## 4 Binary Filler-Based Nanocomposites  
Several research groups have investigated the effects of using a combination of two different carbon nanomaterials (binary fillers) on the properties of the resulting nanocomposites. [PERSON] et al. [7] investigated the thermal and mechanical properties of graphene-based composites by incorporating carbon nanotubes. They developed a new method combining the incorporation of binary fillers (i.e., a combination of graphene particles and carbon nanotubes) into a polymer matrix through in situ microemulsion polymerization. They synthesized graphene/CNT/polystyrene nanocomposites as follows. an aqueous suspension of graphene and multi-wall carbon nanotubes (MWCNTs) was prepared by sonication, and then added to a reactor containing a mixture of monomer styrene, crosslinking divinylbenzene (DVB) and the initiator AIBN. Polymerization took 4 h at 85 \({}^{\circ}\)C. Afterwards, the PS (polystyrene) films were prepared from the graphene/CNT/polystyrene nanocomposites as shown in Figure 12. This resulted in an interconnected network in which the PS-grafted MWCNTs acted as a bridge to bind the graphene sheets to each other and connect the MWCNTs and the graphene via PS chains (SEM and TEM images in Figure 13), which considerably enhanced its thermal and mechanical, but especially its elastic properties (high modulus). This procedure also led to a decrease in the sheet resistance, i.e., an increase in the electrical conduction within the composite film. Figure 12: Preparation flow for graphene/MWCNT/PS film using divinylbenzene (DVB) crosslinker (Reprinted from [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Self Assembled Graphene/Carbon Nanotube/Polystyrene Hybrid Nanocomposite by in Situ Microemulsion Polymerization. _Eur. Polym. J._**2012**, _48_, 252-259 [7], with permission (2020) from Elsevier). [PERSON] et al., used gel permeation chromatography (GPC) to evaluate the effect of binary fillers on two important polymerization parameters: molecular weight (MW) and the polydispersity index (PDI) of polystyrene. The results showed that the use of graphene and MWCNTs increased the molecular weight (~40,000 and ~65,000 g/mol for neat PS and nanocomposites, respectively) so that the binary fillers contributed to consuming the initiator. In this case, the quantity of the initiator diminished in the medium, which thus slowed down the formation of new polymer chains on the surface of the MWCNTs. Similarly, the PDI of the PS chains increased in the nanocomposites (~168,000 and ~228,000 for the neat PS and nanocomposites, respectively), because most of the PS nanoparticles were grafted to the MWCNTs and not to the graphene layers. Brownian motion is likely to have removed the absorbed surfactant SDS on the surface of the fillers, thus creating new active radical centers enabling the initiation of the polymerization reaction. [PERSON] et al. [47] fabricated anti-corrosion coating based on an urushiol formaldehyde polymer (UFP) in the presence of graphene oxide and multiwalled carbon nanotubes (GO/MWCNTs/UFP), which could be used in a marine environment. The two main steps consisted of in situ polymerization of UFP in the presence of MWCNTs followed by the incorporation of modified graphene oxide (MGO) in blending the MWCNTs/UFP. A mixture of urushiol and formaldehyde was prepared in xylene at 90 \({}^{\circ}\)C. Once the temperature dropped to 60 \({}^{\circ}\)C, an ultrasonicated treated solution of MWCNTs was added, producing MWCNTs/UFP (UFP to MWCNTs 100:1). The polymerization temperature ranged from 90 to 130 \({}^{\circ}\)C. FTIR analysis indicated that the in situ polymerization worked efficiently as a result of the decrease in the intensity of the characteristic peaks of O-H groups, proving the existence of chemical bonding between the OH groups from MWCNTs and the phenyl ring of the UFP.