## 2 Covalent Interactions
### Graphene-Based Nanocomposites  
Ultrasonically induced polymerization of the monomer aniline in the presence of graphene nanoparticles has also been widely studied. Various approaches have been explored to fabricate these nanocomposites. [PERSON] et al. [34] produced PANI/graphene nanocomposites by implementing an in situ inverse emulsion polymerization under sonication of aniline in the presence of graphene sheets in chloroform. The initiator APS containing the aqueous phase was added to the organic phase comprising the dopant DBSA, the distilled aniline, and the graphene sheets in a chloroform medium. The graphene sheets were well dispersed in the PANI resulting in a wrapping of graphene by the PANI matrix as shown by the Cryo-TEM images. The TGA images indicated that the composite had higher thermal stability as the graphene content increased. This also pointed to the nanocomposite's potential to be used as an electro- mechanical sensor since the electrical resistivity decreased under pressure as a result of its high graphene content, thus leading to an increase in electric conduction. PANI can also be grafted onto the surface of graphene by first covalently functionalizing the graphene sheets from which the in situ polymerization is initiated. [PERSON] et al. [35] functionalized reduced graphene oxide (rGO), prepared by a modified Hummers method with amine groups under acidic conditions. These reactive moieties located on the surface graphene were used to initiate the growth of aniline chains, resulting in a uniform grafting of PANI on the graphene surface as proved by SEM and TEM. Modification of monomer molecules can also be a way to functionalize graphene for the fabrication of nanocomposites. [PERSON] et al. [13] modified the monomer aniline with perfluorophenyl azide (PFPA) molecules through a coupling reaction confirmed by Fourier-transform infrared spectroscopy (FTIR). Then, the resulting modified-aniline chains were covalently attached to the surface of few-layer graphene (FLG) flakes by microwave-heating. Subsequently, the in situ grafting polymerization of aniline was produced out of modified-aniline functionalized FLG flakes, meditated by APS under sonication, leading to a homogenous vertical grafting of PANI (needle-like structures) on the FLG flakes; the grafted PANI amounted to \(\sim\)26%. an enhancement of the capacitance within the PANI/graphene nanocomposites was demonstrated by cyclic voltammetry that confirmed the preservation of electrochemical properties after grafting. The natural tendency of graphene sheets to entangle because of \(\pi\)-\(\pi\) stacking interactions between different layers is a real issue for the production of stable graphene-based nanocomposites exhibiting high chemical-physical performance. The covalent attachment of the polymer onto the graphene surface appears to be an efficient method to achieve good dispersion of graphene within the matrix. [PERSON] et al. [36] successfully demonstrated good dispersion of GO within a hyperbranched polymer (HP) matrix by an in situ \"grafting-from\" ROP. Prior to the in situ polymerization of the cyclic ether monomer 3-ethyl-3-oxetanethanol initiated by boron trifluoride etherate in the presence of GO, a stable GO dispersion in chloroform was achieved by ultrasonication, resulting in well separated graphene sheets. The HPs grafted to GO were found to have better thermal stability than pristine HPs as well as enhanced mechanical properties including higher tensile strength. an excellent surface contact between the carbon fillers and the polymer also made it possible to obtain very good filler dispersion within the matrix. [PERSON] et al. [17] showed that the high content of polymer nylon-6 (PA6) chains (\(\sim\)78%) grafted onto the rGO surface resulted in improved interfacial contact because of the strong interactions between the carboxylic groups from rGO and the amino moieties located at the PA6 chain ends.