Molecular dynamics simulations of the solubility of chitosan grafted polyacrylamide and its adsorption mechanism with kaolinite: Impact of length and distribution of branched-chain.

Graft modification can effectively improve the flocculation performance of chitosan. In this work, molecular dynamics simulations were employed to investigate the water solubility of chitosan-grafted polyacrylamide (CTS-g-PAM) and its adsorption mechanism with kaolinite, focusing on the effects of branched-chain length and distribution. The solubility parameters obtained from the simulations align better with those calculated using the group contribution method. The radius of gyration (Rg), solvation free energy (∆GSFE), mean square displacement and diffusion coefficient were utilized to analyze changes in solubility of these CTS-g-PAM in aqueous solution. The adsorption interaction between CTS-g-PAM and kaolinite was investigated using interaction energy and diffusion coefficients. The water solubility of CTS-g-PAM initially increased, followed by a subsequent decrease as the length of branched-chain increased along with a decrease in their number. Similarly, the adsorption interaction between CTS-g-PAM and kaolinite increased firstly followed by a decrease with increasing branched-chain length. The magnitude of interaction energy with kaolinite (0 0 1) followed the order of CA10-12 (−826.227 kcal/mol) >CA8-15 (−744.583 kcal/mol) >CA6-20 (−637.366 kcal/mol) >CA12-10 (−598.109 kcal/mol). These trends align with the findings of flocculation tests. Our work provides a theoretical basis for designing chitosan-based flocculants with enhanced water solubility and improved flocculation efficiency. [ABSTRACT FROM AUTHOR]