Ion transport in materials with a developed surface

The experimental data on surface charge and mass transfer in ionic solids (ceramics, composites, nanostructures, and heterostructures) are generalized. Interphase and intergrain boundaries are shown to play an important role in transfer processes. The influence of the wetting phase transition on the transport properties of solids is considered.     

Autoradiography studies of the processes of wetting and spreading

Data of the studies of wetting and spreading in liquid metal-solid metal systems, as well as the modification of various solid surfaces with aqueous surfactant solutions, by the autoradiography technique are reported.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 26–31.Original Russian Text Copyright © 2005 by Dolzhikova, Bogdanova, Summ, Korobkov.     

The condition of mechanical equilibrium on the surface of a nonuniform thin film

The condition of internal mechanical equilibrium of a curved surface layer is derived, and its application to practically important cases of incomplete formation of the surface layer (as is sometimes the case, for example, in thin films) is considered. The notion of a local disjoining pressure is introduced, and the equilibrium condition for a variable-thickness thin film is obtained; this condition is valid both in the absence and in the presence of external fields. The cases of a wedge-shaped film, cylindrical film, spherical film, and transition zone of a wetting film are analyzed.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 235–242.Original Russian Text Copyright © 2005 by Rusanov, Shchekin.     

Additivity of the dynamic curvature of a thermocapillary depression and static curvature of a wetting meniscus

A thermocapillary depression is induced by a laser beam in a layer of a transparent liquid on an absorbing substrate. Two plane-parallel wettable plates are immersed in the liquid in symmetrical positions with respect to the point of incidence of the beam on the liquid. The diameters of the thermocapillary response formed by the laser beam on a screen are studied in their dependence on the curvature of the equilibrium liquid meniscus formed between the plates. The property of additivity is experimentally proved; according to this property, the curvature of the free liquid surface is equal to the algebraic sum of the static curvature of the wetting meniscus and the dynamic curvature of the thermocapillary depression.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 259–267.Original Russian Text Copyright © 2005 by Tarasov.     

Adsorption of cationic and nonionic surfactants on a SiO<Subscript>2</Subscript> surface from aqueous solutions: 1. Adsorption of dodecylpyridinium bromide and Triton X-100 from individual solutions

Adsorption of cationic surfactant dodecylpyridinium bromide and nonionic surfactant Triton X-100 from aqueous solutions on the surface of SiO₂ particles is studied at various pH values (3.6, 6.5, and 10). The data on the adsorption are compared with the data on the wetting of quartz plates by solutions of these surfactants. Adsorption of both studied surfactants on the SiO₂ surface is greatly dependent on solution pH. The mechanism of adsorption of the cationic surfactant is shown to be changed when passing to the alkaline pH region. Triton X-100 does not demonstrate a substantial change in the adsorption mechanism in the pH range from 3.6 to 10.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 274–280.Original Russian Text Copyright © 2005 by Kharitonova, Ivanova, Summ.     

Adsorption of cationic and nonionic surfactants on a SiO<Subscript>2</Subscript> surface from aqueous solutions: 2. Adsorption of dodecylpyridinium bromide and Triton X-100 from mixed solutions

Adsorption of cationic (dodecylpyridinium bromide) and nonionic (Triton X-100) surfactants from their mixed aqueous solutions on a SiO₂ surface at pH 3.6, 6.5, and 10 is studied by the UV spectroscopy, capillary zone electrophoresis, and wetting measurements. It is shown that the adsorption of cationic and nonionic surfactants from mixed solutions is accompanied by synergistic effects manifesting themselves as an enhanced adsorption of both surfactants compared to their adsorption from individual solutions. The effect of second component becomes most pronounced under conditions when differences in adsorption abilities of individual surfactants are rather large (at pH 3.6 and 10). It is shown that the adsorption of surfactants from mixed solutions can be controlled by the adsorption ability of components via the variations in solution pH.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 281–287.Original Russian Text Copyright © 2005 by Kharitonova, Ivanova, Summ.     

