Showing papers in "Langmuir in 1985"

Spontaneously organized molecular assemblies. 1. Formation, dynamics, and physical properties of n-alkanoic acids adsorbed from solution on an oxidized aluminum surface

Abstract: On montre qu'il peut y avoir formation de couches monomoleculaires, orientees, a empilement compact, lors de l'adsorption d'acides n-alcanoiques sur des supports d'aluminium oxyde, a partir de solutions diluees

Spontaneously organized molecular assemblies. 2. Quantitative infrared spectroscopic determination of equilibrium structures of solution-adsorbed n-alkanoic acids on an oxidized aluminum surface

Abstract: Determination de la structure des couches monomoleculaires des acides alcanoiques, a 16-22 atomes de carbone, termines par des groupes methyle, vinyle ou propargyle, formees lors de l'adsorption sur de l'oxyde d'Al, a partir d'une solution dans l'hexadecane

Fluorescence probes for critical micelle concentration determination.

Abstract: The utility of pyrene and pyrene-3-carboxaldehyde as fluorescence probes for determining the critical micelle concentration (cmc) of nonionic (Tergitol25-L-9, Tergitol15-5-40, Neodol91-8), anionic (sodium decyl sulfate), and cationic (cetyltrimethylammonium bromide) surfactanb was investigated. The probes were dissolved in trace amounts (

Acid-base behavior of carboxylic acid groups covalently attached at the surface of polyethylene: The usefulness of contact angle in following the ionization of surface functionality

Abstract: : Oxidation of polyethylene with chromic acid/sulfuric acid generates a material (PE-CO2H) having a high density of carboxylic acid and ketone functionalities in a thin surface layer on the polymer. This paper determines the extent of ionization of the surface and near-surface carboxylic acid groups of these materials in contact with water as a function of pH using three experimental techniques: measurement of attenuated total reflectance infrared (ATR-IR) spectra, measurement of contact angles, and direct potentiometric titration. On the basis of correlations between results obtained using these three techniques, we propose an equation relating the contact angles an aqueous solution having a given value of pH and the extent of ionization (a subscript i) of those carboxylic acid groups that are directly exposed to the solution. These carboxylic acid groups have broad titration curves, and have CO2H groups that are less acidic than soluble carboxylic acids. The initial ionization of these carboxylic acid groups occurs when the solution is approximately pH = 6. The detailed structures of these oxidized polymer surface layers and the nature of the interactions between the carboxylic acid and carboxylate ions in them are still not completely defined. Salt effects on the extent of ionization a subscript i at a particular value of pH are unexpectedly small, and suggest that charge-charge interactions between carboxylate ions may not dominate the titration curves. This work demonstrates the usefulness of contact angle in following chemical changes occurring in organic functional groups of surfaces.

Contact angle hysteresis on heterogeneous surfaces

Abstract: Considerations sur le probleme de montee capillaire sur une plaque verticale dont la surface est partiellement recouverte d'un materiau de faible energie superficielle. L'hysteresis, la difference entre les angles de contact avancant et rentrant, est associee, a l'existence de minima multiples dans la fonctionnelle de l'energie totale

Pseudophase separation model for surfactant adsorption: isomerically pure surfactants

Abstract: Donnees sur un nouveau modele d'adsorption de tensioactif, comprenant les contributions de l'effet hydrophobe, de l'agregation superficielle du tensioactif, des heterogeneites de surface et des concentrations d'ions antagonistes

Liquid-expanded to liquid-condensed transition in lipid monolayers at the air/water interface

Abstract: Cas des couches monomoleculaires des acides n-pentadecanoique et n-hexadecanoique a l'interface air-solution aqueuse de HCl, ainsi que de dihexadecanoylphosphatidylcholine a l'interface air-solution aqueuse de NaCl

