Thermally Driven Unidirectional Crystallization of Charged Colloidal Silica

Dilute charged colloidal silica (particle diameter = 110 nm) containing pyridine exhibits a novel directed crystallization under a temperature gradient. The crystal growth can be explained in terms of a combination of heat conduction and thermally induced crystallization. Well-oriented and large (1 mm × 10 mm × ∼30 mm) single-domain crystals are formed in a short time (<10 min). Moreover, they have sharp and deep transmission dips as well as good spatial uniformity in the Bragg wavelength (∼0.1%).