Study on Mechanism of Surfactant Influencing on Sludge Dewatering Performance: Molecular Dynamics Simulations of the Interaction between Gemini Surfactant and Polyelectrolyte

Surfactants can be adsorbed with extracellular polymeric substances (EPS) to form micelles with the release of both free and bound water molecules, and this process could be used to improve the performance of the sludge dewatering process. In this paper, coarse-grained molecular dynamics ( MD) simulations were adopted to study the formation and structure of complexes resulting from the mixing of a Gemini surfactant and EPS. The hydrophobic or hydrophilic performance of the polyelectrolyte had a significant impact on the adsorption process. The main driving force for adsorption between the hydrophilic polyelectrolyte and the Gemini surfactant was electrostatic attraction, where the head group of the Gemini surfactant was adsorbed onto the chain with the tail chain pointing towards the solvent. The adsorption process between the hydrophobic polyelectrolyte and the Gemini surfactant was influenced by both electrostatic and hydrophobic effects, with the Gemini surfactant being oriented parallel to the configuration of the polyelectrolyte chain. The coupling group length of the Gemini surfactant had very little influence on the adsorption process. Variations in the charge density of the polyelectrolyte chain aided the adsorption of the hydrophilic polyelectrolyte, but had no impact on the adsorption of the hydrophobic polyelectrolyte.