William B. Guenther,Chemical Equilibrium. A Practical Introduction for the Physical and Life Sciences,Plenum Press,New York-London (1975), 248 pp., price U.S. $ 23.40

The adsorption and related interfacial behavior of uracil at a mercury electrode/electrolyte solution interface has been studied by differential capacitance and maximum bubble pressure methods in 0.5 M NaF plus 0.01 M Na₂HPO₄ buffer pH 8.0. At concentrations below 24 mM uracil is adsorbed in a flat orientation on the electrode surface and occupies an area of 63 Ų. At higher concentrations and at potentials close to ?0.5 V the adsorbed uracil undergoes a reorientation and adopts a perpendicular stance on the electrode surface where it occupies an area of 39 Ų. In this perpendicular stance uracil undergoes a strong intermolecular stacking interaction with its neighbors similar to that observed between adjacent pyrimidines in nucleic acids.     

Characterization of thin polymer‐like films formed by plasma polymerization of methylmethacrylate: A neutron reflectivity study

The microstructure of the plasma‐polymerized methylmethacrylate (ppMMA) films is characterized using neutron reflectivity (NR) as a function of the plasma reaction time or film thickness. Variation in the crosslink density normal to the substrate surface is examined by swelling the film with a solvent, d‐nitrobenzene (dNB). In the presence of dNB, uniform swelling is observed throughout the bulk as well as at the air surface, and silicon oxide interfaces. The results indicate that the MMA film prepared by plasma polymerization (ppMMA) has a uniform crosslink density from air surface to substrate surface. Additionally, the scattering length density of the plasma‐polymerized MMA film (SLD ≈ 0.750 × 10⁻⁶ Å⁻²) is much lower than that of a conventional PMMA film (SLD = 1.177 × 10⁻⁶ Å⁻²). The increase in film thickness following dNB sorption is 7.5% and at least 36% for the ppMMA and PMMA films, respectively. This suggests that the films formed by plasma polymerization are different from conventional polymers in chemical structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2522–2530, 2004     

A study by voltammetry and the photocurrent response method of copper electrode behavior in acidic and alkaline solutions containing chloride ions

The electrochemical behavior of Cu electrodes in Cl⁻ solutions was studied in a wide range of pH. The results were compared with those obtained in solutions containing F⁻, Br⁻, I⁻ and So²⁻₄ ions at pH 8.5, and discussed in terms of the competitive formation of Cu₂O and CuCl films on the Cu surface and the influence of CuCl on the properties of Cu₂O. At pH 8.5 or higher, Cu₂O was formed first, whereas at pH 5.7 or lower the Cu₂O film was formed on the Cu surface under the CuCl layer which was formed initially. It is believed that the Cu₂O films doped with Cl⁻ ions exhibited poor protective properties against Cu corrosion.     

Surface Charge Changes upon Formation of the Signaling State in Visual Rhodopsin†

The cytoplasmic surface of G protein‐coupled receptors plays a central role for activation and deactivation of the receptor. To understand the molecular mechanisms which underlie these processes, we determined the surface charge density and its changes upon activation directly at the cytoplasmic surface of bovine rhodopsin and correlated these changes with key events in receptor activation. The surface charge density was calculated from the ionic strength dependence of the apparent pK_a of the surface‐bound pH‐indicator dye fluorescein according to the Gouy‐Chapman theory. The surface charge density at pH 6.5 changes by 0.8 ± 0.2 elementary charge/1000 Ų in rod outer segment disk membranes and by 0.4 ± 0.2 elementary charge/1000 Ų in rhodopsin/dodecylmaltoside micelles upon formation of the active metarhodopsin‐II state. By comparison of these surface charge density values determined with and without the native lipid environment, we calculated the charge change to about 1 elementary charge/cytoplasmic rhodopsin surface. The more positive surface charge density in metarhodopsin‐II decreases back to the dark state level of σ = ?2.0 ± 0.2 elementary charges/1000 Ų in the opsin state, providing further evidence that the cytoplasmic surface properties after metarhodopsin‐II decay resemble almost those of the dark state.     

