Measurement of the optical properties and shape of nanoparticles in solution using Couette flow

Knowledge of the optical properties and shape of nanoparticles is central to many technological applications including the fabrication of advanced materials and the characterization and formation of ordered films for optoelectronic devices. Measurement of such properties typically involves the independent use of advanced instrumentation such as electron and near field optical microscopy. We propose a simple experimental technique for extracting the optical and geometric properties of dilute suspensions of nanoparticles in situ. A theoretical formalism is developed to determine both the dichroic ratio and aspect ratio from a single measurement of the change in extinction of an incident light beam. The validity of this method is demonstrated for hematite nanorods, for which good agreement with independent measurements is found.