Molecular theory for mixed micelles

Abstract: A molecular theory for the formation of mixed micelles is developed here as an extension of our earlier theory for single-component micelles. The theory permits the calcuiation of the cmc, the average micelle size, and the average micelle composition as well as the size and the composition distribution of micelles in mixed surfactant systems. Central to the theory is an explicit molecular thermodynamic expression for the Gibbs energy of formation of the mixed micelle. This Gibbs energy of micelle formation, which is composition dependent, can be decomposed into bulk and interfacial components. The bulk component includes the free energy contributions arising from the transfer of the surfactant tail from water to th'e micelle. The interfacial component includes the free energy contributions due to the micellar core-water interfacial energy, the steric repulsions between the head groups at the micelle surface, and the electrostatic repulsions between the head groups at the micelle surface. If the Gibbs energy of micelle formation is a linear function of the micelle composition, then the excess Gibbs energy is zero and the surfactant mixture behaves ideally. On the other hand, if the Gibbs energy of micelle formation has a nonlinear dependence on the micelle composition, then the excess Gibbs energy is nonzero and the surfactant mixture displays nonideal micellization behavior. It is shown that the bulk component of the Gibbs energy of micelle formation depends linearly on the micelle composition and hence does not account for any nonideal behavior displayed by the mixed micelles. In contrast, the interfacial component has a nonlinear dependence on the composition of the mixed micelle and thus constitutes the source of the observed nonidealities in mixed micellar systems. Therefore, surfactant mixtures displaying markedly nonideal micellization behavior are those for which the interfacial interactions show significant composition dependence. Illustrative results based on this molecular theory are obtained for a number of binary mixtures and are compared against the available experimental data.

Improved techniques for particle size determination by quasi-elastic light scattering

Abstract: Donnees relatives a l'etude de suspensions de particules mono- ou poly-dispersees, subissant le mouvement brownien

Ordered ionic layers formed on platinum(111) from aqueous solutions

Abstract: Mise en evidence de la formation de couches ordonnees d'adsorption lors de l'immersion d'une surface de Pt(111) dans des solutions ioniques aqueuses de KCN, KSCN, K 2 S, KBr, KI et d'hydroquinonesulfonate de K. Resultats d'etudes par diffraction d'electrons lents et par spectrometrie Auger

Interaction of metal hydrous oxides with chelating agents. 7. Hematite-oxalic acid and -citric acid systems

Abstract: Etudes de l'adsorption des ions oxalate et citrate sur des particules spheriques colloidales d'hematite et de leur influence sur l'elimination du fer a partir de celles-ci, en fonction de la concentration du solute, du pH et de la temperature

Carbon monoxide adsorption on a platinum electrode studied by polarization modulated FT-IRRAS. 1. Carbon monoxide adsorbed in the double-layer potential region and its oxidation in acids

Abstract: Resultats d'etudes par FT-IRRAS a polarisation modulee (spectroscopie d'absorpie d'absorption reflexion IR, a transformee de Fourier, a polarisation modulee) du monoxyde de carbone adsorbe sur une electrode de platine lisse, dans des solutions acides (HCl, H 2 SO 4 ou HClO 4 1M). Donnees sur l'oxydation de CO adsorbe

Droplet and bicontinuous structures in microemulsions from multicomponent self-diffusion measurements

Abstract: Utilisation de la spectrometrie RMN, a echo de spin, a gradient d'impulsions, a transformee de Fourier, pour estimer la diffusion moleculaire dans 3 systemes: 1) laurylsulfate de sodium (SDS)-butanol-toluene-eau-chlorure de sodium, 2) SDS-pentanol-toluene-eau et 3) SDS-butanol-toluene-eau

Electrodynamic balance stability characteristics and applications to the study of aerocolloidal particles

Abstract: Extension de la theorie de la balance electrodynamique, dispositif utilise pour l'etude de particules isolees d'aerosols, de 0,1 a 100 μm, a l'analyse des caracteristiques de stabilite de la particule

Adsorption at solid/solution interfaces. 1. Interpretation of surface complexation of oxalic and citric acids with hematite

Abstract: Analyse en termes de modele de complexation en surface, des donnees d'adsorption des acides oxalique et citrique sur des particules d'hematite colloidale, dispersees dans l'eau. Evaluation des contributions chimique et electrostatique et determination des especes de solute qui reagissent avec le solide

Phase behavior of ternary systems: Water-oil-nonionic surfactant as a near-tricritical phenomenon.

Abstract: On a montre precedemment que dans le cas des systemes du type H 2 O-huile-tensioactif non ionique-hydrocarbure, le comportement des phases est semblable que le tensioactif non ionique forme des micelles ou non, et qu'il y ait des mesophases lyotropes ou non. On explique ces phenomenes en considerant que ces systemes sont tricritiques (c'est-a-dire proches d'un point tricritique)

Applications and limitations of boundary-line fractal analysis of irregular surfaces: proteins, aggregates, and porous materials

Abstract: Les methodes d'analyse d'image automatisees sur ordinateur, sont generalisees dans le cas d'analyse fractale des lignes limites des objets possedant des surfaces irregulieres. Les objets analyses sont des proteines, un catalyseur, un gel de silice macroporeux, des flocs colloidaux simules et un agregat de noir de carbone

