Browsing by Author "Deshmukh, Sujay"
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Item Characterization of Nanoscale Reinforced Polymer Composites as Active Materials(2012-02-14) Deshmukh, SujaySingle walled carbon nanotube (SWNT)-based polymer nanocomposites have generated a lot of interest as potential multifunctional materials due to the exceptional physical properties of SWNTs. To date, investigations into the electromechanical response of these materials are limited. Previous studies have shown marginal improvements in the electromechanical response of already electroactive polymers (EAPs) with addition of SWNTs. However, in general, disadvantages of EAPs such as high actuation electric field, low blocked stress and low work capacity remain unaddressed. This dissertation targets a comprehensive investigation of the electromechanical response of SWNT-based polymer nanocomposites. Specifically, the study focuses on incorporating SWNTs in three polymeric matrices: a non-polar amorphous polyimide (CP2), a polar amorphous polyimide ((-CN) APB-ODPA), and a highly polar semicrystalline polymer (PVDF). In the first step, emergence of an electrostrictive response is discovered in the non-polar polyimide CP2 in the presence of SWNTs. Transverse and longitudinal electrostrictive coefficients are measured to be six orders of magnitude higher than those of known electrostrictive polymers like polyurethane and P(VDF-TrFE) at less than 1/100th of the actuation electric fields. Next, the effect of the polymer matrix on the electrostrictive response is studied by focusing on the polar (-CN) APB-ODPA. A transverse electrostriction coefficient of 1.5 m2/MV2 is measured for 1 vol percent SWNT- (-CN) APB-ODPA, about twice the value found for 1 vol percent SWNT-CP2. The high value is attributed to higher dipole moment of the (-CN) APB-ODPA molecule and strong non-covalent interaction between the SWNTs and (-CN) APB-ODPA matrix. Finally, polyvinylidene fluoride (PVDF) matrix is selected as a means to optimize the electrostrictive response, since PVDF demonstrates both a high dipole moment and a strong non-covalent interaction with the SWNTs. SWNT-PVDF nanocomposites fared better than SWNT-CP2 nanocomposites but had comparable response to SWNT-(-CN) APB-ODPA nanocomposites. This was attributed to comparable polarization in both the polar nanocomposite systems. To maximize the SWNT-PVDF response, SWNT-PVDF samples were stretched leading to increase in the total polarization of the nanocomposite samples and decrease in the conductive losses. However, the dielectric constant also decreased after stretching due to disruption of the SWNT network, resulting in a decrease of the electrostrictive response.Item Effect of single walled carbon nanotubes (SWNTs) on the electromechanical properties of polyimide nanocomposites(Texas A&M University, 2007-04-25) Deshmukh, SujayNanocomposites 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 SWNT??????PI 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.