Multifunctional Electroactive Nanocomposites Based on Piezoelectric Boron Nitride Nanotubes.

Space exploration missions require sensors and devices capable of stable operation in harsh environments such as those that include high thermal fluctuation, atomic oxygen, and high-energy ionizing radiation. However, conventional or state-of-the-art electroactive materials like lead zirconate titanate, poly(vinylidene fluoride), and carbon nanotube (CNT)-doped polyimides have limitations on use in those extreme applications. Theoretical studies have shown that boron nitride nanotubes (BNNTs) have strength-to-weight ratios comparable to those of CNTs, excellent high-temperature stability (to 800 °C in air), large electroactive characteristics, and excellent neutron radiation shielding capability. In this study, we demonstrated the experimental electroactive characteristics of BNNTs in novel multifunctional electroactive nanocomposites. Upon application of an external electric field, the 2 wt % BNNT/polyimide composite was found to exhibit electroactive strain composed of a superposition of linear piezoelectric and nonlinear electrostrictive components. When the BNNTs were aligned by stretching the 2 wt % BNNT/polyimide composite, electroactive characteristics increased by about 460% compared to the nonstretched sample. An all-nanotube actuator consisting of a BNNT buckypaper layer between two single-walled carbon nanotube buckypaper electrode layers was found to have much larger electroactive properties. The additional neutron radiation shielding properties and ultraviolet/visible/near-infrared optical properties of the BNNT composites make them excellent candidates for use in the extreme environments of space missions.

Subsurface characterization of carbon nanotubes in polymer composites via quantitative electric force microscopy.

Subsurface characterization of carbon nanotubes (CNTs) dispersed in free-standing polymer composite films was achieved via quantitative electric force microscopy (EFM). The effects of relative humidity, EFM probe geometry, tip-sample distance and bias voltage on the EFM contrast were studied. Non-parabolic voltage dependence of the EFM signal of subsurface CNTs in polymer composites was observed and a new mechanism was proposed taking consideration of capacitive coupling as well as coulombic coupling. We anticipate that this quantitative EFM technique will be a useful tool for non-destructive subsurface characterization of high dielectric constant nanostructures in low dielectric constant matrices.