Jalel Mhalla - Academia.edu (original) (raw)

Papers by Jalel Mhalla

JOURNAL OF ADVANCES IN CHEMISTRY, 2014

In this paper, we propose a new approach in order to interpret the variation of the conductibilit... more In this paper, we propose a new approach in order to interpret the variation of the conductibility of the PSS polyion with the nature and the concentration of the alkaline counter-ions Li+, Na+ and K+, and the hydrophobic cations Et4N+ and Bu4N+. This approach is based on a recent model in which the stretched polyion is represented by a chain of successive charged spheres, partially condensed by the counter-ions. We have found that the moderate variation of the hydrodynamic friction on the polyion with the size RM of condensed counter-ions, cannot completely explain the important decrease (of about 35% from K+ to Bu4N+) of the conductibility (lPSS,M ) of the PSS polyion with the nature of the counter-ions. Consequently, we have proposed a supplementary explanation by taking into account of the translational dielectric friction on the moving polyion. Formal analysis of this friction shows that it is very sensitive to the local structure of water surrounding the polyions. As this loca...

Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 1978

In this study, we derive the general solution of the diffusion equation for multicomponent system... more In this study, we derive the general solution of the diffusion equation for multicomponent systems, even with non-constant diffusion coefficients, in the case of limiting conditions corresponding to the open-end capillary method.For this purpose, it was necessary to obtain the complete expression of the diffusion coefficients Dij by a detailed analysis of the diffusion processes in an electrolyte solution in the framework of irreversible thermodynamics.We show for some particular examples that these methods are powerful in the derivation of the phenomenological coefficients Lij and Dij from experimental measurements; and that the coupling will induce transient concentration gradients for initially homogeneous species.

Berichte der Bunsengesellschaft für physikalische Chemie, 1979

Transient concentration gradients, for initially homogeneous species, in electrolyte solutions, a... more Transient concentration gradients, for initially homogeneous species, in electrolyte solutions, are experimentally observed and theoretically analyzed. These heterogeneous regions are mainly produced by transient diffusion potentials induced by multicomponent diffusion in electrolyte solutions. Similar effects can be produced by gradients of activity coefficients (or by microscopic perturbations, such as effects of electrophoresis or of relaxation). The initial conditions for the creation of such gradients are analyzed in the general framework of irreversible thermodynamics.

Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 1981

The Journal of Physical Chemistry, 1977

Tracer and Mutual Diffusion in Electrolyte Solutions 485-HC1+ Br at 300 and 1000 K. We are not ce... more Tracer and Mutual Diffusion in Electrolyte Solutions 485-HC1+ Br at 300 and 1000 K. We are not certain how close an analogy there is between the C1+ HBr and C1+ HI systems, though it does seem reasonable to expect qualitative similarities in the scattering. Trajectory calculations on C1+ HI-HC1+ I using a surface of the same formulation as used here gave forward scattering a t temperatures of 1000 and 2000 K, but isotropic to backward scattering at 300 K.21 Acknowledgment. D.L.T. wishes to express his graditude to the Departments of Physics and Chemistry at Ole Miss for their hospitality during the course of this work.

Pure and Applied Chemistry, 1985

The use of radioactive isotopes of ions, of labelled molecules of solvents, and of tritiated wate... more The use of radioactive isotopes of ions, of labelled molecules of solvents, and of tritiated water, makes it possible to follow the migration of all individual components in a mixed electrolyte solution. Different kinds of experimental devices were perfected in order to determine the flux of each radioactive component as it migrated by several mechanisms such as : self-diffusion, mutual diffusion, ionic mobility under electric field, solvent drag by ion migration, etc... Even if these results could be qualitatively interpreted in terms of ion-ion and ion-solvent interactions, the best formalism to represent this large number of experimental data was found to be within the framework of the formalism of irreversible thermodynamics so as to extract the phenomenological coefficients, since the flux of each species i can be written as J. =-1.. Vii.-' 1. v i ij j in n j where subscript j indicates an ionic species in the solution and subscript n is used for a neutral molecule of a sol vent component. This description of migration phenomena yields a symmetrical concept for solvation which appears as a reciprocal ionsolvent interaction. It follows, from the theorem of reciprocity, that the transport of solvent molecules by ions can be deduced from the flux of ions induced by the neutral components flow exerted by a gradient of solvent composition. This method, called ion-solvent coupled transport, allows the quantitative determination of preferential solvation numbers. These agree very well with other properties such as those derived by NMR techniques or other transport data. When compared to the values of for transfer from water to the same mixeu electrolyte solutions., useful conclusions are drawn concerning the distinction that must be made between the equilibrium solvation parameters and that obtained from transported solvent by ions in irreversible processes.

