A DFT Study on the Adsorption of Carboxyl-Containing Monomers on CH (001) Surface
Xiaodan Miao, Shiming Zhou, Chunyu Wang
Abstract
This paper studied the adsorption of carboxyl-containing monomers on portlandite (CH) surface based on density functional theory (DFT) method, attempting to explain the retardation of cement slurry due to nucleation. The geometric structure, bond length, adsorption energy, charge transfer, difference charge density and partial density of states (PDOS) were calculated. The results indicated that all four carboxyl-containing monomers (acrylic acid, citraconic acid, itaconic acid, and maleic acid) had strong adsorption energies on CH (001) surface. The adsorption energies of citraconic acid, itaconic acid, and maleic acid on CH (001) had little difference, which were nearly twice that of acrylic acid on CH (001). In addition, the charge density difference and PDOS results proved the strong adsorption. The charge density of the area between O atom of the carboxyl group and Ca atom on CH (001) surface increased. The overlapping of peaks and the hybridization occurred between Ca 3d and O 2p orbits. The study of this paper deepens the understanding of the retarding mechanism on oil well cement.