# Formation of Conductive Networks in Polysulfone Filled with Graphite-Derived Materials
## 3 Results and Discussion
### Dispersion of Filler Particles in the PSU Matrix  
Uniform particle distribution and strong adhesion between graphite filler particles and a polymer matrix are critical for composite quality, especially at temperatures above the polymer's glass transition temperature (Tg). Powder particle shape and size are critical in defining the powder to the binder ratio and the degree of particle alignment, which impact  
Figure 2: SEM-based particle size distribution and SEM image for NG (**a**,**b**), AG (**c**,**d**), and CB (**e**,**f**).  
thermal, electrical, and mechanical characteristics. Under ideal compression circumstances, the plate-like particles would result in increased packing density.  
The SEM images (Figure 3a,b) of unfilled PSU with different resolutions indicate that unfilled polysulfone solution has a dense embedded nonporous structure consisting of a dense top surface layer, which provides the mechanical strength.  
Looking at the SEM micrographs, we can observe how well the filler particles are distributed through the matrix. The NG plates embedded in the polymeric matrix provide good heat transfer compared to AG. NG flakes are introduced in the matrix perpendicular to the direction of the pressure applying at consolidation. The NG particles are overlapping with one another (Figure 3c,e), resulting in significant contact areas between the particles, which increases heat and electrical transmission in this direction. As the NG content of the material increases, the overlap density increases and the thickness of the polysulfone interlayers decreases. In the case of AG fillers (Figure 3d,f), the filler particle has a spherical shape and a smaller size as compared to NG, making it simpler to produce a denser composite but with more pores that enhance the mechanical properties of the composite. The filler and polymer mixed to produce a massive agglomeration, which reduces as the filler quantity increases.  
Figure 3: Scanning electron microscopy (SEM) images of unfilled PSU (**a,b**); 70 wt. % PSU + 30 wt. % NG (**c**); 70 wt. % PSU + 30 wt. % AG (**d**); 30 wt. % PSU + 70 wt. % NG (**e**); 30 wt. % PSU + 70 wt. % AG (**f**).  
Figure 4a,b depicts the morphology of the composite materials at various CB concentrations. The CB aggregates are mixed together to create spherical or linear agglomerates in these photos. The carbon black articles are dispersed in the polymeric matrix well, resulting in a classic island-sea shape. The number of overlaps of polymer interlayers between graphite particles reduces as the filler content of EG increases as shown in Figure 5b-d, which should lead to a decline in the material's mechanical properties. Additional grinding of EG particles enhanced uniformity of their distribution inside the polymer matrix, reduced the number of aggregates and brought the structure of the material closer to that of NG-containing composites.  
The hybrid mixture of carbon black and graphite can affect polymer structure, viscosity, and graphite flake orientation inside the polymer matrix. Carbon black is known to have a high aspect ratio, which implies it creates a network-like structure inside the polymer, increasing stiffness and mechanical strength. Graphite flakes, on the other hand, can generate a more layered structure due to their plate-like morphology, increasing the composite's conductivity. SEM images of such hybrid mixture filled composites are given in Figure 5.  
Figure 4: Scanning electron microscopy (SEM) images of 98 wt. % PSU + 2 wt. % CB (**a**); 96 wt. % PSU + 4 wt. % CB (**b**).  
Figure 5: Scanning electron microscopy (SEM) images of 70 wt. % PSU + (2 wt. % CB + 28 wt. % NG) (**a**); 70 wt. % PSU + (4 wt. % CB + 26 wt. % NG) (**b**); 30 wt. % PSU + (2 wt. % CB + 68 wt. % NG) (**c**); 30 wt. % PSU + (4 wt. % CB + 66 wt. % NG) (**d**).