Synergistic effect of interface and agglomeration on Young's modulus of graphene-polymer nanocomposites

Filler agglomeration can severely hinder the stress transfer at the graphene-polymer interface, leading to deterioration of the interfacial properties and the overall mechanical performance of graphene nanocomposites. However, the correlation between the agglomeration and the interface effect was rarely investigated in the past. We hereby propose a novel and efficient approach to accurately obtain the effective Young's modulus of graphene nanocomposites. We first introduced Cauchy's cumulative probability function to describe the progressive deterioration of the filler-matrix interface as the graphene's volume concentration increases. Then, via the shear-lag approach, we developed a modified Halpin-Tsai model to take into account the effects of the agglomeration threshold, the filler-matrix interfacial moduli, and the surfactant treatment. The entire approach was validated by comparing the predicted results with five groups of experimental data. It was found that the interfacial properties are roughly linearly related to the matrix-to-nanofiller modulus ratio, which illustrates that a severer interfacial modulus mismatch leads to poorer interfacial bonding quality, and thus to a lower overall elastic modulus. The interfacial coefficient can also quantitatively characterize the enhancement effect of surfactant treatment. Besides, the synergistic effect of filler-matrix interface and filler agglomeration in the overall Young's modulus of composites was confirmed by comparison between theoretical and experimental results, and the latter becomes increasingly dominant as the graphene volume concentration increases.