Adsorption Of Polyacrylic Acid Research Articles

Stabilization and Processing of Aqueous BaTiO3 Suspension with Polyacrylic Acid

Polyacrylic acid (PAA) has been chosen to stabilize BaTiO3 powder in aqueous solution. Zeta potential studies show that the Ba‐rich particle surface is positively charged in the pH range from 2 to 11 without PAA. Adsorption of PAA decreases the zeta potential in acidic solution and changes the surface to a negative charge in basic solution. Adsorption of PAA onto BaTiO3 surfaces is found to be related to the pH‐dependent PAA conformation in solution. The amount of PAA adsorbed at pH 1.5 is one order of magnitude more than at pH 10.5, due to a more compact polymer conformation. Colloid stability of aqueous BaTiO3 suspension is related to the dissociation of PAA as a function of pH. BaTiO3 suspensions can be stabilized at pH values higher than 7, where more than 99% of carboxylic groups are ionized. At pH 10.5, suspension stability is related to the PAA coverage on BaTiO3 particle surface. Stabilization can be achieved only when conditions of both PAA ionization and BaTiO3 surface coverage are satisfied, suggesting an electrosteric stabilization mechanism. Green density of 62% can be achieved by slip casting at a pH above 10, compared to the best density of 58.6% by isostatic pressing at 242 MPa.

Selective flocculation of tribasic calcium phosphate from mixtures with quartz using polyacrylic acid flocculant

Selective flocculation of tribasic calcium phosphate (TCP), a model system for apatite, from mixtures with quartz using polyacrylic acid (PAA) was studied as a function of molecular weight of the polymer and suspension pH. A feed (1 : 1 synthetic mixture) assaying 21% P 2O 5 was upgraded to 32% P 2O 5 at recovery levels of 75–80%. Optimum separation was observed in highly alkaline conditions (pH 11). Electroacoustic studies carried out on the TCP/PAA system showed a definite shift in the isoelectric point (i.e.p.) as a result of PAA adsorption. Diffuse reflectance FT-IR investigations strongly suggested the formation of calcium carboxylate bonds in the PAA coated TCP surface. The adsorption of PAA on TCP thus appears to occur primarily by chemical bonding between the carboxyl groups of PAA and calcium sites on the TCP surface.

The electrochemical testing of polyacrylic acid and its derivatives as inhibitors of corrosion

The adsorption of polyacrylic acid (PAAC) and polyacrylamide (PAA) (Mn = 10 4-10 6 g mol −1) on the metal (Au) and/or metal/oxide (Au/Au 2O 3; Au/FeOOH)-solution interfaces was investigated using cyclic voltammetry and double-layer capacity measurements. PAA strongly adsorbs on Au and Au/Au 2O 3 interfaces, from a neutral solution, and has a negligible influence on the Au/FeOOH-solution interface. PAAC also strongly adsorbs on Au, from acidic solutions, but shows a small influence on the Au/Au 2O 3-solution interface. The presence of PAAC in the solution and/or metal-solution interface decreases considerably the rate of the electron transfer reaction Fe 3+ Fe 2+ . This effect can be explained by a conformational behaviour of Fe(H) or Fe(III)-PAAC complex at a metal-solution interface, changing the shape of the potential energy barrier. The stability constants of such complexes depend on the polymer molecular weight and the oxidation state of Fe ions. The application of these polymers as corrosion inhibitors for iron and steel in sulphuric and hydrochloric acids shows a fairly good protection efficiency (up to 80%).

Adsorption of polyacrylic acid on titanium dioxide

The adsorption isotherms of polyacrylic acid on titanium dioxide (anatase) have been determined in aqueous solutions. The influence of pH, polymer's average molecular weight, and calcium concentration was investigated. Particular attention was paid to the substrate's surface charge and to the polymer's dissociation to explain the adsorption level. Incidence of the polymer adsorption on the solid's particle charge and the dispersion stability was examined. At an alkaline pH, unfavorable electrical forces lead to a low adsorption level where the adsorbed polymer was more likely to lie flat on the surface. Calcium ions gave a bidentate complex with the polymer. The adsorption was enhanced and linearly dependant on the calcium concentration. At intermediate pH adsorption was highly favored by the opposite charges of the surface and the polymer. Evidence was obtained for a flat configuration of the adsorbed molecule at low polymer concentrations, and for a gradual change to a configuration where only a few segments were directly associated with the surface, the rest being in tails or loops protruding in the solution. The solid particles' electrophoretic mobility was closely related to the polyacrylic acid adsorption and to the dispersion stability.

Adsorption of polyacrylic acid at oxide/water interfaces

The adsorption of polyacrylic acid (PAA) on rutile (TiO 3) and hematite (Fe 2O 3) has been studied as a function of pH. The uptake of PAA at the adsorption plateau level was observed to decrease with increasing pH until near-zero values of adsorption occurred near the isoelectric point of the oxide. Adsorption of PAA is correlated to the amount of positive surface charge on the oxide particles. Electrophoretic mobility measurements Indicate that some specific adsorption occurs at the pH of the isoelectric point of the oxides.

Selective flocculation of hematite in the hematite-quartz-ferric ion-polyacrylic acid system. Part 1, activation and deactivation of quartz

This investigation has shown that quartz can be activated for polyacrylic acid adsorption by hydrolyzing metal cations, similar to activation in flotation. Detailed experiments on activation phenomena with ferric ions have been performed. The flocculation of activated quartz can be prevented by suitable additions of disodium EDTA, sodium hexametaphosphate or potassium fluoride. Selective flocculation of hematite with polyacrylic acid from a hematite/quartz mixture can be achieved in the pH range 3 to 9, but the process is not selective in the presence of ferric ions. Suitable additions of EDTA or KF are particularly successful in preventing quartz activation by ferric ions and the facilitating selective flocculation of hematite in artificial mixtures of quartz and hematite.