Wettability of a glass surface in the presence of two nonionic surfactant mixtures

Measurements of the advancing contact angle (theta) were carried out for aqueous solution of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol), Triton X-100 (TX100), and Triton X-165 (TX165) mixtures on glass. The obtained results indicate that the wettability of glass depends on the concentration and composition of the surfactant mixture. The relationship between the contact angle and concentration suggests that the lowest wettability corresponds to the concentration of TX100 and TX165 and their mixture near the critical micelle concentration (CMC). The minimum of the dependence between the contact angle and composition of the mixtures for each concentration at a monomer mole fraction of TX100, alpha, equals 0.2 and 0.4 points to synergism in the wettability of the glass surface. In contrast to the results of Zisman ( Zisman, W. A. In Contact Angle, Wettability and Adhesion; Gould, R. F., Ed.; Advances in Chemistry Series 43; American Chemical Society Washington, DC, 1964; p 1 ) there was no linear dependence between cos theta and the surface tension of aqueous solutions of TX100 and TX165 mixtures for all studied systems, but a linear dependence exists between the adhesional tension and surface tension for glass, practically, in the whole concentration range of surfactants studied, the slopes of which are positive in the range of 0.43-0.67. These positive slopes indicate that the interactions between the water molecules and glass surface might be stronger than those between the surface and surfactant molecules. So, the surface excess of surfactant concentration at the glass-water interface is probably negative, and the possibility for surfactant to adsorb at the glass/water film-water interface is higher than that at the glass-water interface. This conclusion is confirmed by the values of the work of adhesion of "pure" surfactants, aqueous solutions of surfactants, and aqueous solutions of their mixtures to the glass surface and by the negative values of glass-water interfacial tension determined from the Young equation in the range of surfactant concentrations corresponding to their unsaturated monolayer at the water-air interface.     

Precipitation of molybdenum(V) as the hydroxide and its separation from rhenium

A study of the conditions for precipitation of molybdenum(V) hydroxide shows that for Mo concentration 1 mg ml about 97.5% of the Mo can be precipitated between pH 5 and 5.8. Lower concentrations of molybdenum(V) or molybdenum(VI) can be precipitated quantitatively by using 20 times the amount of zirconium as collector, at the same pH. On this basis, a simple method is given for quantitative separation of rhenium from large amounts of molybdenum and is attested by analysis of synthetic and molybdenite samples.     

Phase transformations of aluminium hydroxide in the calcination process

In this paper phase transformations were considered that occur in the process of calcination of aluminium hydroxide, and for qualitative phase analysis low-temperature X-ray analysis was used. Two samples were used, one of chemical purity obtained under laboratory conditions and the other obtained under industrial conditions in the alumina production plant at Kidric?evo, Yugoslavia.It was determined that for both samples in the process of calcination of aluminium hydroxide identical transformations appear, and the sequence of transformations present may be shown in the following way:

     

Solvent effect on the aggregate of fluorinated gemini surfactant at silica surface

The aggregate states of partially fluorinated gemini surfactant [(CF3)2CF(CF2)2(CH2)10N(CH3)2]2(CH2)6Br2 (C(F)(5)C10-C6-C10C(F)(5)) on silica surface were investigated with atomic force microscopy (AFM) and water contact angle (CA) measurement by analyzing the effects of bulk concentration and adsorption time on stack state. On surfactant-adsorbed silica surfaces, there was a flat surface layer interspersed with some scattering surfactant aggregates. In the case of short adsorption times, the aggregates would be hemisphere. In the case of long adsorption times, the aggregates would be present in the form of bilayers. With the increase of bulk concentration, the adsorbed amount was enlarged and the surface layer became more compact. The formation of patchy bilayer aggregates indicated the saturation of the surface layer. Furthermore, organic solvent effects on the aggregate state of the surfactant on a silica surface were studied with four organic solvents, including n-hexane, dehydrated ethanol, 1,1,2-trichloro-1,2,2-trifluoroethane, and toluene. With the treatment of different organic solvents, the hemisphere aggregates on the surface layer can rearrange into spherical bilayer, rodlike monolayer, and branched rodlike monolayer aggregates, respectively. The polarity of solvents and affinity of organic solvents for surfactant molecules may have a great impact on the stack state of the fluorinated gemini surfactant molecules.     

Influence of surfactant concentration on the surface morphology of hollow silica microspheres and its explanation

The surface morphology of hollow silica microspheres has influence on their applications. After a thorough investigation of the deposition of silica nanoparticles on polystyrene (PS) beads and the surface morphology and texture of the resultant hollow silica shells with scanning electron microscopy, transmission electron microscopy, and N2-sorption measurements, the influence of surfactant [cetyltrimethylammonium bromide (CTAB)] concentration on the surface morphology of hollow silica microspheres templated by PS beads is explained. Previously, CTAB was believed to turn the surface charge of PS beads from negative into positive so that negatively charged silica could be deposited on the PS template. Here, we show CTA+ cations preferentially assemble with silica species to form silica-CTA+ composite nanoparticles. Since the zeta potential of silica-CTA+ composite nanoparticles is smaller than that of pure silica nanoparticles, these composite nanoparticles encounter less repulsion when they are deposited on the surface of PS beads and close to each other. As more CTAB is added, the silica-CTA+ nanoparticles are less negatively charged, and more compact and smooth hollow silica microspheres are obtained.     

