Preparation of conducting composites of polypyrrole using supercritical carbon dioxide

Supercritical carbon dioxide, saturated with pyrrole, was brought into contact with oxidant‐impregnated films of poly(chlorotrifluoroethylene) (PCTFE), crosslinked poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and porous crosslinked polystyrene (PS) in order to form conducting composites via the in situ polymerization of pyrrole. The two nonporous hosts—PCTFE and crosslinked PDMS—did not form conducting composites with polypyrrole (PPy). On the other hand, the electrical conductivity of the PPy composites with carbon dioxide‐swollen PMMA and porous PS ranged from 1.0 × 10^?4 S/cm to 3.0 × 10^?5 S/cm. In these two cases, the level of pyrrole polymerized on the surface or in the pores of the host polymer was sufficient to attain the interconnected conducting polymer networks necessary for electrical conductivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1113–1116, 2003     

In situ electropolymerization of conducting polypyrrole/carbon nanotubes composites on stainless steel: Role of carbon nanotubes types

In situ electropolymerization was used to prepare polypyrrole-oxidized multi-walled carbon nanotubes and polypyrrole-oxidized single-walled carbon nanotubes composites on a stainless steel surface from 0.1 M oxalic acid by using cyclic voltammetry. The electropolymerization process was investigated and discussed, and the results showed that the addition of the oxidized carbon nanotubes greatly enhanced the electropolymerization process, especially in the case of oxidized single walled carbon nanotubes. The results also showed that increasing the pyrrole monomer concentration leads to increasing the amount of polypyrrole electrodeposited, and this is more pronounced in the presence of the carbon nanotubes. The electropolymerization process was mainly under diffusion control as the process was inhibited by increasing the scan rate. In general, the presence of oxidized carbon nanotubes improved the electropolymerization of the polypyrrole and greatly enhanced its thermal and morphological properties.     

Supercritical carbon dioxide assisted preparation of conductive polypyrrole/cellulose diacetate composites

Supercritical carbon dioxide (SC‐CO₂) has been used to assist the preparation of conductive polypyrrole/cellulose diacetate (PPy/CDa) composites by in situ chemical oxidative polymerization. The morphology and conductivity of resulted composites were investigated with scanning electron microscopy and four‐probe method, respectively. With the assistance of strong swelling effect of SC‐CO₂, composite films were obtained with a macroscopically homogeneous structure and conductivity up to 10^?1 S cm^?1 order of magnitude. Increasing the pressure of SC‐CO₂ increased conductivity, while increasing the temperature decreased conductivity. For comparison, PPy/CDa composite was also prepared with conventional oxidative method in aqueous solution. From the viewpoint of conductivity and environmental protection, the SC‐CO₂ method showed its superiority over the conventional one. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4575–4580, 2006     

Effect of supercritical carbon dioxide on polystyrene extrusion

A study on the extrusion of polystyrene was carried out using supercritical carbon dioxide (scCO₂) as foaming agent. scCO₂ modifies the rheological properties of the material in the barrel of the extruder and acts as a blowing agent during the relaxation at the passage through the die. For experiments, a single-screw extruder was modified to be able to inject scCO₂ within the extruded material. The effect of operating parameters on material porosity was studied. Samples were characterized by using water-pycnometry, mercury-porosimetry and scanning electron microscopy. Polystyrene with expansion rate about 15–25% was manufactured. A rapid cooling just downstream the die is important to solidify the structure. The die temperature allows the control of the porosity structure. CO₂ concentration shows no significant influence.     

Patterns of conducting polypyrrole with tunable morphologies

An effective and reliable method was established to fabricate ordered arrays of conducting polypyrrole (PPy) with tunable morphologies. A polydimethylsiloxane (PDMS) stamp was used to lift up the top layer of silica spheres with a closed-packed hexagonal arrangement on a silicon wafer. The lattice spacing of the silica sphere array on the PDMS stamp could be tuned by controlling the swelling of the stamp. Afterwards, the silica spheres were transferred onto a poly(vinyl alcohol) (PVA) film which was pre-spin-coated on an ITO glass. The silica spheres were etched away with hydrofluoric (HF) acid, and the resulting porous PVA film maintained an identical ordered array but of holes. Electrochemical polymerization of pyrrole monomer was carried out with the ITO glass as a working electrode, on which was the PVA film with ordered holes. Different charge densities applied led to PPy patterns with different morphologies; a possible mechanism was addressed.     

