Abderrahmane Benchirouf

Electromechanical Behavior of Chemically Reduced Graphene Oxide and Multi-walled Carbon Nanotube Hybrid Material

In this paper, we propose strain-sensitive thin films based on chemically reduced graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) without adding any further surfactants. In spite of the insulating properties of the thin-film-based GO due to the presence functional groups such as hydroxyl, epoxy, and carbonyl groups in its atomic structure, a significant enhancement of the film conductivity was reached by chemical reduction with hydro-iodic acid. By optimizing the MWCNT content, a significant improvement of electrical and mechanical thin film sensitivity is realized. The optical properties and the morphology of the prepared thin films were studied using ultraviolet-visible spectroscopy (UV-Vis) and scanning electron microscope (SEM). The UV-Vis spectra showed the ability to tune the band gap of the GO by changing the MWCNT content, whereas the SEM indicated that the MWCNTs were well dissolved and coated by the GO. Investigations of the piezoresistive properties of the hybrid nanocomposite material under mechanical load show a linear trend between the electrical resistance and the applied strain. A relatively high gauge factor of 8.5 is reached compared to the commercial metallic strain gauges. The self-assembled hybrid films exhibit outstanding properties in electric conductivity, mechanical strength, and strain sensitivity, which provide a high potential for use in strain-sensing applications.

Humidity sensitivity of thin films based dispersed multi-walled carbon nanotubes

The electrical transport properties of the thin films based dispersed carbon nanotubes (MWNT) when exposed to humid environment in various temperatures was investigated. The MWNTs dispersed in three different kinds of surfactants (sodium dodecylbenzene sulfonate (SDBS), sodium dodecylsulfate (SDS), and Triton X-100) were deposited on flexible polymer substrates (Polyethylene terephthalate - PET) through drop casting method, these samples were later exposed to humidity change at various temperature. The resistance increases exponentially with relative humidity (RH) from 10% to 90%. Moreover, it shows that MWNT dispersed in an ionic surfactant having a benzene ring in our case SDBS demonstrate higher humidity sensitive properties, this surfactant shows also good dispensability as well as good electrical properties at room temperature, the only drawback was the less stability at high temperatures compared to the other used surfactant, because of the forming of the virtual short circuit effect. Generally, the humidity sensitivity of thin films based MWNT emphasize it potential as a humidity sensitive material.

Investigation of RFID passive strain sensors based on carbon nanotubes using inkjet printing technology

Because of their remarkable properties, carbon nanotubes (CNTs) have been used in many applications [1-5]. Stain sensors based on CNTs can overcome several limitations of the existing conventional sensors, including limited monitoring locations and separation from the structure that is being monitored. Many deposition methods were applied to deposit CNTs on substrate; inkjet technology among others will possibly turn out as a fast and flexible manufacturing method for CNT-based sensors. We report about a wireless passive strain sensor made by inkjet-printing of CNT dispersions on flexible substrates. According to the radio frequency identification (RFID) principles, a square planar coil was patterned using inkjet orienting technology on a flexible substrate (Polyethylene terephthalate - PET) in order to measure strain wirelessly [6, 7]. Several settings of printing were investigated and optimized. Coils of different design parameters including variation of the number of windings, inner diameter, outer diameter and number of printed layers were manufactured using inkjet printing. The investigation of the readout mechanism of the sensor was done by applying the electrical impedance spectroscopy (EIS) analysis. By measuring the change in the complex impedance of the coupled coil, the changes in the resonance frequencies of the sensors were detected wirelessly. The change in the bandwidth is considered to be the main effect of the sensor under strain.

Investigation of physical aging of carbon nanotube/PEDOT:PSS nanocomposites by electrochemical impedance spectroscopy

In this work, thin films based on multi-walled carbon nanotubes (MWCNT)- poly(3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT:PSS) were prepared by solution mixing method. The dispersions were deposited on a flexible thin polyimide Kapton-HN 500 substrate by drop casting technique. The physical aging effect on the thin films as a function of MWCNT concentration ranging from 0.025 wt. % to 0.1 wt. % were investigated at room temperature by electrochemical impedance spectroscopy (EIS) over a wide range of frequency from 40 Hz to 110 MHz. It was found that the MWCNT concentration has a considerable influence not only on the conductivity but also on the aging rate of the nanocomposite films. It was also observed that the influence of aging on the electrical properties of the nanocomposites decreases with increasing amount of MWCNT concentration, due to the electron restriction mobility in the polymer chains at the vicinity of PEDOT:PSS/MWCNT interfaces. While the relative resistance change in the pure PEDOT:PSS polymer is 21.2 %, this change is found to be 6.8 % at 0.1 wt. % of MWCNT. Moreover, the aging effect on the MWCNT/PEDOT:PSS nanocomposites was considered within an equivalent complex R-C circuit model based on the obtained impedance data. This model was used to extract the electrical fitting parameters of the nanocomposites at different MWCNT concentrations.

