## 6 Novel Materials: Organic Nanoparticles  
The problem of chemical compatibility between nanoparticles and the bitumen/asphalt can be solved also if organic nanoparticles are used. This is in our opinion a brilliant solution since in this way the cost of the surface functionalization of inorganic nanoparticles is also avoided.  
[PERSON] et al. [66] found that organic expanded vermiculite compounds (OEVMT) give better resistance to fatigue and higher thermal stability with respect to nano-TiO\({}_{2}\) and nano-ZnO modified on the surface by \(\Upsilon\)-(2,3-epoxypropoxy)propyltrimethoxysilane, even if inorganic nanoparticles nano-TiO\({}_{2}\) showed better resistance to photo-oxidation and, consequently, better anti-aging effect due to their semiconductor nature. However, for further comments on the photo-protection effect given by nanoparticles see below the section about \"Added-Values Given by the Use of Nanoparticles\". In similar way, [PERSON] et al. [68] found that OEVMT, treated with star quaternary alkylammonium chloride to modify its interlayers from hydrophilic to lipophilic, can contrast the thermo-oxidative aging. Another interesting class of organic nanoparticles is that of carbon nanostructures: graphenes, nanotubes and nanofibers. Such nanostructures are schematically depicted in Figure 4. Their main use is in electronics-related applications like in flexible electronic and optoelectronic devices [69] or as electrodes and buffer layers component in polymer solar cells (PSCs) [70], but they were found to behave like reinforcing fillers in composites, photochemical cells, etc. [71]. This \"filling\" behavior can be transferred from to the fields of construction materials [72; 73; 74; 75].  
Generally, the use of nanostructured carbon materials gives more durable substrates [77], so, for example, graphene was used as modifier in bitumens [78,79] conferring increased stiffness and improving elastic behavior. However, the main drawback of the use of graphene as a bitumen modifier--and more generally as an element to improve the mechanical performances of construction materials--is its high production cost. For this reason, the studies on graphene are very few and have been shifted toward graphene-derived nanomaterials like graphene oxide (GO) [80], and graphene nanoplatelets (GNPs) [81,82] or some cheap carbon nanotubes and carbon nanofibers. The general structure of carbon nanotubes and carbon nanofibers is shown in Figure 4A. Carbon nanotubes were found to give stiffness increase and strain decrease regardless of the stress applied [83] improving also the mechanical performance of hot mix asphalt (HMA). Multi-walled carbon nanotubes (MWNTs) were used by [PERSON] et al. to improve the rheological properties of bitumen [84]. In this case, the authors hypothesize that higher defectiveness in MWNTs gives better improvement of the rheological properties, due to a probable formation of networks bridged by MWNTs defects. Finally, an increase by a factor of 2-3 in the fatigue life of bitumens modified with carbon nanofibers and improved characteristics of hot mix asphalts were found by [PERSON] et al. [85] who, highlighting the actual requirement of huge amounts of solvents to disperse CNFs, advise of the need to explore more eco-friendly mixing techniques to use lower amounts of solvents.  
In conclusion, there is no doubt that organic nanoparticles have a chemical nature intrinsically compatible with that of bituminous materials, and that their use avoids the costs of further steps consisting in the chemical modification of nanoparticle surface, like in the case of inorganic nanoparticles. However, their cost is still high in some cases (graphene, nanotubes). The increasing market of carbon and graphene families and the technology development specialized in the production of such kind of materials will cause a decrease in their price, probably making carbon nanostructures more appealing for large-scale applications like in bitumen and asphalt modification.