Fickian to Single-File Diffusion Transition in nano-colloids

• Author / Creator

  Pourmohammadbagher, Mohammad

• Nano-colloids are present or arise in diverse processes, from the manufacturing of solar panels and pharmaceutics, treatment of mine tailings, and a lead example to the production of unconventional hydrocarbon resources and molecular fluids are frequently added to the colloids during processing. A detailed understanding of the relative importance of impacts of Fickian diffusion, Single-File diffusion, and sorption of penetrants on colloid surfaces provides insights on the time scales and outcomes that govern process designs for specific cases. Therefore, first potential roles played by Fickian diffusion, Single-File diffusion arising from constrictions among heavy oils nano-dispersed phase domains, and sorption of penetrants by these dispersed phase domains were explored. Detailed models including diffusion and sorption were prepared and applied to previously published composition profile data for light hydrocarbons diffusing into heavy oils and heavy oil fractions. These data sets showed deviation from Fickian diffusion at high heavy oil mass fractions. These deviations were attributed to a shift in the dominant mechanism from Fickian to Single-File diffusion. The impact of sorption on composition profiles could be ignored even when high sorption rates and equilibrium extents of sorption were assumed. Furthermore, sorption of toluene on carbon nanotubes, nano-diamonds, and nano-silica particles was investigated using a TAM III solution calorimetry module. Toluene was then added to colloidal suspensions comprising polybutene + carbon nanotubes, nano-diamonds and silica nanoparticles. Baseline cases including only Fickian diffusion, as well as Fickian diffusion + Single-File diffusion, and Fickian diffusion + Single-File diffusion + sorption were examined. Diffusion measurements with nanoparticles having different sizes, shapes and surface properties showed that when the average nearest neighbor distance among nanoparticles was ~120 nm or larger Fickian behavior was observed (nw = 0.5). At shorter nearest neighbor distances the diffusion mechanism transitions to Single-File diffusion. When the average nearest neighbor distance among nanoparticles became less than ~20 nm, the transition to Single-File diffusion (nw = 0.25) was complete. Although sorption on colloid surfaces impedes diffusion of solvent into nanocolloids, it did not appear to interfere with the values of nw and active diffusion mechanism identification for the cases studied in this work. The impacts of nanoparticle shape and surface properties on the transition from Fickian diffusion to Single-File diffusion were not resolved in the measurements, suggesting that nearest neighbor distance is the primary parameter impacting the diffusion mechanism. Particle shape and surface properties appear to be secondary variables.

• Subjects / Keywords

  • Nanocolloid
  • Heavy oil
  • Single-File

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3Q52FT8V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.