Length dependence of electrostatically induced carbon nanotube alignment

In situ, real-time polarized Raman spectroscopy was used to measure electrostatically induced carbon nanotube alignment in a polymer matrix. Discrete and reversible asymptotes of carbon nanotube G-band intensity were observed as a function of the applied electric field strength. It is proposed that as the electric field is increased, certain populations of carbon nanotubes attain sufficient alignment energy to overcome the randomizing thermal energy of the system. This is attributed to the electrostatic torque being a function of nanotube length, a relation that has been shown for dielectric rods and is extended here to carbon nanotubes. Nanotube batches of varying length distributions (hundreds of nanometers to micron-length) were created with different amounts of sonication energy. These distributions were quantified with atomic force microscopy measurements, and a model was developed relating these length distributions to the change in nanotube alignment at various electric field strengths. Nanotube polarizabilities determined from the model (alpha = 10(-30) - 10(-32) F.m(2)) were consistent with previously reported values. The effects of processing parameters such as sonication on the degree of achievable alignment as well as its implications are also discussed. (c) 2018 Elsevier Ltd. All rights reserved.