitative agreement with other theoretical predictions with available experimental data.

Although boiling process has been a major subject of research for several decades, its physics still remain unclear and require further investigation. This study aims at highlighting the effects of surface wettability on pool boiling heat transfer. Nanocoating techniques were used to vary the water contact angle from 20 to 110° by modifying nanoscale surface topography and chemistry. The experimental results obtained disagree with the predictions of the classical models. A new approach of nucleation mechanism is established to clarify the nexus between the surface wettability and the nucleate boiling heat transfer. In this approach, we introduce the concept of macro- and micro- contact angles to explain the observed phenomenon.

The response of epicuticular wax of Scots pine (Pinus sylvestris L.) needles to dry- and wet- deposited sulphur and heavy metals was investigated at six sites located 10–110 km from the Monchegorsk Cu-Ni smelter on the Kola Peninsula, North-West Russia, and in a long-term irrigation experiment where pines were exposed over four growing seasons (1991–1994) to either acid rain treatment at pH 3·1 (H2SO4), metal treatment at pH 5·7 (Cu and Ni) or a combination of these at pH 3·1. Needle wettability exhibited a closer relationship with epistomatal wax tube distribution (WTD) than with chemical composition of epicuticular wax. Water droplet contact angles (DCA) decreased towards the smelter, and significant differences due to site were noted for 26-month-old and 38-month-old needles. Significant differences due to site were determined for secondary alcohols, dehydroabietic acid and hydroxy fatty acids, the proportions of which ranged from 22·5 to 48·9%, 6·2 to 22·4% and 0·6 to 2·6% respectively, depending on site and needle age class. The proportion of dehydroabietic acid increased towards the smelter, but no gradient was observed in the proportion of secondary alcohols or hydroxy fatty acids. No major effect of experimentally applied pollutants on the chemical composition or structure of the epicuticular wax was observed. The effect of treatment on DCA was significant in 1993 and 1994 due to a 6·5–13·2 degree greater wettability of the 37–49-month-old acid-treated needles relative to the irrigated or dry controls. Sulphuric acid at pH 3·1 did not increase needle wettability when combined with copper and nickel sulphate in similar concentrations. These data indicate that S deposition, especially H2SO4, plays a more important role in needle surface deterioration than Cu and Ni. Pollutant-induced changes in epicuticular wax structure and needle wettability mimic natural wax ageing, but at an accelerated rate. Changes in wax chemical composition might also be caused by pollutant-induced metabolic changes in elongating needles.