Interfacial physicochemical properties of functionalized conducting polypyrrole particles

Polypyrrole-coated polystyrene latex particles bearing reactive N-succinimidyl ester functional groups (PS-PPyNSE₇₅) were prepared by the in situ copolymerization of pyrrole 1 and the active N-succinimidyl ester-functionalized pyrrole 2 (pyrroleNSE), with initial 1:2 fractions of 25:75 (%) in the presence of sterically stabilized polystyrene (PS) latex particles. PS particles were prepared by dispersion polymerization leading to particles having a diameter of 600±10 nm. The PS-PPyNSE₇₅ particles were characterized in terms of surface morphology and chemical composition. Surface analysis of the colloidal materials by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated a substantial coating of PS by the reactive conducting copolymer. Infrared spectroscopy permitted to detect pyrroleNSE repeat units at the surface of the particles indicating that 1 and 2 did indeed copolymerise.Reactivity of the PS-PPyNSE₇₅ particles has been investigated using 2-aminoethanol and 2-mercaptoethanol, two model molecules bearing functional groups borne by proteins. Incubation of the particles with these model molecules clearly showed that the particles are highly reactive towards amine and thiol groups. The functionalized particles were then tested as bioadsorbents. PS-PPyNSE₇₅ particles were found to be effective in attaching an aminated biotin. The Biotin-decorated PS-PPyNSE₇₅ latex particles were incubated with avidin with a result of a significant change in the surface composition that is in line with the attachment of the protein by specific binding to biotin.     

Facile synthesis and electrochemical capacitance of composites of polypyrrole/multi-walled carbon nanotubes

Composites of polypyrrole (PPy) and multi-walled carbon nanotubes (MWCNTs) were synthesized by a facile method involving one-step electrochemical deposition from a thin-layer of ionic liquid solution attached on a glassy carbon electrode. The morphology of the composites was characterized by field emission scanning electron microscopy, and the capacitance properties were investigated by cyclic voltammetry (CV). The charge-discharge behavior of the composites prepared in this work was examined by chronopotentiometry at a constant current density for multi-cycle scans. The results show that the PPy/MWCNT composites have a porous 3D nanostructure, with high specific capacitance (SC) of 890 F/g (for the mass of the PPy in the composites) calculated from CV at 2 mV/s in 1.0 M KCl. The stability of the composites in 1.0 M KCl electrolyte was also examined by multi-cycle CV and only 9% decrease of SC value was observed for the 1000 cycles.     

Preparation, characterization, and supercritical carbon dioxide foaming of polystyrene/graphene oxide composites

Graphene oxide (GO) was prepared by oxidation of graphite using the Hummers method, and was modified by isocyanate to obtain dispersed GO sheets in dimethylformamide. Polystyrene (PS)/GO composites were prepared by solution blending, and their morphologies and properties were characterized. The addition of GO increased the glass transition temperature of the PS/GO composites. The storage modulus and thermal stability of the composites were also improved compared with PS. Foams of PS and PS/GO composites were prepared by supercritical carbon dioxide foaming. The composite foams exhibited slightly higher cell density and smaller cell size compared with the PS foam, indicating the GO sheets can act as heterogeneous nucleation agents.     

Formation of stable passive film on stainless steel by electrochemical deposition of polypyrrole

Stable passive film has been formed on 304 stainless steel during the electrochemical deposition of polypyrrole (PPy) from sulfuric acid solution. The stability of passive film under PPy increases with aging in H₂SO₄ and this film has much higher resistance to pitting than that formed by anodic polarization under the same condition of aging. XPS studies indicate that the content of chromium components in the oxides under PPy layer is about twice that of the anodically formed passive film with larger value of the ratio Cr₂O₃/Cr(OH)₃. Higher content of iron with a ratio of Fe²⁺/Fe³⁺ more than unity is also observed with a considerable lower hydration and sulfate content in the oxides under PPy layer. It is suggested that sulfate ion is consumed as a dopant in the formation of PPy film and the oxidation of stainless steel is achieved under the environment of lower concentration of water and sulfate molecules. This may result in the enhancement of formation of corrosion-resisting oxides rather than hydroxides and sulfates.     

Functionalized single-walled carbon nanotubes/polypyrrole composites for amperometric glucose biosensors

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO₃⁻). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H₂O₂. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO₃⁻ film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H₂O₂ with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO₃⁻/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM⁻¹ cm⁻²), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.     

