Simulation study of synergistic drag reduction properties of polymers based on polyurethane hydrophobic surface

The drag reduction synergy of four types of high-molecular polymers, namely polyacrylamide, poly(ethylene oxide), xanthan gum, and guar gum, with polyurethane hydrophobic surfaces, was investigated by both experiments and molecular simulations. The synergistic mechanisms of polymers and hydrophobic surfaces were revealed using Monte Carlo and molecular dynamics simulations in terms of interfacial interactions between polymers and water molecules, intermolecular interactions, and the adsorption conformation of polymers on hydrophobic surfaces. The addition of the polymer improved the hydrophobicity of the polyurethane surface, with flexible polymers having a more substantial effect than rigid polymers, according to both simulations and contact angle experiments. Furthermore, based on the transient configuration of polymer and water molecules moving on the hydrophobic surface, the kinetic process is divided into three stages: water molecule aggregation, water molecule-induced deformation, and polymer extension on the hydrophobic surface. Meanwhile, PAM and PEO combine directly with hydrophobic surfaces and form a cover layer with water molecules, whereas XG and GG prefer to form aggregates with water molecules first and then transfer to hydrophobic surfaces. The PAM-polyurethane hydrophobic surface, in particular, has a better synergistic effect than others, and its synergistic mechanism is related to the larger radius of gyration, stronger interaction with water molecules, and higher stability of the drag reduction system.