Characterization of storage modulus of starch suspensions during the initial stages of pasting using Stokesian dynamics simulations

Abstract

This study performs Stokesian dynamics simulations of suspensions of rigid spheres to determine the conditions under which swollen starch granules can be considered rigid for rheology measurements. The first part of the study benchmarks the numerical simulations to experimental measurements of storage modulus (G′) for monodisperse polystyrene suspensions. The second part of the study compares the simulations to experimental measurements of G′ for waxy maize and normal rice starch suspensions swollen to volume fractions 0.4 < φ < 0.6. These starch granules were fractionated before swelling to create a narrow range of swollen granule sizes. For granules with a narrow size distribution, the Stokesian dynamics simulations quantitatively match the experimental G′ for volume fractions φ ≤ 0.5, but deviate significantly when φ > 0.5. These results indicate that granule deformability plays an important role when φ > 0.5, and indicates the range where one can apply theories of rigid suspension rheology.