Gold as a ubiquitous substrate for intense surface-enhanced Raman scattering

Abstract: On propose un procede fonde sur des cycles d'oxydation et de reduction de balayage du potentiel, permettant de preparer des surfaces d'or legerement rugueuses, donnant des spectres Raman augmentes en surface intenses pour une serie d'adsorbats a l'interface or-solution aqueuse. On propose des spectres representatifs pour des adsorbats halogenures, pseudohalogenures et oxyanions, pour les complexes metalliques redox actifs et pour l'ethylene adsorbe

Photoelectrochemistry in particulate systems. 3. Phototransformations in the colloidal titania-thiocyanate system

Abstract: Association of SCN/sup -/ with TiO/sub 2/ colloids in acetonitrile resulted in the appearance of an absorption band with a maximum around 285 nm. The apparent association constant as measured by a Benesi-Hildebrand plot was 350 M/sup -1/. Generation of (SCN)/sub 2//sup -/. was observed within the pulse duration (<8 ns) when the thiocyanate complex of TiO/sub 2/ in acetonitrile to 337-nm laser pulse excitation. The quantum yield for the production of (SCN/sub 2//sup -/. was determined to be 0.04. With the aid of the laser flash photolysis, it has been demonstrated that one can carry out both the oxidation of SCN/sup -/ and the reduction of oxazine dye on the semiconductor particles simultaneously. Effective capture of the holes and electrons enhanced the efficiency of the photoelectrochemical oxidation and reduction processes at these microelectrodes. 22 references, 6 figures, 1 table.

Temperature-Programmed Desorption Study of Ethylene on a Clean, a H-Covered, and an O-Covered Pt(111) Surface

Abstract: Sur une surface propre, l'ethylene est, d'abord converti en ethylidyne et decompose ensuite graduellement en especes superficielles carbonacees, avec degagement d'hydrogene a chaque etape. Mais il peut, aussi, hydrogene en ethane lorsque H adsorbe est actif. En presence d'oxygene adsorbe, l'ethylene est oxyde en CO 2 , H 2 O et CO via un intermediaire, ayant la stœchiometrie de CH

Potential functions for diffusive motion in carbon molecular sieves

Abstract: Calcul des potentiels d'interaction d'une serie de gaz (CO, CO 2 , O 2 , N 2 , He, Ar et H 2 ) avec les micropores des tamis moleculaires carbones. Determination des dimensions critiques des pores et des barrieres pour la diffusion superficielle

C2Hn fragments on metal surfaces

Abstract: : The chemisorption of an acetylene (HCCH), a vinylidene (CCH2) and an ethylidyne (CCH3) on metal surfaces, especially Pt(111) is analyzed in some detail, with an emphasis on the electronic rearrangements ensuing. The bonding is described in terms of semi-localized states, in turn obtained via a deconvolution of the total density of states into fragment orbitals of the hydrocarbon and the surface. The geometrical choices made by the various fragments on surfaces are analyzed by simple perturbation theory. It is found that in general the bonding within both the hydrocarbon fragment and the surface is dramatically weakened, as indicated by the changes in overlap populations that result. The more surface atoms are involved in anchoring the adsorbate, the weaker the bonding within the surface becomes. A non-dissociative chemisorption is the result of a compromise and its operative when the price of the binding energy is evenly distributed over the loss of bonding within the adsorbate and the surface.

Adsorption and desulfurization of thiophene on nickel(111)

Abstract: Etudes par diffraction d'electrons lents, par spectrometrie Auger, par spectrometrie des masses et spectroscopie d'absorption-reflexion IR. Sur Ni(111) pur, le thiophene se polymerise legerement au-dessus de la temperature ambiante, et la decomposition du polymere donne une serie d'hydrocarbures, comprenant des fragments en C 5

Thermally activated magnesium oxide surface chemistry. Adsorption and decomposition of phosphorus compounds

Abstract: Les organophosphates (RO) 3 P=0, les organophosphites (RO) 3 P et les organophosphines R 3 P s'adsorbent fortement sur MgO et CaO, thermiquement actives. Resultats d'etudes par spectroscopie IR et par des essais de traitement thermique

Fluorescence Probes for Aqueous Solutions of Nonionic Micelles

Abstract: : Three fluorescence probes, pyrenecarboxaldehyde (PA), pyrene (P), and an ionic indole labeled detergent (In), have been employed to investigate nonionic (Triton) micelles of varying EO number. PA serves as a probe of the surface of micelle, P serves as a probe of the inner layer of micelles, and In serves as a probe of the inner core of micelles. Measurement of fluorecence parameters for PA, P, and In as a function of variations of surfactant structure and temperature provides direct information of the time-averaged location of the probes in nonionic micelles and indirectly provides information on the nonionic micelles' structure.