Statistical analysis of effective electro-mechanical properties and percolation behavior of aligned carbon nanotube/polymer nanocomposites via computational micromechanics

CNT (carbon nanotube) embedded polymer nanocomposites exhibit significant variation in their electromechanical properties depending upon factors such as CNT volume fraction, CNT dispersion, CNT alignment and properties of the polymer. Of interest is electrical percolation where the electrical conductivity of the CNT/ polymer nanocomposite increases several orders of magnitude with increase in CNT volume fraction. Estimates and distributions for the electrical conductivity and piezoresistive coefficients of the CNT/polymer nanocomposite are obtained and analyzed with increasing CNT volume fraction and varying barrier potential, a parameter that controls the extent of electrical tunneling. The barrier potential is seen to play a key role in determining electrical percolation in terms of the CNT volume fractions that correspond to this percolation transition. The effect of CNT alignment is analyzed by comparing the electro-mechanical properties in the alignment direction versus the transverse direction, where it is found that the properties in the alignment direction are larger than that of the transverse direction. Estimates of piezoresistive coefficients are converted into gage factors and discussed in the context of experimental sources in literature. The methodology for this work involves generating several semi-random 5 mu m x 5 mu m computational realizations for different CNT volume fractions with randomized CNT seeding. These realizations are then analyzed using finite elements to obtain volume averaged effective values, which are then subsequently used to generate estimates (mean from several realizations) for mechanical stiffness, electrical conductivity and piezoresistive coefficients. The distribution in these properties is also studied using measures of coefficient of variation, skewness and kurtosis. It is found that electrical percolation can be captured by the transition of these measures of variation from low to high and back down to low values with increase in CNT volume fraction.

Automated summary

Carbon nanotube embedded polymer nanocomposites exhibit varied electromechanical properties depending on factors such as CNT volume fraction, dispersion, alignment, and polymer properties. Of interest is electrical percolation, where the electrical conductivity increases significantly with CNT volume fraction. The role of barrier potential in determining electrical percolation, as well as the influence of CNT alignment on properties, are key areas of focus in the study.