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Insights into the complex interaction between hydrophilic nanoparticles and ionic surfactants at the liquid/air interface


Combinations of nanoparticle and surfactant have been widely employed in many industrial processes, i.e., boiling and condensation in heat transfer and hydraulic fracturing in shale oil and gas production, etc.. However, the underlying mechanism for various phenomena resulted from the addition of nanoparticles into the surfactant solutions is still unclear. For instance, there are contradictory conclusions from the literatures regarding the variations of surface tension upon the addition of nanoparticles into surfactant solutions. In this work, the dominating factors, determining if the surface activity of the surfactant solution will increase or conversely decrease when adding certain kinds of nanoparticle, have been investigated. Two typical hydrophilic nanoparticles, SiO2 and TiO2 with anionic or cationic surfactants, respectively, have been considered. The surface tension has been measured in a wide range of nanoparticle and surfactant concentrations. It was found that the surface tension of ionic surfactant solution can be further reduced only if nanoparticles of same charge were added. For instance, a system containing 0.25 CMC SDS and 1 wt% SiO2 behaves similar to a 0.34 CMC SDS-only solution. Interestingly, the observed synergistic effect is found to be more significant if the surfactant concentration is much lower than its CMC for a given nanoparticle content. Moreover, the effect is perfectly reversible. When the nanoparticles were separated from the system, the surface tension values recovered fully to that of pure surfactants. If nanoparticles of opposite charge were added, however, the surface tension of surfactant solution will increase. Zeta potential measurement and centrifugal treatment have been employed to reveal the interplay between nanoparticle and surfactant and the adsorption behavior of their assemblies at the liquid/air interface. Based on the experimental outcomes, a possible physical mechanism was proposed. It was concluded that the electrostatic repulsion between surfactant molecules and nanoparticles should be of the dominant factor responsible for the observed reversible synergistic effect. Our study is expected to contribute to a better understanding of the interfacial phenomenon in nanoparticle-surfactant complex systems.

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Publication details

The article was received on 22 Mar 2018, accepted on 03 May 2018 and first published on 03 May 2018

Article type: Paper
DOI: 10.1039/C8CP01838C
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Insights into the complex interaction between hydrophilic nanoparticles and ionic surfactants at the liquid/air interface

    J. Jin, X. Li, J. Geng and D. Jing, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP01838C

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