Electro-optics of metal particles: electric birefringence of gold rods

The electro-optical response of aqueous suspensions of gold rods of diameter and length of 15 and 260 nm respectively, stabilized with poly(vinylpyrrolydone) was studied by electric birefringence. The electric polarizability of gold rods was calculated from the birefringence measurements as 1×10−29 F m2 and corresponds to that deduced from dichroism (van der Zande ʹ98). This value is of the same order of magnitude as the electric polarizabilities determined for non-metallic rods of similar dimensions (length about 300 nm and axial ratio about 20) such as TMV, palygorskite, oxides, etc. However, distinct differences in the optical anisotropy and the dispersion behaviour in stationary electric fields between non-metallic and metallic rods were observed. The optical anisotropy was determined (g1–g2)=0.7, which is two orders of magnitude higher than that for non-metallic rods of similar size and form. Moreover, an unexpected oscillating dispersion behaviour of the steady-state electric birefringence effect and a slow build up of the electro-optical effect compared to the decay were observed.