Giant Crystalline Molecular Rotors that Operate in the Solid State

Molecular motion in the solid state is typically precluded by the highly dense environment, and only molecules with a limited range of sizes show such dynamics. Here, we demonstrate the solid-state rotational motion of two giant molecules, i.e., triptycene and pentiptycene, by encapsulating a bulky N-heterocyclic carbene (NHC) Au(I) complex in the crystalline media. To date, triptycene is the largest molecule (surface area: 245 Ų; volume: 219 ų) for which rotation has been reported in the solid state, with the largest rotational diameter among reported solid-state molecular rotors (9.5 Å). However, the pentiptycene rotator that is the subject of this study (surface area: 392 Ų; volume: 361 ų; rotational diameter: 13.0 Å) surpasses this record. Single-crystal X-ray diffraction analyses of both the developed rotors revealed that these possess sufficient free volume around the rotator. The molecular motion in the solid state was confirmed using variable-temperature solid-state ²H spin-echo NMR studies. The triptycene rotor exhibited three-fold rotation, while temperature-dependent changes of the rotational angle were observed for the pentiptycene rotor.     

Synthesis of Sub‐nanometer Porous Carbon Film for Energy Storage

Carbon‐based supercapacitors are a kind of supercapacitors with very promising applications because of their low cost, good stability and adjustable properties. Simple and rapid syntheses of carbon materials with a high surface area and narrow pore size distribution are of great significance to practical applications of carbon‐based supercapacitors. Here we report a new strategy to synthesize sub‐nanometer porous carbon films (Snp‐CF) via a condensation reaction under mild conditions. Carbon films exhibit a narrow pore size distribution (6.6 Å) and high surface area (508 m² g^?1) after annealing at 700 °C. Snp‐CF‐700 displays a good specific capacity and excellent cycle performance (130 F g^?1 after 5000 cycles, 118 % of initial 110 F g^?1).     

Molecular organization and aggregation of mucin at air–water interface in the presence of chromium(III) complexes

The interfacial organization of mucin (glycoprotein) in the presence of chromium(III) complexes has been assessed from the surface pressure–molecular area (π–A) isotherms in Langmuir films at air–water interface and the surface energy of their LB films through contact angle measurements. At pH 7.0, the electrostatic interaction of [Cr(en)₃]Cl₃ with mucin was found to bring about changes in the average surface area from 3.26 to 1.47 nm²; suggesting the possible formation of large aggregates of mucin. Adsorption experiments using surface potential measurements reveal that [Cr(en)₃]Cl₃ binds at a much faster rate to the available binding sites in mucin when compared to [Cr(salen)(H₂O)₂](ClO₄) which binds coordinatively to mucin.     

Influence of the electrolyte composition of the subphase on the structure of 2D films of fullerene C60

The morphology of 2D films of fullerene C₆₀ on interfaces has been studied by Brewster angle microscopy and atomic force microscopy. Fullerene C₆₀ tends to aggregate, forming supramolecular structures with a surface area per C₆₀ molecule from 21.6 to 2900 Ų. As the area per C₆₀ molecule decreases, monomolecular clusters gradually transform into multiplayer structures. The introduction of an electrolyte into the system prevents the formation of fullerene globules and favors the formation of more homogeneous films.     

Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO₂) films. The films were formed on Corning glass and p‐Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6×10^?2 Pa and at different substrate temperatures in the range 303 – 673 K. The films formed at 303 K were X‐ray amorphous whereas those deposited at substrate temperatures ≥ 473 K were transformed into polycrystalline nature with anatase phase of TiO₂. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO₂. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO₂/p‐Si sandwich structure was fabricated and performed current–voltage and capacitance–voltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8 × 10^?6 to 5.4 × 10^?8 A/cm² with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler‐Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterisation of Xerogels Derived from Sucrose Templated Sol-Gel Synthesis

This work presents the results of the nanostructural characterisation of the effect of sucrose as a template added to a sol derived from a tetraethoxysilane acid catalysed process. By increasing the sucrose template ratio, N₂ adsorption isotherms showed that the xerogel samples changed from a micropore to a mesopore nanostructure as evidenced by the formation of hysteresis at 0.5 partial pressure. In turn, this led to a direct increase in surface areas, pore volumes and average pore sizes. Sucrose has two molecular components of the same molecular weight: D-fructose and D-glucose. D-fructose resulted in the formation of higher pore volumes and pore sizes, while D-glucose formed higher surface area xerogels. Depending of the template ratio employed in the xerogel synthesis, average pore radius ranged from 8.8 to 26 Å, while surface areas increased by over two fold up to 750 m²·g^?1. However, pore volumes increased by as much as six fold, from 0.15 to almost 1 cm³·g^?1.     

