## 3 Composite Matrices and Applications
### Polymers
[PERSON] et al. developed microwave-absorbing composite films for electronic applications by adjusting electromagnetic properties through varying compositions [[PERSON]]. This study synthesized BaTiO\({}_{3}\) nanoparticles using a sol-gel process, combined them with PVDF and MWCNTs to create hybrid films, and further stacked the resulting hybrid material into multi-layer slabs. The films showed a significant increase in dielectric constant and a moderate increase in loss factor, which made them suitable for high-dielectric microwave applications [80]. The integration of mechanically superior materials, such as CNTs and graphene, into polymer composites has shown promising results in enhancing mechanical, electrical, and thermal properties. Notably, solid-phase molding techniques, along with filler functionalization, have demonstrated significant improvements in dispersion and functional properties [81]. These findings underscore the importance of filler selection, processing methods, and compatibility in tailoring the properties of polymer composites for diverse applications, ranging from automotive components to electronic devices. Another emerging versatile thermoplastic is polyphenylene sulfide (PPS), which has gained popularity due to its easy manufacturing process, high-temperature stability, and chemical resistance. As a consequence, it is abundantly used in the automobile, aerospace, and chemical industries. However, as previously mentioned, pure PPS, like PVDF, is not characterized by good thermal conductivity and mechanical strength [82; 83; 84]. A study led by [PERSON] et al. investigated the incorporation of CNTs in 3D-printed PPS. The experiment involved the preparation of Carbon Nanotube Molecularly Imprinted Polymers (CNT-MIPs) and polyphenylene sulfide (PPS) filaments. High-purity CNTs were combined with a polymer mix (including N-phenyl maleimide, methyl methacrylate, and other chemicals) and processed through heating, cooling, and purification steps to form CNT-MIPs. These CNT-MIPs were then mixed with PPS at various mass fractions, extruded into smaller filaments, and further processed into controlled-diameter filaments. Figure 7: (**a**) Thermal conductivity of PVDF composites with GE, p-MWCNTs, and p-MWCNTs/GE. (**b**) Thermal conductivity of PVDF composites with different contents of s-MWCNTs/GE, a-MWCNTs/GE, and p-MWCNTs/GE [79]. The printing parameters were controlled, resulting in high shape accuracy of the printed samples, as seen in Figure 8[85]. The temperature and heat flow curves, along with corresponding enthalpies and crystallinities of the composites, were analyzed. As the CNT content increased, so did the crystallinity values, with the 0.9 wt% CNT prints exhibiting almost double the crystallinity of pure PPS prints. Pure PPS exhibited an obvious glass transition around 90 \({}^{\circ}\)C, which became less pronounced with increasing CNT content. The formation of the glass transition peak is linked to the movement of amorphous chain segments in PPS. However, as the crystallinity of the samples increased with a higher CNT content, the number of amorphous molecular chains decreased, and some became constrained by crystallites [85]. The same study also investigated friction processes by analyzing friction coefficient curves under loads of 100 N and 196 N. During the running-in stage, the friction coefficient generally increased with sliding distance, especially under higher loads due to transfer film formation and changes in surface contact. However, the friction coefficient curve of the 0.9 wt% CNT composite showed smoother behavior due to increased PPS crystallinity from a high CNT content. This higher crystallinity led to stable wear under lower loads (Figure 9). The average friction coefficient decreased for certain CNT contents, particularly at 0.5 wt%, due to a shift from adhesive to abrasive wear.