Molecular dynamics study of linear and comb-like polyelectrolytes in aqueous solution: effect of Ca²⁺ ions

Abstract

All-atom molecular dynamics simulations were employed to provide microscopic mechanism for the salt tolerance of polyelectrolytes dispersants. The conformational variation of polyelectrolytes and interactions between COO⁻ groups and counterions/water molecules were also studied via radius of gyration and pair correlations functions. Sodium polyacrylate (NaPA) and sodium salts of poly(acrylic acid)–poly(ethylene oxide) (NaPA–PEO) were selected as the representative linear and comb-like polyelectrolyte, respectively. The results show that Ca²⁺ ions interact with COO⁻ groups much stronger than Na⁺ ions and can bring ion-bridging interaction between intermolecular COO⁻ groups in the NaPA systems. While in the NaPA–PEO systems, the introduced PEO side chains can prevent backbone chains from ion-bridging interactions and weaken the conformational changes. The present results can help in selecting and designing new-type efficient polyelectrolyte dispersants with good salt tolerance.

Keywords:

• molecular dynamics simulation
• comb-like polyelectrolytes
• Ca²⁺ tolerance
• radius of gyration
• pair correlations functions

Acknowledgements

Thanks to Dr Guoping Xiao and Dr Jing Zhou, Shanghai Institute of Applied Physics, for the generous allocations of computing time. We are thankful to Prof. George Jackson and the reviewer for their constructive comments, which are helpful to improve the quality of our manuscript.