**3. Results and Discussions**

The scanning electron microscope (SEM) is a common characterization method to observe the microscopic information of polymer materials. By analyzing the electron signals excited by the interaction of incident electrons with the sample, information about the surface of the sample can be obtained. The excited signal when the incident electron interacts with the sample is shown in Figure 3 [24]. In this work, the condition of the sample surface is mainly characterized by analyzing the secondary electron signal and the backscattered electron signal.

**Figure 3.** Signals excited when the incident electron interacted with the sample.

*3.1. Analysis of Secondary Electron Signal Results of TPSiV Made of MVSR and SEBS-SBS with Different Relative Contents*

Figure 4A–H are the SEM images of samples 1–8 after being etched by chloroform, during which the MVSR phase was dissolved by the solvent. As the content of silicone rubber increases, the diameter of the pores left by the etching and dissolution of the silicone rubber gradually increases. By observing the marked parts in Figure 4A–D, we can find that with the increase of the content of silicone rubber, the diameter of the pores left by the

etching and the dissolution of the silicone rubber gradually increases. However, by comparing the secondary electron signal results of the silane coupling agent KH-907 (for example, Figure 4A,E), we found that the silane coupling agent KH-907 could not distinguish the MVSR and SEBS-SBS interface. Therefore, it cannot explain the improvement of mechanical properties after adding the silane coupling agent KH-907. Except for Figure 4A,B, it is difficult to distinguish the dispersed phase from the continuous phase. Moreover, we observed the marked parts in Figure 4D,H and found that the unetched phase was attached to the cross-section. Since the hardness of the SEBS-SBS phase is relatively small when the relative content of silicone rubber increases, the etching degree of the etched phase also increases, and the remaining SEBS-SBS phase will easily adhere to the cross-section and affect the observation (for example, Figure 4G,H).

**Figure 4.** *Cont*.

**Figure 4.** SEM diagrams obtained by etching method (**A**–**H**) correspond to samples 1–8, respectively. *3.2. Analysis of the Backscattered Electron Signal of TPSiV Made of MVSR and SEBS-SBS with Different Relative Contents*

Among many electronic signals, backscattered electrons are the part of primary electrons reflected from the surface of the sample after the elastic and inelastic scattering of the incident electrons from colliding with the atoms on the surface of the sample. Elastically backscattered electrons are incident electrons reflected from the nucleus of the sample after a single or few large-angle elastic scatterings, and their energy does not change. We usually put reflected electrons with slightly varying energies in this category as well. Inelastic backscattered electrons are those incident electrons that are eventually reflected from the sample surface after tens or hundreds of inelastic collisions. Backscattered electrons are reflected in an irregular direction. However, their number is related to the angle of incidence and the average atomic number *Z* of the sample. The larger the value of *Z*, the stronger the signal strength of the backscattered electrons. Experiments show that when the energy of incident electrons is 10–40 keV, the backscattering coefficient *η* of the sample increases with the increase of element atomic number *Z*. The relationship between the backscattering coefficient *η* and the backscattered electron signal intensity *ib* and the incident electron intensity *ip* is as follows:

$$
\eta = \frac{i\_b}{i\_p} \tag{1}
$$

When the atomic number is greater than 10, the backscattering coefficient *η* has the following quantitative relationship with the atomic number *Z*:

$$\eta = \frac{\ln Z(\overline{Z})}{6} - \frac{1}{4} \tag{2}$$

Figure 5 shows the relationship between the atomic number *Z* and the backscattering coefficient *η*. From Figure 5, we can see that for elements with *Z* < 20, *η* increases rapidly and linearly with the increase in *Z*. Therefore, the MVSR phase (the main constituent element is silicon) and the SEBS-SBS phase (the main constituent element is carbon) in TPSiV can be distinguished in the backscattering signal diagram, and the difference in the backscattering coefficient *η* of the two phases is about 0.08 [25].

The larger the atomic number *Z* is, the stronger the backscattered signal is. Therefore, in Figure 4, the brighter area is the MVSR phase, and the darker area is the SEBS-SBS phase. From Figure 6, we can observe that the atomic number contrast of the two phases in TPSiV achieves the effect of distinguishing them. According to the marks in Figure 6A,B, we also found that when the silicone rubber content was low, a distinct "sea-island" structure was formed between the dispersed phase and the continuous phase. However, as the silicone rubber content increases, especially when the amount of silicone rubber reaches 70 phr, through the observation of the marks in Figure 6D,H, there is a tendency for a co-continuous

phase in some regions, and it is difficult to distinguish between the continuous phase and the dispersed phase, which may affect some properties of the material. Through the image analysis system built into the software used when taking the SEM image, we obtained the size distribution of the dispersed phase, as shown in Figure 7. By comparing the dispersed phase size distribution of samples with the same content of silicone rubber and different content of silane coupling agent KH-907 (for example, samples 1 and 5), we found that adding silane coupling agent KH-907 would make the area of the dispersed phase smaller. We think that it may be that the promotion of interfacial interaction by silane coupling agent KH-907 improves the dispersion of the dispersed phase, but this needs to be further verified by other quantitative characterization methods.

**Figure 5.** Relationship between atomic number *Z* and backscattering coefficient *η*.

*3.3. Characterization of the Compatibility between MVSR and SEBS-SBS by Fourier Transform Infrared Spectroscopy*

Fourier transform infrared spectroscopy is one of the common methods used to qualitatively characterize the compatibility of two polymers after blending. According to the information provided in Table 2, for MVSR, we usually take 1260 and 1010 cm−<sup>1</sup> as characteristic peaks.



