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Simulation of Water Inside Carbon Nanotubes

Sadeghi Hassanabadi, Mohsen | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45624 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Parsafar, Gholam Abass
  7. Abstract:
  8. This thesis presents a research on the physical behavior of water inside carbon nanotubes (CNTs). Molecular simulations are carried out using the Monte Carlo method in the canonical and grand canonical ensembles. Due to the difference between the inter-molecular forces in the axial and radial directions, the anisotropic pressure tensor is calculated for water confined inside the CNTs with the diameters of 0.88, 1.08, 1.28, and 1.48 nm at different densities using the Monte Carlo simulations. Using the assumption of effective extended Lennard-Jones interactions between the nearest neighbors, a set of new equations of state for water confined inside the CNTs is derived and shown to be applicable to the simulated cases. Different molecular arrangements of water inside the CNTs at different densities are studied and liquid-liquid phase transitions between these molecular configurations at 298 K and pressures below 5.0 kbar are shown. Separate molecular clusters, disordered dense liquid, and ordered phases with square, pentagonal, hexagonal, and heptagonal cross-sections are observed for water inside the CNTs with different diameters. Using free energy calculations, stable and metastable phases of water inside the 1.28 nm CNT in the temperature range of 250-350 K are studied. Stable cluster sizes of water in low-density states are obtained and shown to agree with experiments. Also, the existence of an intermediate metastable disordered phase between the low-density states of small molecular clusters and high-density states of ordered molecular structure is shown. Using Monte Carlo simulations in grand canonical ensemble, a system consisting of CNTs with different diameters of 1.17, 1.30, 1.34, 1.38, and 1.44 nm in contact with a reservoir of saturated water vapor is simulated. By changing the temperature in the range of 160-330 K, adsorption and the liquid-solid phase transition temperautres are determined based on the changes of density, order parameter, grand potential and molar entropy of water inside the CNTs and verified with experiments. The structures of the ice phases are obtained in agreement with experimental data
  9. Keywords:
  10. Water ; State Equation ; Phase Transition ; Carbon Nanotubes ; Monte Carlo Simulation ; Nano Sized ; Molecular Arrangements

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