Droplet spreading and imbibition on microporous membranes

• Author / Creator

  Bhattacharjee, Debanik

• The phenomena of droplet spreading and imbibition has widespread application in membrane science. It is widely believed that the membrane flux increases with greater hydrophilicity. In porous membranes, the spreading and
  permeation occur at the same time, and these separate but competitive phenomena must be considered when reporting the contact angle results. In the
  first phase, the role of characteristic parameters (radius and height of droplet)
  is investigated by considering an existing mathematical model formulated on
  the basis of lubrication approximation. Under partial wetting conditions, the
  contact line singularity prevails which is relieved using precursor film assumption and disjoining pressure. Based on two main stages of spreading (initial
  and equilibrium), characteristic radius and height were first evaluated. The
  model predictions were then compared with experimental results in literature
  for both impermeable and permeable substrates. It was found that the choice
  of characteristic length scales based on either stage enables accurate prediction of the droplet base radius and contact angle. A new scaling relation for
  the prediction of the numerical disjoining pressure for both impermeable and
  permeable wetting systems, with an error of ±5%, is proposed.

  In the second part, experimental and numerical study of water droplet spreading and imbibition on lab-fabricated and commercial polyethersulfone (PES)
  membranes is performed. The characterization technique used for permeability is filtration test, for cross-section thickness is FESEM images, for surface
  roughness is AFM data, and for hydrophilicity is dynamic contact angle experiments. The theoretical disjoining pressure calculated in the case of apolar and
  polar interactions is found to be related to the numerical disjoining pressure
  parameter obtained after good agreement with experiments. The pinning observed in the contact angle experiments is well predicted by the mathematical
  model used in the first phase of the study. The hydrodynamic permeability of a membrane as a function of its cross-section thickness and resistance
  is compared to the effective permeability which is calculated after validating
  numerical predictions with contact angle experiments. An attempt has been
  made to correlate the local property realized through droplet dynamics to its
  global property interpreted through resistance of the membrane.

• Subjects / Keywords

  • Droplet spreading
  • droplet imbibition
  • precursor film
  • disjoining pressure
  • microporous membrane
  • polar
  • apolar interactions

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3RF5KX63

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.