(484i) Collapse of Particle-Laden Interfaces: Effects of Surfactants

Emulsions have been used in various applications, including enhanced oil recovery, food processing, pharmaceuticals, etc. [1] Surfactants and nanoparticles (NPs) are the commonly used emulsifiers to stabilize emulsions by preventing the droplets or bubbles from coalescence or flocculation. The surfactants hinder the coalescence by reducing the interfacial tension (IFT) [2], while the NPs adsorption to the fluid/fluid interface forms an aggregated layer that prevents droplets from coming together [3]. In the coalescence process, the interface undergoes large deformations that result in compressive and shear stresses. Thus, the stabilization of the interface depends largely on the behavior under deformation in presence of stabilizers [4].

In this study, we investigate the behavior of NPs and surfactants at the oil/water interface under compression using dissipative particle dynamics simulation [5]. NPs with different patterns of surface coverage with hydrophilic and hydrophobic sites, and different wettability are studied. The surfactant used is the non-ionic Octaethylene glycol monododecyl ether (C₁₂E₈). The model for surfactant is validated by comparing it to the experimental data for the change in the oil/water interfacial tension with surfactant concentration. Meanwhile, the contact angle is used as the criterion to verify the model parameters for NPs. When compressing the particle-stabilized interface, the collapse mechanism largely depends on the particle surface wettability, which agrees with previous findings [4]. When both surfactants and NPs are present, the three-phase contact angles of the NPs change due to the competitive adsorption of surfactants on the interface. The presence of surfactants affects the collapse mechanism of NPs with different magnitudes depending on the wettability of the NPs. In the case of Janus particles with a 50% hydrophobic surface, adding surfactant does not change the resulting behavior; while with other coverages, the collapse mode could switch from buckling to particle expulsion. Our results provide a mechanism that could be beneficial in the design of NPs and surfactants to achieve desired collapse behavior for different applications.

ACKNOWLEDGEMENTS

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, and to NSF for grant CBET 1934513. 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.

REFERENCES

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