Direct Visualization of Carbon Black Aggregates in Nitrile Butadiene Rubber by THz Near-field Microscope

Abstract

The use of filling agents for rubber reinforcement is beneficial in various industrial applications, and several experimentalmethods have been used to study the effect of fillers on rubber. However, due to the lack of a suitable imaging technique, fillerdispersion and distribution in rubber cannot be easily displayed. Thus, we utilize the THz near-field microscope (THz-NFM)to directly visualize the distribution of carbon black (CB) aggregates in nitrile butadiene rubber (NBR). The THz time-domainspectroscopy (THz-TDS) was used to evaluate the optical properties of the NBR specimens. Results revealed significantindices contrast between CB and NBR at the THz regime, which was attributed to the variation in electrical conductivities. Themicrographs of NBR in the THz-NFM revealed the distribution of CB aggregates. The area fraction (AF) of the CB aggregateswas calculated using a binary thresholding algorithm to compare with the transmission electron microscope method. Bothmethods yielded comparable AF values, suggesting, for the first time, that CB can be detected in the NBR without preprocessingthe specimens.