Reversible Interfacial Assembly of Nitrogen-Doped Carbon Dots for Tunable Emulsion Dynamics and Sustainable Oil Recovery

In situ emulsification is a promising enhanced oil recovery technique but faces challenges including environmental concerns and high operational costs. To address this, we developed amphiphilic nitrogen-doped carbon dots (NCDs) via a facile one-pot synthesis. The NCDs exhibit high interfacial activity and undergo a three-step self-assembly with endogenous naphthenic acids in crude oil─via hydrophobicity-driven diffusion, electrostatic adsorption, and interfacial jamming─to form a rigid film with ultralow interfacial tension (∼0.66 mN/m). The resulting emulsion shows a bridged network structure and high stability. Microfluidic experiments reveal that stable oil-in-water emulsions form over a wide concentration range, with three distinct flow regimes (squeezing, dripping, and jetting) governed by capillary number and droplet size scaling as ( D / D h ) ∝ Ca c –1.5 . The emulsion also exhibits fully reversible, CO 2 -responsive demulsification with minimal NCDs loss over cycles. Under simulated reservoir conditions, NCDs maintain ultralow tension and high elasticity in heavy oil, show good thermal and salinity stability, and enhance oil recovery by 33.45% over water flooding, demonstrating strong field potential. This work offers a sustainable strategy for developing efficient oilfield chemicals with lower cost and environmental impact.