Browsing by Author "Montazami, Reza"

Now showing 1 - 9 of 9
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    Basins of attraction of tapping mode atomic force microscopy with capillary force interactions
    Hashemi, Nastaran; Montazami, Reza (AIP Publishing, 2009-06-01)
    We perform a large number of simulations over a wide range of system parameters to approximate the basins of attraction of steady oscillating solutions. We find that the basins of attraction vary as a function of system parameters and initial conditions. For large equilibrium separations, the basin of attraction is dominated by the low-amplitude solution. The location of the fixed point is shifted toward the higher values of instantaneous displacement and velocity for larger equilibrium separations. We show that the basin of attraction in the neighborhood of the fixed point is dominated by low-amplitude solutions as relative humidity is increased.
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    Fabrication and Characterization of Layer by Layer Assembled Single and Dual-Electrochrome Electrochromic Devices
    Montazami, Reza (Virginia Tech, 2009-12-04)
    This thesis presents applications of the layer-by-layer (LbL) assembly technique in fabrication of thin films with a primary focus on design and development of electrochromic devices. The optical properties of electrochromic materials change as they alter between redox states. The morphology and properties of LbL-assembled thin films can be modified by varying several processing factors such as dipping duration, ion type, ion concentration, pH, molecular weight, and ionic strength. In the present work, several factors of LbL assembly process were manipulated to tailor electrochromic thin films of desired attributes. An electrochromic device (ECD) with fast optical switching speed was designed and constructed based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This device exhibited optical switching speeds of 31 and 6 ms for coloration and decoloration respectively, on a 60 mm2 area. Poly(aniline 2-sulfonic acid) (PASA) is a relatively new ionic polymer, and its electrochromic properties have not been previously investigated in much detail. PASA thin film showed several redox states corresponding to color changes from dark blue to gray as it passed different redox states. One particularly interesting and promising design for ECDs is dual electrochrome. Dual electrochrome ECDs based on PANI and polyaniline (PASA) are investigated in this thesis. The PANI/PASA thin film showed superior spectroelectrochemical properties compare to other ECDs reported here or elsewhere. An electrode with single wall carbon nanotubes (SWCNTs) coating was tested as the substrate for an ECD based on poly[2-(3-thienyl) ethoxy-4-butylsulfonate] (PTEBS) to examine performance of the electrochromic polymer on a substrate other than an indium tin oxide (ITO) electrode. Compared to ITO, the SWCNT based device exhibited superior properties.
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    Ion transport and storage of ionic liquids in ionic polymer conductor network composites
    Liu, Yang; Liu, Sheng; Lin, Junhong; Wang, Dong; Jain, Vaibhav; Montazami, Reza; Heflin, James R.; Li, Jing; Madsen, Louis A.; Zhang, Q. M. (AIP Publishing, 2010-05-01)
    We investigate ion transport and storage of ionic liquids in ionic polymer conductor network composite electroactive devices. Specifically, we show that by combining the time domain electric and electromechanical responses, one can gain quantitative information on transport behavior of the two mobile ions in ionic liquids (i.e., cation and anion) in these electroactive devices. By employing a two carrier model, the total excess ions stored and strains generated by the cations and anions, and their transport times in the nanocomposites can be determined, which all depend critically on the morphologies of the conductor network nanocomposites. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432664]
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    Layer-by-layer self-assembled conductor network composites in ionic polymer metal composite actuators with high strain response
    Liu, S.; Montazami, Reza; Liu, Y.; Jain, V.; Lin, M. R.; Heflin, James R.; Zhang, Q. M. (AIP Publishing, 2009-07-01)
    We investigate the electromechanical response of conductor network composite (CNC) fabricated by the layer-by-layer (LbL) self-assembly method. The process makes it possible for CNCs to be fabricated at submicron thickness with high precision and quality. This CNCs exhibits high strain similar to 6.8% under 4 V, whereas the RuO(2)/Nafion CNCs exhibit strain similar to 3.3%. The high strain and submicron thickness of the LbL layers in an ionic polymer metal composite (IPMC) yield large and fast actuation. The response time of a 26 mu m thick IPMC with 0.4 mu m thick LbL CNCs to step voltage of 4 V is 0.18 s.
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    Millisecond switching in solid state electrochromic polymer devices fabricated from ionic self-assembled multilayers
    Jain, V.; Yochum, H. M.; Montazami, Reza; Heflin, James R. (AIP Publishing, 2008-01-01)
    The electrochromic switching times of solid state conducting polymer devices fabricated by the ionic self-assembled multilayer method has been investigated. The devices were composed of bilayers of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) and poly(allylamine hydrochloride) on indium tin oxide substrates. Devices fabricated from 40 bilayer thick films have coloration and decolaration switching times of 31 and 6 ms, respectively, with low applied voltage (1.4 V) for an active area of 0.6 cm(2). The switching times have been shown to decrease with the active area of the electrochromic device suggesting that even faster electrochromic switching times are possible for devices with smaller areas. (C) 2008 American Institute of Physics.
