# Functionalization and Modification of Bitumen by Silica Nanoparticles
## 3 Results and Discussion
### Functionalization of SiO\({}_{2}\) Nanoparticles. Having checked that the **SNPs**\({}^{\prime}\) dimension has no significant influence on the rheological properties of bitumen, we functionalized the surface of the **SNPs** differently to probe the effect of peripheral functional groups. Chemical modifications of the SNPs were performed as described in Scheme 2. First, **SNP-3** was reacted with 3-aminopropyltriethoxysilane (APTES) after careful dispersion in methanol through intense sonification process. After 24 h of reaction time, the resulting solution was centrifuged and the resulting residue was thoroughly washed with methanol and dried to yield **NH\({}_{2}\)@SNP-3** nanoparticles embedded with free NH\({}_{2}\) pending groups. In a second step, the NH\({}_{2}\)@SNPs obtained were re-dispersed in ethanol and after a strong sonification process, reacted with tetradacyl aldehyde in order to obtain the **C\({}_{\textbf{14}}\)N@SNP-3** nanoparticles embedded with C\({}_{\textbf{14}}\) alkyl length chains. SEM images of **SNP-3** and the corresponding functionalized **NH\({}_{2}\)@SNP-3** and **C\({}_{\textbf{14}}\)N@SNP-3** samples are reported in ESI. All samples show rather identical features with nanoparticles similar in size and size distribution highlighting that no significant increase in diameter was observed with chemical functionalization. The success of the reactions was established by coupling the FT-IR spectra with the thermogravimetric curves obtained for all compounds. All FT-IR spectra are reported in Figure 3. The FT-IR spectrum of silica particles **SNP-3** showed an intense peak at 1100 cm\({}^{-1}\) and a wide weak peak in the range between 3200 and 3500 cm\({}^{-1}\), which is associated with vibrations of the Si-O-Si network and the stretching vibration of the peripheral OH groups (-Si-OH) bonds, respectively. The absorption band at 1637 cm\({}^{-1}\) is characteristic of the OH bending vibration. The FT-IR spectrum of the amine-modified silica sample **NH\({}_{2}\)@SNP-3** showed in contrast the presence of a small broad peak at 2931 cm\({}^{-1}\), associated with the stretching vibrations of the saturated C-H bonds of the alkyl chains of the grafted APTES moieties. Although a wide band is observed at 3100-4000 cm\({}^{-1}\), the expected double amine absorption band that should be observed in this region cannot be distinguished clearly, probably due to the presence of Si-OH groups suggesting an incomplete functionalization of the **SNPs** with APTES. This is further confirmed by the absorption band at 1637 cm\({}^{-1}\) being still present although of less relative intensity when compared to the FT-IR spectrum of SNP-3 sample. Finally, the FT-IR spectrum of the **C\({}_{\textbf{14}}\)N@SNP-3** clearly shows an increment in intensity and a sharpening of the bands at 2931 cm\({}^{-1}\) and 2929 cm\({}^{-1}\) relative to stretching vibration modes of the saturated C-H bonds of the long alkyl chains, accompanied by an increment in intensity of the band at 1000-1100 cm\({}^{-1}\) relative to the carbon skeleton of the alkyl chains, which overlap the vibration band associated with the Si-O-Si network. Although the stretching vibration of the C=N imine bond that should be observed at ca. 1650 cm\({}^{-1}\) is not clearly visible, probably overlapped with the 1637 cm\({}^{-1}\) bending vibration of the peripheral Si-OH residual groups, these modifications of the FT-IR features reveals the successful conversion of the NH\({}_{2}\) peripheral groups. To confirm the success of the functionalizations performed and estimate the quantity of functional groups grafted onto the surface of the SNPs, thermogravimetric analyses were performed on all samples. TGA curves are reported in Figure 4.  
The TGA trace of **SNP-3** is characterised by an initial loss in weight (ca. 3%) at temperature below 100 \({}^{\circ}\)C owing to the dehydration of the nanoparticles, before reaching a plateau correlated to the thermal stability of the silica nanoparticles up to 900 \({}^{\circ}\)C as expected.