A complex impedance analysis of the ionic conductivity of Na1+xZr2SixP3−xO12 ceramics

The ionic conductivity of pressed pellets of Na_1+xZr₂Si_xP_3?xO₁₂ (1.6<x<2.4) has been determined by the measurement of their complex impedance in the range of 5 Hz?108 MHz. The respective contributions of the grains and intercrystalline boundaries of the ceramics have been established and their activation energies for conduction (0.36 eV and 0.41 eV) calculated between 224 and 348 K. In most cases the intergrain resistance was as high or higher than the grain resistance. Samples totally free of impurities, mainly zirconium dioxide, were never prepared. The large intergrain resistance was attributed to these impurities, and the relatively low packing density of the grains.     

To the theory of wetting

Young’s equation is considered as applied to describe the behavior of ideal systems in thermodynamic equilibrium with the classification of the solid bodies into bodies having low-energy and high-energy surfaces. This classification verifies the validity of categorizing real systems into wetting and nonwetting ones with the wetting boundary lying at the contact angle having a value of θ = 90° and allows the nonwetting systems to be represented by three ranges of manifestation of contact angles, namely: a nonwetting range with contact angles of θ > 106°, an equilibrium wetting range (74° < θ < 106°), and a nonequilibrium incomplete wetting range (θ < 74°).     

Microstructure and Conduction of Composites Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi₂CuO₄ + xBi₂O₃ (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi₂CuO₄, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi₂O₃ and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi₂CuO₄ crystallites.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 596–601.Original Russian Text Copyright © 2005 by Lyskov, Metlin, Belousov, Tret’yakov.     

Modification of one side of mulberry silk fabric by monochromatic VUV excimer lamp

One side of mulberry silk fabric surface was irradiated with monochromatic VUV excimer lamp (172 nm). Change in surface morphology due to one side (I) and two side (II) irradiation was analyzed using high resolution scanning electron microscope (SEM) and atomic force microscope (AFM). The irradiated samples were further characterized through measurement of wetting time, vertical and horizontal wicking. Surface nanopores of 100 nm × 10 nm were formed on the irradiated side, however, on back side change in morphology was not observed. Upon one side irradiation the wettability and wickability improved significantly. One side irradiated silk surface (I) showed average wetting time of 14.7 s and 7.2 s while the two side irradiated silk surface (II) showed a wetting time of 9.3 s and 3.1 s for irradiation period of 1 min and 5 min, respectively. Beyond 5 min of irradiation the wettability of both the surfaces stabilized. Mechanism responsible for wetting behaviour of one side irradiated sample has been proposed. The influence of lamp geometry on irradiation effect was found to be noticeable for irradiation timings <5 min.     

Early stage spreading: Mechanisms of rapid contact line advance

Inertial spreading occurs at the onset of a droplet wetting a solid; for low viscosity, highly wetting liquids, very high contact line velocities have been observed during this regime. Initial wetting kinetics are so rapid that careful experimental exploration of this phenomenon has only occurred over the past ~ 10 years. Herein, we review recent experimental and computational investigations into inertial spreading. We highlight results and discussion from literature that bear out an initially surprising conclusion: even nanometer scale drops exhibit a regime of early stage wetting kinetics that are well described as inertia dominated. Given this, some focus is placed on reviewing results from atomic scale simulations of inertial wetting and how they can be used to battle the lack of understanding regarding fundamental mechanisms of rapid contact line advancement. To bolster this discussion, new results are also presented from molecular dynamics simulations exploring inertial wetting in metallic systems. It is demonstrated that atomic scale simulations can reveal nanoscale size effects on inertial wetting and that, after accounting for these nanoscale effects, inertial regime spreading data for nanodrops are fully explained by otherwise continuum fluid mechanics theory. Data obtained are thus used to explore the role of order in liquid films near solid surfaces in controlling contact line advancement. In exploring the structure of an ordered liquid layer adjacent to the solid surface that undergoes significant slip during inertial spreading, it is demonstrated that a tensile strain gradient manifests in the layer as the film edge is approached.     

