# Sedimentation of microparticles in Highly Concentrated Non-Newtonian Emulsions
## 2 Materials and Methods  
Glass microspheres produced by Alumetal-Technik were used in the sedimentation process studies. The material was characterized by a smooth surface, round shape, and chemical inertness. Their density was 2.5 g/cm\({}^{3}\) and bulk density 1.45 g/cm\({}^{3}\). The chemical composition of the microspheres was as follows: 70-73%--SiO\({}_{2}\), 13-15%--Na\({}_{2}\)O + K\({}_{2}\)O, 7-11%--CaO, 3-5%--MgO, 0.5-2.0%--Al\({}_{2}\)O\({}_{3}\), and TiO\({}_{2}\)\(\leq\) 0.1%. Microspheres of five different grain size fractions were used in this study, with the range of diameters shown in Table 1.  
The experiments were conducted at three different concentrations of microspheres relative to the volume of emulsion: \(\varphi_{x}\) = 0.2 g/mL; \(\varphi_{x}\) = 0.3 g/mL; and \(\varphi_{x}\) = 0.4 g/mL. The emulsions in which the sedimentation of microspheres took place were oil-in-water systems. Vegetable oil \"Zlota Kraina\" from Zloto Polskie company was used as a dispersed phase. Its dynamic viscosity at 20 \({}^{\circ}\)C was 65 mPa-s and density 910 kg/m\({}^{3}\). Distilled water was used as a continuous phase, while Rokacet from PCC EXOL SA was used as an emulsifier in an amount of 2% by volume. Emulsions with three different volume concentrations of the internal phase were used in the study: 60%, 65%, and 70%. These emulsions exhibited properties of shear, diluted non-Newtonian liquids. These liquids were subjected to rheological tests using BOHLIN CVO 120 rheometer with a cone-plate system. Changes of viscosity with the rate of shearing were set. The temperature of measurements was 20 \({}^{\circ}\)C. The flow curves of the obtained emulsion systems are presented in Figure 11 (Appendix A). Emulsions were formed by mechanical mixing, using a high-speed homogenizer with a rotational speed of 20,000 rpm. Three different mixing times were used to obtain different oil droplet diameter sizes (while keeping the other mixing parameters constant). The mixing times used were D\({}_{1}\) = 360 s, D\({}_{2}\) = 180 s, and D\({}_{3}\) = 60 s. The obtained emulsion systems were subjected to oil droplet size analysis using Anton Paar PSA 1190 Particle Size Analyzer. This allowed the determination of oil droplet parameters. The oil droplet size distributions of the 70% emulsion at different mixing times are shown in Figure 12 (Appendix A). The average oil droplet diameter calculated by the volume d\({}_{2.3}\) for the 70% emulsions at 360 s, 180 s, and 60 s mixing were d\({}_{\rm el}\) = 8.24 \(\upmu\)m, d\({}_{\rm e2}\) = 11.52 \(\upmu\)m, and d\({}_{\rm e3}\) = 15.72 \(\upmu\)m, respectively. The 60 and 65% emulsions were formed with only one mixing time, which was 360 s, resulting in oil droplets with average diameters of 10.54 and 10.98 \(\upmu\)m, respectively. The sedimentation process was analyzed using a TurbiscanLAB(tm) instrument equipped with Turbisoft-Lab software. TurbiscanLAB(tm) operates in scanning mode: the optical readout head scans the length of the sample (up to 55 mm), acquiring transmission and backscattered light data every 40 \(\upmu\)m. The operating principle is based on measuring the backscattered light (RW) and transmitted light (T) flux along the height of the sample with the liquid under test. The light source is an electroluminescent diode emitting a focused beam of near-infrared light with a wavelength of 880 nm. Depending on the initial particle size (smaller or larger than the wavelength, 880 nm), the level of backscatter increases or decreases. The stability of the produced emulsions was also checked using the Turbiscan LAB(tm) instrument. The samples were scanned for 5 h and overlapping backscattered light (RW) and reflected light (T) curves were obtained, indicating that no destabilizing processes (coalescence, creaming) were occurring, and the systems were stable. The sedimentation process was carried out in a measuring cell with a volume of 25 mL.