Adsorption of sodium/calcium poly(acrylic acid) salts on anatase: effect of the polyelectrolyte molecular weight and neutralization
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Arkema Group
Publication date: 2019-11-24
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Christian Jacquemet   

Arkema Group
Physicochem. Probl. Miner. Process. 2020;56(1):113-123
Interactions of poly(acrylic acid)s (PAAs) of two different molecular weights (Mw = 9,560 g/mol and 4,220 g/mol) 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 (∆Gads) 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 ∆Gads are higher for the highest molecular weight polymers suggesting that they are more strongly adsorbed to anatase surfaces. The absolute values of ∆Gads 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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