Asphaltene-Induced Deactivation and Solvent Regeneration of Polymer-Grafted Magnetic Nanodemulsifiers

The widespread application of magnetic nanodemulsifiers (MNDs) in sustainable oil-water separation is hindered by their progressive deactivation during cyclic operation, yet the underlying molecular mechanisms remain poorly understood. Here, we elucidate the deactivation pathways of polymer-grafted MNDs and propose a designed regeneration strategy based on intermolecular interaction analysis. Using a combination of surface-sensitive spectroscopy, dynamic light scattering, and molecular dynamics simulations, we reveal that asphaltenes, rather than bulk organic deposition, constitute the primary cause of performance degradation. Heteroatom-rich asphaltene molecules anchor to both the polymer brush and the underlying silica surface via a cooperative hydrogen-bonding network, forming patchy deposits that mediate nanoparticle bridging. This aggregation reduces the mean diffusion coefficient by 66% and severely compromises interfacial activity, leading to a >90% loss in demulsification efficiency. Guided by this mechanistic insight, we develop a synergistic regeneration protocol using a xylene/ethanol binary mixed solvent under ultrasonic-thermal agitation. This approach disrupts the hydrogen-bond network and removes 70.5% of surface-bound asphaltenes, restoring ∼71% of the original activity and extending the service life from 3 to 8 cycles. These findings establish a molecular-level framework for understanding deactivation and provide a scalable regeneration strategy, paving the way for sustainable nanotechnology applications in petroleum processing and beyond.