Increase In Surface Concentration Research Articles

Effect of added sodium chloride on the molecular environment and photoionization of N,N,N′,N′-tetramethylbenzidine in micellar solutions as studied by electron spin echo and electron spin resonance spectroscopy

The electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the cation radical of N,N,N′,N′-tetramethylbenzidine (TMB) in frozen sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) micelles were studied as a function of sodium chloride concentration. TMB+⋅ was produced by photoionization at 350 nm of the parent compound in the micelles at 77 K. From the ESEM analysis it is found that the cation–water interactions increase with salt addition in both anionic and cationic micelles to a maximum near 0.2 M NaCl and then decrease somewhat. The increase is interpreted in terms of an increase in the water density at the micellar surface due to an increased surface concentration of hydrated counterions. The decrease may be due to TMB moving further from the polar micellar surface with added salt. From ESR spectra the photoionization yields of TMB at 77 K were determined. For DTAC micelles the yields are found to decrease with salt addition as expected from electrostatic considerations. For SDS micelles the photoionization yields increase for salt concentrations up to about 0.15 M and decrease for greater salt concentrations up to 0.5 M. The initial increase in cation yield correlates with electrostatic expectations. The decrease may be due to TMB moving further from the polar micellar surface with added salt. The possible effect of differing TMB protonation equilibria between anionic and cationic micelles on the photoionization yields was found to be unimportant by adjusting the bulk solution pH. An important conclusion is that salt addition can be used to optimize charge separation for photoionized solutes in anionic micelles.

Adsorption isotherms of insulin onto various materials.

Insulin adsorption isotherms on various materials have been measured to begin to clarify the role of material surface energy in insulin aggregation. Using 125I-insulin and direct gamma-counting of the exposed material, more insulin (per unit area) was adsorbed to hydrophobic materials (Teflon, Silastic) than to the hydrophilic ones (polyacrylamide, glass) from insulin solutions ranging from 0.1 to 100 U/ml. For example, after 30 min at room temperature, Teflon disks adsorbed 4.0 X 10(4) microU/cm2 and glass beads adsorbed 3.0 X 10(3) microU/cm2 from a phosphate-buffered, 100-U/ml solution (pH 7.4). The Teflon value exceeded, by a factor of six, an estimated plateau surface concentration based on the molecule area (750 A2), suggesting the occurrence of multilayer adsorption. Changing the buffer to acetate and lowering the pH to 3.5 resulted in an increased surface concentration, while the addition of glutamic or aspartic acid at pH 3.5 reduced the surface concentration to be comparable with that observed on glass and less than that observed on Teflon from phosphate buffer. Increasing the temperature to 37 degrees C resulted in a small decrease in adsorption, consistent with the exothermic adsorption of other proteins on similar materials. However, the significance of the adsorbed molecules in nucleating aggregate formation relative to other contributing factors remains to be assessed.

Kinetic Study of the Oxidation of Formate by Iodine in Micellar Solutions of Alkyltrimethylammonium Chlorides

Abstract The spectrophotometric study was made of the oxidation of formate by iodine in micellar solutions of decyl- and dodecyltrimethylammonium chlorides. In the presence of the cationic surfactant micelles, the reaction was found to take place only at the micellar surface according to the same mechanism as in water. The experimental second-order rate constant rose steeply to a maximum at the critical micelle concentration and then decreased monotonously with increasing surfactant concentration. A tentative estimation based on a charged-phase separation model led to the true second-order rate constant in micellar phase of 0.03–0.07 mol−1 dm3 s−1 at 30 °C, which is comparable with that in water. Thus the observed rate enhancement in cationic surfactant solutions can be interpreted in terms of an increase in surface concentration of the formate ion arising from an electrostatic interaction with the micellar ion. The micellar effects on the formation constant of triiodide ion are also discussed.

