# Functionalization and Modification of Bitumen by Silica Nanoparticles
## 3 Results and Discussion  
### Influence of the Diameter Size of SNPs  
All **SNPs** were prepared by following a modified Stober method. In particular, cetyltrimethylammonium bromide (CTAB) was utilized as template agent to obtain spherical-shaped **SNPs** (Scheme 1).  
\[\begin{array}{c}\text{{\it Studied parameters:}}\\ \text{{\it i}}\text{{\it EtOH/Water ratio}}\\ \text{{\it ii}}\text{{\it Reaction Temperature}}\\ \text{{\it TEOS}}+\text{CTAB}\end{array}\]  
\[\begin{array}{c}\text{{\it Fixed parameters:}}\\ \text{{\it Ammonia}}\text{{\it (25\%), 2 h stirring}}\\ \text{{\it of specific diameter}}\end{array}\]  
\[\begin{array}{c}\text{{\it Scheme 1.}}\\ \text{{\it Scheme 1.  
By varying the experimental conditions, SNPs of different sizes were prepared (**SNP1-4**). The influence of two parameters was studied, relative content of ethanol/water of the reaction medium and temperature at which the reaction took place. Experimental conditions and obtained results are presented in Table 2. The average size was determined by SEM microscopy.  
With the temperature increase (from 25 to 50 \({}^{\circ}\)C), the size of the SNPs increases (from 300 to 900 nm, samples **SNP-3**, **SNP-3a** and **SNP3b**), similarly the diameter of the nanoparticles also increases by increasing the amount of ethanol with respect to water (Samples **SNP-1-4**). Thus playing with these two parameters allowed us to obtain 6 samples of nanoparticles with diameter size ranging from ca. 100 nm to 1 \(\upmu\)m (Table 1). SEM images of the synthesized **SNPs** are reported in Figure 1. The experimental conditions adopted here allowed us to obtain spherical shaped nanoparticles, however, as observed in Figure 1a,b, for the smallest size nanoparticles, their morphology tended to be more similar to flakes than true spheres.  
The influence of the size of the nanoparticles on the rheological properties of bitumen was probed by incorporating all SNPs in bitumen (1% weight ratio). This low ratio was chosen according to the literature [16] keeping in mind that the main goal in asphalt binder uses is to reduce at the maximum the quantity of additive for economic purposes but also to minimize its eventual aggregation that could result in sedimentation phenomenon over a long-term period. Obtained results in terms of the time cure test (tan \(\delta\) versus temperature) are reported in Figure 2. The performed analysis showed that the size of the nanoparticles with diameter ranging from 100 nm to 1 \(\upmu\)m, does not have any significant influence on the rheological properties of the bitumen. All additives, independent of their size act as an inert filler such as CaCO\({}_{3}\), that we used and tested in the same experimental conditions for direct comparison. Consequently, smaller size nanoparticles are preferred in order to minimize over time eventual sedimentation phenomena, in fact, effects of sedimentation in the bitumen related to the particles size are well known in literature [17].  
Figure 1: SEM images of synthesized SNPs. **(a)** SNP-1, **(b)** SNP-2, **(c)** SNP-3, **(d)** SNP-4, **(e)** SNP-3a and **(f)** SNP-3b. Note that all images were taken at identical magnification to allow immediate comparison (scale bar: 1 \(\upmu\)m).  
Figure 2: Semi-log plot of temperature ramp tests for the pristine and modified bitumens formulated with 1 wt% of nanomaterials added as solid powder dispersion. The effect of an inert filler CaCO\({}_{3}\) (1 wt%) was also determined. Loss tangent tan \(\delta\) is plotted, the asymptotic value identifies the sol-transition temperature.