Influence of surfactant counterions during electrophoretic particle deposition.

This study demonstrates the influence of a cationic surfactant on colloidal particle electrodeposition (migration and adhesion). Three cetyltrimethylammonium salts (CTA+) with various counterions (bromide, chloride, and hydrogenosulphate) were studied. Particle transport toward the electrode was driven by the electrophoretic force. Once particles reached the electrode, a wide variety of behaviors were observed, depending on surfactant concentration and counterions: particles would stick permanently or slide along the electrode surface, remain or detach upon potential switching, act as nuclei for aggregate growth, or produce a homogeneous particle film. The experimental results also demonstrate the specific influence of surfactant counterions on the deposited film morphology.

Stability of self-assembled polymer films investigated by optical laser reflectometry.

We studied the influence of post-treatment rinsing after the formation of self-assembled polyelectrolyte films made with the weak base poly(allylamine hydrochloride) (PAH) and the strong acid poly(styrene sulfonate) (PSS). The stability of the film was studied using optical fixed-angle laser reflectometry to measure the release of polymeric material and AFM experiments to reveal the change of morphology and thickness. We found that the polymer films were stable upon rinsing when the pH was the same in the solution as that used in the buildup (pH 9). The films released most of the polymeric material when rinsed at higher pH values, but a layer remained that corresponded to a PAH monolayer directly bound with the silica surface. Films containing at least four bilayers were stable upon rinsing at lower pH values, but the stability of thinner films depended on the type of the last polymer deposited. They were stable in the case of PSS as an outermost deposit, but they released a large part of their material in the case of PAH. The stability results were determined using a simple model of the step-by-step assembly of the polymer film described formerly.

Removal of some divalent cations from water by membrane-filtration assisted with alginate.

The removal of divalent metal ions from hard waters or galvanic wastewater by polymer-assisted membrane filtration using alginate was investigated. The ability of this natural polymer to form aggregates and gels in presence of metal ions was studied, in order to carry out metal removal by ultra or micro-filtration. Alginate titrations have shown the presence of amine groups in addition to carboxylates onto the polymer backbone. The binding properties of alginate with divalent cations have been studied, showing an increasing affinity for Ca2+ over Mg2+ as polymer concentration increases, and the relative affinity Pb2+ > or = Cu2+ > Zn2+ > Ni2+. The softening of hard natural waters was achieved successfully and easily, but needs an optimal alginate concentration approximately 4 x 10(-2) M. The alginate powder can be directly added to hard waters. Except for Ni2+, metal-removal was efficient. Polymer regeneration has shown that Cu2+-complexes are labiles.

Adsorption of barium and calcium chloride onto negatively charged alpha-Fe(2)O(3) particles.

Adsorption of cations (Na(+), Ca(2+), Ba(2+)) onto negatively charged (pH 10.4) hematite (alpha-Fe(2)O(3)) particles has been studied. The oxide material was carefully prepared in order to obtain monodisperse suspensions of well-crystallized, quasi-spherical particles (50 nm in diameter). The isoelectric point (IEP) is located at pH 8.5. Adsorption of barium ions onto oxide particles was carried out and the electrophoretic mobility was measured throughout the adsorption experiment. Comparison with calcium adsorption at full coverage reveals a higher uptake of Ba(2+). In both cases it shows also that chloride ions coadsorb with M(2) ions. Simultaneous uptake of the positive and negative ions explains why the electrophoretic mobility does not reverse to cationic migration. A theoretical study of the surface speciation has been carried out, using the MuSiC model. It reveals the presence of negative as well as positive sites on both sides of the point of zero charge (PZC) of the hematite particles, which may explain the coadsorption of Ba(2+) and Cl(-) at pH 10.4. The effective charge of the oxide particles, calculated from the electrophoretic mobility, is in very good agreement with the results found with the MuSiC modelization and the chloride/barium adsorption ratio. It also verifies the theory of ionic condensation. Calorimetric measurements gave a negative heat for the overall reaction occurring when Ba(2+)/Cl(-) ions adsorb onto hematite. Despite the fact that anions (Cl(-) and OH(-)) adsorption onto mineral oxides is an exothermic phenomenon, it is likely that barium and calcium adsorption is endothermic, denoting the formation of an inner-sphere complex as reported in the literature.