Pattern formation in colloidal monolayers at the air-water interface

Using video-microscopic techniques, single layers (monolayers) of charged c olloidal particles of 1- and 3-mum diameter were studied at an air-water in terface. The particles normally arranged themselves in an ordered lattice-l ike array. However, occasionally, the monolayer formed loosely bonded cryst allite clusters, here called mesostructures. The monolayer was exposed to a number of external influences: ions, electric current, and ultraviolet lig ht. Depending on the perturbation applied, the lattice-like structure forme d fractal aggregates, clusters (mesostructures), and two other particular s tructures, here referred to as striations and loops. The mechanisms of form ation and implications of the different patterns are discussed. (C) 2001 Ac ademic Press.