## 4 Discussion
### Expelling Effect between Coagulated Structures with the Same Charge Type  
In Figure 22, the density peaks of different cation species in Ar/SF\({}_{6}\) plasma before the collapse of the coagulated structure are compared. In Figure 23, the density peaks of different anions species in Ar/SF\({}_{6}\) plasma before the disperse of coagulated structure are compared, and it is noticed that the densities of SF\({}_{6}^{-}\) and SF\({}_{5}^{-}\) have been summed together. It is seen from Figures 22 and 23 that the density peaks of SF\({}_{3}^{+}\) and Ar\({}^{+}\) are the most close, and the density peak of F\({}^{-}\) and the peak of summed SF\({}_{6}^{-}\) and SF\({}_{5}^{-}\) density are the most close. In Figure 24a, the Coulomb's force between the two point-charge models transformed that are positive is presented. In Figure 24b, when fixing the charge amount of two point-charge models, it is noted that Coulumb's expelling force is maximal when the charge amounts of the two models are equal. This explains the collapses of coagulated anions and cations in Figures 5 and 6 since their density peaks are the closest to their opponents shown in Figures 22 and 23. It is easily seen from Figure 24 that if the two point-charge models carry negative charge, the maximum of force still appears when the total charge amount is averaged.  
In addition, in Section 3.3, the dispersion of cation coagulation in Figure 6 is more severe than the anions in Figure 5. It is caused by the fact that the coagulation of anions is a chemical process, while the coagulation of cations is a more physical process that is sustained by the ambipolar self-coagulation (see Section 4.2.2(b)). As analyzed, the ambipolar process that coagulates the cations originates from the chemical self-coagulation of anions and is ultimately sustained by means of the electrically appealing interaction between the anions and cations to keep the neutrality. Herein, the chemical factor is stronger than the physical factor.  
Moreover, the light species are more coagulated, as shown in Figures 5 and 6. This is caused by the inertial effect of density quantity. In the analytical theory of Section 4.1, it is seen that the self-coagulation is caused by the negative chemical source, i.e., recombination. The dimensional analysis of Section 3.1 reveals that the chemical source can be transformed into the drift of the _effective_ field, and the negative source plays the electrical role then. In the continuity equation of species, the inertial term can be multiplied by the species mass.  
Figure 22: Simulated density peaks of all considered _cation species_ in Ar/SF\({}_{6}\) plasma, by means of fluid model at a simulating time before the collapse happens. The discharge conditions are the same as in Figure 4. The self-coagulated density peaks of SF\({}_{3}^{+}\) and Ar\({}^{+}\) are the closest to each other, hence treated as the point-charge models (_positive_ type) with equal charge amount.  
The electrical interaction is independent of the species mass. The species with large mass are thereby difficult to coagulate since the accelerating velocity is determined by a fixed drifting force, but for an object with a large mass this is small.