The piezoresistive performance investigation of multifunctional genuine nanocomposites thin films

In this work, piezoresistive properties of thin films based on carbon nanomaterials dispersed in intrinsically conductive polymer were investigated. The high conductive multiwalled carbon nanotubes / graphene oxide and Poly (3,4-ethylenedioxythiophene) polymerized with poly (4-styrenesulfonate) (PEDOT:PSS) thin films were prepared and deposited on flexible polymer substrates (Kapton HN500, 125 μm) by solution drop casting. The influences of mixing ratio of MWCNT:GO to PEDOT:PSS and of the chemical reduction on the electromechanical thin film properties such as electrical conductivity and strain sensitivity were investigated. For the non-treated thin films, a negative resistance coefficient was observed for the applied strain force with low strain sensitivity around -1.9. This behavior was independent on the mixing ratio between the MWCNT:GO to PEDOT:PSS. However, and for the chemically reduced thin films, two strain regions were distinguished with sensitivity up to 92. In general, MWCNT:GO/ PEDOT:PSS films have potential as a high conductive, high strain sensitive material for advanced structural health monitoring and aerospace applications.

Piezoresistive behavior of Epoxy/MWCNTs nanocomposites thin films for strain sensing application

In this present work, the influence of processing parameters such as sonication time and curring time on the electromechanical properties of thin films based thermosetting polymer known as Epoxy filled with untreated multiwalled carbon nanotube (CNTs) were investigated systematically. For this reason, a predefined CNT content (0.3 wt.%) was directly mixed with epoxy at different sonication time i.e. (20, 25, 30 and 35 min) and differnt curring time i.e. (3 and 5 hours). Experimental results show that these processing parameters have an inversal effect on the electrical and mechanical behavior. It was found that, the films made based on nanocomposite sonicated for 30 min and curried for 5 hours had the highest conductivity. On the other side, under a cyclic loading, thin films show higher sensitivity in compression and especially sample has a high sensitivity in both tension and compression.

DC-bias effect on dielectric properties of multiwalled carbon nanotubes SDBS/PEDOT:PSS nanocomposites

Multiwalled carbon nanotubes (MWCNTs) dispersed in sodium dodecylbenzenesulfonate (SDBS) then mixed with poly(3, 4-ethylenedioxythiophen)/poly (4-styrene-sulfonate) (PEDOT:PSS) nanocomposites containing MWCNTs content between 0.025 wt.% and 0.1 wt.% were prepared and deposited on a flexible thin substrate (Kapton HN) using the drop casting technique. Alternating current (AC) electrical properties of thin films were investigated using a complex impedance analyzer over a wide range of frequency from 40 Hz to 110 MHz. The complex impedance responses indicate that DC-bias plays a crucial role in the complex impedance mechanism of MWCNT:SDBS/PEDOT:PSS nanocomposites. It was found that the DC-bias leads to increase of conductivity of the nanocomposite due to the formation of additional conducting paths within the nanocomposite. It was also found that the DC-bias is more effective on the conduction mechanism of nanocomposite at low MWCNTs content. Furthermore, the dielectric constant of nanocomposite increases with the DC-bias due to enhancement of conducting electrons release in the nanocomposite. The Bode diagram of nanocomposite containing 0.025 wt.% MWCNTs shows that the DC-bias has also influence on the relaxation mechanism of nanocomposite and the applicable DC-bias voltage value is limited and it is proportional to MWCNT concentration of nanocomposite.

Investigation of the electrode surface of a liquid quality sensor by local impedance spectroscopy

Local electrochemical impedance spectroscopy (LEIS) is a suitable technique for the investigation of electrode surfaces. In this paper, we investigate the correlation between changes on the electrode surface with the results of LEIS. For LEIS measurements, a novel measurement set-up is developed with high mechanical stability and a sufficient space resolution of 200nm. Three identical liquid quality sensors were exposed to aging with different immersion time. Using scanning electronic microscopy (SEM), the results depict that the deposits increase with immersion time and have typical dimensions of 0.7 mm2. The LEIS investigation shows a good sensitivity to deposits on electrode surfaces and results are confirmed by the SEM investigation.

Modeling of the resistance between metal electrodes and metallic SWNT

Contact effects of carbon nanotubes (CNT) to metallic electrodes have a big impact on the electronic transport in CNT-based structures. In general there are two expected types of contacts, Schottky type with semiconducting tubes and ohmic contact with semiconducting and metallic tubes. However not always perfect contacts come, it is rather a tunneling barrier contact because of the weak coupling to the metal electrode or the formation of thin layer of oxides at the interface, for example. We propose a simple model for non-ideal contacts of metallic single walled nanotube (SWNT) in order to calculate the overall resistance and hence the contact resistance. The model takes into account the findings of both experiments and theories such as effect of work function, electron phonon scattering in low and high bias voltage, image potential and van der Waals distance at the interface. The model can be developed to calculate the contact resistance for strips of several SWNTs or multiwalled carbon nanotubes MWNTs.