Design of Amphiphilic Silicon Quantum Dots to Reinforce Nonionic Surfactant Foam Stability for Enhanced Oil Recovery

Silicon quantum dots (SiQDs) with an ultrasmall size and high specific surface area exhibit great application in enhanced oil recovery, especially in foam flooding. In this study, a series of amphiphilic silicon quantum dots (C3SPX-n) with tunable surface modification degrees were synthesized by using polyethylene glycol (PEG) and propyltrimethoxysilane (PTMS) as functional modifiers to enhance the foam stability of the nonionic surfactant PMIE. The chemical structure, surface composition, thermal stability, particle size distribution, and morphology of C3SPX-n were systematically characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Foam volume, foam half-life, film drainage half-life, Turbiscan Lab analysis, and microscopic foam morphology demonstrated that C3SP400-1.0 could more effectively enhance the stabilization of PMIE foam, even at a reduced surfactant concentration. Dynamic surface tension, wettability, and interfacial dilatational modulus measurements revealed that the 0.1% PMIE + C3SP400-1.0 system possessed superior interfacial adsorption behavior, improved surface viscoelasticity, and enhanced liquid film strength. The C3SP400-1.0-reinforced PMIE foam exhibited excellent tolerance under harsh reservoir conditions and efficiently increased crude oil recovery by 21.41% in sandpack flooding experiments. This work provides a new strategy for developing low-concentration, high-stability foam flooding systems and offers valuable guidance for achieving efficient water control and oil production enhancement.