Electro-Optic Characterisation of Anisotropic Sub-Micron Particles

Abstract

Optical anisotropy can be manifest for colloidal particles through a number of phenomena [1]. Birefringence, dichroism and light scattering arise from variability of refractive index, absorption coefficient or geometry associated with the different principal axes of the particles. Furthermore, anisotropic particles are generally anisodiametric, and are most conveniently represented by the principal shapes of spheroids of revolution. Whereas many of the theories which account either for colloidal behaviour or for the methods used to characterise the same assume spherical models [2,3], this is far from an adequate description of real systems. Commercially important colloids are continuously being exploited for their needle-like, discotic, tabular or aggregated nature. Furthermore, naturally occurring colloids are seldom of a single monodisperse size species and samples are engineered for specific narrow, broad or truncated size distributions.