Study on Boundary Layer and Surface Hardness of Carbon Black in Natural Rubber Using Atomic Force Microscopy

The mechanical properties and wear resistance of carbon black/natural rubber (CB/NR) composites are significantly influenced by the degree of CB dispersion in rubber. Here, we present a novel reinforcement theory using atomic force microscopy (AFM) to quantify the adhesive thickness of rubber molecules around the CB particles as well as the height, area, and volume in NR. The thickness of the bonded rubber (BR) was found to vary between 3 and 7 nm depending on the values of the nitrogen surface area (NSA) for CB. This indicates that a higher BR content is a result of a higher CB NSA with a smaller particle size, showing a higher number of active positions to anchor rubber molecules. The nanoindentation of AFM was used to determine the surface hardness of CB in NR; the value decreases with increasing BR height. In this study, we demonstrate a well-defined reinforcement mechanism of CB in NR with the factors of BR, surface hardness, 100%/300% modulus, and tensile strength.