Browsing by Subject "Electrical conductivity"
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Item Conductive nickel nanostrand-reinforced polymer nanocomposites(2013-05) Lu, Chunhong; Krifa, MouradConductive and flexible nanocomposites can have wide applications in textiles, including wearable sensors, antenna, electrodes, etc. The objective of this research is to develop electrically conductive fibers and films that are flexible and deformable for use in textile structures able to accommodate the drape and movement of the human body. To achieve this objective, we evaluate the electrical properties of PEDOT:PSS/nickel nanostrand as well as nylon 6/nickel nanostrand nanocomposites. Nickel nanostrands (NiNS) were first used to reinforce an intrinsically conductive polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT:PSS), in order to fabricate nanocomposite films with high electrical conductivity. The electrical properties of the films were evaluated by the Van der Pauw method. The addition of 10 wt% nanostrands in PDOT:PSS provided a two order of magnitude improvement in electrical conductivity. In addition to PDOT:PSS, nylon 6/NiNS nanocomposite fibers were produced using electrospinning and exhibited diameters in the sub-micron range. The NiNS-reinforced fibers had electrical conductivity that exceeded the ESD range, which offers the potential for use in protective textile applications.Item Energy Carrier Transport In Surface-Modified Carbon Nanotubes(2012-11-30) Ryu, YeontackCarbon nanotubes are made into films or bulks, their surface or junction morphology in the networks can be modified to obtain desired electrical transport properties by various surface modification methods. The methods include incorporation of organic molecules or inorganic nanoparticles, debundling of nanotubes by dispersing agents, and microwave irradiation. Because carbon nanotubes have unique carrier transport characteristics along a sheet of graphite in a cylindrical shape, the properties can be dramatically changed by the modification. This is ideal for developing high-performance materials for thermoelectric and photovoltaic energy conversion applications. In this research, decoration of various organic/inorganic nanomaterials on carbon nanotubes was employed to enhance their electrical conductivity, to improve thermoelectric power factor by modulating their electrical conductance and thermopower, or to obtain n-type converted carbon nanotube. The electrical conductivity of double-wall nanotubes (DWNTs) decorated with tetrafluoro-tetracyanoquinodimethane (F4TCNQ) was increased up to 5.9 ? 10^5 S/m. The sheet resistances were measured to be 42 ?/sq at 75% of transmittance for HNO3/SOCl2-treated DWNT films, making their electrical conductivities 200~300% better than those of the pristine DWNT films. A series of experiments at different ion concentrations and reaction time periods were systematically performed in order to find optimum nanomaterial formation conditions and corresponding electronic transport changes for better thermoelectric power factor. For example, the thermoelectric power factors were improved by ~180% with F4TCNQ on DWNTs, ~200% with Cu on SWNTs, and ~140% with Fe on single-walled nanotubes (SWNTs). Also SWNTs was converted from p-type to n-type with a large thermopower (58 ?V/K) by using polyethyleneimine (PEI) without vacuum or controlled environment. This transport behavior is believed to be from charge interactions resulted from the difference between the work functions/reduction potentials of nanotubes and nanomaterials. In addition, different dispersing agents were utilized with DWNT and SWNTs to see a debundling effect in a film network. The highest electrical conductivity of ~1.72?10^6 S/m was obtained from DWNT film which was fabricated with a nanotube solution dispersed by chlorosulfonic acid. Debundling of nanotubes in the film network has been demonstrated to be a critical parameter in order to get such high electrical property. In the last experiment, Au nanoparticle decoration on carbon nanotube bundle was performed and a measurement of themophysical properties has done before and after modifying carbon nanotube surface. Carbon nanotube bundle, herein, was bridged on microdevice to enable the measurement work. This study demonstrates a first step toward a breakthrough in order to extract the potential of carbon nanotubes regarding electron transport properties.Item A model to determine effective electrical resistivity of shale gas SEM images(2015-05) Armutlu, Enes Taha; Fisher, William L. (William Leslie), 1952-; Javadpour, Farzam; Rowe, HarryUnderstanding electrical conductivity of organic shale plays an important role in unlocking mystery about pore network in shale. I present a systematic and novel approach to determine effective electrical conductivity of shale samples from readily available SEM images. The method includes (1) analyzing SEM images to identify different components like quartz, clay, organic matter, and pores and (2) use a numerical solver to solve voltage field imposed to the analyzed images to compute effective electrical resistivity of the sample. I extended the method to 3D images generated from SEM images and computed effective electrical conductivity of the generated 3D images. The study shows that electrical conductivity is sensitive to pore network and water saturation. I found estimated electrical conductivity of the 2D SEM images are very different from 3D images, hence not a good representative of the shale samples. I also compared numerical results with different analytical averaging techniques, e.g., arithmetic mean, harmonic mean, geometric mean, and the incomplete layer methods. None of the analytical methods predicts close enough to the