Van-Tan Truong

Carbon nanotube and polyaniline composite actuators

The actuation of a single-wall carbon nanotube (CNT) mat, an electrically conducting polyaniline (PAn) film and a composite of these two materials has been investigated in NaNO3 (1 M), NaCl (1 and 3 M) and HCl (1 M) solutions. The expansion and contraction patterns of the PAn, CNT and CNT/PAn samples are similar in these solutions. Fabrication of the CNT/PAn samples by coating PAn (CNT:PAn = 3:1 by weight) substantially enhanced the actuation strain (0.2?0.5%) of the CNT/PAn composite compared to the low actuation strain (0.06%) of the pure CNT mat. The actuation of PAn and CNT operates via different mechanisms. Non-Faradaic electrochemical charging of the CNT bundles is the main factor behind the expansion of CNT, while the expansion/contraction of PAn is dependent on the redox reactions of the polymer. The displacement pattern of the composite is dominated by the PAn component. However, when a load is applied to the sample (up to 1.2 MPa) the CNT/PAn sample behaves similarly to CNT samples, i.e. the actuation strain is almost independent of the applied loads in contrast to pure conducting polymers. This implies that the reinforcing effect of the CNT component is possibly due to the inherent high Youngs modulus of the CNT bundles (~640?GPa).

Ordering and stability in conducting polypyrrole

X-ray diffraction (XRD) was employed to characterize electrochemically synthesized polypyrrole (PPy) films with 1,5-naphthalene disulfonate (1,5-NDS) counterions treated with simple acid and base. Results show that the as-synthesized film is amorphous with short-range ordering in the polymer backbone. This ordering is soon lost after thermal ageing at 150°C for 60 days and there is evidence of counterion degradation. Base treatment of the PPy/1,5-NDS films has similar effects leading to a complete loss of ordering in the polymer backbone and dedoping of the polymer. Acid treatment at high temperatures increases the ordering of the polymer backbone and results in the development of a secondary interdopant peak confirming that ion exchange has occurred. Conductivity of the PPy was also increased substantially. The enhanced ordering was maintained even after thermal ageing. Room-temperature acid treatment also results in improved ordering of the polymer as well as the counterion but the increase in conductivity is only marginal and most of the ordering is soon lost after thermal ageing. Increase in ordering of the polymer structure seems to lead to better conductivity, although not necessarily improved thermal stability.

Spectroscopic study of thermo-oxidative degradation of polypyrrole powder by FT-IR

Abstract Thermal ageing of compressed polypyrrole powder, with FeCl 4 − as a dopant, at 90 °C has been monitored by IR spectra and evolved gas analysis (EGA). The thermo-oxidative degradation results in a decrease in the absorption of the electronic transition band, reduction in intensity and slight shift in position of most of the IR absorptions, the loss of the 870 cm −1 absorption shoulder, and the formation of hydroxyl, nitrile and carbonyl species. In both air and nitrogen ageing environment, the evolution of carbon monoxide (CO), carbon dioxide (CO 2 ), water (H 2 O) and ammonium chloride (NH 4 Cl) is detected. The dopant decomposes to form ferric oxide and to produce chlorine and/or hydrogen chloride, which in turn reacts with the pyrrole moiety in both air and nitrogen atmosphere. The source of oxygen for the thermal oxidation in nitrogen is the oxygen present in the polymer, probably as a dopant, O 2 − . Thermal degradation results in ring-opening reactions and the formation of oxidation species, which shorten the conjugation length leading to a rapid loss of conductivity. The loss of conductivity does not correspond exactly with the loss or formation of any individual species, but is best matched by the production of water and the decrease in the 870 cm −1 shoulder. This indicates that the mechanisms of thermo-oxidative degradation are complex and the conductivity decay is likely to be caused by a number of different mechanisms.

Corrosion protection of magnesium by electroactive polypyrrole/paint coatings

The effectiveness of the corrosion protection of an acrylic paint containing electrically conductive polypyrrole (PPy) (5, 10 and 20 parts) for a magnesium alloy (98.14% Mg and 1.64% Mn) has been investigated. Salt spray and electrochemical tests were conducted to examine the effect of PPy in acrylic paint on corrosion protection of the magnesium alloy. The salt spray test results demonstrated that the paint containing PPy coated magnesium samples showed insignificant corrosion and little blistering in a salt spray chamber after 1000 h exposure. The open circuit potential (OCP) measurements displayed large potential fluctuations in the control sample due to electrochemical activities in the defect, while the magnitude of fluctuations in the measured potential for the paint containing PPy coated sample were much smaller. The anodic potentiodynamic scans showed a displacement value of Epit−EOCP increasing from 57 mV for the control sample to 223 mV for the paint containing PPy (20 parts) coated sample. However, data obtained from the cathodic potentiodynamic scans and the electrochemical impedance spectroscopy (EIS) for the paint containing PPy coated sample showed large cathodic current densities and overall low impedance values, respectively. The high cathodic current densities were attributed to the cathodic reaction(s) with low overvoltage at the PPy particles. Such cathodic reaction(s) and the relatively high conductivity of the PPy lead to an overall decrease in the measured impedance values in the EIS scans.