Development of the specific surface areas of natural coal in the course of thermolysis in the presence of potassium hydroxide

The development of the surface of natural coal from Donets field in the course of thermolysis with KOH was studied. The dependences of the specific surface area of coal containing 90% carbon on the activation time, temperature (400–800°C), and KOH/coal ratio (0.75–4.5 g g^–1) were determined. The effect exerted on the development of the porous coal structure by low-temperature (20±2°C) oxidative modification causing formation of oxygen functional groups and reorganization of the coal three-dimensional structure was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1452–1455.Original Russian Text Copyright © 2004 by Tamarkina, Kucherenko, Shendrik.     

Thermal stability and flame retardancy of LDPE/EVA blends filled with synthetic hydromagnesite/aluminium hydroxide/montmorillonite and magnesium hydroxide/aluminium hydroxide/montmorillonite mixtures

The combination of organophillised montmorillonite (MMT), synthetic hydromagnesite and aluminium hydroxide (ATH) as flame retardant system for polyethylene-based materials was studied and compared with a similar system with magnesium hydroxide, ATH and MMT. The thermal stability and the flame retardant properties were evaluated by thermogravimetric analysis (TGA), differential thermal analysis (DTA), limiting oxygen index (LOI) and cone calorimeter tests. The results indicated that the addition of montmorillonite makes it possible to reduce the total filler content to achieve the flame retardant requirements. The thermal stability of filled LDPE/EVA blends increases to a higher extent for the samples containing MMT. In the cone calorimeter tests we observed a reduction of the peak heat release rate for the sample containing montmorillonite in comparison with a sample with higher filler loading without this nanoclay. An increase of the stability of the char formed could be responsible for this favourable behaviour when montmorillonite is added.In addition, mechanical properties significantly improved for the composites containing montmorillonite both for the filler loading reduction and the reinforcement effect of the nanoclay.     

A comparative study of surface acidity in the amorphous, high surface area solids, aluminium fluoride, magnesium fluoride and magnesium fluoride containing iron(III) or aluminium(III) fluorides

The behaviour of the sol–gel prepared, amorphous solids, high surface area (HS) aluminium fluoride and magnesium fluoride in promoting room temperature dehydrochlorination of tert-butyl chloride (Bu^tCl), in their catalytic activity for the dismutation of chlorodifluoromethane and in the temperature programmed desorption of ammonia is similar, indicating that, unexpectedly, both solids exhibit significant surface Lewis acidity. Using a similar approach, it has been demonstrated that surface Lewis acidity in HS-MgF₂ is enhanced by the incorporation of amorphous iron(III) fluoride and probably also by amorphous aluminium(III) fluoride. A second, unexpected feature is the substantial retention of anhydrous hydrogen chloride by all the solids, which is observed by the use of chlorine-36 labelling, when they are exposed at room temperature either to Bu^tCl or to HCl directly. The detailed behaviour of H³⁶Cl towards HS-AlF₃ depends on the fluorinating agent, dichlorodifluoromethane or anhydrous hydrogen fluoride, which is used in the second stage of HS-AlF₃ synthesis. This observation and the pattern of the results obtained overall lead to the proposal that strongly adsorbed HCl behaves as an unconventional Lewis base towards these solids.     

The surface pressure effect of pentaoxyethylene and maltoside surfactant head groups

From experimental surface tension data for water solutions of dodecyl-β-maltoside, C₁₂M, and dodecyl-penta-(ethylene oxide), C₁₂EO₅, in the range below the CMC, the corresponding head group surface pressure functions vs. packing density were derived. These functions were compared with theoretical expressions based on some different models of the mixed head group/water film. Tentatively, we concluded that the two-dimensional hard fluid approach provides a convenient starting-point in order to account for the observed surface pressures of both the maltoside and EO head groups.     

Role of aerosil surface in reaction of exciplex formation in the presence of the nonionic surfactant triton X-100

In the formation of a pyrene/N,N-dimethylaninline exciplex solubilized in micelles of the nonionic surfactant Triton X-100, under conditions of adsorption on the surface of Aerosil (pyrogenic silica), the features of the reaction are determined by the restructuring of the Aerosil surface in the aqueous micellar medium and by encapsulation of the fluorophore molecules.Institute of Surface Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, Kiev 252039, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 320–323, September–October, 1996. Original article submitted June 16, 1995.     

