Interaction between Ca ions and poly(acrylic acid) chains in macro-defect-free cements: A theoretical study

Several experimental and theoretical studies have related the peculiar mech anical properties of the macro-defect-free polymer-cement composites with t he existence of a cross-linking of the polymer chains by Al or Ca ions comi ng from the hydration reactions of the cement. In the present study, the in teraction of Ca ions with the -COO- groups of one or two poly(acrylic acid) (PAA) chains has been investigated with first-principles theoretical metho ds in order to achieve evidences of PAA cross-linking. The present results show that a stable CaO4 complex can be formed by a Ca ion and the O atoms b elonging to the -COO- groups of two polymer chains, This implies the existe nce of a quite efficient cross-linking because a Ca ion becomes anchored to four points of two PAA chains. The stretching frequencies of several Ca-O and C=O bonds have also been estimated. The achieved results suggest that i ndirect evidence of the PAA cross-linking could be obtained by infrared spe ctroscopy measurements,