**3. Experimental results**

Initially, schungit powder samples, after deposition on the surface of highly oriented pyrolytic graphite (HOPG) from a suspension in toluene, were tested by AFM. The AFM topography and phase contrast images established the particle sizes of the original schungit from provider in the range from 1 to 5 μm. AFM images of the schungit particles deposited on the HOPG after milling in a ball planetary mill PM100 are shown in **Figure 1**. The agglomerates of nanosized schungit in the range from 50 to 250 nm are clearly detected.

AFM images of surface of pure C 300 rubber CKTH-A are shown in **Figure 2**. The scans visualized typical nodular polymer structure.

In **Figure 3**, an example of AFM scan on sample C 308 from the synthesized composites listed in **Table 2** is displayed. The distribution and size of schungit fillers, presented as bright color in the background of polymeric matrix, clearly are visualized.

**Figure 1.** AFM images of the schungit agglomerates after milling, deposited on the HOPG surface. Scan XY = 0.646 × 0.646 microns. Left—topography and right—3D view.

The AFM images data processing showed that the aggregate sizes of these nanostructured schungit fillers in composite C 308 are located in the range from 50 nm to 2 μm, and the nearest distance between them on average is 300 nm.

used. Image processing was performed using the SPIP™—advanced software package for processing and analyzing microscopy images at nano- and microscale (Image Metrology, Denmark). The scanning electron microscope (SEM) Merlin (Carl Zeiss, Germany) worked with an accelerating voltage of 5 kV and beam current of 300 pA. Investigations of the physical-mechanical properties of the composites were conducted on universal testing machine UTS-10 (Ulm, Germany), and nanoscale mechanical properties were studied with

Initially, schungit powder samples, after deposition on the surface of highly oriented pyrolytic graphite (HOPG) from a suspension in toluene, were tested by AFM. The AFM topography and phase contrast images established the particle sizes of the original schungit from provider in the range from 1 to 5 μm. AFM images of the schungit particles deposited on the HOPG after milling in a ball planetary mill PM100 are shown in **Figure 1**. The agglomerates

AFM images of surface of pure C 300 rubber CKTH-A are shown in **Figure 2**. The scans

In **Figure 3**, an example of AFM scan on sample C 308 from the synthesized composites listed in **Table 2** is displayed. The distribution and size of schungit fillers, presented as

**Figure 1.** AFM images of the schungit agglomerates after milling, deposited on the HOPG surface. Scan XY = 0.646 × 0.646

of nanosized schungit in the range from 50 to 250 nm are clearly detected.

bright color in the background of polymeric matrix, clearly are visualized.

NanoTest 600 (MicroMaterials, UK) [8].

18 Characterizations of Some Composite Materials

visualized typical nodular polymer structure.

microns. Left—topography and right—3D view.

**3. Experimental results**

Electron microscopic photographs of the C 308 composite are shown in **Figure 4a** and **b**. The SEM surface topography C 308 composite, prepared in the form of plate samples, is presented in **Figure 4a** and SEM images of its perpendicular cross section in **Figure 4b**. It is well known that the quality of many materials in particular of composites depends on a large extent on the homogeneity of the materials realized. Visualized by these methods

**Figure 2.** AFM images of the surface of the pure CKTH -A rubber C 300. Scans XY = 36.9 × 36.9 microns. Left—topography and right—phase contrast.

**Figure 3.** AFM surface images of C 308 composite. Scans 31.5 × 31.5 microns. Left—topography and right—phase contrast.

**Figure 6.** AFM images of the surface structure of composite C 313. Scans XY = 34.8 × 34.8 microns. Left—topography and

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**Figure 7.** SEM images of the surface structure of sample C 311. Unite scales: (a) 1 micron and (b) 300 nm, respectively.

right—phase contrast.

**Figure 4.** SEM images of the top surface topography plate C 308 composite (a) and of the plate perpendicular cross section (b). Unite scales: (a) 300 and (b) 200 nanometer, respectively.

**Figure 5.** AFM images of the surface structure of composite C 311. Scans XY = 36.5 × 36.5 microns. Left—topography and right—phase contrast.

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**Figure 6.** AFM images of the surface structure of composite C 313. Scans XY = 34.8 × 34.8 microns. Left—topography and right—phase contrast.

**Figure 4.** SEM images of the top surface topography plate C 308 composite (a) and of the plate perpendicular cross

**Figure 5.** AFM images of the surface structure of composite C 311. Scans XY = 36.5 × 36.5 microns. Left—topography and

section (b). Unite scales: (a) 300 and (b) 200 nanometer, respectively.