Energetics of the interaction of water and other liquids with the surface of hydrophilic and hydrophobic sorbents according to data on the heats of wetting

Papers on the energetics of the interaction of various substances with the surface of hydrophilic and hydrophobic sorbents using the data from heats of wetting are reviewed. The thermodynamics of wetting is examined, and the important role of the heats of wetting for the production of quantitative data on the surface energy of solids is demonstrated. The uniqueness of the information on the physicochemical characteristics of the sorbents and catalysts obtained from the immersion wetting isotherms is emphasized, and up-to-date information on the extent, structure, and characteristics of the boundary layers of water is analyzed. It is shown that the calorimetric data serve as an experimental base for obtaining data on the structural ordering-disordering of the boundary layers of water. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 1, pp. 1–23, January–February, 2008.     

Temperature dependence of positron lifetime in ordered porous silica (SBA-3)

The temperature dependence of positron lifetime in uniform mesopores was analyzed. We used SBA-3 as the sample material, which possesses an ordered porous structure with uniform cylindrical mesopores. The positron lifetime corresponding to the annihilation in the mesopores increased gradually with a decrease in temperature down to 100 K, and its relative intensity also increased concomitantly. This result was attributed to the lower probability of the escape of the ortho-positronium (o-Ps) from the mesopores into the intergrain space at lower temperatures. An anomalous and sudden increase in the lifetime was observed at around 100 K; this result was in agreement with an increase in the positron lifetime reported in a previous study. It was revealed that the increase in the lifetime is very steep in cases of uniform mesopores, suggesting that the temperature dependence is influenced by the pore size.     

Foam and wetting films from amphiphilic block copolymers: Isoelectric state and stability

Foam and wetting films from PEO-PPO-PEO triblock copolymers Synperonic P85 and F108 are studied under the identical conditions, using microinterference method. The range of background electrolyte concentration, where DLVO (electrostatic and van der Waals) forces and non-DLVO (steric) forces act in the films, is determined. From the dependence of the film thickness on pH, it is unambiguously shown that electrostatic interactions (i.e., the potential and surface charge) in the foam and wetting films caused by the presence of nonionic polymer surfactants arise due to the preferential adsorption of OH⁻ ions at the solution-air interface. The films obtained below the critical pH values are sterically stabilized; i.e., a decrease in pH induces a transition from electrostatic to steric stabilization. Three-layer models are designed for both types of films that allow to calculate electrostatic disjoining pressure Π_el. The values of ϕ₀ potential of the foam film are used to calculate Π_el in wetting films. A relation between the isoelectric state of foam and wetting films and their stability is found to exist in the range of pH corresponding to electrostatic stabilization. Metastable films, film rupture, or the transition to sterically stabilized films were also found. The text was submitted by the authors in English.     

When tethered chains meet free ones; the stability of polymer wetting films on polymer brushes

We present a combined experimental and theoretical self-consistent field (SCF) investigation of the wetting behavior of a polystyrene melt (composed of chains with degree of polymerization P) on top of a polystyrene brush (composed of chains with length N) grafted onto a silica surface. The control variables are the grafting density σ of the brush chains and the length of mobile chains P. Experiments show in agreement with the theory that there is a window of complete wetting. Both at very low and at high grafting densities the system remains partial wet. At large degree of polymerization P, there is a difference between the experimental and theoretical results. Theory predicts partial wetting only, whereas the window of complete wetting persists in the experiments even when P >> N. This difference is attributed to the double-well structure of the disjoining pressure as revealed by the SCF theory. With this type of disjoining pressure it is conceivable that a metastable zero contact angle remains present for very long times.     

Chemical and Physical Analysis of Acetate-Oxide Sol-Gel Processing Routes for the Y-Ba-Cu-O System

The formation of three sols by fluorine-free aqueous and non-aqueous processes were analyzed and modified to vary the chemical properties of the sols (inks) to suit a variety of deposition processes such as dip-coating and ink-jet coating/printing. Ink-jet printing requires high wetting angles; choosing the right complexing agents to modify the ink allows the formation of droplets with high wetting angles on the surface. Dip-coating and ink-jet coating require low wetting angles; additives added to the sols reduce wetting angles to 10^∘ and allow complete coverage of the substrate surface. The deposition theories and requirements are briefly discussed, as are some initial tests with the printing and converting of the developed superconducting inks.     

