(552g) Investigation on the Synergistic Effect of Surfactant and Amphiphilic Nanoparticles at Oil-Water Interface By Dissipative Particle Dynamics Simulations

Tuan V. Vu and Dimitrios V. Papavassiliou

School of Chemical, Biological, and Materials Engineering

The University of Oklahoma, Norman, OK 73071

ABSTRACT

Due to the presence of both hydrophilic and hydrophobic components, surfactants and amphiphilic nanoparticles (or Janus particles, JPs) can accumulate at the interface of oil and water. However, the driving forces for their tendency to move at the interface are completely different. To decrease the excess free energy, surfactants lower interfacial tension, while JPs reduce the contact area between oil and water. A system consisting of both surfactants and JPs can demonstrate synergistic effects of these components on the interface [1, 2], and can find applications in enhanced oil recovery (EOR) possesses. When surfactants and JPs are suspended together, the adsorption of surfactants on the surface of the JPs reduces the loss of surfactant to irreversible adsorption on the rock of an oil reservoir [3]. In addition, surfactants prevent the aggregation of JPs [4]. Finally, the combined effect of surfactant and JPs results in further reduction of interfacial tension, which is crucial to oil mobilization [5]. In this study, we focus on the behavior of surfactants and JPs in the vicinity of the oil-water interface by using mesoscale dissipative particle dynamics (DPD) simulations. Sodium dodecyl sulfate (SDS) and hexadecane are used to represent surfactant and oil, respectively. First the determination of the DPD model parameters so that the simulation can be validated with experimental measurements of the IFT in oil-water interfaces will be discussed. Then Janus nanoparticles with various ratios of hydrophobic to hydrophilic coverage, as well as particles with heterogeneous surface, are investigated to determine the type of particles that result to the most change of the IFT. It is found that the fraction of the nanoparticle surface that is hydrophobic affects the IFT, as does the surfactant concentration when the concentration of nanoparticles remains constant. The presence of JPs can reduce the IFT to about a third of its value when only surfactants are present at the oil-water interface. The concentration of nanoparticles and surfactant is also important for the stability of the oil-water interface. Results from these simulations can assist the design of particles for EOR applications.

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.

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