The effect of substrate pore size on the network interconnectivity and electrical properties of dropcasted multiwalled carbon nanotube thin films

Abstract

Four-layer multiwalled carbon nanotube (MWNT) thin films were deposited via dropcasting (1 mg/mL MWNTs and 10 mg/mL SDBS) onto filter papers that vary in pore size (1, 5, 25, and 40 lm) to determine the effect of the underlying substrate structure on the in-plane properties of the films. The films (,100 nm thick) were dried using vacuum filtration, and drying in a 65°C heater with and without a ceramic heating board. DC resistance of the films ranged from 6 Â 10 3 to 9.3 Â 10 9 X. Impedance spectroscopy analysis revealed a low and a high frequency inductive response and two parallel R-C circuits for the more conducting thin films. High resistance films were fit by a single RC circuit with a constant-phase element. The differences in the in-plane electrical responses of the different MWNT films can be explained by the degree of carbon nanotube surface coverage, obtained as a result of using different pore size filter papers. The drying method utilized also affected the CNT network formation and its resultant electrical properties.

Effect of graphitic filler size and shape on the microstructure, electrical percolation behavior and thermal properties of nanostructured multilayered carbon films deposited onto paper substrates

“…First, there is a high frequency parallel R-C (R 1 -C 1 ), which describes MWNT bundle behavior. The resistance of the bundles (R 1 5 ;900 X) matches those reported in a previous publication, 20 which is expected since the same type of MWNT was used in this experiment. The low frequency parallel R-C (R 2 -C 2 ) describes the MWNT-MWNT junction behavior.…”

“…Weight (%) and heat flow (W/g) versus temperatures graphs were analyzed for weight loss events. Figure 2 displays the low frequency resistance for the in-plane measurements for all of the films fabricated and characterized as a function of the number of layers deposited (this is equivalent to DC resistance as described before 20 ). It is clear that the films made from the CB dispersion never achieve a fully interconnected state as they remain highly resistive even after 20 deposition layers.…”

“…In contrast, AC electrical characterization techniques are more sensitive to the various electrical processes present in the material, allowing for the separation of the resistance due to each process from the overall resistance of the material. 20,[25][26][27][28] Impedance spectroscopy was carried out using two equipment setups: Solartron 1260 alone for the more conducting samples and Solartron 1296 connected to the Solartron 1260 for the more insulating samples (Hampshire, U.K.). For the in-plane measurements, a two-probe measurement technique was used to determine the surface behavior, and the measurements were carried out by scanning the frequencies from 21 MHz to 0.01 Hz using an AC voltage of 0.1 V for the MWNT and SWNT samples to ensure completion of the impedance response.…”

“…Variables explored include dispersion concentration and number of layers, 19 as well as drying technique. 20,21 It was shown that when the pore size of the paper substrate is comparable to the length of the carbon nanotubes, the drying method has a minimal impact on the structure and electrical properties of the film because film formation is occurring mostly at the surface of the paper. When the pore size of the paper is much larger than the length of the tubes (.25x), drying technique results in a large variation in microstructure and electrical properties.…”

“…When the pore size of the paper is much larger than the length of the tubes (.25x), drying technique results in a large variation in microstructure and electrical properties. 20,21 The main goal of this paper is to provide further insight into the structure-property relationships of paper-based carbon nanomaterial layered composites, by studying composites made up of 1-20 layers of a variety of carbon nanomaterials deposited on the same type of paper substrate with a small pore size of 1 lm. The smallest pore size was used to focus on the effect of the filler shape and size.…”