Temperature effects on the surface acidity properties of zirconium diphosphate

As part of the temperature effects study on the sorption of metallic cations onto zirconium diphosphate, we have first investigated the intrinsic surface properties of this synthetic compound for different temperatures (25, 50, 75 and 90 degrees C). A physico-chemical study (IR, XRD) assessed its purity, and the measured N(2)-BET specific area was 13.4+/-0.2 m(2)g(-1). Mass and potentiometric titrations showed that the experimental point of zero charge (pH(pzc)=2.6+/-0.2) and the surface site density remained constant between 25 and 90 degrees C. The potentiometric titration data were simulated with the constant capacitance model, considering two reactive surface sites, with a total surface site density equal to 7.2 sites nm(-2). The intrinsic protonation and deprotonation constants were found to increase with the temperature, as well as the calculated apparent constants. The simulation results showed that the capacitance increased with the temperature. The proportions of the neutral, protonated and deprotonated forms for each site type were quantified thermodynamically by application of the Van't Hoff relation.     

The effect of counterions on the surface adsorption and micelle formation in mixed surfactant systems of dodecyl sulfates

 The surface tension of the aqueous solutions of sodium dodecyl sulfate (SDS) and tetramethylammonium dodecyl sulfate (TMADS) was measured as a function of total molality of the surfactants at fixed composition of TMADS at 298.15 K under atmospheric pressure. The phase diagrams of adsorption and of micelle formation, the activity coefficients, and the excess Gibbs energy were calculated to estimate the deviation from the ideal mixing quantitatively. The preferential adsorption and the micelle formation for TMA⁺ to Na⁺ is attributable to some extent to the hydrophobicity of the methyl groups of TMA⁺. The composition of TMA⁺ in the micelle is larger than that in the adsorbed film at equilibrium. That is, a larger hydrated counterion is more likely to exist in the micelle than in the adsorbed film owing to geometrical benefit. The negative values of the excess Gibbs energy of the adsorbed film and of the micelle arise from the positive ones of the excess entropy greater than that of excess enthalpy. The counterions of very similar size are mixed ideally in the micelle and the size effect appears sensitively in the adsorbed film. Received: 23 May 2001 Accepted: 16 July 2001     

Precipitation of lignin and extractives on kraft pulp: effect on surface chemistry, surface morphology and paper strength

The effect of pH on the formation of precipitates (lignin, extractives and metals) on kraft pulp surfaces was examined by electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectrometry and atomic force microscopy (AFM). A softwood kraft pulp slurry from an oxygen delignification stage was diluted to 3% consistency with water or an acidic Z filtrate. After heating to 70 °C the pH was lowered from 11 to 2–5, using sulphuric acid. Lignin and extractives precipitated at pH values below 6, and their amounts increased with decreasing pH. Most of the precipitated lignin was found on the pulp surface after sheet forming, whereas the main part of the precipitated extractives could be easily washed away with water. The layer of precipitated lignin was apparently thicker than the layer of extractives. AFM showed the precipitated material as a granular phase. Neither surface morphology nor surface coverage depended on the addition of Z filtrate. The amount of metals ID the pulp and on the pulp surface decreased when pH was lowered to 2. More metals, such as Ca and Mg, were detected ID the pulps as well as on the sheet surfaces when the pulp was diluted with Z filtrate. Strength and bonding properties of the pulp sheets were slightly impaired by the precipitated material. Acidification appears to be the main reason for the precipitation of both lignin and extractives on the pulp surfaces. This should be taken into account when filtrates are recycled ID the bleaching or washing of pulps.     

Reaction of menthol and phenol in the presence of aluminium alkoxides

Phenol was alkylated with menthol in the presence of organoaluminium catalysts such as aluminium phenoxide and aluminium isopropoxide. Reaction products were isolated and characterized. Certain features of the process were determined. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 363–366, July–August, 2008.     

Determination of the surface acidity of solid catalysts

A novel method has been developed for determining the surface acidity of white, as well as deeply colored porous solids. The method, which was tested on Al₂O₃, SiO₂–MgO–Al₂O₃ and Fe₂O₃ catalysts, is based on the adsorption of pyridine or benzylamine on acidic sites and subsequent displacement of the adsorbed bases by n-butylamine. A linear correlation was found between the concentration of acidic sites on Al₂O₃ and Fe₂O₃ catalysts and their activity in the dehydration oftert-butyl alcohol.

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, . , Al₂O₃, SiO₂–MgO–Al₂O₃ Fe₂O₃, -. Al₂O₃ Fe₂O₃ - .

     

Fine tuning the surface acidity of titanate nanostructures

The effect of protonation on the surface acidic properties of titanate nanowires (TiONWs) was investigated. Nanowires were synthesized by the alkali hydrothermal method which resulted in one dimensional nanostructures of large external surface area and well-defined lamellar interlayer structure. The Na⁺/H⁺ ratio in the structure can be tuned by ion-exchange. Our aim was to characterize the morphology of the as-synthesized nanostructures by HRTEM and SEM measurements and assess their surface acidity using in situ infrared spectroscopic measurements and temperature programmed desorption. It was found that the numbers of Lewis and Brönsted acidic sites in the Na-form and the H-form of the TiONWs is different. The ratio and the nature of acidic sites can be tuned by the ion exchange process. The wire-like morphology and the tunable acidity are features of titanate nanowires that may render them a promising material in various heterogeneous catalytic applications.