CHARACTERIZATION OF PARTICLE DISTRIBUTION IN A BLACK CARBON-FILLED ELASTOMER VIA NANOINDENTATION

摘要

A new method to characterize the distribution of hard particles dispersed into a soft elastomer matrix is developed using nanoindentation. It is based on the measurement of the contact stiffness from the continuous stiffness measurement module (CSM). Theoretically, for a homogeneous material, the contact stiffness is directly proportional to the contact depth. However, when indenting a carbon black-filled fluoroelastomer (FKM) this relation is no longer valid and abnormal contact stiffness evolutions are measured (jumps). The tip-particle model developed in this work is simply based on the hypothesis that all the deformation is supported by the elastomer matrix and that black carbon aggregates play the role of hard extensions of the diamond tip, when touching it (grey particles 1,2 & 3, Fig. 1a). As a result, each abnormal variation of contact stiffness is related to a new aggregate in contact with the tip. By knowing the stiffness amplitude of a jump AS and the relative stiffness where it appeared S, the equivalent projected area of a particle can be calculated (Fig. 1d). From this calculation, one can extract the distribution of particles surface density from nanoindentation measurements only. Ten experimental indentation tests have been performed and the results are displayed in Fig. 1e. The distribution of particles surface density extracted from experiments is compared to measurements performed by image analysis of a 100 nm thick slide of the material observed by Transmission Electron Microscopy (TEM) (black squares). Furthermore, the tip-particle model is simulated numerically on the same image analysis (down pointing triangles). The results obtained from this model are in excellent agreement with the TEM observation which is really promising. Indeed, this model is an alternative to microscopy characterization which can be complicated to implement.