Effect of single walled carbon nanotubes (SWNTs) on the electromechanical properties of polyimide nanocomposites
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Nanocomposites show promise in various fields, ranging from aerospace vehicles to microelectronics. Specifically, electro-active nanocomposites would enable a whole new set of applications, where the nanocomposite material would exhibit strength, toughness, and electromechanical coupling. The broad goal of this thesis was to investigate potential electromechanical behavior in single walled carbon nanotube (SWNT)-polyimide (PI) composites. The specific objective was to measure and characterize the actuation response of SWNTÃ¢ÂÂPI nanocomposites. Two different polyimides, non-polar CP2, and a weakly piezoelectric polymer (beta-CN) APB-ODPA are used in the study. Electrical and dielectric characterization of the nanocomposites were carried out to better understand the effect of SWNTs on the different physical properties of the composites, and to identify the electroactive mechanism in the resulting composites. (beta-CN) APB-ODPA composites show a higher increase in both conductivity and dielectric constant with SWNT content as compared to the CP2 composites. The effect of SWNTs on remnant polarization (PR) is quantified using the dielectric relaxation tests and Thermally Stimulated Current (TSC) experiments. Both experiments show an increase in the remnant polarization with SWNT content and a higher value for the (beta-CN)APBODPA nanocomposites over CP2 nanocomposites. Actuation tests employing a cantilever bending experiment were carried out on the nanocomposite samples while varying the SWNT content and electric field. The strains are seen to be proportional to the square of the electric field, indicating an electrostrictive response. Strain rate and the coefficient of electrostriction (M1333) values are seen to increase with SWNT content and are higher for (beta-CN) APB-ODPA nanocomposites than the CP2 nanocomposites. Electrostrictive strains can also be expressed as the square of polarization; hence the findings of the dielectric relaxation studies and TSC measurements can be correlated to the measured electrostrictive effect. The cause for the enhancement in dielectric, dielectric relaxation and actuation response of the nanocomposites with the increase in the SWNT content and polarity of the matrix was explored. Among different possible causes special emphasis was given to the importance of the interface between the SWNTs and the matrix and the resulting increase in polarization as the main factor driving the enhancement.
Deshmukh, Sujay (2006). Effect of single walled carbon nanotubes (SWNTs) on the electromechanical properties of polyimide nanocomposites. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from