Understanding of surface tension?

The importance of the molar dimensions for surface properties of not too large molecules is stressed. The understanding of surface properties of pure liquids is described in molar units with a simple model of normal liquids. The increasing knowledge makes it necessary to use idealized models. A hypothesis is given for the temperature constancy of the surface energy of small molecules without H-bonds, and a model is developed for the free energy σ_m and its temperature dependency. This seldom example of the direct measurement of the isothermic work or the free energy could help to illustrate the difference between energy and free energy. Received: 24 July 2000 Accepted: 26 October 2000     

Enzymatic surface modification of Kevlar fibers

Horseradish peroxidase catalyzed grafting of acrylamide (AM) onto Kevlar fibers has been studied. The modified fiber has been characterized with scanning electron microscopy (SEM), elemental analysis and the grafting yield. From the SEM micrographs, the surface of the grafted Kevlar fiber is rougher than that of the untreated fiber, and the elemental analysis indicated that the nitrogen content of the treated fibers is higher than that of the untreated fiber. All the results suggested that AM must have been grafted onto the Kevlar surface through HRP-mediated radical initiated grafting reaction. The probably mechanism of HRP catalyzed grafting of AM onto Kevlar surface is proposed.     

A reëxamination of surface conductivity

The problem of calculating the surface conductivity at an electrolyte-solid interface is reconsidered. Some of the limitations of the existing definitions and theoretical approaches are pointed out, and the problem is reworked to include the effects of non-zero space charge and ion concentration on the conductivity. An approximate method is presented for calculating the mobility of an ion in a non-neutral environment. These considerations are illustrated by the problem of the local conductivity in a cylindrical pipe and the local conductivity near a half plane.

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Zusammenfassung Das Problem der Berechnung der Oberflächenleitfähigkeit in einer Grenzfläche Elektrolyt/Festkörper wird betrachtet. Einige Einschränkungen und Gültigkeitsgrenzen der existierenden Definitionen und der theoretischen Näherungen werden ausgeführt, und das Problem ist wieder aufgegriffen, um die Auswirkung einer nicht verschwindenden Raumladung und der Ionenkonzentration auf die Leitfähigkeit einzubeziehen. Eine Näherungsmethode für die Berechnung der Beweglichkeit eines Ions in nicht neutraler Umgebung wird präsentiert. Diese Betrachtungen sind durch die Probleme der lokalen Leitfähigkeit in einer zylindrischen Röhre und nahe einer Halbebene illustriert.

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The research reported in this paper was supported by Grant 21869 of The National Science Foundation.     

Heterogeneous reaction of NO_2 on the surface of NaCl particles

Sodium chloride is the major constituent of sea salt particles in atmospheric environment, with an esti- mated annual contribution of 1012 kg of sea salt parti- cles to the atmosphere[1]. Many studies have shown a significant chloride deficit in these particles when compared to bulk seawater[2,3]. This deficit has been attributed to reactions with NOx and SO2[4]. Simulta- neously, NO2 is one of the main pollutants of mobile vehicles. Reaction (1) may be particularly important to the atmosph…     

Ab initio intermolecular potential energy surface of He-LiH

The intermolecular potential energy surface of He-LiH complex was studied using the full-electronic complete forth-order Miller-Plesset perturbation (MPPT) method.In ab initio calculations,the bond length of LiH was fixed at 0 159 5 nm.The potential has two local minima of Vm=-179.93 cm for the linear He LiH geormetrv at Rm=0.227 nm and Vm=-10.44 cm-1 for the linear He-HL1 geometry at Rm=0.516 nm The potemal exhibits strong anisotropy The analytic potential function with 31 parameters was determined by fitting to the calculated ab,mtio potentials The influence of variation of LiH bond length on the potential energy surface was also studied     

The role of the activity coefficients of surface groups in the formation of surface charge of oxides. Part II: Ion exchange and ζ potentials

A new method is developed to calculate the surface charge densities and potentials of oxides in contact with electrolyte solution as functions of pH and ionic strength. For low ionic strength and not too far from p.z.c. (up to 3 pH units for 10^–3 mol dm^–3 NaCl) the previous model (Kosmulski, 1992) neglecting the ion exchange can be used but farther from p.z.c., correction for the ion exchange is necessary for some systems. This correction leads to increase of the calculated titration charge (that is not necessarily equal to the surface charge), but does not affect the diffuse charge and potential.     

