# Sedimentation of microparticles in Highly Concentrated Non-Newtonian Emulsions
## 3 Results
### Effect of Emulsion Parameters on the Sedimentation Process of Solids  
When analyzing the sedimentation process of microspheres in highly concentrated emulsions, one should keep in mind that they exhibit non-Newtonian behavior. This property additionally influences the speed of sedimentation process. Rheological properties of emulsions depend on their concentration. It is estimated that oil-in-water emulsions with concentrations above 50% of internal phase start to exhibit non-Newtonian shear-thinning behavior. Increasing the concentration of the oil phase enhances these properties. Such liquids exhibit high viscosity at low shear rates. This increased viscosity can affect the sedimentation process, especially in the initial and final phases. To evaluate the influence of viscosity on the sedimentation process of microspheres in emulsions, an experimental study was carried out using emulsions with three different concentrations--60, 65, and 70%. The dependence of viscosity on shear rate is shown in Figure A1. The differences between the curves are clear, and the emulsions with a concentration of 70% at a shear rate of 50 1/s show more than three times the viscosity of the emulsions with a concentration of 60%. Sedimentation of microspheres with a concentration of 0.2 g/mL was carried out in these liquids. Figure 9a,b shows the plots of sediment layer height versus time and velocity versus time, respectively, for the precipitation of microspheres with a size range of 300-400 \(\upmu\)m.  
Figure 9: Dependence of (**a**) sediment layer height and (**b**) sedimentation velocity versus process time for sedimentation of 0.2 g/mL microspheres in the size range of 300–400 \(\upmu\)m in emulsions with different concentrations, \(\mathrm{d_{e1}}\). Comparing the curves of sediment layer height changes in time obtained at different emulsion concentrations (Figure 9a), one can see that for the process at 70% concentration, the curve has a smoother shape than the others. The final obtained value of sediment height h\({}_{\text{sk}}\) is also the smallest in this case. In addition, the sediment velocity reaches the smallest value for the emulsion with the highest concentration (Figure 9b); however, it fluctuated somewhat in the first stage of the process. The shape of the obtained curves is a result of the fact that at higher concentrations, the number of oil droplets is higher, and consequently, the density of the system is also higher. In such systems, the solid particles have less space to move freely and therefore can become trapped in the structure of the medium. At the beginning of the process there is a cluster settling, and the sedimentation velocity is the highest, but with time, it decreases. Considering non-Newtonian shear-thinning properties, at low flow velocities, the increased viscosity of the system slows down the process. Therefore, for the emulsion with the highest concentration, after about 17 min, the sedimentation process is established, and the observed increase in sediment layer changes little, while for emulsions with lower concentrations, larger changes are observed after this time. However, the overall sedimentation rate depends on the available space in the system. At low concentrations of emulsions, there is enough space for particles to find enough space to sink (Figure 10a), while at high concentrations, there is not enough space for particles to move (Figure 10c). Oil droplet size is another emulsion parameter that can affect the settling rate of particles suspended in the emulsion. To test the effect of this parameter on the process, emulsions with different oil droplet sizes were produced. The average droplet diameter corresponded to d\({}_{\text{e1}}\) = 8.24 \(\upmu\)m, d\({}_{\text{e2}}\) = 11.52 \(\upmu\)m, and d\({}_{\text{e3}}\) = 15.72 \(\upmu\)m, respectively.