Liu Shasha, Zhang Heng, Yuan Shideng, Yuan Shiling
School of Chemistry and Chemical Engineering, Qilu Normal University, Jinan 250000, PR China.
School of Chemistry and Chemical Engineering, Shandong University, Jinan 250000, PR China.
ACS Omega. 2024 Nov 26;9(49):48232-48245. doi: 10.1021/acsomega.4c05623. eCollection 2024 Dec 10.
The application of an electric field to demulsification of oil-in-water (O/W) emulsions has received extensive attention. However, microcosmic information about the effect of surfactant type on the demulsification of an O/W emulsion under an electric field is still rare. In this work, the effects of cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS) on oil droplet demulsification in an emulsion under a pulsed-DC electric field were studied by molecular dynamics (MD) simulation. The MD simulation results show that oil droplets underwent directional movement under the action of an electric field. The larger the electric field strength, the shorter the time required for the oil droplets to coalesce. However, the movement direction of the oil droplets in the electric field was different depending on the type of surfactant. Compared to oil droplets containing SDS, oil droplets containing CTAB molecules exhibited faster deformation and easier migration coalescence under low electric field strength. It was mainly attributed to the fact that the deformation of oil droplets will be accelerated when oil droplets contain asphaltene molecules and surfactant molecules with different electronegativities under an electric field. During the demulsification of oil droplets containing CTAB molecules, CTAB molecules generated electrostatic attraction with asphaltene molecules in adjacent oil droplets, strengthened the interaction between oil droplets, and promoted the demulsification of oil droplets. In the process of oil droplet demulsification containing SDS molecules, the potential energy of the electrostatic interaction between oil droplets did not change, and the demulsification mainly depended on the van der Waals force between oil droplets.
将电场应用于水包油（O/W）乳液的破乳已受到广泛关注。然而，关于表面活性剂类型对电场作用下O/W乳液破乳效果的微观信息仍然很少。在这项工作中，通过分子动力学（MD）模拟研究了阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）和阴离子表面活性剂十二烷基硫酸钠（SDS）对脉冲直流电场作用下乳液中油滴破乳的影响。MD模拟结果表明，油滴在电场作用下发生定向运动。电场强度越大，油滴聚结所需时间越短。然而，油滴在电场中的运动方向因表面活性剂类型而异。与含有SDS的油滴相比，含有CTAB分子的油滴在低电场强度下表现出更快的变形和更容易的迁移聚结。这主要归因于在电场作用下，当油滴含有沥青质分子和具有不同电负性的表面活性剂分子时，油滴的变形会加速。在含有CTAB分子的油滴破乳过程中，CTAB分子与相邻油滴中的沥青质分子产生静电吸引，增强了油滴之间的相互作用，促进了油滴的破乳。在含有SDS分子的油滴破乳过程中，油滴之间静电相互作用的势能没有变化，破乳主要取决于油滴之间的范德华力。
