## 3 Results and Discussion  
The initial gel formation near the tip of the needle can be seen in Figure 4a-c, which shows the droplet's growth stage, its initial necking stage, and its final separation stage. All the monodispersed thermosensitive gels used in this study were generated in the microfluidic device by setting various flow rates for the silicone oil (\(50\times 10^{-6}\) m\({}^{2}\)/s and \(300\times 10^{-6}\) m\({}^{2}\)/s) within a range of \(3.96\)-\(15.8\times 10^{-9}\) m\({}^{3}\)/s. The growth stage of the droplet was defined as the point at which the new gel solution was ejected from the tip of the nozzle. Simultaneously, the continuous-phase flow (silicone oil) with a constant flow rate generated drag in a vertical direction (in line with gravity), which, in this case, tended to separate the developing droplet from its gel solution on the tip of the nozzle. Droplet separation could either exist in a dripping regime or in a jetting regime. In the dripping regime, droplet breakage occurred at the tip of the nozzle (capillary tube). Meanwhile, in the jetting regime, droplet separation existed at the tip of a jet located far from the nozzle tip. In this research, droplet formation occurred in the dripping regime rather than in the jetting regime as the velocity of the inner fluid (dispersed phase) was much slower than that of  
Figure 4: Images showing a droplet’s formation at: (**a**) growth stage; (**b**) necking stage; (**c**) immediately after separation. Figure 3: Schematic of the apparatus for mechanical observations. the continuous-phase fluid [27]. Hence, the condition supported the breakage of droplets (separation), which occurred near the tip of the nozzle, as shown in Figure 4. When the continuous-phase flow rate was gradually increased from \(5.94\times 10^{-9}\) m\({}^{3}\)/s to \(15.8\times 10^{-9}\) m\({}^{3}\)/s (for the both values of viscosity), the diameter of the gel droplets visibly decreased (as shown in Figure 5a with the reference letters A-D). The relationship between an increasing continuous-phase flow rate and the average droplet diameters for the both viscosities (\(50\times 10^{-6}\) m\({}^{2}\)/s and \(300\times 10^{-6}\) m\({}^{2}\)/s) are shown in Table 1.  
A correlation was evident between the diameter of the generated droplet (\(d_{g}\)) and the flow rate of the continuous-phase flow (\(Q_{c}\)) for each of the silicone oils' viscosities, which can be expressed as follows:  
\[d_{g}=2.2Q_{c}{}^{-0.32}\text{ for }50\times 10^{-6}\text{ m}^{2}\text{/s silicone oil}, \tag{1}\]  
and  
\[d_{g}=1.8Q_{c}{}^{-0.43}\text{ for }300\times 10^{-6}\text{ m}^{2}\text{/s silicone oil}. \tag{2}\]  
The correlations indicate that the flow rate of the continuous phase significantly affected the diameter of the generated droplets. The two curved lines shown in Figure 5a define the correlation between the continuous-phase flow rate and the average diameter of the droplets with respect to the two kinematic viscosity values of \(50\times 10^{-6}\) m\({}^{2}\)/s and \(300\times 10^{-6}\) m\({}^{2}\)/s. During the experiment, gel particles were prepared in nine cases by varying the continuous-phase flow rate and the kinematic viscosity. The coefficient of variations, the ratio of standard deviation, and the average value of the droplets' diameter calculated from hundreds of droplets for all the nine cases were \(<\)10%; therefore, droplet formation was considered to be monodispersed [25]. From the graph, it is apparent that the diameter of the droplets decreased as the continuous-phase flow rate increased; the same trend was evident for both kinematic viscosity values. In particular, the \(50\times 10^{-6}\) m\({}^{2}\)/s silicone oil could generate larger gel diameters than the \(300\times 10^{-6}\) m\({}^{2}\)/s silicone oil at the same continuous-phase flow rate values. A key result of these results