Effects of pressure and surface initiation efficiency on the flowing H2O2+ NO2+ CO + N2 chain reaction system

The yields of CO2 from the H2O2+ NO2+ CO reaction system in flowing carrier gas at 298 K have been measured at total pressures (P) of 13.3, 40.0 and 93.3 kPa. The variations of the yield as functions of [NO2] and [S](S = acetaldehyde or diethyl ether) have been shown to indicate that the efficiency of conversion of H2O2 to OH radicals in the heterogeneous initial step H2O2+ NO2→ OH + HNO3(1) is independent of total pressure for a particular surface activity. The results are consistent with the pressure dependence of k2 for the propagation step CO + OH → CO2+ H (2) indicated by other work. For the rate constant of the termination reaction OH + NO2(+ M)→ HNO3(+ M)(4) low apparent values (k′4) are indicated compared with literature values of k4. At P= 40.0 kPa, for three surfaces of apparent efficiencies of ca. 20%, ca. 53% and ca. 81% in converting H2O2 to OH in reaction (1), k′4/k4 values were ca. 0.45, ca. 0.65 and ca. 0.85, respectively. This trend is interpreted in terms of decreasing activity of these surfaces for adsorption of H2O2, producing decreasingly localized reaction zones: depletion of [NO2] in the reaction zone depresses k′4/k4 while increased surface concentrations of H2O2 decrease the apparent H2O2 to OH conversion efficiency by inducing an additional route for destruction of the active centre involved in reaction (1).

Influence of phosphorus additives on the properties of Fe−Sb−O oxide catalysts

Modification of the surface of Fe−Sb−O oxide catalysts by phosphorus additives increases the yield of acrylonitrile in the oxidative ammonolysis of propylene, which can be attributed to the increase of the surface concentration of weakly acidic aprotic centers, viz. Sb3+ ions.

Antimony Diffusion from Spin‐On Doped Oxide

A new antimony diffusion process using spin‐on doped oxide source was characterized and developed. Diffusion is enhanced in dilute oxidizing ambient due to increased surface concentration while diffusivity remains essentially the same in both nitrogen and dilute oxidizing ambient. Wright etch reveals no diffusion induced dislocation when surface concentration is less than . The thinner and less concentrated glass diffused in lower oxygen concentration ambient is less prone to glass devitrification. This process was proven to be suitable for buried layer formation in the fabrication of bipolar integrated circuits.

Low energy ion scattering study of Be and Sn segregation in their alloys with Cu

A quantitative study of the segregation of Be and Sn in their respective alloys with Cu has been carried out using low energy ion scattering spectroscopy (LEIS) as an experimental tool for surface analysis. Both Be and Sn show a somewhat unexpected behaviour which cannot be accounted for within the framework of classical segregation theories [1]. The Be segregation is completely driven by its surface oxidation: at the very surface of Cu-Be samples (with a bulk concentration of 12.5 mole% Be) and after equilibrium conditions have been reached, only oxygen can be detected. As far as Sn segregation in Cu-Sn alloys is concerned, one observes an unusually pronounced increase in the surface concentration of Sn with increasing temperature: in a sample (with a bulk concentration of 4.0 mole% Sn) the Sn surface concentration increases from about 17 mole% at room temperature till 85 mole% at 350°C. Moreover, the appearance of a Sn-Sn double collision peak in the low energy ion spectra indicates a certain ordering of the segregated species.

Rate of carburizing of steel

1. The coefficient of mass transfer decreases during carburizing with increasing surface concentrations of carbon in the steel due to the effect of the adsorbed carbon on the rate of the reaction. 2. With rising temperatures the variation of the mass transfer coefficient with the surface concentration of carbon increases.

