# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 6 Forefront/Vanguard Techniques Facing Complexity in Bitumen
### Probing Complexity
#### 6.2.3 Applications of Scattering Techniques to Bitumen  
Due to the high diffusion of X-ray scattering techniques and the development of lab-scale instrumentation giving adequate data quality, X-ray scattering was used for the analysis of bitumen even in the '60 [17]. Of course, when exploring the structure, taking into account values of typical length scales longer than a few nm small-angle scattering is best suitable [102]. However, in the wide angle range, the spectrum gives already a significant amount of information: it will be now briefly shown how to interpret it taking as an example of the representative spectrum, reported in Figure 27, as a function of a scattering vector \(q\) (\(q=(4\pi/\lambda)\) sin\(\theta\)). Let us pay attention to the following features:  
1. A prominent broad band centered around 1.3 A\({}^{-1}\) dominates the spectrum;
2. A weak and broad band around 3 A\({}^{-1}\);
3. There is a tiny, but sharp, peak around 0.5 A\({}^{-1}\), not always present;Different peaks (in Figure 27 indicated with progressive numbers) indicate that there are different characteristic distances belonging to various atomic and molecular organizations of different levels of complexity. The position of the center of each peak gives the characteristic distance (d), according to the Bragg law (Equation (7)) which, readapted, gives the following:  
\[\mathbf{d}=\frac{n\mathbf{\lambda}}{2\,\text{sin}\theta}. \tag{7}\]  
As above, \(d\) is the interplanar distance, \(\theta\) is the scattering angle, and \(\lambda\) is the wavelength of the incident radiation. Table 3 resembles the peculiarities and meaning of the peaks. The most prominent band centered at around 1.3 A\({}^{-1}\) deserves some attention. In alkyl-based fluids, this band has been attributed to a characteristic intermolecular lateral distance of 4.4-4.7 A [96,100,103] usually present in the conventional liquid (disordered) state [96,97,99,100,101,102,103]. Aromatic compounds are characterized by shorter distances, due to their tendency to form stacks, so they give the so-called graphene band (the lateral distance of about 3.6 A) [22]. Due to the simultaneous presence of both aliphatic and aromatic compounds in the bitumen, it is reasonable to treat this band as a not-resolved superposition of these two contributions. Deconvolution in terms of bell-shaped curves is sometimes necessary to discriminate all the signals. Two noteworthy observations are due:  
1. The fitting procedure will also help in analyzing the weaker band at higher angles (around 2.9 A\({}^{-1}\) and which is a characteristic distance \(d\) of about 2.2 A) which is sometimes partially overlapped;
2. The fitting allows to derive, from each curve, also the Full Width at Half Maximum (FWHM)  
The shorter distance, of about 2.2 A, can be surely attributed to some particular interatomic distance. The value is in the range of the typical distance between non-adjacent carbons reported for polycyclic aromatic compounds [106] so such attribution can be safely hypothesized. In the range \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Position** & **Features** & **Characteristic Distance (Å)** & **Meaning** \\ \hline
1.3 & Dominant and broad & \(\sim\)4.7 & combination of various intermolecular distances between alkyl and aromatic parts: See text interatomic distance within asphaltene; \\
2.9 & Broad and weak & 2.2 & interatomic distance within asphaltene; \\ \(\sim\)0.5, & Not always present & \(\sim\)13 & supra-molecular aggregation: Repetition distance of aggregates of local asphaltene aggregates \\ varying & usually tiny & & aggregates of local asphaltene aggregates \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Bands in the WAXS profile with the corresponding characteristics. Figure 27: A typical X-ray scattering spectrum together with the Lorentzian deconvolution. 0.3-0.8 A\({}^{-1}\) it can be present at a tiny peak.