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
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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