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    Modification of single-walled carbon nanotube electrodes by layer-by-layer assembly for electrochromic devices
    Jain, Vaibhav; Yochum, Henry M.; Montazami, Reza; Heflin, James R.; Hu, Liangbing; Gruner, George (American Institute of Physics, 2008-04-01)
    We have studied the morphological properties and electrochromic (EC) performance of polythiophene multilayer films on single wall carbon nanotube (SWCNT) conductive electrodes. The morphology for different numbers of layer-by-layer (LbL) bilayer on the SWCNT electrode has been characterized with atomic force microscopy and scanning electron microscope, and it was found that the LbL multilayers significantly decrease the surface roughness of the nanoporous nanotube films. The controlled surface roughness of transparent nanotube electrodes could be beneficial for their device applications. We have also fabricated EC devices with LbL films of poly[2-(3-thienyl) ethoxy-4-butylsulfonate/poly(allylamine hydrochloride) on SWCNT electrodes, which not only have high EC contrast but also sustain higher applied voltage without showing any degradation for more than 20 000 cycles, which is not possible in the case of indium tin oxide electrodes. Cyclic voltammetry of the LbL films formed on SWCNT shows higher current at low potential, revealing the feasibility of SWCNT electrode as a good host for electrolyte ion insertion. (C) 2008 American Institute of Physics.
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    Optical Properties of an Electrochromic Device Based on Poly (aniline 2-sulfonic) acid (PASA) Film, Formed by Ionically Self-Assembled Multilayers (ISAM) Technique
    Montazami, Reza (Virginia Tech Department of Materials Science and Engineering, 2008-03-20)
    A new ElectroChromic Device (ECD) was designed and constructed based on Ionically Self Assembled Multilayers (ISAM) technique, in which oppositely charged polymers are used to construct films of multiple layers.The ECD device proposed and studied in this work was based on Poly (aniline 2-sulfonic) acid, (PASA), as the active electrochromic polyanion, and Poly (allylamine hydochloride), (PAH), as the inactive polycation.Cyclic Voltammetry (CV) technique was employed to study redox properties of the polymer film and to help to determine the operating voltage of the device.It was determined that the PAH/PASA ECD has two redox states between –700mV and +700mV.The ECD with 40 bilayers demonstrated dark green to light brown to dark gray electrochromism, in the –700mV to +700mV window.The major transmittance occurred at –600mV (dark green) and +600mV (dark gray).The ECD in the relaxed state, i.e. no voltage applied, is light brown.At –600mV, in visible spectrum, the highest contrast (∆T=27%) appeared at approximately 690nm (dark green) and at +600mV the highest transmittance in visible range was a broad range between approximately 600nm to 710nm.
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    Smart Polymer Electromechanical Actuators for Soft Microrobotic Applications
    Montazami, Reza (Virginia Tech, 2011-06-03)
    Ionic electroactive polymer (IEAP) actuators are a class of electroactive polymer devices that exhibit electromechanical coupling through ion transport in the device. They consist of an ionomeric membrane coated with conductive network composites (CNCs) and conductive electrodes on both sides. A series of experiments on IEAP actuators with various types of CNCs has demonstrated the existence of a direct correlation between the performance of actuators and physical and structural properties of the CNCs. Nanostructure of CNC is especially important in hosting electrolyte and boosting ion mobility. This dissertation presents a series of systematic experiments and studies on IEAP actuators with two primary focuses: 1) CNC nanostructure, and 2) ionic interactions. A novel approach for fabrication of CNC thin-films enabled us to control physical and structural properties of the CNC thin-films. We, for the first time, facilitated use of layer-by-layer ionic self-assembly technique in fabrication of porous and conductive CNCs based on polymer and metal nanoparticles. Results were porous-conductive CNCs. We have studied the performance dependence of IEAP actuators on nano-composition and structure of CNCs by systematically varying the thickness, nanoparticle size and nanoparticle concentration of CNCs. We have also studied influence of the waveform frequency, free-ions and counterions of the ionomeric membrane on the performance and behavior of IEAP actuators. Using the LbL technique, we systematically changed the thickness of CNC layers consisting of gold nanoparticles (AuNPs) and poly(allylamine hydrochloride). It was observed that actuators consisting of thicker CNCs exhibit larger actuation curvature, which is evidently due to uptake of larger volume of electrolyte. Actuation response-time exhibited a direct correlation to the sheet-resistance of CNC, which was controlled by varying the AuNP concentration. It was observed that size and type of free-ions and counterion of ionomeric membrane are also influential on the actuation behavior or IEAP actuators and that the counterion of ionomeric membrane participates in the actuation process.
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    Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly
    Montazami, Reza; Liu, Sheng; Liu, Yang; Wang, Dong; Zhang, Qiming; Heflin, James R. (American Institute of Physics, 2011-05-15)
    Ionic electroactive polymer (IEAP) actuators containing porous conductive network composites (CNCs) and ionic liquids can result in high strain and fast response times. Incorporation of spherical gold nanoparticles in the CNC enhances conductivity and porosity, while maintaining relatively small thickness. This leads to improved mechanical strain and bending curvature of the actuators. We have employed the layer-by-layer self-assembly technique to fabricate a CNC with enhanced curvature (0.43 mm(-1)) and large net intrinsic strain (6.1%). The results demonstrate that curvature and net strain of IEAP actuators due to motion of the anions increase linearly with the thickness of the CNC as a result of the increased volume in which the anions can be stored. In addition, after subtracting the curvature of a bare Nafion actuator without a CNC, it is found that the net intrinsic strain of the CNC layer is independent of thickness for the range of 20-80 nm, indicating that the entire CNC volume contributes equivalently to the actuator motion. Furthermore, the response time of the actuator due to anion motion is independent of CNC thickness, suggesting that traversal through the Nafion membrane is the limiting factor in the anion motion. (C) 2011 American Institute of Physics. [doi:10.1063/1.3590166]