Supercritical carbon dioxide immobilization of glucose oxidase on polyurethane/polypyrrole composite

Glucose oxidase (GOX) was immobilized on polyurethane/polypyrrole (PU/PPY) composite foam via supercritical fluid immobilization (SFI) towards the preparation of biosensors. Buffer solution was used as the immobilization medium along with scCO₂. To provide insight into the relation between the scCO₂ and the GOX-buffer solution, the GOX-buffer solutions were subjected to scCO₂ and the protein amounts of the GOX-buffer solutions before and after scCO₂ exposure were determined at 80, 100 and 150 bar and 30, 40 and 50 °C for an exposure time of 24 h. The protein amount in GOX-buffer solution decreased in all cases after exposure to scCO₂. The lowest and highest loss in GOX amounts observed were 2.9 and 36.4 μg at 80 bar, 30 °C and 100 bar, 50 °C, respectively. The effects of immobilization pressure (80, 100 and 150 bar), temperature (30, 40 and 50 °C) and time (4, 24 and 72 h) on the activities of the GOX-immobilized PU/PPY composites were investigated. At 30 °C immobilization temperature, the activity values of the GOX-immobilized PU/PPY composites were slightly increased as the pressure was increased from 80 to 100 bar. Further increase in immobilization pressure from 100 to 150 bar at 30 °C caused a decrease in the activity values. At 40 °C immobilization temperature, increasing the immobilization pressure from 80 to 100 bar did not provide an increase in activity values, but further increase to 150 bar caused a decrease in the activity values. At 100 bar immobilization pressure, decrease in temperature enhanced the activity values of the samples. When immobilization was performed via SFI, the activity values were doubled compared to the immobilization at atmospheric conditions. Among all the immobilization pressures and temperatures investigated, both the highest activity (U/cm²) and the highest specific activity (U/mg) were obtained for the samples processed at 100 bar, 30 °C.     

Preparation of conductive polypyrrole composites by in‐situ polymerization

Two kinds of conductive polypyrrole composites were prepared by in‐situ polymerization of pyrrole in a suspension of chlorinated polyethylene powder or in a natural rubber latex using ferric chloride as oxidizing agent. The preparation conditions were studied and the results showed that it is better to swell the chlorinated polyethylene powder with the monomer first, followed by addition of the oxidant, than to add the oxidant first, and that conversion can reach 98% for 6 h at room temperature. The conductivity percolation threshold of the composite is about 12%. The composites can be processed repeatedly, exhibiting a maximum tensile strength over 9 MPa and a maximum conductivity near 1 S cm⁻¹. The polypyrrole/natural rubber composites were prepared successfully by using a nonionic surfactant (Peregal O) as stabilizer at pH less than 3 with a molar ratio of FeCl₃/pyrrole = 2.5 below 45 °C. The latter composites show a low conductivity percolation threshold about 6%, a maximum tensile strength over 10 MPa and a maximum conductivity over 2 S cm⁻¹. The composites were characterized by FTIR and TGA. The polypyrrole/chlorinated polyethylene composites are very stable in air and almost no decrease of conductivity was observed for over 10 months examined. © 1999 Society of Chemical Industry     

Flexible and conducting composites of polypyrrole and polydimethylsiloxane

Conductive and flexible polydimethylsiloxane (PDMS)/polypyrrole (PPy) composites were synthesized electrochemically. Electrochemical syntheses were performed at +1.10 V by using p‐toluene sulfonic acid (PTSA) as supporting electrolyte and water as solvent. Composites were characterized by cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy. Conductivity measurements and mechanical tests were also performed. The observed conductivities were in the range of 3.5–7.6 S/cm, indicating that the conductivities of PDMS/PPy composites and that of pure PPy were in the same order of magnitude. Tensile tests revealed that higher percent elongation was obtained by the addition of PDMS. Highly flexible and foldable PDMS/PPy composites were successfully synthesized, which have high conductivities and improved mechanical properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 736–741, 2004     

Effect of polypyrrole deposition of carbon fiber on the thermal expansion of carbon fiber-epoxy composites

Polypyrrole (PPy) was deposited onto carbon fibers via continuous electrochemical deposition (ECD). Composites of PPy-deposited carbon fiber and epoxy were prepared. The thermal expansion coefficients of these materials were determined using either a thermal mechanical analyzer or an imbeded strain gauge. The results show that PPy has a negative thermal expansion coefficient while carbon fiber and epoxy have positive thermal expansion coefficients. The resulting composite has a smaller thermal expansion coefficient, higher interlaminar shear stress and a smaller critical fiber length than the composite using untreated carbon fiber. This suggests that the deposition of PPy can effect an improvement in the fiber-matrix interfacial bonding of the composite.     

