Unravelling the roles of nano-modification in enhancing demulsification: Size effects and strengthened non-covalent interactions

Emerging nano-demulsifiers are efficient functional materials for separating emulsions. However, the size effects of nanoparticles on demulsification and the mechanisms of enhanced demulsification by nano-modification are still unclear. Herein, a nano-demulsifier (SiO2-mANP) was prepared by modifying carboxyl-modified aliphatic nonionic polyether (mANP) with nano-SiO2. Compared to single polyether, the SiO2-mANP significantly reduced the demulsification temperature from 60 °C to room temperature. The demulsification efficiency of the asphaltene-stabilized water-in-oil emulsion reached 91.0% within 10 min at room temperature (dehydration over 99.5% in less than 2 min at 60 °C). The size effects study showed that smaller SiO2-mANP nanoparticles (∼10 nm) performed better in demulsification due to their superior diffusion ability in continuous phase and greater adsorption at the oil-water interface. The electrostatic potential (ESP) and independent gradient model (IGM) were used for the first time to analyze the changes in non-covalent interactions between demulsifiers and water. Nano-modification facilitated the formation of more non-covalent interaction sites, notably hydrogen bonding sites such as silanol groups. This rearranged the molecular surface ESP of the demulsifier. As a result, the non-covalent interactions between demulsifier and water were greatly enhanced, leading to a significant reduction in the coalescence time of water droplets. This primary study on the size effects and non-covalent interactions of nano-demulsifiers will provide guidance for the design and development of highly efficient demulsifiers.