Experimental study of the break-up of starch suspension droplets in step-up shear flow

Abstract

International audienceThe deformation and break-up of a droplet of suspension of swollen-in-water starch granules placed in an immiscible fluid, silicon oil, are investigated. The study was carried out on a physically modified waxy maize starch suspension with a theoretical granule volume fraction of 100%. Granules were swollen to their maximum; they were highly deformable. Measurements were carried out using a counter rotating shear cell. The starch suspension was shear thinning above a yield stress of about 90-100 Pa showing elasticity (first normal stress difference) above 300 Pa. The rheo-optical experiments were carried out by stepping up the stress from zero to a constant value and deformation of suspension droplets of various sizes was observed with time. Critical break-up capillary numbers Ca-* were calculated and correlated with droplet-to-matrix viscosity ratio p. At low p values Ca-* were found to be smaller or close to those determined for Newtonian fluids. No break-up was observed for viscosity ratios above 0.1, a limit that is roughly 40 times lower than that for the Newtonian fluids. This result was assumed to be due to the fact that internal stress in the droplet is lower than the mean one applied, because of inter-particle interactions and friction, thus shifting suspension from low to extremely high viscosity fluid if applied stress is close to the yield transition

Emulsification of particle loaded drops in simple shear flow

“…Our findings correlated qualitatively well with the experimental and numerical results reported in literature for particle-free shear thinning liquids [27,33] as well as micelles- [31] and swollen starch suspensions [29] with strong shear thinning behavior. The increase in Ca * crit as well as the shear stress dependency of Ca * crit coincides with the shear thinning behavior of the suspensions.…”

“…Usually, in single drop experiments under quasi-static conditions, the interfacial area is slowly increased. So it is most likely, that friction between particles and reorientation processes within the particle loaded drops have a pronounced effect on the slow drop deformation and breakup under quasi-static conditions as reported for other shear thinning disperse phases [29,31].…”

“…If the zero-shear viscosity is considered, the deformation of shear thinning drops is higher than the deformation of the corresponding Newtonian liquid [28]. If instead the viscosity at the applied shear stress is considered, shear thinning drops are less deformed and breakup occurs at a higher capillary number in comparison to Newtonian liquids [29][30][31][32]. In case of shear thinning disperse phases, the critical capillary number is dependent on the degree of shear thinning behavior [33] and the applied shear stress [31].…”

Relationship between Food Rheology and Perception

“…8.10. It shows the well-known Grace curve for shear-induced droplet break-up of Newtonian droplets immersed in second immiscible Newtonian fluid as well as experimental data obtained for the starch droplets (Desse et al, 2009). The situation for the starch droplets is quite complex, for example variation of the viscosity ratio p, see caption of shear rate and taking the shear viscosity measured for the starch suspension at the shear rate applied to calculate p. Hence, since the viscosity of the second immiscible fluid was kept constant, larger p values coincide with lower applied shear rates and therefore flow stresses.…”

Dynamics of sheared droplets filled with non-Brownian particles

“…Besides in polymer blends, droplets encapsulating particles are also of great importance in the oil, printing, and food industry (Smith and van de Ven 1985b;Desse et al 2009;Usta et al 2009;Bonnoit et al 2012;Mehrabian et al 2015;Merkel et al 2015). Consequently, several studies focus on the droplet dynamics of water/oil systems containing particles suspended in the dispersed phase.…”