Atomistic Molecular Dynamic Simulation of Dilute Poly(acrylic acid) Solution: Effects of Simulation Size Sensitivity and Ionic Strength

Physical properties of polyelectrolytes have been shown to be significantly related to their chain conformations. Atomistic simulation has been used as an effective method for studying polymer chain structures, but few simulations have focused on the effects of chain length and tacticity in the presence of monovalent salts. This paper investigated the microscopic conformation behaviors of poly(acrylic acid) (PAA) with different chain sizes, tacticities, and sodium chloride concentrations. The hydrogen behaviors and corresponding radial distribution functions were obtained. The results showed that the increase of salt concentrations led to the collapse of PAA chains, especially for longer chains. It was found that the effects of salt were mainly attributed to the shielding screening effect by sodium ions rather than the hydrogen bonding effect. Two different structures were formed by isotactic PAA and syndiotactic PAA, respectively, which were due to the deprotonation patterns along the PAA chain.