The effect of sonication time during the synthesis of multiwalled carbon nanotubes – polymethylmethacrylate (MWCNT/PMMA) composites by coagulation technique on the MWCNT distribution in the bulk of the composites close to the percolation threshold was systematically studied by SEM and by measurements on specific resistivity in a wide range of voltages and external pressure. It was found that the resistivity of composites is irreversibly reduced up to 105 times during the first 1–3 measurements, while further measurements are characterized by high repeatability. Change of the composite resistivity during the measurements is discussed assuming that several types of contacts between the nanotubes changing during the measurement are present. It was found that an increase of the sonication time changed the ratio between ohmic and non-ohmic contacts. It affected the type of changes in the sample resistivity during the voltage variation in the range of 0–103 V/mm and resulted in a nonuniform dependence of the composite specific resistivity on the sonication time. An increase of the composite volume during the resistivity measurements was observed at the current densities above 4·10–8 A/cm2. New ohmic contacts were found to form when external pressure was applied due to squeezing of the polymer matrix from the space between adjacent nanotubes.
- Contacts between nanotubes
- Current-voltage characteristic
- Multiwalled carbon nanotube