20 Characterizations of Some Composite Materials

right—phase contrast.

**Figure 7.** SEM images of the surface structure of sample C 311. Unite scales: (a) 1 micron and (b) 300 nm, respectively.

These SEM images show the same approximate pictures of fillers dispersed distributions in the elastomer matrices and mean values of their aggregate sizes as deduced from AFM measurements; additionally SEM scans of the plate perpendicular cross sections visualized the

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The application of SEM and AFM methods to visualize topography of surfaces and cross sections of investigated silicone rubber composites with schungit and silica SIPERNAT 360 fillers allowed direct observation of changes in the structure of composite elastomers on the micro- and nanometer range by increasing their concentrations. It is known that in silicone compositions, along with the interactions between the filler and the polymer matrix, there is also a process of agglomeration and structuring of the filler particles [1, 2]. As established by the data of AFM and SEM (**Figures 3**–**8**), a rather homogeneous distribution of the filler in the elastomeric matrix takes place in the investigated composites. Correlation of these results with the physical-mechanical properties of these materials, studied in [8], makes it possible to understand the cause of the enhancing ability of nanostructured schungit in organosilicon elastomers, due to the formation of a spatial filler network in the polymer matrix. These data make it possible to understand the reasons for the schungit filler manifestation of the reinforcing properties in the CKTH-A rubber, as conditioned not only by the chemical affinity of the amorphous carbon and the silica with the polydimethylsiloxane matrix, but also by a fairly uniform spatial distribution of the filler in the composite. The role of polar hydroxyl groups (OH) bounded to silica part of the schungit (silanol groups) interacting with siloxane segments (Si–O–Si) of matrix is also important, because the formed complex prevents the macroscopic agglomeration of initial schungit particles during the introduction of the polymer. The resulting increase in the interaction surface of the nanostructured filler with the polymer macromolecules leads to an effective reinforcement of the initial polydimethylsiloxane matrix. As reported in [8], the tests of these composites on a machine UTS-10 showed an increase in the tensile strength from about 0.5 MPa in original CKTH-A rubber to 3.6 MPa in C 308 composite, and tear resistance from 1.3 to 7.0 kN/m, respectively. It was also showed that these rubber composites with nanostructured schungit fillers have values of the specific work deformation for destruction belonging to the same regions of magnitude as silica filled composites with the same matrix. These results, when compared with traditional silicon dioxide filler [1, 2], show good effectiveness of the present nanostructured schungit as reinforcement filler in polydimethylsiloxane.

The obtained images of the topography and material contrast of the surface of the composites with silica SIPERNAT 360 fillers also made it possible to visualize a fairly uniform distribution of silica particles in a matrix of silicone rubber. Tests of vulcanizates of these mixtures on a tensile machine UTS-10 showed an increase in the tensile strength from about 0.5 MPa in C300 to 3.0 MPa in C 311 composites, and tear resistance from 1.3 to 3.4 kN/m, respectively, and in C313 composite to 4.1 MPa and 7.1 kN/m accordingly [8]. Studies on the NanoTest 600 measuring system by the method of nanoindentation are in accord with these results. The obtained data make it possible also to understand the reasons for the manifestation of the

space arrangement of fillers in these composites.

**4. Discussions**

**Figure 8.** SEM pictures of the structure of the cross sections of the surface of sample C 311. Unite scales: (a) 1 micron and (b) 200 nm, respectively.

of AFM and SEM, the composite C 308 surface morphology shows that the nanosized schungit fillers are homogeneously dispersed in the polymer matrix and are well adhered to the polymer matrix. This finding is very important for understanding the reasons of reinforcing the physical-mechanical properties of initial CKTH-A rubber with used nanostructured schungit filler.

AFM surface images of C 311 composite CKTN-A rubber with silica SIPERNAT 360 fillers are shown in **Figure 5**, and of composite C313 in **Figure 6**. The internal microstructure and agglomerates sizes of this filler in composites are of the same dimensions as in the case of nanosized schungit filler.

SEM images of the top surface topography of the plate of the same C 311 composite are shown in **Figure 7** and of the plate perpendicular cross section in **Figure 8**.

These SEM images show the same approximate pictures of fillers dispersed distributions in the elastomer matrices and mean values of their aggregate sizes as deduced from AFM measurements; additionally SEM scans of the plate perpendicular cross sections visualized the space arrangement of fillers in these composites.