Influence of strong heterocoordination on surface properties of Li–Pb melts

The influence of the strong heterocoordination tendency of the Li–Pb liquid alloy on its surface properties has been studied using a statistical thermodynamic model based on compound formation and that based on the layered structure near the interface. In addition to the already proposed saltlike structure Li₄Pb compound formed in the liquid alloy, the study shows that the compound Li₃Pb also has a profound influence on the thermodynamic properties of the liquid alloy. The surface study suggests that the formed compounds in the liquid alloy segregate to the surface about 0.8 atomic fraction of Li. The calculated surface tension of the liquid alloy exhibits a pronounced hump above equiatomic composition.     

Microarray of DNA probes on carboxylate functional beads surface

The microarray of DNA probes with 5' -NH2 and 5' -Tex/3' -NH2 modified terminus on 10 um carboxylate functional beads surface in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) is characterized in the preseni paper. it was found that the microarray capacity of DNA probes on the beads surface depends on the pH of the aqueous solution, the concentra-tion of DNA probe and the total surface area of the beads. On optimal conditions, the minimum distance of 20 mer single-stranded DNA probe microarrayed on beads surface is about 14 nm, while that of 20 mer double-stranded DNA probes is about 27 nm. If the probe length increases from 20 mer to 35 mer, its microarray density decreases correspondingly. Mechanism study shows that the binding mode of DNA probes on the beads surface is nearly parallel to the beads surface.     

Relationships of surface oxygen vacancies with photoluminescence and photocatalytic performance of ZnO nanoparticles

ZnO is one of important semiconductor materials,applied widely in the fields such as the cerams, piezo-electric sensors, catalysts and luminescence apparatus.ZnO nanoparticles not only are ideal materials to pre-pare newly electronic apparatus[1], but als…     

Solution and surface properties of amphiphilic drug – nonelectrolyte systems

The surface tension values of amphiphilic drugs amitriptyline hydrochloride (AMT, an antidepressant) and promethazine hydrochloride (PMT, a phenothiazine) solutions in the presence of different fixed concentrations of alcohols (ethanol to octanol) and sugars were measured by the ring detachment method. The results indicated that long-chain alcohols form mixed micelles with both the drugs (as critical micelle concentration, cmc, decreases in their presence). Short-chain alcohols remain in aqueous phase and almost constant cmc values were obtained. Sugars, by increasing the hydrophobic interactions, decrease the drug cmcs. Maximum surface excess concentration at the air/solution interface (Γ_max) decreases for long-chain alcohols and sugars, but remains constant for short-chain alcohols. The minimum area per drug molecule (A _min) follows the opposite trend.     

Path dependence of surface–tension scaling in binary mixtures

A mean-field free-energy functional for an n-component mixture with an integral non-local interaction is introduced and then written explicitly for a binary mixture. We use this functional to calculate the liquid–vapor surface tension with parameters chosen to model CO₂/n–C₄H₁₀ and CO₂/n–C₁₀H₂₂, and we examine the scaling of the surface tension as a function of the difference in density between the liquid and vapor phases as various critical points are approached. Each critical point is approached on either a constant-temperature or constant-pressure path; we investigate the path dependence of the scaling behavior. For the constant-temperature paths in the CO₂/n–C₄H₁₀ mixture, we compare our calculated results with experimental data. We find no significant dependence of the scaling on the path to the critical point. We note that the asymptotic scaling holds for a larger range of densities the higher the temperature of the critical point.     

A novel family of green ionic liquids with surface activities

Ionic liquids have many unique properties as a new and remarkable class of environmental benign solvents,which promises widespread applications in industry and other areas. However,the ionic liq-uids with surface activity are rarely reported. In this work,a series of novel ionic liquids was synthe-sized by using N-methyl-2-pyrrolidone and alkyl bromide. The physical properties of this family of ionic liquids have been characterized,which shows that these compounds have ionic liquids characteristics,surface activity and biocompatibility.     