The passive state of stainless steels

With the advent of surface-sensitive techniques it has become possible to determine the surface composition of alloys. Analyses using electron spectroscopy for chemical analysis of CrNiMo alloyed steels exposed in acids and neutral solutions show that the reaction products formed on the surface consist mainly of chromium oxide and hydroxide. Nickel is not present in the passive films. The molybdenum content in the oxide is of the same order of magnitude as in the alloy. It is suggested that the beneficial effect of molybdenum is not related to the molybdenum content in the oxide. It is shown that the alloy elements nickel, molybdenum and chromium are accumulated in the metal phase underneath the oxide and that the enrichment of chromium seems to be dependent on the molybdenum content of the alloy. The enrichment of these elements is explained by selective dissolution of iron during the active phase preceding passivation. It is postulated that increased surface concentrations of chromium and molybdenum in the metal synergistically lower the dissolution rate in the active phase and provoke the formation of passive films of high chromium content both at first passivation and during repassivation in conditions of pitting and crevice attack.

The change in the interface-state Fermi level of M.I.S. solar cells when going from dark to illuminated conditions

Current/voltage characteristics obtained under dark and illuminated conditions have been examined for Al-p-Si M.I.S. solar cells. The results show that the voltage drop across the oxide is changed, owing to the increased surface concentration of minority carriers when going from dark to illuminated conditions. The inverse slopes nof the linear region have been measured and the interface-state densities NSS have been calculated. From the voltage changes and interface state densities obtained, the changes in the interface-state Fermi levels have been calculated to be about 0.05–0.1 eV for short-circuit currents of 25–30 mA cm−2

Intermolecular interaction in the egg lecithin monolayers spread on aqueous alcohol solutions (author's transl)

The egg lecithin (PC) monolayer was spread on an aqueous butanol or hexanol solution, and the surface pressure-molecular area curves were obtained. From the increase of surface pressure by penetration of alcohol molecules into lecithin monolayer, the amount, penetrated or adsorbed amount, was calculated from the following equation [numerical formula] and the adsorption isotherms of Langmuir type were obtained. The amount of saturated adsorption of alcohol and k, the parameter which represents the affinity of adsorption, were calculated from the linear relation between C/T and C (alcohol concentration). The saturated amount of alcohol decreased with increase in surface concentration of lecithin, but k became minimum. This was explained by the cavity model. The lecithin monolayer penetrated by alcohol molecules forms a mixed monolayer of lecithin and alcohol. The mean area of mixed monolayer was larger than the area calculated by assuming additivity of the area of each component. It was concluded that alcohol molecules penetrating into the lecithin monolayer decrease the cohesive force between lecithin molecules.

Enzymic activity at interfaces. II. Enzymic activity of microsomal nuclease and bovine pancreatic ribonuclease at the air/water interface

The adsorption isotherms and the spreading tendency of microsomal nuclease (nucleate 3′-oligonucleotidohydrolase, EC 3.1.4.7) and bovine pancreatic ribonuclease (ribonucleate 3′-pyrimidino-oligonucleotidohydrolase, EC 3.1.4.22) in the presence of isopropyl alcohol as spreading agent have been determined, using enzymes radioactively labelled by acetylation. In parallel, the concentration-surface pressure relations have been established. The enzymic activity of microsomal nuclease spread from isopropyl alcohol containing aqueous solutions was only a few percent of its activity in bulk, while the activity of the adsorbed enzyme was only slightly reduced. Adsorbed monolayers of RNAase were almost inactivated, while the spread monolayers in the presence of isopropyl alcohol became reactivated after exposure to the substrate for several hours. The exposure time for the reactivation decreases with increasing surface concentration.

Analysis of some adsorption experiments with activated carbon

A simple method is proposed whereby the film transfer coefficient and coefficient of diffusion in the particles may be determined from finite bath adsorption experiments. The method also makes it possible to separate pore and surface diffusion. Under certain conditions it is also possible to determine the influence of particle phase concentration on the surface diffusivity. The method is based on models describing the instationary diffusion in the solids. Data from six different adsorption systems were analysed using this method. The adsorbed components were: phenol, paranitrophenol, parachlorophenol, bensoic acid, phenylacetic acid and 2-4-dichlorophenoxyacetic acid. In all systems surface diffusion was the determining transport mechanism in the particles. In the system phenol and phenylacetic acid the surface diffusion coefficient increased by about a factor 3 with an increase in surface concentration of about 40%. For parachlorophenol the increase was somewhat less. For the other systems there was no significant increase. The increase in diffusivity is explained by a decrease in bonding forces with increasing concentration.