Biodetergent IV. Monolayers of corynomycolic acids at the air-water interface

The effects of alkyl chain length and of differences in the length of the two alkyl chains on the formation of a monolayer of chemically synthesized corynomycolic acid (2-alkyl-3-hydroxy fatty acid) at the air-water interface were examined. Hydrophobic interactions between the two alkyl chains are required for the formation of a condensed film, which is most stable when the total number of carbon atoms in the two alkyl chains is 25 or more and the difference in their lengths is one. Syn-isomers form condensed films but usually not anti-isomers. However, films may also be formed by the anti-isomer when the alkyl chain at the carboxy group (the 2-position) is longer than the alkyl chain at the hydroxy group (the 3-position). That is, the contribution of anti-isomers to condensed film formation depends on the polar carboxy group which has greater involvement in this formation. The extrapolated area for the condensed film of corynomycolic acid was 40 Ų per molecule, thus confirming that both the carboxy and hydroxy groups are present on the water surface when a bipolar monolayer is formed.     

Adsorption of Eu(III) on titanate nanotubes studied by a combination of batch and EXAFS technique

The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure(EXAFS) techniques.Macroscopic measurements show that the adsorption is ionic strength dependent at pH < 6.0,but ionic strength independent at pH > 6.0.The presence of humic acid(HA) /fulvic acid(FA) increases Eu(Ⅲ) adsorption on TNTs at low pH,but reduces Eu(Ⅲ) adsorption at high pH.The results of EXAFS analysis indicate that Eu(Ⅲ) adsorption on TNTs is dominated by outer-sphere surface complexation at pH < 6.0,whereas by inner-sphere surface complexation at pH > 6.0.At pH < 6.0,Eu(Ⅲ) consists of ～ 9 O atoms at REu?O ≈ 2.40  in the first coordination sphere,and a decrease in NEu-O with increasing pH indicates the introduction of more asymmetry in the first sphere of adsorbed Eu(Ⅲ).At long contact time or high pH values,the Eu(Ⅲ) consists of ～2 Eu at REu-Eu ≈ 3.60  and ～ 1 Ti at REu-Ti ≈ 4.40 ,indicating the formation of inner-sphere surface complexation,surface precipitation or surface polymers.Surface adsorbed HA/FA on TNTs modifies the species of adsorbed Eu(Ⅲ) as well as the local atomic structures of adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids.Adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids forms both ligand-bridging ternary surface complexes(Eu-HA/FA-TNTs) as well as surface complexes in which Eu(Ⅲ) remains directly bound to TNT surface hydroxyl groups(i.e.,binary Eu-TNTs or Eu-bridging ternary surface complexes(HA/FA-Eu-TNTs)).The findings in this work are important to describe Eu(Ⅲ) interaction with nanomaterials at molecular level and will help to improve the understanding of Eu(Ⅲ) physicochemical behavior in the natural environment.     

The effect of impregnation conditions on the surface structure of silica-supported CuO catalysts

CuO/SiO₂ catalysts with varying amounts of copper were prepard using meso- and microporous silica supports at pH > 10 and pH = 4.5. Structural and textural changes were followed using X-ray diffraction, TG and DTA techniques. Impregnation for periods > 10 days at high pH produces crystalline catalysts with two distinct peaks at d-spacings of 2.33 and 2.03 Å resulting from a surface silicate which is structurally stable up to 800°C. At copper concentrations > 5% CuO also forms. Catalysts prepared at pH = 4.5 are amorphous to X-rays in spite of the presence of CuO which may either be < 50 Å or from a surface solid solution. The copper ammine complex, if adsorbed on mesoporous silica, attains its maximum coordination number as [Cu(NH₃)₄(H₂O)₂]²⁺, whereas on microporous silica it loses the two water molecules as a result of pore restrictions. The surface complex releases its coordinated ammonia exothermally in the temperature range 200–400°C, whereas chemisorbed ammonia is evolved endothermally at ～280°C. Ligand water is evolved at <200°C. An exotherm at ～545°C is observed for all catalysts, resulting form the shrinkage of the solid/void matrix which disappears upon aging. Increase of copper content to 22.7% at high pH lowered the temperature of constant weight attainment from 1000°C for the pure silica to 750°C.     

On the nature of the processes occurring in silver doped SiO<Subscript>2</Subscript> films under heat treatment

The processes taking place on air-heating of SiO₂−Ag⁺ films and xerogels produced from the SiO₂ sols of different pH (3.7 or 9.5) were investigated. Silver nanoparticles 10–40 nm in size tolerant to oxidation at temperatures above 600 °C were found to be formed in the systems whatever the pH value of the starting sol. SiO₂ crystallization giving the cristobalite phase in the temperature range from 500 to 800 °C was shown to proceed only in the films produced from the acidic sol, while in those formed from the alkali one SiO₂ remained amorphous. A mechanism by which the formation of Ag nanoparticles and the cristobalite phase occurs in the films at the oxidative conditions is suggested.     