numerical results, although incomplete layer method showed the closest results.Item Understanding the processing-structure-property relationships of water-dispersible, conductive polyaniline(2009-05) Yoo, Joung Eun; Sanchez, Isaac C., 1941-Polyaniline (PANI), when doped with small-molecule acids, is an attractive candidate for organic and polymer electronics because of its high electrical conductivity. Its utility as functional components in electrical devices, however, has been severely restricted because such PANI has limited processibility stemming from its limited solubility in common solvents. To overcome this barrier, we have developed water dispersible PANI that is template polymerized in the presence of a polymer acid, poly(2-acrylamido-2-methyl-1-propanesulfonic acid), or PAAMPSA. The polymer acid serves two roles: it acts as a dopant to render PANI conductive and excess water soluble pendant groups provide dispersibility of PANI in aqueous media. While the introduction of polymer acids renders the conducting polymer processible, such gain in processibility is often accompanied by a significant reduction in conductivity. As such, PANI that is doped with polymer acids has only seen limited utility in organic electronics. Given the promise of conducting polymers in organic electronics in general, this thesis focuses on the elucidation of processing-structure-property relationships of PANI-PAAMPSA with the aim of ultimately improving the electrical conductivity of polymer acid-doped PANI. By controlling the molecular weight and molecular weight distribution of the polymer acid template, we have improved the conductivity of PANI-PAAMPSA from 0.4 to 2.5 S/cm. The conductivity increases with decreasing molecular weight of PAAMPSA, and it further increases with narrowing the molecular weight distribution of PAAMPSA. Strong correlations between the structure and the conductivity of PANI-PAAMPSA are observed. In particular, the crystallinity of PANI increases with increasing the conductivity of PANI-PAAMPSA. Given that the crystallinity qualifies the molecular order in PANI-PAAMPSA, we observe a linear correlation between molecular order and macroscopic charge transport in PANI-PAAMPSA. PANI-PAAMPSA forms electrostatically stabilized sub-micron particles during polymerization due to strong ionic interactions between the sulfonic acid groups of PAAMPSA and aniline. When cast as films, the connectivity of these particles must play an important role in macroscopic conduction. The size and size distribution of PANI-PAAMPSA particles is strongly influenced by the molecular characteristics of polymer acid template. Templating the synthesis of PANI-PAAMPSA with a higher molecular weight PAAMPSA results in larger particles, and templating with a PAAMPSA having a larger molecular weight distribution results in a large size distribution in the particles. Because conduction in PANI-PAAMPSA films is governed by how these particles pack, the macroscopic conductivity of PANI-PAAMPSA films increases with increasing particle density, that is reducible from the molecular characteristics of PAAMPSA. Moreover, PANI-PAAMPSA particles are structurally and chemically inhomogeneous. The conductive portions of the polymer preferentially segregate to the particle surface. Conduction in these materials is therefore mediated by the particle surface and conductivity thus scales superlinearly with particle surface area per unit film volume. We further have improved the electrical conductivity of PANI-PAAMPSA by more than two orders of magnitude via post-processing solvent annealing with dichloroacetic acid (DCA). Since DCA is a good plasticizer for PAAMPSA and its pKa is lower than that of PAAMPSA (pKas of DCA and PAAMPSA are 1.21 and 2.41, respectively, at room temperature), DCA can effectively moderate the ionic interactions between PANI and PAAMPSA, thereby relaxing the sub-micron particulate structure arrested during polymerization. PANI-PAAMPSA can thus rearrange from a “compact coil” to an “extended chain” conformation upon exposure to DCA. Efficient charge transport is thus enabled through such “extended chain” PANI-PAAMPSA structure. DCA-treated PANI-PAAMPSA exhibits an average conductivity of 48 S/cm. The DCA treatment is not only specific to PANI-PAAMPSA. This treatment can also enhance the conductivity of commercially-available poly(ethylene dioxythiophene) that is doped with poly(styrene sulfonic acid), or PEDOT-PSS. Specifically, DCA-treated PEDOT-PSS exhibits a conductivity of 600 S/cm; this conductivity is the highest among polymer acid-doped conducting polymers reported so far. PANI-PAAMPSA can effectively function as anodes in organic solar cells (OSCs) whose active layer is a blend of poly(3-hexylthiophene), P3HT, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Specifically, the OSCs with PANI-PAAMPSA anodes exhibit an average short circuit current density of 1.95 mA/cm², open circuit voltage of 0.52 V, fill factor of 0.38, and efficiency of 0.39 %. The use of DCA-treated PANI-PAAMPSA as anodes increases device performance (i.e., short circuit current density and thereby efficiency) of OSCs by approximately two and a half fold. The OSCs with DCA-treated PANI-PAAMPSA anodes exhibit short circuit current density and efficiency as high as 4.95 mA/cm² and 0.97 %, respectively. We demonstrated several factors that govern the electrical conductivity of polymer acid-doped conducting polymers. Design rules, such as those illustrated in this study, can enable the development of conducting polymers that is not only easily processible from aqueous dispersions, but also sufficiently conductive for electronic applications, and should bring us closer to the realization of low-cost organic and polymeric electronics.