Forced spreading and rheology of starch gel: Viscoelastic modeling with fractional calculus

We study spreading and rheological properties of potato starch gel which is a non-Newtonian fluid. An interesting oscillatory behavior is observed when the gel spreads on a glass surface under compression. The interface at the boundary of the area of contact of fluid and solid also shows an instability. The smooth circular boundary becomes wavy when oscillations in the contact area appear. A rheological study shows strong shear thinning and creep. We develop a non-linear visco-elastic model incorporating generalized calculus, which successfully reproduces the peculiarities in the oscillatory spreading as well as the creep measured at constant stress.

Potato starch gel confined in a Hele-Shaw cell is compressed. The nature of spreading of the fluid is quite different from Newtonian fluids subjected to the same conditions. The boundary of the area of contact between the gel and surrounding air expands and shrinks, showing oscillations and fingering. The outer boundary in the figure is a still photo taken 2 s earlier than the inner blob. Colors are edited for clarity. Figure optionsDownload as PowerPoint slideHighlights
► Spreading of starch gel shows oscillatory behavior in time.
► Interface shows fingering.
► Visco-elastic model with fractional calculus may explain experimental nature.