Measurement of the radii of low axial ratio ellipsoids using cross correlation spectroscopy

Abstract

The intensity cross correlation from a system of Brownian rotating ellipsoids is calculated using the Rayleigh–Gans–Debye (RGD) approximation. In principle, estimates of the rotational diffusion coefficient, radii, and axial ratio can be made from one measurement. Close to the Rayleigh–Gans–Debye minimum the technique appears sensitive to very low axial ratios (∼1.025). The theory is tested well below the RGD minimum using cross-linked and swollen polystyrene latex particle approximating an ellipsoid of revolution of low axial ratio (∼1.5). Measurements of the initial decay of the field autocorrelation function at various angles are used to confirm the estimated radii and axial ratio and illustrate some advantages of the cross-correlation technique.