(623a) Synergies between Heterogeneous Nanoparticles and Surfactants to Stabilize Emulsions

Emulsions of oil and water have been used in various applications, including enhanced oil recovery (EOR) and food processing. The emulsions are generally stabilized by emulsifiers, such as surfactants and sometimes nanoparticles (NPs). Surfactants hinder the coalescence of emulsions by reducing the interfacial tension (IFT), which leads to the reduction of the energy needed to create new droplets, resulting in a more stable emulsion [1]. NPs at the emulsion interface can prevent coalescence by either a steric effect, in which they block droplets from coming together, or by changing the interfacial rheological properties of the fluid inside the emulsion [2].

In this study, we investigate the stability of emulsions through dissipative particle dynamics (DPD) computations. An oil-water model is constructed based on the approach reported in previous studies [3, 4]. First, the change of oil-water IFT with the presence of surfactants and s[herical nanoparticles is studied. We have found that while NPs alone do not affect the IFT, they further reduce the IFT when surfactants are also present [5]. Then, the stability of emulsions with different emulsifiers is examined by allowing two oil-in-water droplets to collide. The stability is quantified as the force needed to break the droplets. It is shown that the presence of spherical NPs increases the emulsion stability in comparison to the case where there are only surfactants. Among different types of NPs, the Janus particles, which possess both hydrophobic and hydrophilic properties in two opposite sides show the highest effect in preserving the emulsions. This observation could be explained by the strong tendency to settle on the oil-water interface of Janus particles. The results provide details of the mechanism for the co-effect of NPs and surfactants in stabilizing emulsions.

ACKNOWLEDGEMENTS

The use of computing facilities at the University of Oklahoma Supercomputing Center for Education and Research (OSCER) and at XSEDE (under allocation CTS-090025) is gratefully acknowledged. Acknowledgment is made to the donors of The American Chemical Society Petroleum Research Fund for partial support of this research through grant PRF # 58518-ND9.

REFERENCES

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[2] H. Fan, A. Striolo, Mechanistic study of droplets coalescence in Pickering emulsions, Soft Matter 8(37) (2012) 9533-9538.

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[4] T.V. Vu, D.V. Papavassiliou, Oil-water interfaces with surfactants: A systematic approach to determine coarse-grained model parameters, The Journal of Chemical Physics 148(20) (2018) 204704.

[5] T.V. Vu, D.V. Papavassiliou, Modification of Oil–Water Interfaces by Surfactant-Stabilized Carbon Nanotubes, The Journal of Physical Chemistry C 122(48) (2018) 27734-27744.