Direct current conductance and 1/f-noise in cellulose nanofiber–multi-walled carbon nanotube composites for applications in flexible electronic devices

We report on the studies of conduction mechanism, direct current conductance, and 1f-noise of cellulose nanofiber (CNF) and multiwalled carbon nanotube (MWCNT) composites. The composites were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. The temperature- and voltage-dependence of the dc conductance Σ were, respectively, probed to investigate the charge transport mechanism and the electrical response of the composite. At room temperature, the increase in Σ with wt. % of MWCNT ϕ showed typical percolation behavior. The Σ−T behavior was fitted to the combination of one-dimensional variable range hopping and the fluctuation-induced tunneling, which were attributed to hopping of charge carriers through 1D MWCNTs and the tunneling of charge carriers between the bundles of MWCNTs, respectively. The non-Ohmic electrical conduction was characterized by the onset voltage V0(T) which scaled with Ohmic conductance Σ0 as V0(T)∼Σ0(T)xT, with xT being the onset exponent increased with ϕ. A scaling description based on the data collapse method was adopted to find the parameters V0(T) and xT. The noise power spectrum SV(f) followed the relation SV(f)∼Vβ with two different power-laws: β1 in the Ohmic and β2 in the non-Ohmic region (β1>β2). Interestingly, this change in power-laws occurs at the same V0(T) obtained from Σ−V curves. A simple model was proposed to explain the noise behavior after V0(T). It is expected that such electrical characterization of CNF-MWCNT nanopaper composite would open up their possibility of application in flexible electronic devices, intelligent networks, sensors, and actuators.