# Sedimentation of microparticles in Highly Concentrated Non-Newtonian Emulsions
## 3 Results
### Influence of Solid Parameters on the Sedimentation Process in Emulsion
When the size of microspheres is small (Figure 5a), their weight is small. The gravity force in this case is not large enough to overcome the flow-resistance forces. The beads are not able to tear through the emulsion structure, so they remain trapped in it. Therefore, the final sediment height \(\rm{h_{sk}}\) for small-sized microspheres is small. The situation is different when the microspheres are of larger size, as shown in Figure 5b. Then their gravity is high enough to be able to break through the emulsion structure. The emulsion droplets move closer to each other, creating space for the solid to flow. In such a situation, the most intensive sedimentation process occurs, which explains the highest heights of the final sediment layer for medium-sized microspheres (300-400 \(\rm{\upmu m}\) fraction). It might seem that a further increase in particle size, i.e., a corresponding increase in particle weight, would result in an even more intense increase in the sedimentation process, but this is not the case. This is because, in the case of large particle sedimentation, although the weight is large enough to overcome flow resistance, the size of the particles itself becomes important. When they are large, in order to break through the emulsion structure, they cause oil droplets to come as close as possible to each other. These droplets start to form a compact structure. In a limited space, they form a barrier to the flow of solids, as shown schematically in Figure 5c. This explains the fact that for beads of the largest size, a lower height of the sediment layer is ultimately observed compared to the medium sizes. Due to the fact that the sedimentation process took place from the whole volume, the particles closer to the bottom had a greater ease in overcoming this compact structure and therefore fell faster. This is explained by the fact that the sedimentation intensity is higher at the beginning of the process and is lower and lower in further stages. When analyzing the structure of solid particles and oil droplets of emulsions, the number of individual phases in the system is not without significance. Therefore, analogous tests were carried out for the case when the concentration of micro particles in the system was lower and when it was higher than previously presented. Figure 6 presents plots of (a) sediment layer height and (b) velocity versus time for sedimentation of 0.2 g/mL microspheres in 70% emulsion with \(\rm{d_{e1}}\) droplet diameter. Figure 5: (**a**–**c**) Scheme of transport of solid particles through the emulsion structure at different particle sizes. Figure 6: Dependence plot of (**a**) sediment layer height and (**b**) sedimentation velocity during the process for the sedimentation of microspheres with a concentration of 0.2 g/mL in an 70% emulsion, \(\rm{d_{e1}}\). From the analysis of the curves of the dependence of h\({}_{\text{s}}\) and u on t, shown in Figure 6, it can be seen that the trend of these curves was similar to those obtained for sedimentation at a concentration of 0.3 g/mL. Obviously, the sediment layer heights obtained here will be smaller because fewer particles are in the system and may eventually form smaller layers. However, the highest sediment height h\({}_{\text{sk}}\) was obtained for microspheres of smaller size than in the previous case, i.e., in the range of 200-300 \(\upmu\)m. For the largest size of microspheres, the changes in h\({}_{\text{s}}\) height are rapid in the first minutes of the process, but quickly, the process establishes itself, and the sediment height in the later stages did not change much anymore. It can be seen that the trend is more pronounced here than for sedimentation at 0.3 g/mL concentration. Figure 7 shows analogous plots of the sediment layer growth (a) and velocity (b) relationship during the sedimentation process at the higher microspheres concentration of 0.4 g/mL. For sedimentation at higher particle concentrations, some temporal turbulence can be observed in the sediment growth and velocity curves.