Mechanically Robust, Electrically Conductive and Stimuli‐Responsive Binary Network Hydrogels Enabled by Superelastic Graphene Aerogels

The architecture of the nanofiller phase in polymer nanocomposites matters! Polymer hydrogels that can combine stimuli-responsiveness with excellent electrically conductivity and mechanical strength can be fabricated by incorporation of the polymer into an ultralight and superelastic graphene aerogel to form a binary network.

Enhanced control and stability of polypyrrole electromechanical actuators

The practical application of polypyrrole (PPy) actuators requires a stable strain response and a high degree of reproducibility from sample to sample. The use of symmetrical voltage cycling to control the actuation of polypyrrole is shown to lead to a slow net oxidation of the polymer after several tens of cycles. The result is a slow deterioration in the actuation strain. The use of current pulsing reduces this problem and gives a more stable strain response. Current pulsing in combination with an ionic-liquid (IL) electrolyte allowed a strain of 3% to be achieved repeatably for many different samples for at least 100 cycles.

Ultrafast Dynamic Piezoresistive Response of Graphene‐Based Cellular Elastomers

Ultralight graphene-based cellular elastomers are found to exhibit nearly frequency-independent piezoresistive behaviors. Surpassing the mechanoreceptors in the human skin, these graphene elastomers can provide an instantaneous and high-fidelity electrical response to dynamic pressures ranging from quasi-static up to 2000 Hz, and are capable of detecting ultralow pressures as small as 0.082 Pa.

Thermal degradation of polypyrrole: effect of temperature and film thickness

Abstract Thermal degradation of a series of polypyrrole films doped with p -toluene sulfonate has been investigated by examining the effect of film thickness (12–68 μm) and temperature (70–150 °C) on the rate of decay of electrical conductivity. The kinetics are complex: for thin films and thick films at higher temperatures, the decay is proportional to t 1 2 and a similarity to diffusion kinetics is noted; at low temperatures the conductivity decay of thicker films follows first-order kinetics for at least 100 h. It is suggested that the decay is explained by oxidation and that either chemical reaction or oxygen diffusion will be rate determining, depending on the film thickness and ageing temperature. At higher temperatures, the deduced diffusion coefficient D was independent of film thickness. The Arrhenius plot of D or of the time-temperature shift factor a T showed a change of slope at 90 °C, suggesting the possibility of a glass transition temperature in the film.

Enhanced thermal properties and morphology of ion-exchanged polypyrrole films

The thermal stability of electrochemically prepared polypyrrole (PPy) films with p-toluenesulfonate (pTS) or perchlorate (ClO4−) counterion (PPy/pTS and PPy/ClO4−) is improved by simple treatment with aqueous sulfuric acid, sodium sulfate or sodium bisulfate. The degree of stabilization achieved depends on the solution, temperature and duration of treatment. Although the mechanism for improved stability is not yet clear, it is apparent that the level of ion exchange and the original polymer microstructure are important. A model for the conductivity decay as a function of thickness has been proposed. The early stages of ion exchange are not symmetrical, and diffusion is facilitated at the electrode side of the film. Furthermore, X-ray diffraction shows no evidence of morphological change after treatment of PPy/pTS (43 μm), but in PPy/pTS (12 μm) and PPy/ClO4− (41 μm) films an additional peak is indicative of more ordered structure following treatment. The glass transition temperature, Tg, of PPy/pTS and PPy/ClO4− films obtained by modulated differential scanning calorimetry is approximately 155°C.

Complex conductivity of a conducting polymer composite at microwave frequencies

A model is proposed for the complex conductivity σ∗ of a conducting polymer composite as a function of frequency ω, based on an equivalent electrical network of series and parallel circuits containing resistors and capacitors. The results are similar to the power laws derived from percolation theory, i.e. ∥σ∗∥ ∝ ωα. The effect of frequency and volume fraction of polypyrrole dispersant on the complex conductivity of a sample conducting polymer composite is analysed according to the model. The relationships between α, dispersant volume fraction and loss tangent of the composite permittivity can be predicted on a semi-quantitative basis.