Microscopic stabilization mechanism of nanoparticle-laden droplets under external electric fields: A molecular dynamics study

Electric dehydration process of crude oil is frequently accompanied by water droplet breakup, result-ing in efficiency reduction of oil-water separation. To reveal the microscopic stabilization mechanism of nanoparticle-laden droplet, molecular dynamics (MD) simulations were adopted to investigate the electro-deformation and breakup dynamics. Good qualitative and quantitative agreements were observed between the present simulations and the literature experiments. The effects of electric fields (electrocapil-lary numbers and frequencies) and nanoparticles (concentrations and types) on the droplet stability were analyzed in terms of intermolecular total interactions. The analysis of quantum chemical calculations and weak interactions shows that stable hydrogen bonds can be formed between the silicon dioxide (SiO2) and water (H2O) molecules, enhancing droplet stability. The droplet stability under alternating current (AC) electric fields are higher than that under direct current (DC) electric fields, and the stability in-creases with increasing AC frequencies. At the total interactions of the nanoparticle-laden droplet system after switch-off electric field stronger than that after switch-on electric field, fast droplet recovered pro-cess was observed. The modified SiO2 NPs can efficiently enhance droplet stability, and high nanoparticle (NP) concentrations lead to high droplet stabilities. Eventually, the ranking of NP-laden droplet stabili-ties is roughly consistent with that of droplet pair electrocoalescence efficiencies, i.e., CAC (SiO2 modified with 6 carboxylic acid chains) > CAAL (SiO2 modified with 3 carboxylic acid chains and 3 alkane chains) > ALC (SiO2 modified with 6 alkane chains) > SiO2. The results of this work will be potentially valuable for optimizing the design of compact and efficient oil-water separators.(c) 2023 Elsevier Ltd. All rights reserved.