S. Partyka

Surface Gibbs free energy of minerals: some values

In this paper it is demonstrated that it is possible to determine the surface Gibbs free energy of minerals by combining classical measurements of adsorption and van Oss theory. Some practical examples are discussed, using certain approximations. The approximations and questions relevant to different thermodynamic variables and theories of solid surface tensions are also reviewed and discussed.

Adsorption of benzoic acid from organic solvents on calcite and dolomite: Influence of water

Abstract A study has been carried out of the adsorption of benzoic acid from cyclohexane solution onto the hydrophilic surface of calcite. We determined initially the chemical and mineral composition of the solid, its specific surface area and its granulometry. This was followed by the determination of the enthalpies of immersion of calcite in different solvents. These thermodynamic properties gave information on the energetics of calcite—solvent interactions. In this way, we could construct a scale of affinities of the different organic molecules and water for the calcite surface. It was noted that the enthalpies were higher in unsaturated than in saturated organic solvents, and higher in water than in the organic solvents. The adsorption isotherms and the differential molar enthalpies of displacement were determined in the presence and the absence of water. The role played by water in the adsorption of polar organic molecules from the oil phase has not been clearly explained previously. In this paper, we indicate how the presence of water can modify the adsorption of aromatic compounds on the surface of calcite. As regards the adsorption isotherms, the presence of water essentially increases the amount of adsorption. The results of the calorimetric studies were found to be surprising; we observed that the differential molar enthalpies of displacement were endothermic. Similar experiments were carried out with dolomite and n-heptane solution and the results compared with those obtained with calcite and cyclohexane, leading to the formulation of a general model concerning the adsorption of small polar organic molecules from organic solvents onto the surfaces of the carbonates.

Thermodynamic investigation of surface of minerals

Abstract In this paper values of surface enthalpies and surface Gibbs free energies are given in order to characterize subsurface minerals. These values are obtained by combining standard measurements of adsorption and the Van Oss–Chaudhury–Good model [Van Oss, C.J., Chaudhury, M.K., Good, R.J., 1987. Monopolar surfaces. Adv. Coll. Interface Sci. 28, 35; Van Oss, C.J., Good, R.J., Chaudhury, M.K., 1988. Additive and nonadditive surface tension components and the interpretation of contact angles. Langmuir 4, 884; Van Oss, C.J., Giese, R.F., Costanzo, P.M., 1990. DLVO and non-DLVO interactions in hectorite. Clays Clay Min. 38, 151; Van Oss, C.J., Giese, R.F., Li, Z., Murphy, K., Norris, J., Chaudhury, M.K., Good, R.J., 1992. Determination of contact angles and pore sizes of porous media by column and thin layer wicking. J. Adhesion Sci. Technol. 6, 413.]. This model is reviewed and modified with a view to identify the types of interactions at solid–fluid interfaces and interpreting experimental results.

Adsorption of a cationic gemini surfactant from aqueous solution onto aluminosilicate powders of the MCM-41 type: effect of pore size and co-adsorption of phenol.

The adsorption of cationic gemini dodecanediyl-alpha,omega-bis(dodecyldimethylammonium) bromide (i.e., C12C12C12) from aqueous solution onto aluminosilicate powders of the MCM-41 type (referred to as SiAl32dx, where x is the mean pore diameter in A) has been studied at 298 K under the conditions of free pH of the aqueous phase. Macroporous silica gel XO15M was used for comparative purposes. The discussion was based on the interpretation of experimental adsorption isotherms and differential enthalpies of displacement obtained on various solid samples. For the hydrogen-exchanged SiAl32d28 sample (i.e., H+-SiAl32d28), the adsorption of bromide counterions Br- at the solid-solution interface, the isotherm of the pH evolution in the equilibrated supernatant liquid, and the electrophoretic mobility of the solid particles coated with the adsorbed C12C12C12 were additionally measured. The uptake of phenol (PhOH) by a surfactant-solid system from a 1.5 mmolkg(-1) PhOH solution and the related thermal effect of displacement onto SiAl32d50 were quantified with the use of the solution depletion technique combined with UV spectrophotometry and the titration calorimetry technique. Titration calorimetry was also used to determine the molar enthalpy change accompanying micellization of C12C12C12 in pure deionized water and in a 1.5 mmolkg(-1) PhOH solution at 298 K. The adsorption of C12C12C12 occurs simultaneously on the external surface and on the pore walls and it is a strongly co-operative phenomenon. Surfactant aggregates forming at adsorption saturation are thought to be composed of the adsorbed surfactant units having their cationic head groups mostly oriented outward with respect to the solid surface. Therefore, they can provide co-adsorption sites for polarisable phenol molecules. On average, there is one phenol molecule retained for one gemini cation adsorbed. Transfer of phenol from the aqueous phase to either the bulk micelles or to the interfacial aggregates is enthalpically favourable.

