Dense, orientationally and translationally ordered two-dimensional (2D) monolayers of colloidal ellipsoids are fabricated at air-water interfaces. Kinetic arrest and disordered structures from long-range quadrupolar capillary attraction are overcome by synthesizing polystyrene microellipsoids with surface roughness, specifically nanoscale concavities, which attenuate capillary attraction. With increasing area fraction, the particle assembly shows a disorder-order transition from isotropic to plastic crystal at low ellipsoid aspect ratio (AR) and an isotropic to nematic transition at high AR, agreeing qualitatively with simulated hard ellipse close packing in two dimensions. The ordered particle assembly is successfully transferred to solid substrates via Langmuir-Blodgett deposition, demonstrating the potential of using rough particles to create anisotropically ordered 2D patterns via interfacial templating.

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• Capillary interactions
• Coatings
• Emergence of patterns
• Nematic order
• Phase diagrams
• Roughness
• Self-assembly
• Structural order parameter
• Surface & interfacial phenomena