# Sedimentation of microparticles in Highly Concentrated Non-Newtonian Emulsions
## 2 Materials and Methods
Measured masses of glass microspheres were poured into the cell, and then, the cell was filled with emulsion to a cell height of 55 mm. The cell was then capped, and the \begin{table}
\begin{tabular}{c c c} \hline
**Fraction** & **Range of Diameters (\(\upmu\)m)** & **Average Diameter dp (\(\upmu\)m)** \\ \hline
1 & 100–200 & 150 \\
2 & 200–300 & 250 \\
3 & 300–400 & 350 \\
4 & 400–600 & 500 \\
5 & 600–800 & 700 \\ \hline \end{tabular}
\end{table} 
Table 1: Range of microspheres diameters (given by producer Alumetal-Technik). system was shaken vigorously to thoroughly mix the microspheres in the entire volume of emulsion. Immediately after, the measuring cell was placed in the Turbiscan LAB(tm) measuring chamber, and the measurements were started instantaneously. Scanning of the sample lasted for 30 min in each case. For the study, three samples of each system were created and tested by turbidimetric measurements. The results obtained were then compared with each other. Deviations between them did not exceed more than 8% in any case. For the presentation of the results, a sample presenting average values was adopted. The photo labeled in Figure 1a shows the prepared emulsion-microspheres system after formation (t = 0 s), while Figure 1b shows it after the sedimentation process (t = 1800 s). As can be observed from the above images, the prepared system can be schematically represented in Figure 1c, where three phases can be distinguished--the solid phase (microspheres), the oil phase (drops of the internal phase of the emulsion), and the continuous phase (aqueous phase of the emulsion). The system was subjected to reflected light scanning for 30 min, which allowed to determine the growth of the sediment layer as schematically presented in Figure 2.  
During the turbidimetric measurement, the system was subjected to scans every 30 s for 30 min. As a result of these scans, changes in the backscattered light value RW were  
Figure 1: Photo of emulsion with glass microspheres—(**a**) just after preparation, (**b**) after 1800 s, and (**c**) scheme of the system. Figure 2: Increase in sediment thickness over time for a measurement of 70% emulsion (D1), with 0.3 g/mL of glass microspheres in the 300–400 \(\upmu\)m diameter range. obtained along the sample height H. This allowed us to obtain graphs of the dependence of RW on H for each system under study. An example of such a plot for the sedimentation of microspheres with a diameter range of 300-400 \(\upmu\)m at 0.3 g/mL in an emulsion of 70% concentration (D\({}_{1}\)) is presented in Figure 3.  
In Figure 3, colored curves can be observed indicating the percentage of backscattered light along the sample height. The blue curve refers to the first scan. Subsequent curves in red refer to subsequent scans. The red curve refers to the last scan after 30 min. As can be seen in the graph presented in Figure 3 in the lower part of the sample (from 0 to about 10.5 mm), the values of RW decrease in time from about 78% to about 52%. These changes in values are indicative of the sedimentation process taking place. For glass microspheres deposited at the bottom of the cell, the reflected light value is lower than for emulsions. As can be observed, the height at which the RW value reached 52% was increasing. This height will be denoted in this work as h\({}_{\text{s}}\) and will determine the thickness of the sediment layer. Considering the upper part of the sample (above 11 mm), it can be observed that the RW values increase slightly with time. This means that the emulsion becomes more and more free of solid particles during the sedimentation process, and for pure emulsion, the RW values are the highest. Similar graphs were obtained for all studied systems. Since the growth of the sediment layer with time is an important parameter in the analysis of the sedimentation process, it was possible to read the changes in h\({}_{\text{s}}\) values with time from the graphs of the changes in backscattered light with height.