Supercritical carbon dioxide assisted blending of polystyrene and poly(methyl methyacrylate)

A method for blending polystyrene and poly(methyl methacrylate), (PMMA), with the addition of supercritical carbon dioxide has been investigated. The first series of blends was a PMMA and polystyrene with similar melt viscosities. The second series of blends was a PMMA and polystyrene with a viscosity ratio (ηPMMA/ηpolystyrene) of about 20. The results show that a reduction in the size of the minor or dispersed phase is achieved when supercritical carbon dioxide is added to the blend system. A high-pressure mixing vessel was used to prepare the blends under pressure with carbon dioxide for batch blending. The solubilities of CO₂ in PMMA and polystyrene, measured in the high-pressure mixing vessel at 200°C and 13.78 MPa (2000 psi) was 5.8 and 3.6 wt%, respectively. A single screw extruder was used to study the effects of carbon dioxide on the viscosity of polymer melts. The melt viscosity of PMMA was reduced by up to 70% with approximately 0.4 wt% CO₂. The melt viscosity of polystyrene was reduced by up to 56% with a CO₂ content of 0.3 wt%. A twin screw extruder was used to study the effects of injecting carbon dioxide in a continuous compounding operation.     

Study of the anticorrosive properties of polypyrrole/polyaniline bilayer via electrochemical techniques

In this work, using electrochemical techniques the authors investigated the protective properties of a polypyrrole/polyaniline bilayer as a conductive polymer. A polypyrrole/polyaniline bilayer was deposited on carbon steel substrate by potentiostatic method. The electric capacitance and resistance of the films were monitored with the immersion time in a corrosive solution to investigate the water permeability of the films. Polypyrrole/polyaniline bilayer has a relatively low permeability and good catalytic behavior in passivation of carbon steel in longer periods. The results show that the bilayer has a better anticorrosive behavior compared to homopolymers (polypyrrole and polyaniline).     

Morphology and electrical conductivity of injection-molded polypropylene/carbon black composites with addition of high-density polyethylene

This work attempts to clarify the influence of carbon black (CB) addition on the microstructure of injection-molded high-density polyethylene (HDPE)/polypropylene (PP) blends and effect of shear-induced polymer deformation on the conductive network structure. We observed that HDPE molecules are strongly interacted with carbon surfaces and CB particles are selectively located in HDPE domains. Morphology of the injection-molded specimen consists of three parts, namely, CB-HDPE complex domain, free HDPE domain and PP domain. The volume and microstructure of the free HDPE domain are significantly influenced by HDPE and CB concentration, CB structure, and PP viscosity. We also confirmed that the CB particles are capable of self-assembly to form random conductive networks even under high shear rate within very short time. The morphological changes were finally correlated to the variation of electrical conductivity.     

Electrochemical impedance study of polyaniline electrocoated porous carbon foam

Electropolymerization of aniline on mesophase pitch based carbon foam has been studied in order to evaluate the influence of conductive polymer coating on the properties of carbon foam. The surface morphology of the coating was determined by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of resulting modified carbon foam samples. Polyaniline (PANI) electrocoated-mesophase pitch based carbon foam showed good capacitor behavior in 0.5 M H₂SO₄. Better capacitive behavior is obtained for 100 and 150 mV/s compared to other scan rates, under these faster scan rates thinner films of PANI coatings were combined with more porous structure of carbon foam. Conductivity of the carbon foam was increased from 9.23 to 13.73 S/cm by electrocoating of PANI.     

Conducting composite film based on polypyrrole and crosslinked cellulose

Polypyrrole/crosslinked cellulose conductive composite films were prepared by vapor‐phase polymerization of pyrrole on the silicon crosslinked cellulose network using anhydrous ferric chloride as oxidant. The properties of the composite film depend on their synthetic conditions such as the amount of ferric chloride and tetraethyl orthosilicate crosslinker, the reaction time, the solvent, etc. Interestingly, it was found that the conductivity was strongly affected by the nature of the solvents and their amount in pyrrole solution. When the weight ratio of methanol/pyrrole is 1 : 1, the conductivity was as high as 1.1 S/cm, increased by two orders of magnitude compared to that without solvent, and the mechanical properties was good. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1368–1373, 2001     

Hybrid nanostructure of polypyrrole and porous silicon prepared by galvanostatic technique

Nanostructured porous silicon (PS) layer is prepared in a lightly doped p-type substrate (with pores < 5 nm) and used as a working electrode to deposit conducting polypyrrole (PPy) by the electrochemical oxidative polymerization technique in an organic liquid phase. Three distinguishable stages of PPy deposition are observed and recorded under constant applied current: nucleation of polymer at the pore bottom, unidirectional growth of PPy inside the pores, and polymerization outside the PS surface. The hybrid nanostrucutre of PS/PPy shows a significant improvement of electrical conductivity as opposed to the unmodified PS layer. The improved conductivity is observed in spite of the formation of insulating layer of silicon oxides as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. Systematic study of fabrication and characterization of this organic-inorganic heterosystem, quantification of the PPy in the PS matrix, and the mechanism of filling the nanopores with polymer are presented and thoroughly discussed.