Impact of Various Parameters Over the Adsorption of Polyvinylpyrrolidone onto Kaolin

The adsorption of water-soluble polymer, polyvinylpyrrolidone having molecular mass 9.1 ± 1.43 × 10³Kg mole^?1 on kaolin has been investigated. The effect of different parameters like pH, molecular mass of polymer and pre-heat treatment on the adsorption of PVP has been deliberated. The 20.7% decrease in adsorption in pH ranging from 2–10 have been found, which was an indication of the fact that with the increase in pH the kaolin surfaces sites charge amount and ultimately sign changes. Maximum adsorption was observed at pH 5.6 that was also molecular mass dependent. By increasing the pretreatment temperature, the amount of polymer adsorbed was also increased. However, above the specific temperature adsorption of PVP was decreased and attributed to decrease in specific surface area of kaolin.     

Plasma Polymerization on Metals

An ellipsometric technique is described for accurately measuring the film thickness of plasma-polymerized polymers on metallic substrates. The index of refraction n and absorption index Kof the plasma polymer film can also be studied by ellipsometry. Films of plasma polystyrene and polyepichlorohydrin were deposited on evaporated aluminum substrates and their thickness and optical constants determined. Plasma polystyrene films from 20 to 1600 Å thick have optical constants n = 1.63 and K =0 independent of film thickness. Plasma polyepichlorohydrin films over the same range of thickness give n ? 1.70 and K? 0.01. By utilizing the ellipsometric method the effect of plasma polymer film thickness on surface energy properties was determined. Advancing contact angle measurements and surface energy analysis detail the polar γSV^P dispersion γSV^Pcontributions to the solid-vapor surface tension γSV = γSV^d + γSV^P Polystyrene and polyepichlorohydrin films on etched aluminum. For thin plasma polystyrene films (600 Å), anomalies in the calculated surface energy are discussed and related to possible surface nonuniformity caused by film growth. Thicker films of plasma polystyrene are shown to have normal surface energy properties as does plasma poly-epichlorohydrin over the entire range of film thickness measured. The adhesive and cohesive properties of plasma polystyrene and polyepichlorohydrin films are discussed as estimated from a lap-shear bond strength study. Etched aluminum coated with various thicknesses of these two polymers and bonded with an epoxy-phenolic adhesive shows a decreasing shear strength with increasing plasma film thickness but begins to level off at ～1600 psi for films >1600 Å thick.     

Molecular basis of healing and fracture at polymer interfaces

The interdiffusion of polymer chains across a polymer–polymer interface, and subsequent fracture to re-create the interface is reviewed. In particular, films formed via latex coalescence provide a very large surface area. Of course, latex film formation is a very important practical problem. Healing of the interface by interdiffusion is treated using the de Gennes reptation theory and the Wool minor chain reptation model. The self-diffusion coefficients of polystyrene and the polymethacrylates obtained by small-angle neutron scattering, SANS, direct non-radiative energy transfer, DET, and other techniques are compared. Reduced to 150,000 g/mol and 135°C, both polystyrene and poly(methyl methacrylate) have diffusion coefficients of the order of 10^?16?10^?17 cm²/sec. Variations in the diffusion coefficient values are attributed to the experimental approaches, theoretical treatments and molecular weight distribution differences. An activation energy of 55 kcal/mol was calculated from an Arrhenius plot of all polystyrene data reduced to a number-average molecular weight of 150,000 g/mol, using an inverse square molecular weight conversion method. Interestingly, this is in between the activation energies for the α and β relaxation processes in polystyrene, 84 and 35 kcal/mol, respectively. Fracture of polystyrene was considered in terms of chain scission and chain pull-out. A dental burr apparatus was used to fracture the films. For low molecular weights, chain pull-out dominates, but for high molecular weights, chain scission dominates. At 150,000 g/mol, the energy to fracture is divided approximately equally between the two mechanisms. Above a certain number average molecular weight (about 400,000 g/mol), the number of chain scissions remains constant at about 10²⁴ scissions/m³. Energy balance calculations for film formation and film fracture processes indicate that the two processes are partly reversible, but have important components of irreversibility. From the interdiffusion SANS data, the diffusion rate is calculated to be about 1 Å/min, which is nine orders of magnitude slower than the dental burr pull-out velocity of about 0.8 cm/sec.     