Journal of Molecular Liquids, 2016

Abstract In this paper we have generalized on the basis of the superposition principle, the Debye... more Abstract In this paper we have generalized on the basis of the superposition principle, the Debye-H u ckel model in the case of a spatial distribution of “n” fixed ions surrounded by an ionic atmosphere. According to this approach, the mean electrostatic potential at a position M is written as a sum of individual screened Coulomb potentials: ∑ n i = 1 (Z i e/e)A i exp(− χr i )/r i . The electro-neutrality condition allows the obtaining of the exact expression of the superposition coefficients {A i } in terms of the elements {D i j } of an explicit n–n matrix [ D ] which depend on the effective radii R i of the ions and on their distances of separation d ij . As applications: a) we have improved the expression of the PMF's approximation of Debye; b) we have simplified and resolved in the limits of this model, the BBGKY hierarchy, in order to obtain the PMF potential W ij (d ij ) and hence the screen parameter χ from the second Stillinger–Lovett restriction; c) we have also proposed an explicit expression for the electrostatic part of the DLVO potential; and finally, d) we have justified and improved the potentials of interaction of Yukawa between chain groups in the case of polyelectrolyte solutions.

Journal of Radioanalytical and Nuclear Chemistry, 2009

ABSTRACT The capillary electrophoresis method has been applied to the speciation study of uranium... more ABSTRACT The capillary electrophoresis method has been applied to the speciation study of uranium(VI) at room temperature, in 0.02M citrate buffer solutions, at pH values between 2.5 and 5.5 and at citrate/U ratios between 20 and 40. No negatively charged species have been pointed out at pH values lower than 3. For a pH value higher than 5, the electropherograms are ill-defined and the signals cannot be analyzed simply (owing to a highand rough baseline). In the pH range 3–5, up to 4 peaks can be attributed to U(VI) species. Two of them are likely due to the expected monomer [(UO2)(Cit)]–and dimer [(UO2)2(Cit)2]2– complex species and these species are shown to be in quasi-equilibrium with two other species possessing slightly lower migration velocities, [(UO2)H(Cit)(OH)]– and [(UO2)2H2(Cit)2(OH)2]2–, respectively. Speciation diagrams calculated by an exact analytical approach are proposed in order to explain the experimental results. A complete agreement between theoretical and experimental results needs to take into account kinetic and hydrolysis effects.

Journal of Molecular Liquids, 2007

In a previous work, we have verified that sodium chondroitin sulfate in water at 25 °C, presents ... more In a previous work, we have verified that sodium chondroitin sulfate in water at 25 °C, presents a correct Manning behavior (αM=0.81). In contrast, we expect that the rate of condensation α is shifted from its Manning value (αM=0.36) in water–dioxane (50% wt) mixture at 25 °C, (α≅0.47). In order to verify this dioxane effect, we have compared experimental equivalent conductibility Λexp of sodium chondroitin sulfate in water (no shift) and water–dioxane (50% wt) mixture (positive shift), to their theoretical values ΛM, Λcth and Λsth corresponding respectively to the Manning cylindrical and spherical models. Indeed, except some cases, α must obey to Ostwald's principle of dilution (α→1 when CNa+→0), according to the following “rod-like model” approximation:(1−α)≈|Zi|(πbS)[4⁢πZi2Lb][−bS″α][αCiR2][1−bS″α];with:bS″=αM−1However, only in pure water at 25 °C (ε=78.3), the exponent [1−bS″α] of sodium chondroitin sulfate is zero and therefore: α=αM.