Calorimetric study of phenol adsolubilisation by cationic surfactants adsorbed on a flat silica surface or confined within small mesopores of powdered MCM-41 aluminosilicates

Abstract Adsolubilisation of phenol by cationic surfactants adsorbed on a flat silica surface or confined within small mesopores of powdered MCM-41 aluminosilicates has been studied at room temperature by means of titration calorimetry. In aqueous solution of dodecyltrimethylammonium bromide (DTAB), the transfer of phenol to the outer portions of the surfactant micelles was considered to account for the slight depression of the CMC value and for the marked exothermic effect adding to that of the micellisation process. For the system containing non-porous X015M and DTAB, the determination of surfactant adsorption and phenol adsolubilisation isotherms was supplemented by calorimetric measurements of the differential enthalpy changes accompanying both phenomena. The displacement process was more exothermic when carried out in the presence of phenol. The uptake of aromatic molecules in the DTAB-X015M system was markedly increased compared with the adsorption of phenol onto bare silica surface. Aluminosilicate-encapsulated surfactant aggregates were prepared using two alkyltrimethylammonium bromides, i.e. C12 and C16, as the solid-structure-directing agents. The phenol adsolubilisation isotherms in both aluminosilicate–surfactant systems and the related enthalpy curves were determined over a wide range of phenol molality in the equilibrium bulk solution. For the two adsolubilisation host systems both with porous and non-porous substrate, phenol was shown to be localised on at least two different types of adsolubilisation sites, in order of decreasing thermal effect of transfer from the aqueous phase.

Micellar structure of gemini cationic surfactants: influence of the spacer length

The enthalpies of micellisation of gemini and conventional cationic surfactants have been determined using calorimetric measurements as a function of temperature. The differential molar enthalpies of micellisation depend on the structure of the surfactants as well as on the temperature. As expected, a drastic increase of the enthalpies of micellisation are observed with an increase of the temperature. Moreover, calorimetric investigation of self-association process shows that the enthalpies of micellisation are much more exothermic for the gemini surfactants than for the conventional cationic surfactant. The higher values of the micellisation enthalpies are due to a higher micellar density of gemini surfactant micelles.

The adsorption of polyoxyethylenated octyl and nonylphenol surfactants on carbon black and sulfur from aqueous solutions

Abstract The adsorption of nonionic surfactants from water solutions on the hydrophobic surfaces of sulfur and carbon black has been investigated. The isotherms and calorimetric experiments were also carried out after characterization of the solid particles. The isotherms of adsorption show the existence of a saturation plateau. The adsorption quantity depends on the length of polar and aliphatic chains. Calorimetric investigations of adsorption on the carbon black indicate the existence of considerable energetic heterogeneity. At low coverage ratios the enthalpy of adsorption is very high and exothermic. Subsequently it becomes progressively weaker and reaches the value of zero at θ = 0.

Interfacial properties of zirconium dioxide in aqueous solutions of sodium alkylbenzenesulfonates

Abstract The interfacial properties of crystalline zirconium dioxide in aqueous solutions of anionic surfactants at an initial pH value of 3.8 have been studied. Adsorption isotherms, electrophoretic mobilities of the zirconia particles, and the pH of the supernatants were measured for two sodium n-alkyl-p-benzenesulfonates, the heptyl compound (SHBS) and the octyl compound (SOBS), and were compared with those for sodium benzenesulfonate (SBS), a molecule containing no alkyl chain. These traditional experiments were supplemented by calorimetric measurements of the enthalpy of dilution and the enthalpy of adsorption. The system satisfies the condition of charge regulation; the “head-on” adsorption of surfactant ions causes the pH of the equilibrium bulk solution to increase along the isotherm. The patchwise-like topography of the zirconia surface brings about a non-uniform distribution of surface charge and activates tail-tail attraction even at relatively low surface coverages. The primary surface aggregates grow and possibly fuse together in a direction parallel to the surface but for the most part within the surface patches. In consequence, only submonolayer coverages can be achieved, and at higher bulk concentrations aggregates grow into compact and fragmented three-dimensional-like structures.

Surface heterogeneity of passively oxidized silicon carbide particles: vapor adsorption isotherms

The surfaces of silicon carbide particles subjected to two different passive oxidation treatments have been characterized by immersion calorimetry and vapor adsorption techniques. Surface enthalpies and surface free energies have been computed using semiempirical models and are compared to theoretical estimations. The surface entropy term appears higher than in the case of other solids studied with the same analysis. The definition of the surface entropy term is discussed in order to explain the discrepancy between calculation and experiment. An explanation of results is proposed, which is related to the constitution of silicon oxide layers at the surface of silicon carbide, a fact demonstrated by previous XPS measurements.

Assessment of the surface tension of various divided solids

We have attempted to calculate the surface tension of some solids using immersion calorimetry measurements along with the interfacial model of van Oss [1, 2, 3, 4].ZusammenfassungUnter Berücksichtigung des van Ossschen Grenzflächenmodelles [1, 2, 3, 4] wurde mittels Immersionskalorimetriemessungen ein Versuch zur Berechnung der Oberflächenspannung von Feststoffen unternommen.