# Micromechanism of the Dispersion Behavior of Polymer-Modified Rejuvenators in Aged Asphalt Material
## 3 Results
### Atomic Force Microscopy Test Results  
As shown in Figure 5a-c, there are numerous continuous peaks in a sequence on the relatively smooth surface. Additionally, as the dispersal depth increases, the peaks increase in intensity. This type of structure is referred to as \"bee-like\" and is caused by the heterogeneous asphalt colloid structure. This structure can also be distinguished in the phase image (Figure 5d-f), in which the solid asphaltene particles (black and white streaks) appear to be covered by solid particles of resin (light grey areas) surrounded by an oil matrix (yellow areas), in which asphaltene micelles are dispersed [28]. Compared to the D3 slice, the D1 and D2 slices show fewer contact regions, i.e., the contact area of the 'bee-like' structures (Figure 5f) and smaller 'bee-like' structures (\(<\)4 um). Therefore, the addition of the CR rejuvenator increases the development of an oil matrix, and effectively decreases contact phenomena between asphaltene particles. The dispersed asphaltene micelles and continuous oil network lower the cohesive force inside the aged asphalt binder and soften it.  
Figure 4: The molecular weight distribution curves for asphalt binder samples: (**a**) virgin binder, aged binder, CR rejuvenated binder in D1, D2 and D3 slices; (**b**) virgin binder, aged binder, MR-1 rejuvenated binder in D1, D2 and D3 slices; (**c**) virgin binder, aged binder, MR-2 rejuvenated binder in D1, D2 and D3 slices.  
Figure 6 shows the obtained AFM micrographs for the D1, D2, and D3 layers of the MR-1 rejuvenated sample. The D2 and D3 layers show the typical structure of aged asphalt binders. However, in contrast to the results shown in Figure 5, the surfaces of the slices from the MR-1 rejuvenated sample (Figure 6a) were relatively rougher than the D2 and D3 slices from the CR rejuvenated sample (Figure 6b,c), where the MR-1 rejuvenator was not permeated in. Previous research [29] has shown that the appearance of a roughened surface structure is caused by the presence of the SBS modifier, due to the formation of a molecular chain network in the asphalt binder.  
Figure 7 shows the AFM micrographs of the D1, D2, and D3 slices from the MR-2 rejuvenated sample. As in the MR-1 rejuvenated sample (Figure 6a), the D1 and D2 slices from the MR-2 rejuvenated  
Figure 5: AFM images for the CR rejuvenated sample: (**a**) 3D height images of D1 slices; (**b**) 3D height images of D2 slices; (**c**) 3D height images of D3 slices; (**d**) phase images of D1 slices; (**e**) phase images of D2 slices; (**f**) phase images of D3 slices.  
Figure 6: AFM images for the MR-1 rejuvenated sample: (**a**) 3D height images of D1 slices; (**b**) 3D height images of D2 slices; (**c**) 3D height images of D3 slices; (**d**) phase images of D1 slices; (**e**) phase images of D2 slices; (**f**) phase images of D3 slices.  
sample showed a roughened surface morphology under 3D height mode. Additionally, the 'bee-like' structure in the D1 and D2 slices was smaller (<4 um) and dispersed, as can be clearly observed in the phase images (Figure 7d,e). Furthermore, the contact phenomena between the asphaltenic micelles are less than for the CR and MR-1 rejuvenators. Therefore, comparing the AFM results between the MR-1 and MR-2 samples, the use of dispersing agents in the polymer-modified rejuvenator can be concluded to have significantly improved the colloid structure of the aged asphalt binder.  
In the AFM results, several bright spots can be observed (Figure 7d,e). These are distributed relatively uniformly, are differently sized (0.5-3 um), and have a large phase difference compared to other components. Based on the slice number (D1 and D2) and their large phase difference, these bright spots may be caused by the SBS modifier not completely swelling with the light component of the rejuvenator. SEM was subsequently used to confirm the composition of the bright spots.