Reza Montazami

Ion transport and storage of ionic liquids in ionic polymer conductor network composites

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.

Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly

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. V C 2011 American Institute of Physics. [doi:10.1063/1.3590166]

Layer-by-layer self-assembled conductor network composites in ionic polymer metal composite actuators with high strain response

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 ∼6.8% under 4 V, whereas the RuO2/Nafion CNCs exhibit strain ∼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 μm thick IPMC with 0.4 μm thick LbL CNCs to step voltage of 4 V is 0.18 s.

Millisecond switching in solid state electrochromic polymer devices fabricated from ionic self-assembled multilayers

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 6ms, respectively, with low applied voltage (1.4V) for an active area of 0.6cm2. 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.

The single-band red upconversion luminescence from morphology and size controllable Er3+/Yb3+ doped MnF2 nanostructures

Er3+/Yb3+ doped MnF2 nanostructures have been prepared via a solvothermal method. The morphology of the nanocrystals could be well controlled from nanoparticles to nanoclusters and nanolanterns by varying the volume ratio between oleic acid and ethanol in the solvent. Moreover, the size is tuned from 200 nm to 1.5 μm with the increase of reaction temperature from 110 to 200 °C. It is shown that controlling the doping concentration (Yb3+ ≤ 20 mol%) is essential to preserve the single phase and morphology of the MnF2 host. Single-band red upconversion (UC) emission can be generated in Er3+ single and Er3+/Yb3+ codoped MnF2 nanoclusters due to the energy transfer between host Mn2+ and dopant Er3+ ions. The detailed studies suggest that our MnF2:Er3+/Yb3+ nanocrystals have the strongest single-band luminescence feature at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (20 mol%). The brighter red emission from the current nanostructure compared with those from NaYF4:Er3+/Yb3+ has shown its suitability as an efficient UC luminescence host. It is expected that the achieved intense pure red emission may have potential application in in vivo bioimaging.

Influence of conductive network composite structure on the electromechanical performance of ionic electroactive polymer actuators

The influence of the nanostructure of the conductive network composite (CNC) on the performance of ionic electroactive polymer (IEAP) actuators has been examined in detail. We have studied IEAP actuators consisting of CNCs with different volume densities of gold nanoparticles (AuNPs) and the polymer network. Varying the concentration of AuNPs in CNC thin films was used as a means to control the CNC–ion interfacial area and the electrical resistance of the CNC, with minimum effect on the mechanical properties of the actuator. Increasing the interfacial area and reducing the resistance, while maintaining porosity of the composite, provide means for generating motion of more ions into the CNC at a significantly shorter time, which results in generation of strain at a faster rate. We have demonstrated that cationic strain in actuators with denser CNCs is improved by more than 460%. Denser CNC structures have larger interfacial areas, which results in attraction/repulsion of more ions in a shorter time, thus generation of a larger mechanical strain at a faster rate. Also, time-dependent response to a square-wave voltage was improved by increasing the AuNP concentration in the CNC. Under 0.1 Hz frequency, the cationic strain was increased by 64% when the AuNP concentration was increased from 4 to 20 ppm.

Ionic Liquid-Doped Gel Polymer Electrolyte for Flexible Lithium-Ion Polymer Batteries

Application of gel polymer electrolytes (GPE) in lithium-ion polymer batteries can address many shortcomings associated with liquid electrolyte lithium-ion batteries. Due to their physical structure, GPEs exhibit lower ion conductivity compared to their liquid counterparts. In this work, we have investigated and report improved ion conductivity in GPEs doped with ionic liquid. Samples containing ionic liquid at a variety of volume percentages (vol %) were characterized for their electrochemical and ionic properties. It is concluded that excess ionic liquid can damage internal structure of the batteries and result in unwanted electrochemical reactions; however, samples containing 40–50 vol % ionic liquid exhibit superior ionic properties and lower internal resistance compared to those containing less or more ionic liquids.

High contrast solid state electrochromic devices based on Ruthenium Purple nanocomposites fabricated by layer-by-layer assembly

Electrochromic Ruthenium Purple-polymer nanocomposite films, fabricated by multilayer assembly, were found to exhibit sub-second switching speed and the highest electrochromic contrast reported to date for any inorganic material.

On-chip development of hydrogel microfibers from round to square/ribbon shape

We use a microfluidic approach to fabricate gelatin fibers with controlled sizes and cross-sections. Uniform gelatin microfibers with various morphologies and cross-sections (round and square) are fabricated by increasing the gelatin concentration of the core solution from 8% to 12%. Moreover, the increase of gelatin concentration greatly improves the mechanical properties of gelatin fibers; the Youngs modulus and tensile stress at break of gelatin (12%) fibers are raised about 2.2 and 1.9 times as those of gelatin (8%) fibers. The COMSOL simulations indicate that the sizes and cross-sections of the gelatin fibers can be tuned by using a microfluidic device with four-chevron grooves. The experimental results demonstrate that the decrease of the sheath-to-core flow-rate ratio from 150 : 1 to 30 : 1 can increase the aspect ratio and size of ribbon-shaped fibers from 35 μm × 60 μm to 47 μm × 282 μm, which is consistent with the simulation results. The increased size and shape evolution of the cross-section can not only strengthen the Youngs modulus and tensile stress at break, but also significantly enhance the tensile strain at break.

Investigation of spray-coated silver-microparticle electrodes for ionic electroactive polymer actuators

We have employed the easy-to-scale-up method of spray-coating in combination with layer-by-layer self-assembly technique to fabricate ionic electroactive polymer actuators (IEAPAs). IEAPAs with spray-coated silver microparticle electrodes demonstrate enhanced strain and response time when compared to nearly identical, optimized conventional IEAPA with gold leaf electrodes. The results demonstrate that strain of these IEAPAs increases with the decrease of thickness of the outer silver microparticle electrodes. In addition, the response time of the actuators at frequencies of 1 and 10 Hz improves compared to optimized conventionally fabricated IEAPA. It was found that samples consisting of spray-coated silver electrodes can charge up to ∼3 times faster than conventional actuators at 1 Hz frequency. Faster charging/discharging results in higher mobility of ions within the actuator and thus, faster actuation. Given the relatively large thickness of the silver microparticle electrodes (∼50× gold leaf), similar...