The two-dimensional crystalline-like ordering at the surface of a bulk colloidal suspension

Abstract

Ordering in dilute charged colloidal suspensions is investigated using an optical reflection microscope, a video camera and an image processor. The surface of the bulk suspension contained in a glass container is imaged and analysed. The fraction of six coordinated particles and the distribution of nearest-neighbour distances are computed from the micrograph and are used to characterize the degree of ordering in different layers. The degree of ordering is found to reduce from the surface layer towards the inner layers. The pair-correlation functions and angular correlation functions are computed from the micrographs. Algebraic decay of the pair correlation function and the distance independent angular correlation function indicates two-dimensional crystalline-like ordering of the particles at the surface of the bulk colloidal suspension. A possible cause for such an ordering is discussed.