Head Group-Induced Interfacial Water Rearrangement during Demulsification: A Study at the Molecular Level

Moreover, electrostatic potential analysis of demulsifier molecules verifies that the strength of such hydrogen bonding is not directly correlated with the electronegativity extremum of the head group, but with the area of the electrostatic potential region of the whole demulsifier molecule. Specifically, a larger regional area corresponds to more exposed hydrogen-bond acceptor sites and stronger hydrogen-bonding interactions.

Calculations of the radius of gyration and solvent-accessible surface area confirm that demulsifier molecules adopt a more extended conformation in aqueous solution, resulting in higher interfacial coverage at the oil–water interface and more sufficient displacement of asphaltenes. More importantly, two-dimensional water density distribution profiles clearly visualize that anionic-nonionic block polyethers can induce the formation of multilayer ordered hydration layers around their head groups, which is distinctly different from the featureless uniform water distribution observed for nonionic demulsifiers.

Finally, we define the concepts of interfacial water and bulk water in the demulsification process, and find that a higher proportion and greater thickness of interfacial water accelerate the rearrangement of the hydrogen bond network and the construction of water channels between droplets, thereby facilitating water droplet coalescence. These theoretical findings are highly consistent with reported experimental results showing that strongly electronegative functional groups in demulsifiers reconstruct the interfacial hydrogen bond network and break the rigid interfacial film, achieving a dehydration rate of up to 98.3% for tight oil emulsions.

This study reveals the regulatory mechanism of head group type on demulsification performance at the molecular level and enriches the microscopic understanding of demulsification behaviors.