Estimating the Conductivity of a Partial Interphase and Its Impact on the Tunneling Conductivity of Carbon Nanofiber-Filled Samples

A robust interphase can effectively transfer the conduction of carbon nanofibers (CNFs) to the surrounding medium, whereas a deficient interphase fails to achieve this, thereby diminishing the composite conductivity. Consequently, it is crucial to evaluate the influence of a partial interphase on the conductivity of samples. In this paper, the conductivity of a partial interphase (ѱ) in CNF-filled composites (PCNFs) is characterized based on CNF dimensions and interphase depth. The parameter ѱ is then utilized to estimate the minimum CNF length required to fully transfer conductivity to the surrounding medium, L_c, which determines the effective volume fraction and inverse aspect ratio of CNFs in PCNFs. Moreover, the Jang-Yin model is extended to predict the PCNF effective conductivity by incorporating the resistances arising from the partial interphase and tunneling effects. The influences of various factors on ѱ, network fraction, and the effective conductivity are systematically analyzed and justified. Additionally, the predictions of the advanced model are validated with experimental data. The effective conductivity of PCNFs reaches 0.022 S/m at L_c = 2 μm and a contact diameter (d) of 40 nm. However, L_c > 14 μm or d < 10 nm causes an insulating composite. Therefore, reducing L_c and increasing the contact diameter are critical for enhancing the effective conductivity.