**Figure 6.** BSE diagrams of TPSiV, (**A**–**H**) correspond to samples 1–8, respectively.

**Figure 7.** Bar diagrams of the size distribution of the dispersed phase in the backscattered signal diagrams.

According to Figures 8 and 9 and Table 3, we found that no matter whether the silane coupling agent KH-907 was added or not, it can bring about the shift in characteristic peaks, and with the decrease in the relative content of silicone rubber, the wavenumber shift is more obvious. However, after adding silane coupling agent KH-907, the value of the wavenumber shift is larger. For example, comparing pure MVSR with samples 1 and 5, the stretching vibration peak of Si(CH3)2 in sample 1 is shifted by eight wavenumbers compared to the same characteristic peak of pure MVSR, while the stretching vibration peak of Si(CH3)2 in sample 5 is shifted by six wavenumbers compared to the same characteristic peak of pure MVSR.

**Figure 8.** *Cont*.

**Figure 8.** FI-IR diagrams of 100% MVSR, 50% SEBS + 50% SBS and samples 1–4. (**A**) Complete spectrum; (**B**) Enlarged detail near wavenumber 1260 cm<sup>−</sup>1; (**C**) Enlarged detail near wavenumber 1010 cm<sup>−</sup>1.

**Table 3.** Peak wave numbers of FI-IR diagrams of 100% MVSR, 50% SEBS + 50% SBS and samples 1–8.


**Figure 9.** FI-IR diagrams of 100% MVSR, 50% SEBS + 50% SBS and samples 5–8. (**A**) Complete spectrum; (**B**) Enlarged detail near wavenumber 1260 cm<sup>−</sup>1; (**C**) Enlarged detail near wavenumber 1010 cm<sup>−</sup>1.

Usually, we use the compatibility results obtained by infrared spectroscopy as the basis for qualitative analysis and do not use the absolute magnitude of the wavenumber offset as the basis for the quantitative comparison of the compatibility of the two phases. The infrared spectrum results in this experiment can only show that the blend system of MVSR and SEBS/SBS has certain compatibilities, and we cannot further draw a quantitative conclusion regarding the compatibility of MVSR and SEBS/SBS.

#### *3.4. Analysis of the Results of the Quantitative Characterization Test of the Compatibility Layer*

We usually use three parameters, *L*, *A* and *B*, to represent the chromaticity value of the color of the object. The size of these three values represents the color space coordinates of a certain color, and every color has a unique color space coordinate value. Among them, *L* stands for lightness and darkness, black and white; *A* stands for red and green; and *B* stands for yellow and blue. Since the BSE image obtained by scanning electron microscopy is black and white—that is, the values of *A* and *B* are both 0—in the experiment, we only measure the chromaticity value of the color of a certain point in the BSE image by the *L* value.

We printed the 1000 x BSE diagrams on A3 size (420 × 297 mm) photo paper with a high-definition printer, as shown in Figure 1, and moved the colorimeter, as shown in Figure 2. In each direction, we recorded the *L* value every time the colorimeter moved by 1 mm and took the arithmetic average of the thickness of the compatible layer obtained from each direction as the final experimental result.

The field of view of the BSE diagram is not related to the size of the photo paper, so we can first find the field of view of the BSE diagram. According to the size of the scale bar in the BSE map and the measurement of the vernier caliper, we can calculate that the field of view of the BSE diagram was 27.19 × 18.54 μm. Next, as shown in Figure 1, we divided the BSE diagram into eight parts, randomly selected one of them, and printed it out on photo paper. According to the segmentation method in Figure 1, we can calculate that the field of view of the divided diagrams was 6.80 × 9.27 μm. We converted this field of view with the A3 size photo paper (420 × 297 mm), and we found that 1 mm length of photo paper represents 0.0162 μm of the diagram length and 1 mm width of photo paper represents 0.031 μm of the diagram width.

Before the start of the experiment, we tested the *L* value of the MVSR and SEBS/SBS phases. We found that the *L* value of the MVSR phase was between 70 and 72, and the *L* value of the SEBS/SBS phase was between 47 and 50. Therefore, we inferred that the distance with the *L* value of 50–70 can be regarded as the thickness of the compatibility layer between the MVSR phase and the SEBS/SBS phase.

According to the data in Table 4, with the increase in the relative content of MVSR, the thickness of the compatibility layer between the MVSR and the SEBS/SBS phases gradually decreased. Since the thickness of the compatibility layer can be used as a measure of the degree of interaction between the MVSR and the SEBS/SBS phases, combined with the statistical data in Figure 7, we believe that the dispersed phase size of TPSiV with a high proportion of MVSR was larger, and the "sea-island" structure tended to disappear because the force of the two phases was reduced. By comparing the thicknesses of the compatibility layers of several groups with the same MVSR content, with the variable only being the content of silane coupling agent KH-907 (for example, samples 1 and 5), we found that the thickness of the compatibility layer significantly increased after adding silane coupling agent KH-907, which shows that the silane coupling agent can promote the interaction between the MVSR and the SEBS/SBS phases. This can serve as a microscopic explanation for the improved macroscopic properties after adding the silane coupling agent KH-907. It can be seen that this characterization method overcomes the disadvantage that the etching method and infrared spectroscopy cannot quantitatively characterize the thickness of the compatibility layer and also avoids the defect that when the MVSR content is high, and the etching method is used, the non-etched phase collapses and then adheres to the section.


**Table 4.** Compatibility layer thickness of samples 1–8.
