Solidification and ordering during directional drying of a colloidal dispersion

Lucas Goehring1,2,3, William J. Clegg1, and Alexander F. Routh2,3

University of Cambridge

    1Department of Materials Science and Metallurgy

    2Department of Chemical Engineering and Biotechnology

    3BP Institute for Multiphase Flow

Langmuir, 26, 9269-9275 (2010).

Download preprint pdf: Goehring_2010_preprint.pdf

Supplementary movies: here

During drying, colloidal dispersions undergo processes such as solidification, cracking, and the draining of interstitial pores.  Here we show that the solidification of polystyrene and silica dispersions, during directional drying, occurs in two separate stages.  These correspond to the initial ordering, and subsequent aggregation, of the colloidal particles.  Transitions between these stages are observed as changes in transparency and color that propagate as distinct fronts along the drying layer.  The dynamics of these fronts are shown to arise from a balance between compressive capillary forces, and the electrostatic and van der Waals forces described by DLVO theory.  This suggests a simple method by which the maximum inter-particle repulsion between particles can be measured through the optical inspection of the dynamics of a drying dispersion, under a microscope.