Colloids and Surfaces最新文献

By varying the ratio of the ethylene oxide (EO) to propylene oxide (PO) units in a series of poly(ethylene oxide—propylene oxide—ethylene oxide) (EPE) non-ionic copolymers we have been able to quantify the relative hydrophobic energy contribution of the EO and PO units in bulk solution and interfacial processes. These polymers are known to form aggregates in solution which consist of a hydrophobic PO core surrounded by a hydrophilic EO shell. In order to determine the hydrophobic character of the respective EPE polymers the partitioning of pyrene, a strongly hydrophobic probe, between the aqueous environment and the hydrophobic polymer environment was monitored as a function of polymer concentration. Aggregate hydrophobicity was found to be dependent on both the EO and PO chain lengths such that the hydrophobic contribution per PO unit is ten times the hydrophilic contribution per EO unit. The ability of EPE to stabilise an aqueous colloidal dispersion of hydrophobic particles (carbon black) was measured as a function of EPE concentration. The critical stabilisation concentration, which represents the onset of colloidal stability, was round to be inversely related to the hydrophobicity of the polymer aggregates in the bulk solution. The information gathered in this study allows the optimum EO:PO:EO ratio for stabilisation of a hydrophobic colloidal dispersion to be predicted.

Interactions between poly(acrylic acid) (PAA) and sodium dodecyl sulfate (SDS) in aqueous solution were studied using fluorescence spectroscopy. Pyrene labeled PAA was used to study changes in conformation of the polymer on its association with SDS. Externally added pyrene was used to study the aggregation behavior of the surfactant in the absence and presence of PAA. Effects of polymer concentration and pH were determined. It was observed that PAA and SDS interact, under acidic pH conditions, when the PAA concentration is low. Under conditions where the PAA is ionized, there are no interactions between PAA and SDS, but if the polymer concentration is high then an increase in ionic strength due to the dissociation of a large number of carboxylic acid groups results in aggregation of the surfactant, even at concentrations much lower than its critical micelle concentration in the absence or any polymer.

The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxidans as well as selected minerals have been studied by microelectrophoresis, contact angle and hexadecane/aqueous phase partition measurements. Adhesion measurements were conducted on sized fractions of quartz, pyrite, chalcopyrite and other copper sulphides in order to establish the relationships between cell surface properties and cell adhesion to specific mineral surfaces. It was found that the bacteria had an isoelectric point at pH 3.0 and that they were slightly hydrophobic, showing a water contact angle of 20–24 and extraction recoveries into hexadecane in the range 14–22 wt.% Adhesion mechanisms involved in the interaction between Thiobacillus ferrooxidans and mineral surfaces as a function of the electrokinetic and hydrophobic properties of bacteria and minerals are illustrated. Calculated free energies of bacterial adhesion to quartz, chalcopyrite and pyrite indicated that adhesion appears to occur at the secondary minimum according to the Derjaguin—Landau—Verwey—Overbeek theory.

The interaction between FeEDTA and two calcareous soils (a chernozem and a clayey meadow soil) were investigated to estimate the changes in the ion-activity product (IAP) of Fe(OH)₃ over a period of 4 weeks, using the radiotracer technique. ⁵⁹Fe was used to determine the quantity of iron. ¹⁴C to assay for EDTA and ⁴⁵Ca to measure the calcium.

The loss of chelating ligand by sorption onto soil was taken into account. The IAP of Fe(OH)₃ for the two soils continuously decreased with time and changed between lg IAP −36.0 and −37.3 Fe(OH)₃ precipitates because of the slow decomposition of FeEDTA above pH 7 and this process is influenced by the competition between calcium (the most significant cation in this pH range) and iron(III) for the ligand and by the slow aging of Fe(OH)₃ precipitates.

The surface and interfacial activity of cationic surfactants depends on the polarity of the bulk phase. If concentrated sulphuric acid is mixed with water, physical properties such as density, and surface and interfacial tension go through a maximum as the molar composition is changed. Also the properties of surfactants, i.e. surface activity and CMC, do not vary linearly in such aqueous mixtures. However, if concentrated sulphuric acid is mixed with methane sulphonic acid we find a linear relationship.

The adsorption isotherms of n-hexadecyltrimethylammonium bromide at the surface (interface) of mixtures of H₂SO₄ and CH₃SO₃H/air (n-hexane) and the CMC were determined for various compositions of the acid phase and approximated by the Von Szyskowski equation. The change in the energy of micelle formation, — Δ_MG, and the energy of adsorption, — Δ_AG°, were calculated as a function of solvent composition. The surface concentration as a function of bulk concentration, the maximum surface coverage and the percentage surface concentration were also calculated.

We found a linear dependence of the CMC, and of the lowering of σ and γ at the CMC, on the mole fraction of the acid phase. Also the constant A of the Von Szyskowski equation decreases and the logarithm of B increases linearly with the mole fraction of methane sulphonic acid. Therefore it is possible to calculate all the data needed for the characterization of systems of different acid composition. A special pattern was found for acid mixtures with X_CH3SO3H < 0.1. This can be explained by the transformation of micelle structure and the possibility that micelles can solubilize hydrocarbons in this region.

The method described is based on static light scattering measurement of solutions obtained by the direct dissolution of latex in a suitable organic solvent without intermediate isolation of solids. In the case of latices of acrylate copolymers with acrylic or methacrylic acid, often used in the paint industry, 2-ethoxyethanol proved to be the best solvent for this purpose. Static light scattering can also be used to estimate the mass and size of the dispersion particles prior to their dissolution.

Asphalt adsorption from from water-saturated tolene on Na⁻ kaolinite, Ca²⁻ kaolinite, Na⁻ illite and Ca²⁻ illite clays was investigated. It was found that the kaolinite surface adsorbed more asphalt than illite for both the Na⁻ -and the Ca²⁻ exchanged forms. Adsorption from aqueous solutions of sodium dodecylbenzenesulphonate (SDBS) and sodium dodecyl sulphate (SDS) on various asphalt-covered clays was also studied. The shape of the isotherms depended on the asphalt-clay substrate and showed a much lower adsorption of SDBS beyond the CMC. Desorption of asphalt from various clays with SDBS and SDS surfactants was measured spectrophotometrically. The percentage weight of asphalt desorbed with SDBS was twofold higher than that desorbed with SDS surfactant.

Single solubilization of Sudan IV and anthracene has been studied in aqueous surfactant systems of sodium dodecyl sulphate, cetyltrimethylammonium bromide and Triton X-100 at 30°C by a spectrophotometric technique. Sudan IV was found to be more highly solubilized in micellar solutions than anthracene. Solubilization of Sudan IV and anthracene in the presence of each other was also studied in the surfactant systems. It was found that Sudan IV is preferentially solubilized over anthracene when solubilized jointly. This is reflected in the calculated values of the number of moles of surfactant solubilizing 1 mol of dye, the free energy change and the number of molecules of dye solubilized in a micelle. From the successive solubilization studies of Sudan IV and anthracene it has been found that the absorbance of one solubilizate does not change after the addition of the second solubilizate. The solubilization behaviour of dyes was discussed with respect to the aggregation number, occupancy of different solubilization sites and the chemical nature of the two dyes.

Thermal desorption of liquids was measured using a derivatograph. Alcohols and aliphatic hydrocarbons were used as liquid adsorbates. Pore size distribution curves of silica gels were determined on the basis of thermogravimetric curves using the Kelvin equation. Calculated distributions and total pore volumes were compared with those obtained from the nitrogen method and mercury porosimetry. The influence of heating programs on the shape of the distribution curves is discussed.