Auto-stratification in drying colloidal dispersions: A diffusive model

The mechanism by which the particles in a drying film come into close packing during solvent evaporation has an important role to play in the final film morphology. During drying the particles can develop non-uniform concentrations across the vertical height of the film, depending on their diffusion rate. By applying the principles of classical diffusion mechanics to a hard sphere system, a theory for this novel method of stratification during drying of a two component film has been derived. The model is dependent on the particle Peclet numbers and when one is above unity and the other below, maximum stratification is observed.

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► Derive diffusional law for bi-disperse particle mixture.
► Predict auto-stratification in drying colloidal dispersion.
► Predict condition to maximise stratification.