Ultimate strength of a colloidal packing

Abstract

The phenomenon of cracking in drying colloidal dispersions is investigated with a focus on the role of flaws on the critical stress required to nucleate cracks. Experiments show that the stress required to fracture a cylindrical colloidal packing saturated with solvent under axial tension varies inversely with the three-half powers of the diameter. The predicted critical stress required to initiate cracks from flaws shows the same scaling with flaw size. Close inspection of the failed sections of the packing revealed flaws entrapped during the drying process. The maximum capillary pressure sets the critical flaw size below which the crack will not nucleate, thereby giving the ultimate strength of the colloidal packing. The experiments show that if the flaw size can be restricted below the critical value, large colloidal packings free of cracks can be synthesized.