Journal of Molecular Liquids, 2010

We present an accurate generalization of the Zwanzig's approach in order to calculate the transla... more We present an accurate generalization of the Zwanzig's approach in order to calculate the translational dielectric friction ξ D and the effective mobility u eff of an ellipsoidal polyion of Z S e charge, R minor axis and (γ = L/2R) eccentricity. ξ D = (2/3)τ(ε 0 − ε ∞)ε 0 − 2 (α c Z S e) 2 (R app) − 3 , τ is the dielectric relaxation time, ε 0 and ε ∞ are the static and high-frequency dielectric constants of the solvent. u eff = u p (1 + β′ df) − 1 , where u p = |(α c Z S e)/6πηC ap ′ | expresses both hydrodynamic friction and electrophoretic effect. η is the viscosity of the solvent, (1 − α c) is the degree of condensation of the counterions on the surface of the polyion and C ap ′ is its "Gouy capacitance". β′ df = (2/3)|(α c)Z S | 2 (1 − ε ∞ ε 0 − 1)(R w ∕ R app) 3 (L B ∕ C ap ′), where R w is the solvent radius, L B is the Bjerrum length. R 3 app appears as an "apparent volume" (different from the volume of the polyion) from which the dielectric medium must be excluded. Indeed, R app depends on the shape of the polyion: R app =R for spheres (γ = 0), R app ≈ b R N (mean radius) for spheroids (γ b 1) and R app ≈ L/2 for ionic prolates (γ N 1). A more precise (i.e. not ad hoc) expression of R app (γ) is also presented. These practical formulas are useful for the study of the dependence of the conformation of micelles and coiled polyions with the concentration.

Journal of Molecular Liquids, 2012

ABSTRACT Above the cmc, aqueous solution of sodium dodecyl sulfate SDS is an ionic mixture consti... more ABSTRACT Above the cmc, aqueous solution of sodium dodecyl sulfate SDS is an ionic mixture constituted of micelles of apparent charge number Zap, free counterions Na+ and free monomers SD-. The degree of micellization and the degree of condensation of Na+ on the micelles are calculated according to the mass-action model and by the generalization of the Fuoss ionic association theory. In the first part of thiswork, conductance data of thismixture are analyzedwithin the framework of the Onsager–Kim–MSA conductivity theory of mixed electrolytes and that of the Zwanzig dielectric friction theory. It appears that the micellization process is a progressive continuous “micro-phase transition” highly correlated to the degree of condensation of counterions. In the second part, we show how (in contrast with spectroscopic techniques) the high precision conductivity technique, combined to the theories mentioned above, can detect the absorption of the hydrophobic BPh4 - anions by SDS micelles in dilute aqueous solutions: Because of the affinity of the BPh4 - ions to the nonpolar side chains inside SDS, eachmicelle incorporates nBPh4–anions (hydrophobic reactivity). This number is determined by adjusting theoretical specific conductance to its corresponding experimental value. Results show that Na+ condensation facilitates this absorption and that “nBPh4–” increases with dilution.

Chemical Physics, 2006

In this work, we generalized the (Bjerrum–Debye–Fuoss–MSA) double layer model to an ellipsoidal p... more In this work, we generalized the (Bjerrum–Debye–Fuoss–MSA) double layer model to an ellipsoidal polyion (chondroitin sulfate) of (∣Zs∣e) structural charge, Ls structural length, R minor axe and (R2+L2/4)1/2 major axe. With L⩽Ls. Na+ counter ions are distributed on the contact (or condensed) layer and on the Debye layer (ionic atmosphere). Both layers are ellipsoidal equipotentials of, respectively, R and d

The Scientific World Journal, 2014

We have proved in details that the dielectric friction remains the principal frictional effect fo... more We have proved in details that the dielectric friction remains the principal frictional effect for a stretched polyion modeled as a chain of charged spheres, whereas, in the case of Manning’s model (infinite thread with a continuous distribution of charge), this friction effect is nonexistent. According to this chain model, it is therefore possible to detect by conductivity measurements any transition from a coiled configuration (ellipsoidal model) to a stretched configuration during dilution process. We have also underlined the important interdependence between the dielectric friction and the ionic condensation of the counterions, in order to distinguish between the Ostwald regime and the Manning regime for which the degree of condensation is practically constant in a large range of concentrations.

Journal of Chemistry, 2013

We present a general description of conductivity behavior of highly charged strong polyelectrolyt... more We present a general description of conductivity behavior of highly charged strong polyelectrolytes in dilute aqueous solutions taking into account the translational dielectric friction on the moving polyions modeled as chains of charged spheres successively bounded and surrounded by solvent molecules. A general formal limiting expression of the equivalent conductivity of these polyelectrolytes is presented in order to distinguish between two concentration regimes and to evaluate the relative interdependence between the ionic condensation effect and the dielectric friction effect, in the range of very dilute solutions for which the stretched conformation is favored. This approach is illustrated by the limiting behaviors of three polyelectrolytes (sodium heparinate, sodium chondroitin sulfate, and sodium polystyrene sulphonate) characterized by different chain lengths and by different discontinuous charge distributions.