All-atom molecular dynamics simulation of acrylamide-based triblock copolymers with thermal responsive end blocks in a mixed salt solution containing divalent cations

Abstract

In this work, a new smart copolymer based on polyacrylamide with the triblock classification was presented in order to propose an efficient associating polymeric material to create a physical network structure in saline water. To tune the desired copolymer, the effect of amide's type and hydrophobic pendant moieties of the potentially thermoresponsive end blocks on the physicochemical characteristics of the intermediate water-soluble block was studied in a solution containing Ca2+, Mg2+ and Cl− via atomistic simulations. The investigation of ions' mechanism of action on the water's perturbations via the calculation of water's orientational order parameter demonstrated that the divalent ions, as strong chaotropic agents, changed the water's tetrahedrality. Moreover, the coordination complexes created by the divalent ions as the coordination center and the negatively charged elements of the blocks' amides as the complexing agents intensified this issue in the block-water interface via increasing the interfacial concentration of the cations. This phenomenon has affected the blocks' hydrophilicity and hydration levels, capturing and ordering of water by changing the water's interfacial tetrahedral H-bond network structure. These behavioral variations in the solution led to changes in the dimensional, conformational, dynamic and interactional characteristics of the copolymers' blocks.