G. Pardo

On the adsorption of sodium alkylsulfonates at the air-aqueous solution interface

Abstract Data on the surface tension of sodium alkylsulfonate solutions at different surfactant concentrations and at 10, 20, and 30°C are presented. By applying the Gibbs adsorption equation to the γ vs C curves, the adsorption isotherms of alkylsulfonate ions at the air-aqueous solution interface were obtained. These correspond to adsorption isotherms of the Langmuir type. It is suggested that the adsorption of these surface active agents could take place by two different mechanisms, depending on the surfactant concentration range considered. The pressure vs area data for charged monolayers at the air-water interface have been examined in terms of limiting coarea and cohesional pressure. The Tajima equation derived for the dodecyl sulfate ion is moderately applicable to the alkylsulfonate ions, while the Davies equation does not fit the data well. The results indicate that the alkylsulfonate ions possess cohesional attraction for each other within the monolayer even at a very low concentrations. Adsorbed monolayers obey the adsorption isotherm which is derived assuming immobility of the ions in the air-aqueous solution interface. This adsorption isotherm leads to consistent values for the standard free energy of adsorption. Finally, a predominating role of the entropic effects in the process of adsorption of these surfactants at the air-water interface was found.

Comparative sedimentation and streaming potential studies for ζ potential determination

An experimental investigation on the ζ potential of the quartz-aqueous solutions of KCl is described. Two electrokinetic methods (streaming potential and sedimentation potential) were used to determine the ζ potential of the system. The surface conductivity had a great influence on the streaming potential measurements. Levines theory, referring to the capillary model, was used to determine the ζ potential from streaming potential data, and the correction factor Fc was significantly different from one for κr < 160. The ζ potential thus obtained was nearly equal to that obtained from sedimentation potential data.

Irreversible thermodynamics of transport processes through porous media composed of particles of different size

An experimental investigation on liquids transport through porous media is described. Porous diaphragms of pyrex glass particles, whose sizes were in three ranges, between 150 and 500 micrometers, as well as water, methyl-, ethyl-, and isopropyl alcohols have been used to perform the hydrodynamic and electroosmotic experiments. The hydrodynamic flow is linearly dependent of the pressure difference and independent on the direction of the flow. The dependence of L11 on the size of the particles forming the porous diaphragm agrees with that predicted by the classic theory of the electrokinetic phenomena. The electroosmotic coefficient L12 has been found to decrease as the particle size increases, this being verified for all the permeants used. This fact is explained on the basis of the Anderson and Kohs model. 31 references.

Flotation of fluorite with n-alkylammonium chlorides

Abstract Experimental study on the electrokinetic and flotation behaviour of fluorite in solutions of n-alkylammonium chlorides (with 10, 12 and 14 carbon atoms) is given. The zero point of charge (ZPC) of luorite was determined by measuring zeta potential (streaming potential method) as a function of pH. Two conditioning times of the mineral with the solution were used (10 minutes and 48 hours) and the respective ZPC were located at pH 2.2 and 8.4. Decyl-, dodecyl- and tetradecylammonium ions seem to be strongly adsorbed on the interface because they made the zeta potential more positive as the concentration increases. Hallimond tube flotation of fluorite was studied and shown to be influenced by the chain length of the collector and both collector and hydrogen ion concentrations. Flotation recovery for a given concentration of collector increases with the number of carbon atoms of the chain. The results have been discussed in the light of the electrical double-layer theory.

On the adsorption of n-alkylammonium chlorides at fluorite/solution interface

Abstract Experimental adsorption isotherms of alkylammonium chlorides (with 10, 12 and 14 carbon atoms) on fluorite are given. For the monolayer region two straight segments have been obtained. They are interpreted, on the basis of the Frumkin-Fowler model of adsorption on heterogeneous surfaces, as being due to the adsorption on two different domains with different potential energies. The model has been used to obtain the normal interaction energy adsorbate-adsorbent. Also, chain-chain interaction has been discussed on the basis of the theory of Cases et al., based on the Frumkin-Fowler model discussed above. The changes in the thermodynamic quantities enthalpy and entropy related to the process were calculated using the Clausius-Clapeyron equation. Isosteric heat of adsorption has been found to be negative for 0 θ θ = 0.1. The global change in entropy is only positive for θ θ

On the electrokinetic energy conversion in liquid mixtures

Abstract The dependence of the maximum efficiency of the electrokinetic energy conversion (η) max on the composition of the liquid mixtures can be correlated to changes of the absolute viscosity, the dielectric constant and the specific electric conductance of these mixtures.

Determination of the Electrokinetic Coefficient L 12 from Sedimentation Potential Measurements

The phenomenological coefficients Ln and L12 describing the electric conductivity and the electrokinetic effect respectively, for the systems pyrex-water and pyrexaqueous KC1 have been obtained from sedimentation potential measurements. The dependence of L12 from the amount of particles sedimenting between the electrodes W, i. e. the function L12 = f(W) was found to be linear in the range 0 < W < 1,4 g. The coefficient L12/M has been introduced, M being the density of particles sedimenting between the electrodes. This coefficient varied linearly with the temperature in the range 17—35 °C. Finally, the dependence of L12/M on the concentration of KC1 and on the size of the sedimenting particles has been determined. Introduction The study of electrokinetic phenomena from the viewpoint of Thermodynamics of Irreversible Processes has as an important goal the characterization of the phenomenological coefficients, that appear in the equations which relate the generalized fluxes to the forces of the system. The electrokinetic measurements most frequently effected are those of the streaming potential, the electroosmotic flow, and above all the electrophoretic mobility, while very litle attention is paid to sedimentation potentials. This fact has been repeatedly stated [1—2], with the warning that the apparent simplicity of the physical basis of the phenomenon is misleading. Effectively, very few results appear in the scientific literature [3—7], owing to the exceedingly difficult setting up of this technique, as well as to the multiplicity of factors that affect the reproducibility of the measurements. We have proposed in a previous publication [8], an experimental device and a procedure which allow a simple determination of sedimentation potentials with a good reproducibility (~ 3%). In this work we have tried to determine the coefficient L12, which characterizes the electrokinetic effect produced by the sedimentation of particles. For this effect, we propose the use of the intensive magnitude L12/M, with M 0340-0204/79/0004-0119S02.00

Thermodynamic excess quantities in the adsorption of sodium alkylsulfonates at the air-solution interface

Data on the surface tension of sodium alkylsulfonate solutions at different temperatures and surfactant concentrations are presented. By applying the thermodynamic treatment of Guggenheim, changes in the thermodynamic excess quantities associated with the adsorption were evaluated. The entropy, enthalpy and internal energy of interface formation are positive and become more positive as both the surfactant concentration and the temperature increase. The adsorption of alkylsulfonate ions at the air-solution interface is a favorable process from the entropic viewpoint, while it is an unfavorable one from the energetic viewpoint. The increase of the entropy overcomes the disadvantage of the gain of energy.