Impact of molecular structure on zeta potential and adsorbed conformation of α-Allyl-ω-methoxypolyethylene glycol - Maleic anhydride superplasticizers

Abstract

α-Allyl-ω-methoxypolyethylene glycol - maleic anhydride copolymers were synthesized with side chain lengths nEO from 0-130 and characterized by aqueous GPC. A representation of their molecular conformation (e.g. worm-, brush- or star-like polymers) was developed. The amount of polymer adsorbed on cement rapidly decreases with increasing side chain length nEO. Zeta potential measurements using the electroacoustic method in cement paste with w/c = 0.5 indicate that worm-like copolymers with nEO ≤ 7 adsorb flat ("train" type) and form a densely packed, thin polymer film. In this case, the adsorbed amount of copolymer is high. For star polymers with nEO ≥ 34, preferred orientation of the polymer main chain is perpendicular to the cement surface ("tail" type). The result is a thick polymer layer, with a second electrochemical double layer on top. For star polymers, the adsorbed amount is low because of the higher surface occupancy of horizontally layered side groups. Copyright © 2006 Japan Concrete Institute.