Adsorption of sodium/calcium poly(acrylic acid) salts on anatase: effect of the polyelectrolyte molecular weight and neutralization

Abstract: Interactions of poly(acrylic acid)s (PAAs) of two different molecular weights (Mw = 9,560 g×mol-1 and 4,220 g×mol-1) with surfaces of an untreated anatase TiO2 were assessed through adsorption isotherm measurements. Those dispersants were tested under different sodium-calcium neutralization states (molar ratio r = Ca2+/CO2- varying from 0 to 0.35). Their behavior towards the TiO2 surfaces can be described by the Langmuir adsorption model. For both polymers, surface coverage (Γmax) evolves linearly with the molar ratio r. For a given r value, a lower surface coverage was observed with the polymer having the highest molecular weight. The free energy of adsorption (ΔGads) of PAAs was estimated from adsorption experiment data. This calculation indicates that sorption occurs spontaneously and is unlikely to be of chemical nature. The absolute values of ΔGads are higher for the highest molecular weight polymers suggesting that they are more strongly adsorbed to anatase surfaces. The absolute values of ΔGads per mole of sodium-calcium macromolecules are found to be lower than those calculated for their homologues 100% sodium neutralized suggesting that they are bound with the solid by a fewer number of segments.

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Opracowanie rekordu ze środków MNiSW, umowa Nr 461252 w ramach programu "Społeczna odpowiedzialność nauki" - moduł: Popularyzacja nauki i promocja sportu (2020).