Improving the performance of perovskite solar cells by surface passivation

NiO has a perfect-aligned energy level with CH3 NH3 Pb I3 perovskite such that it serves as a hole transport layer(HTL),but Ni O-based perovskite solar cells(PSCs)still suffer from low efficiency due to the poor interface contact between the perovskite layer and the Ni O HTL,and haphazardly stacked perovskite grains.Herein,poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1,3}-thiadiazole)](PFBT)is introduced between the Ni O and perovskite layers in the form of a polymer aggregate to enhance perovskite crystallinity and decrease the interface charge recombination between perovskite and Ni O in PSCs,resulting in an improved performance.Moreover,PFBT modified perovskite films showed sharper,smoother,and more compact crystalline grains with fewer grain boundaries,leading to the decreased nonradiative recombination.This study offers a simple strategy to achieve highly efficient PSCs with the incorporation of polymer semiconductor aggregates to passivate the interface between the perovskite and Ni O layers.     

Quantum-chemical study of the singlet potential energy surface of the nitrene—dioxygen system

The potential energy surfaces of the HN—O₂ and PhN—O₂ systems were calculated by the MP2 and B3LYP methods. The mechanism of photooxidation of azides was refined. Photooxidation produces the nitrene—O₂ adducts with dioxaziridine and non-cyclic structures. The parameters of IR spectra of the adducts were calculated. The rearrangement of dioxaziridine to a nitro compound is likely a reason for chemiluminescence accompanying the photooxidation of azides.     

Electrochemical determination of the surface composition of Pd–Pt core–shell nanoparticles

Different amounts of Pt atoms were deposited onto the surface of Pd nanoparticles supported on carbon black by hydroquinone reduction method in anhydrous ethanol. Here, we surveyed electrochemical probing of surface compositions of Pd–Pt surface alloys. They were calculated from hydrogen desorption, carbon monoxide adlayer oxidation, and reduced carbon dioxide oxidation charges. The surface composition of Pt drastically increased up to Pt[0.3]/Pd/C (23.1 at.% of Pt) and then approached that of pure Pt with the moderate rate of increase.     

Calculation of the molecular exchanging energy of binary surfactants system on the surface monolayer of aqueous solution

By using the binary anionic/cationic surfactants system CH3(CH2)nOSO_3/CH3(CH2)nN (CH3)3 as an ex-ample, the molecular exchanging energy (ε) of adsorption on the surface monolayer of aqueous solu-tion has been studied. ε can be obtained with two methods. One is from the relationship between ε and the molecule interaction parameter (β). This relationship is founded by considering that the adsorption of mixed surfactants on the surface monolayer of solution satisfies the dimensional crystal model condition under which β can be obtained by testing the surface tension of solution. The other is directly from the molecular structure of surfactants with the Lennard-Jones formula. The results for the studied system show that these two methods coincide well.     

Influence of phosphorus concentration on the state of the surface layer of Pd–P hydrogenation catalysts

Phase composition and surface layer state of the Pd–P hydrogenation catalyst formed at various P/Pd ratios from Pd(acac)₂ and white phosphorus in a hydrogen atmosphere were determined. Palladium on the catalyst surface is mainly in two chemical states: as Pd(0) clusters and as palladium phosphides. As the P/Pd ratio increases, the fraction and size of palladium clusters decrease, and also the phase composition of formed palladium phosphides changes: Pd₃P_0.8 → Pd₅P₂ → PdP₂. The causes of the modifying action of phosphorus on the properties of palladium catalysts for hydrogenation of unsaturated compounds were considered.     

Complex surface engineering meets simple and beautiful surface chemistry

Surface chemistry of solids is the fundamental for processes on solid surfaces and properties of solid surfaces,such as heterogeneous catalysis,electrochemistry,corrosion,thin film growth,sensing,friction and lubrication[1].Understanding surface chemistry of solids is not only of great scientific interest,but also of important technological value for optimizing surface properties and processes.Due to the complexity of solid surface structures,it is challenging to unambiguously elucidate the surface chemistry of surface properties and processes at a molecular level.