Microporous Cyclic Titanium‐Oxo Clusters with Labile Surface Ligands

By using ethylene glycol and monocarboxylic acid as surface ligands, a series of cyclic Ti‐oxo clusters (CTOC) with permanent microporosity are successfully synthesized. With a cyclic {Ti₃₂O₁₆} backbone made of eight connected Ti₄ tetrahedral cages that are arranged in a zigzag fashion, the clusters have a “donut” shape with an inner diameter of 8.3 Å, outer diameter of 26.9 Å and height of 10.4 Å. While both inner and outer walls of the “donut” clusters are modified by double‐deprotonated ethylene glycolates, their upper and lower surfaces are bound by carboxylates and mono‐deprotonated ethylene glycolates. The clusters are readily packed into one‐dimensional tubes which are further arranged in two different modes into crystalline microporous solids with surface areas over 660 m² g⁻¹, depending on the surface carboxylates. The solid with olefin‐bearing carboxylates exhibits a superior CO₂ adsorption capacity of 40 cm³ g⁻¹ at 273 K under 1 atm. Moreover, the mono‐deprotonated ethylene glycolates on the clusters are demonstrated to be highly exchangeable by other alcohols, providing a nice platform for creating microporous solids or films with a wide variety of surface functionalities.     

Compression of Self‐Assembled Nano‐Objects: 2D/3D Transitions in Films of (Perfluoroalkyl)Alkanes—Persistence of an Organized Array of Surface Micelles

Understanding and controlling the molecular organization of amphiphilic molecules at interfaces is essential for materials and biological sciences. When spread on water, the model amphiphiles constituted by C_nF_2n+1C_mH_2m+1 (FnHm) diblocks spontaneously self‐assemble into surface hemimicelles. Therefore, compression of monolayers of FnHm diblocks is actually a compression of nanometric objects. Langmuir films of F8H16, F8H18, F8H20, and F10H16 can actually be compressed far beyond the “collapse” of their monolayers at ～30 Ų. For molecular areas A between 30 and 10 Ų, a partially reversible, 2D/3D transition occurs between a monolayer of surface micelles and a multilayer that coexist on a large plateau. For A<10 Ų, surface pressure increases again, reaching up to ～48 mN m^?1 before the film eventually collapses. Brewster angle microscopy and AFM indicate a several‐fold increase in film thickness when scanning through the 2D/3D coexistence plateau. Compression beyond the plateau leads to a further increase in film thickness and, eventually, to film disruption. Reversibility was assessed by using compression–expansion cycles. AFM of F8H20 films shows that the initial monolayer of micelles is progressively covered by one (and eventually two) bilayers, which leads to a hitherto unknown organized composite arrangement. Compression of films of the more rigid F10H16 results in crystalline‐like inflorescences. For both diblocks, a hexagonal array of surface micelles is consistently seen, even when the 3D structures eventually disrupt, which means that this monolayer persists throughout the compression experiments. Two examples of pressure‐driven transformations of films of self‐assembled objects are thus provided. These observations further illustrate the powerful self‐assembling capacity of perfluoroalkyl chains.     

Analysis of Aluminum-Brass Corrosion Products in Sea Water and in Chloride Solutions

Abstract

A separation and chemical analysis method has been developed of corrosion products forming on aluminum brass surfaces immersed in sodium sulfate solutions at pH= 7.25 (simulating river water) and in sea water at pH= 8.2. This method is based upon a selective solubilization of various oxidation compounds with the aid of proper solvents (i.e. dissolving the metal matrix only to a negligible extent).

These analyses can be performed on oxidation films of more than 100 Å thickness. The following solvents were used:

1) Methanol for solubilization of Na⁺, Cu⁺⁺ and Zn⁺⁺ chlorides and sulfates;

2) Glycine to solubilize bivalent metal compounds:Cu and Zn oxydes oxysulfates, oxycarbonates, oxychlorides of Cu and Zn;

3) NH₄ OH to solubilize Cu⁺⁺ and aluminum compounds.

A fair agreement was observed between the formulae derived by stoichiometric calculation applied to chemical analyses and the values obtained by X-ray analysis.

Agreement was satisfactory for all compounds, except aluminum, determined by chemical analysis and identified by X-rays only in very thick oxidation films (≥ 10³ Å). The role of chemical analysis is therefore determinant to finalize the formation mechanism of aluminum brass passivation films.