Abstract This study focuses on the segregation of carbon black within a blend of NR/EPDM rubber at different mixing proportions (especially 70/30, 30/70). The research was exclusively conducted using microscopic techniques such as TEM, STEM-Mapping, FESEM, and AFM. Despite the challenges typically encountered in microscopy, these methods were extensively utilized to analyze the characteristics of the rubber matrix, from pristine rubber to the final filled blend. The investigation spans from the unfilled rubber to ultimate filled blends with low (25 phr) and high (50 phr) carbon black content. The use of osmium tetraoxide (OsO4) for selective chemical staining, in conjunction with microscopy, has made it possible to distinctly understand each rubber phase within the blend, greatly aiding in the identification of filler migration to the preferred rubber phase. In addition, the STEM-mapping confirmed the phase distribution by identifying the continuous and dispersed phase through precise detection and validation of the stained areas. Ultimately, the combined outcome of the microscopic study (TEM, FESEM, and AFM) revealed that the carbon black filler is more inclined to move towards the unsaturated NR phase due to its active graphitic edges, making it more compatible with the NR phase, which has a higher degree of unsaturation compared to EPDM.
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