Efficient phase separation of oil and water in emulsions is critical for water treatment and hydrocarbon processing. Our research aims at elucidating the separation of water-in-oil emulsions using silica nanoparticles (SNPs). By probing the surfactant–nanoparticle interactions, we show that surfactant-stabilized emulsions can be destabilized depending on the nanoparticle wettability and the mode of nanoparticle addition. The efficiency of nanoparticles to demulsify surfactant-stabilized emulsions depended on both the nanoparticle and surfactant concentration. Water-in-oil emulsions were destabilized when partially hydrophobic nanoparticles were added to the surfactant-stabilized emulsion after emulsion formation (post-mixing). Hydrophilic and partially hydrophobic nanoparticles adsorb the surfactants via hydrogen bonding which in turn leads to depletion of surfactants at the oil–water interface. Upon the addition of hydrophilic nanoparticles, the preferential distribution of nanoparticles in the water phase led to lower adsorption of surfactants from the oil phase, resulting in inefficient destabilization as compared to that of partially hydrophobic nanoparticles. Water-in-oil emulsions were not destabilized upon post-mixing hydrophobic nanoparticles due to weak hydrophobic interactions between surfactants and hydrophobic nanoparticles. For a fixed concentration of nanoparticles of specific wettability, changing the mode of nanoparticle addition altered the flow behavior and the network strength of surfactant-stabilized water-in-oil emulsions.

中文翻译：

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表面活性剂稳定化的油包水（环己烷）乳液的二氧化硅纳米颗粒破乳

乳液中油和水的有效相分离对于水处理和烃加工至关重要。我们的研究旨在阐明使用二氧化硅纳米颗粒（SNP）分离油包水乳液的方法。通过探测表面活性剂与纳米颗粒之间的相互作用，我们表明，取决于纳米颗粒的润湿性和纳米颗粒的添加方式，表面活性剂稳定的乳液可能会不稳定。纳米颗粒使表面活性剂稳定的乳液破乳的效率取决于纳米颗粒和表面活性剂的浓度。当在乳液形成后（后混合）将部分疏水性纳米颗粒添加到表面活性剂稳定的乳液中时，油包水乳液不稳定。亲水性和部分疏水性的纳米颗粒通过氢键吸附表面活性剂，从而导致油水界面的表面活性剂消耗。在添加亲水性纳米颗粒后，纳米颗粒在水相中的优先分布导致表面活性剂从油相中的吸附降低，与部分疏水性纳米颗粒相比，导致不稳定的效率低下。由于表面活性剂和疏水性纳米颗粒之间的弱疏水相互作用，油包水型乳液在后混合疏水性纳米颗粒时不会不稳定。对于固定浓度的具有特定润湿性的纳米颗粒，改变纳米颗粒的添加方式会改变表面活性剂稳定的油包水型乳液的流动行为和网络强度。