Screening-enhanced effect enables poly(hexamethylene biguanide) hydrochloride to effectively overcome charge screening limitations

Abstract The charge screening caused by ionic strength always brings about negative effects. Poly(hexamethylene biguanide) (PHMB) was found to possess screening-enhanced effect and could effectively overcome charge screening limitations. However, the mechanism of action is unknown. We hereby combine flocculation experiments and theoretical simulations through density functional theory and molecular simulation to unravel the screening-enhanced effect. The biguanide groups of PHMB serve as primary active adsorption sites and activate the hydrogen atom in neighboring alkyl chains, which raises the binding possibility in the flocculation process. Electrolyte ions hardly affect the weak interactions but increase PHMB inter-segment stacking absorption and promote the hydrophobic effect of flocculation complexes, thereby enhancing the flocculation performance. The results suggest that the binding forces primarily arose from dispersion-dominant weak interactions, indicating a weak-interaction-dependent mechanism. This study may lay a solid foundation for developing screening-enhanced materials with the powerful capabilities of anti-charge screening limitations for specific application scenarios.