Alignment of rod-shaped gold particles by electric fields

The electro-optical response of colloidal dispersions of rod-shaped gold pa rticles is studied for various aspect ratios (2.6 < L/d < 49; d = 15 nm) by monitoring the absorbance spectra in the visible wavelength regime. The ab sorbance spectra strongly depend on the degree of orientational order of th e rods and the direction of the polarization of the incident light with res pect to the applied electric field. From the change in absorbance of the tr ansverse resonance the electro-optical effect is deduced: at low electric f ield strengths a linear dependence on the squared electric field strength i s observed, and at sufficiently high electric field strengths saturation oc curs. This is in agreement with electro-optical theory. With increasing len gth, the anisotropy in electric polarizability increases from 6.10(-30) F.m (2) to 12.10(-30) F.m(2). It is found that the anisotropy in electric polar izability depends on the square root of the particle length.