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Molecular Simulation of Adsorption of Surface-Modified Silica Nanoparticles at Liquid-Liquid Interfaces

Azizpour Hassanabad, Ali | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53582 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mohammadi, Ali Asghar
  7. Abstract:
  8. With rising oil prices and predictions about the future of hydrocarbon reserves, issues of enhanced oil recovery and optimal production of existing reservoirs are of particular importance. In this study, molecular dynamics simulation was used to study the absorption of silica nanoparticles with surface groups at the interface of water and decane. The effect of surface chemistry of silica nanoparticles on the interface properties of water-decane with changing the surface groups was simulated. The initial surface factor of nanoparticle is hydroxyl (OH), which is called a hydrophilic surface agent. Nanoparticles were modified by methyl and ethyl surface agents to increase the hydrophobicity and CH2OH surface agent increase the hydrophilicity of them. After the equilibrium of the water-decane system, the nanoparticles were inserted in the water-decane interface. Three-dimensional periodic boundary conditions were implement- ted and the short-range potential cutoff was set to 15 Å for all simulations. Long-range coulumbic interactions were computed using the Ewald summation method to a precision of 0.00001. The equations of motion were integrated using the velocity-Verlet algorithm and the canonical (NVT) ensemble was employed. The temperature was kept constant at 300 K by means of a Nose–Hoover thermostat. For all simulations a time step of 1fs and total simulation time of 2.5ns has been used. The TIP3P model was used for water and for decane and silica nanoparticles with its surface agents the CHARMM force field has been used. It was observed that absorption of nanoparticles at the water-decane interface reduced the interfacial tension and increased interfacial thickness. Furthermore, increase of hydrophobic surface agents has lower effect on the level of interfacial tension compared to the fully hydrophilic state. Reduction of interfacial tension increases capillary number which causes improved enhanced oil recovery. Increasing hydrophilic surface agents reduced the number of hydrogen bonds of water oxygen with hydrogen in the surface of the nanoparticles and indicates the tendency of nanoparticles to diffuse into the oil phase
  9. Keywords:
  10. Molecular Dynamic Simulation ; Interfacial Tension ; Radial Distribution Functions ; Enhanced Oil Recovery ; Three-Phase Contact Angle ; Interfacial Thickness ; Mean Square Displacement ; Water-Decane Interface

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