Study of interactions at water-soluble polymer/Ca(OH) 2 or gibbsite interfaces by XPS

Abstract

In an attempt to better understand interactions occuring at hydrated cement/organic polymer interfaces, the reaction mechanism and products formed at the interfaces between poly(acrylic acid), p(AA) or poly(acrylamide), p(AM), and Ca(OH) 2 or gibbsite, Al 2O 3·3H 2O, were explored using x-ray photoelectron spectroscopy (XPS). It was estimated that at p(AA)/Ca(OH) 2 interfaces, a Ca-complexed carboxylate interfacial reaction product was formed by an ionic reaction between the COOH in p(AA) and Ca 2+ ions from Ca(OH) 2. A similar reaction product was formed at p(AM)/Ca(OH) 2 interfaces as a result of an inter-facial transformation of amide in p(AM) into carboxylic acid, caused by the alkali-catalyzed hydrolysis of the amide. The proton-accepting hydroxyl groups existing at the outermost surface sites of Al 2O 2·3H 2O react favorably with proton-donating COOH groups in p(AA). This acidbase interaction at the p(AA)/Al 2O 3·3H 2O joint formed hydrogen bonds. Whereas, when the p(AM) was applied on Al 2O 3·3H 2O surfaces, interfacial electrostatic bonds were formed through charge-transferring reaction mechanisms in which the charge density was transferred from the Al in Al 2O 3·3H 2O to the C=0 oxygen in p(AM).