The Effect of Treatment of Polyphosphate Surface with Amines on the Heats of Immersion in Organic Solvents

Organic cations were substituted for some of alkali cations on the surface of metaphosphates by immersion in aqueous solutions of hydrochlorides of ethylamine, hexamethylenediamine and aniline. The heats of immersion of the surface-treated phosphates in benzene and methanol were measured with a twin microcalorimeter, and the following results were obtained.(1) When the phosphates were treated with ethylamine, little change of their surface properties was observed.(2) The specific surface area of surface-treated phosphate increased with the amount of organic cation substituted.(3) The heat of immersion of the phosphates treated with hexamethylenediamine increased, especially in benzene, with increasing surface concentration of the organic cation.(4) In benzene the heat of immersion of the phosphates treated with aniline decreased with increasing surface concentration of the anilinium cation, while the immersional heat in methanol increased with the concentration. This dependence in methanol can be interpreted in terms of the OH-π interaction between the anilinium cations on the surface of the phosphate and the methanol molecules.

The effect of surfactants on the flow characteristics of falling liquid films

AbstractExperimental values of the wave length and wave velocity have been obtained for dilute solutions of valeric and hexanoic acid for a vertical falling liquid film. The wave length was unaffected by the surfactants for Reynolds numbers in the range 5 to 100; however, the wave velocity was decreased for increased surface concentrations of the two acids. This is in direct contradiction to previous theoretical work, and the explanation for the anomaly is that the free surface velocity is greatly retarded by the adsorption of the surface active agents. In an effort to determine the extent of this retardation, an approximate form of the diffusion equation and the equations of motion were solved subject to boundary conditions describing the effect of the absorbed surfactant on the surface stress. The results indicate that the entrance length can be increased several orders of magnitude by the addition of small amounts of surfactant.

Porosity Effects in the Ionization of Cesium on Tungsten

The ionization characteristics of cesium on a porous tungsten substrate may be much different from those of solid tungsten. Cesium vapor diffuses through a porous structure en route to the ionizing surface, creating gradients in the surface concentration of atoms. Therefore, some regions experience increased surface coverage, over and above that corresponding to ionization on solid tungsten. Increased surface concentration diminishes ionization efficiency, producing a higher level of neutral emission. These increased concentrations are calculated by equating mass flow of atoms into the pore to mass flow diffusing to the surface and evaporating directly from the pore. Ionization characteristics as a function of local surface coverage is available from established results for solid substrate tungsten. The parameters used in this study are those of interest in cesium-contact ion rockets: ion emission current densities on the order of 10 mA/cm2, with ionization efficiency of about 99%. The results indicate that porosities of less than 106 pores/cm2 will appreciably decrease ionization efficiency; but with higher porosities, ionization characteristics can approach those of solid tungsten.

The effect of monolayers on surface concentration of solutions under evaporation

The effect of monolayers on the surface evaporation and the subsequent surface concentration increase of the aqueous solutions was measured by the radiotracer technique. The presence of various kinds of monolayers on water not only retards the evaporation but also affects the concentration especially near the surface of the solution by interfering with the convection current of the underlying water; this produces a decrease in the concentration difference between the surface and bulk of the solution. The effect of monolayers on the surface concentration increase of the solution was correlated with the flow resistance of the monolayer, which was measured by its action against the rotation of a needle floating on the surface. A monolayer of stearic acid of varying flow resistance, controlled by adding aluminum salt to the substrate solution, showed an increase in surface concentration with increase of the flow resistance. The result with a monolayer of cetyl alcohol was similar. This relation is worth noting since in the case of the retardation of evaporation, such a simple relation has been reported not to hold.