Cracks form in hard colloidal films during drying because the normal stress imposed by the suspending medium through interfacial tension gives rise to a transverse stress in the plane of the film that exceeds the tensile stress the substrate-bound particles which are in a close packed arrangement can withstand. The tensile stress at the onset of cracking has been demonstrated to only depend on the film thickness, particle shear modulus, particle packing fraction, and the liquid-air interfacial tension. This indicates that for a given particle type, solvent, and film compaction mechanism, cracking will only be observed above a critical film thickness. But our recent experiments have uncovered that with subsequent deposition of thin crack-free, hard nanoparticle layers, films having thicknesses above the theoretically predicted and experimentally observed critical values can be constructed. This suggests that a close packed film composed of hard nanoparticles behaves simply as a rigid substrate.

Avoiding the formation of cracks in hard colloidal films

244th National Meeting (2012)

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