Lars Hamberg

Shapes and shaping of biopolymer drops in a hyperbolic flow

Abstract The shaping of drops in a model system based on κ-carrageenan-emulsion drops in the millimetre range in silicon oil has been studied. The drops were shaped by exposing them to drag forces in a hyperbolic flow, while their shape was fixed simultaneously by introducing gel formation of the biopolymer in the drop. The shape and the shaping process were studied and evaluated with image analysis of macrograph sequences of the shaping. The effect of process conditions, flow speed and cooling temperature on the final shape and shape progress was investigated as well as the effect of different κ-carrageenan drop characteristics, such as drop viscosity and gel strength. Drop viscosity was altered by addition of locust bean gum, LBG, and the gel strength was altered by addition of ions. The κ-carrageenan solutions in the drop were characterised by rheological investigations. With the same type of flow, different shapes could be achieved with small process changes and with high reproducibility. The fixation of the characteristic drop features, perimeter, area, Ferets X and Y , does not occur at the same time and position. For the different process parameters investigated, a change in speed affected the process in a similar way to a change in the viscosity ratio. This applies if the viscosity ratio is changed at a constant temperature, but if the change in the viscosity ratio is temperature-induced, the effect is different. The final shape of the produced drops could be graded into three classes, correlated to the position in the flow field where the drops were fixed. A shape map of the different drop shapes obtained was presented.