Colloidal assembly is one of the most sophisticated analogues to nature’s hierarchical assembly, in which simple building blocks are used to fabricate crystalline functional materials with nano/microscale features. We describe the fabrication of polycrystalline colloidal films using evaporative assembly and confinement within square wells in which both the height (h) and spacing (sp) of the boundary are much less than the diameter of the particle. At high volume fractions, the colloids experience a long-range osmotic force that propagates upward from the evaporation front and induces a phase shift from hexagonal closed packed (HCP) to tetragonal packed regions (TP); in contrast to the open-to-closed packed transitions typically observed for colloidal self-assembly in suspension or onto non-pattered substrates. The shifts in packing density over time and as affected by geometric templates with boundaries of various h and sp values are quantified using a connectivity matrix. We investigate the optimal osmotic force necessary to produce square packed lattices and provide insight on controlling colloidal crystal order using geometric confinement, which will ultimately be extended to analyze evaporative packing of shape anisotropic particles into open lattices.

Controlled packing and phase transitions via templated evaporative colloidal assembly

256th National Meeting (2018)

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