Anisotropic light scattering by asymmetric starch granules

Abstract

Solid-state light-scattering patterns from the shoti variety of starch have been recorded using a red continuous wave laser as light source. The laser beam was vertically polarized and the scattered light was observed after passage through a horizontal analyzer so that only scattering due to fluctuations in anisotropy was observed ( H v scattering). Because of their ellipsoidal shape, these granules do not yield a scattering envelope with a 4-fold axis of symmetry, as most starches do; rather a propeller-shaped envelope with a center of symmetry and two orthogonal planes of symmetry was observed. The over-all envelope including higher order maxima could be accounted for by a lamellar model with the lamellae at right angles to the axis of symmetry of the particle. Within the lamellae the orientation distribution of induced dipoles is a function of a radial and a longitudinal co-ordinate. The loci of induced dipoles whose vector orientation is orthogonal to a common surface create shell-like structures similar to the familiar growth layers of starch ultrastructure.