Interfacial mechanism of amphiphilic polymers with Tuned Hydrophilic-Hydrophobic balance for enhanced oil recovery

Amphiphilic polymers are widely used to regulate oil–water interfaces and improve oil displacement, yet the role of hydrophilic–hydrophobic balance in coupling interfacial behavior, self-aggregation, and residual-oil mobilization remains unclear. Here, lignin-based graft copolymers (ALGCs) with systematically varied HLB values were synthesized and investigated using interfacial measurements, atomic force microscopy (AFM), sand-pack flooding, and molecular dynamics (MD) simulations. Increasing hydrophobicity accelerated the apparent interfacial response and reduced oil–water interfacial tension (IFT), but oil recovery did not vary monotonically with IFT. The ALGC with an intermediate HLB achieved the highest incremental oil recovery of 31.1%, showing that IFT reduction alone cannot predict displacement performance. AFM measurements showed that ALGC adsorption reduced the pull-off adhesion between model asphaltene-coated surfaces. MD simulations indicated competing effects of hydrophobicity: stronger hydrophobic interactions enhanced ALGC–asphaltene association, whereas excessive hydrophobicity promoted polymer self-aggregation and potentially decreased the availability of freely dispersed chains for effective interfacial interactions. These results indicate that oil-displacement performance is governed by the coupled effects of interfacial adsorption, self-aggregation, and asphaltene-associated adhesion. These findings provide mechanistic insights for the rational design of sustainable amphiphilic polymers for EOR and other interfacially controlled transport processes.