## 4 Results and Discussion
### Stabilization of Graphite
#### 4.1.2 Effect of pH Value on Zeta Potential
Figure 5 illustrates the pH dependence of PVP without and with graphite nanoparticles. Figure 5 displays the pH value for various PVP contents without particles, while Figure 5 shows the pH values of disper  
Figure 4: Zeta potential of graphite dispersions at various pH values for (**a**) a PVP content of 20 m% (see Table 10) and (**b**) a TX-100 content of 40 m% (see Table 10). sions with a different graphite content and at a constant PVP fraction of 20 m%. Figure 6 illustrates the same relations for TX-100. The influence of the graphite nanoparticles on the pH value could not be individually examined, as graphite displays low initial stability in an aqueous medium. Thus, it was not possible to create a homogeneous dispersion. In the samples without particles, the amount of added PVP or TX-100 content related to the amount of 10 m% particles. The standard deviation was calculated from three single measurements. Figure 5a shows that, with a PVP fraction of between 5 m% and 20 m%, the pH value is approximately constant. In the range between 20 m% and 50 m%, the pH value decreases roughly linearly from 8.2 to 7.3. For the dispersion containing a constant amount of 20 % PVP and a varying content of graphite, no distinct pH value dependence can be noted between a graphite fraction of 5 m% and 20 m% (see Figure 5b). As is evident from Figure 6a, the pH value as a function of TX-100 content fluctuates by about 0.2 measurement units. This deviation lies within the limits of accuracy of the measuring instruments. Thus, it appears that the TX-100 content has no significant influence on the pH value in the investigated value range. However, the dispersion with a constant content of 40 m% TX-100 and a varying amount of graphite shows a pH value dependence (see Figure 6b). The pH value decreases almost linearly from 3.8 at a proportion of 5 m% graphite to 2.7 at a proportion of 20 m%. Comparing Figures 5b and 6b shows that, for TX-100, the pH value shifts more towards acidity than with PVP. While the differences were moderate for a solid content of 10 m%, they were substantial for higher solid contents. This corresponds with the fact that the required amount of NaOH is higher with TX-100 than with PVP at a solid content of 10 m%. Figure 5: PH value as a function of (**a**) PVP content for a solution without nanoparticles (see Table 7) and (**b**) graphite content for aqueous dispersions containing 20 m% PVP (see Table 8). Figure 6: PH value as a function of (**a**) TX-100 content for a solution without nanoparticles (see Table 9) and (**b**) graphite content for aqueous dispersions containing 40 m% TX-100 (see Table 10). Without graphite particles, there are only interactions between the water and existing dispersant. Figure 5a corroborates the occurrence of a hydrolysis reaction. Water releases a hydrogen atom, which causes a transformation of the lactam ring of the PVP to an amino acid group. The amino acids, in turn, react with the water, resulting in the production of H\({}_{3}\)O\({}^{+}\) ions, which directly determine the pH value. For small amounts of PVP, the ions do not yet have a considerable effect on the pH value of the total dispersion. It appears that, between 20 and 30 m\(\%\), a threshold value is exceeded, from which the ions directly influence the pH value of the total system. The observations in Figure 6a correspond well with the findings of [PERSON] et al. [45]. They stated that TX-100 does not show a pH value dependence due to the non-existence of functional groups that can react with water. When adding graphite particles to the water-dispersant mixture, the dispersants may interact with both the particles and water. Because of the non-existence of functional groups at the graphite surface, PVP adsorbs homogeneously, forming a uniform film [30]. The hydrophilic tail group adsorbs at the hydrophobic graphite surface, while the hydrophilic polar head group is oriented towards the water [31].