Temperature effects in carbon monoxide and methanol electrooxidation on platinum–ruthenium: influence of grain boundaries

The temperature dependence of methanol and CO monolayer oxidation is studied on carbon-supported PtRu (1:1 atomic ratio) electrodes with different metal percentages (5, 30, and 60 wt.%) in an aqueous H₂SO₄ electrolyte. High-resolution transmission microscopy confirms that at high (30 or 60 wt.%) metal percentage PtRu nanostructures with a high concentration of intercrystalline boundaries are formed. These nanostructures comprise multiple-twinned particles, particles with intersecting randomly oriented intergrain boundaries, or particles with parallel intergrain boundaries. Formation of such nanostructures leads to a decrease of the apparent activation energy of the methanol and CO monolayer oxidation, while the Tafel slope and the reaction order in methanol show minor dependence on the type of nanostructure. Materials with a high concentration of grain boundary regions may be of interest for practical applications in direct methanol or proton exchange fuel cells fed with reformate.     

The application of thermodynamic perturbation theory to the calculation of excess free energy of small systems: 2. Excess free energy and disjoining pressure in the wetting layer of apolar liquid

Isotherms of disjoining pressure in the wetting film of apolar liquid on unmodified and modified solid surfaces were studied based on the thermodynamic perturbation theory. Specific calculations were performed for two systems: (1) the wetting film of decane on aluminum surface and (2) the wetting film of decane on aluminum surface modified by pentanol. It was shown that the results of calculation agree with experimental data.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 850–855.Original Russian Text Copyright © 2004 by Samsonov, Rumyantsev, Khashin.     

Condensation-induced wetting state and contact angle hysteresis on superhydrophobic lotus leaves

In this paper, we demonstrate how condensed moisture droplets wet classical superhydrophobic lotus leaf surfaces and analyze the mechanism that causes the increase of contact angle hysteresis. Superhydrophobic lotus leaves in nature show amazing self-cleaning property with high water contact angle (>150°) and low contact angle hysteresis (usually <10°), causing droplets to roll off at low inclination angles, in accordance with classical Cassie–Baxter wetting state. However, when superhydrophobic lotus leaves are wetted with condensation, the condensed water droplets are sticky and exhibit higher contact angle hysteresis (40–50°). Compared with a fully wetted sessile droplet (classical Wenzel state) on the lotus leaves, the condensed water droplet still has relatively large contact angle (>145°), suggesting that the wetting state deviates from a fully wetted Wenzel state. When the condensed water droplets are subjected to evaporation at room conditions, a thin water film is observed bridging over the micropillar structures of the lotus leaves. This causes the dew to stick to the surface. This result suggests that the condensed moisture does not uniformly wet the superhydrophobic lotus leaf surfaces. Instead, there occurs a mixed wetting state, between classical Cassie–Baxter and Wenzel states that causes a distinct increase of contact angle hysteresis. It is also observed that the mixed Cassie–Baxter/Wenzel state can be restored to the original Cassie–Baxter state by applying ultrasonic vibration which supplies energy to overcome the energy barrier for the wetting transition. In contrast, when the surface is fully wetted (classical Wenzel state), such restoration is not observed with ultrasonic vibration. The results reveal that although the superhydrophobic lotus leaves are susceptible to being wetted by condensing moisture, the configured wetting state is intermediate between the classical Cassie–Baxter and Wenzel states.     

Effect of nanobubbles on friction forces between hydrophobic surfaces in water

Micro- and nanoscale combined hierarchical polymer structures were fabricated by UV-assisted capillary force lithography. The method is based on the sequential application of engraved polymer molds with a UV-curable resin of polyurethane acrylate (PUA) followed by surface treatment with a trichloro(1H,1H,2H,2H-perfluorooctyl) silane in vapor phase. Two distinct wetting states were observed on these dual-roughness structures. One is “Cassie–Wenzel state” where a water droplet forms heterogeneous contact with microstructures and homogeneous contact with nanostructures. The other is “Cassie–Cassie state” where a droplet makes heterogeneous contact both with micro- and nanostructures. A simple thermodynamic model was developed to explain static contact angle, hysteresis, and wetting transition on dual-roughness structures.