Exploration of the morphological transition phenomenon of polyaniline from microspheres to nanotubes in acid‐free aqueous 1‐propanol solution in a single polymerization process

Polyaniline micro‐ or nanostructures have been widely investigated due to their unique physical and chemical properties. Although several studies have reported the synthesis of polyaniline microspheres and nanotubes, their mechanisms of formation remain controversial. This study reports our observation of the morphological transition of polyaniline from microspheres to nanotubes in a single polymerization process and also tries to propose their mechanisms of formation. The polymerization of aniline monomer in acid‐free aqueous 1‐propanol solutions (1 and 2 mol L^?1) produces polyaniline microspheres and nanotubes at different reaction stages through a morphology transition process with treatment using ultrasound. In the initial reaction stage, Fourier transform infrared spectra indicate that the aniline monomers form phenazine‐like units, producing polyaniline microspheres with an outside diameter of 1–2 µm. The hydrogen bonds between 1‐propanol and polyaniline serve as the driving force for the polyaniline chains to build microspheres. As the reaction continues, observation indicates the microspheres decompose and reform one‐dimensional nanotubes. In this stage, a structure consisting of a head of phenazine‐like units and a tail of acid‐doping para‐linked aniline units develops. The protonation of the para‐linked aniline units provides the driving force for the formation of nanotubes through a self‐curling process. We report here the unique morphology transition of polyaniline from microspheres to nanotubes in a single polymerization process. The results indicate that the structural change of polyaniline leads to this morphological change. The mechanisms of formation of the microspheres and nanotubes in a polymerization process are also well explained. Copyright © 2010 Society of Chemical Industry     

Ring‐opening polymerization of caprolactone using novel polyaniline salt catalyst

Hybrid composite of polyaniline metal oxide composite, polyaniline‐dodecyl hydrogen sulfate salt with ferric oxide, was prepared for the first time via simple one‐step process of oxidizing aniline with ferric tris(dodecyl sulfate). Ferric tris(dodecyl sulfate) acts as an oxidant, emulsifier, dopant for polyaniline and also source of ferric oxide. Polyaniline salt composites were prepared via aqueous, emulsion, and interfacial polymerization pathways. Polyaniline salt composite was successfully demonstrated as polymer based solid acid catalysts in the ring‐opening polymerization of ε‐caprolactone for the first time. This methodology gave low molecular weight poly(ε‐caprolactone) (MW‐4035) with highly crystalline polymer of flower petals like morphology in 52 wt% yield (with respect to the amount of ε‐caprolactone used). Advantages of this methodology are the use of easily synthesizable, easily handlable, recyclable, cheaper, and eco‐friendly nature of the catalyst. POLYM. ENG. SCI., 55:2245–2249, 2015. © 2015 Society of Plastics Engineers     

Characterization of polyaniline/Ag nanocomposites using H2O2 and ultrasound radiation for enhancing rate

Polyaniline/Ag nanocomposites have been synthesized via in situ chemical oxidation polymerization of aniline in silver salt by sonochemical method using H₂O₂ as an external medium. H₂O₂ was used to reduce AgNO₃ to Ag nanoparticles as well as to polymerize aniline to polyaniline in the same pot. The ultrasound radiation as an energy source was applied to facilitate the reaction by reducing the reaction time. Reduction of the silver salt in aqueous aniline leads to the formation of silver nanoparticles which in turn catalyze oxidation of aniline to polyaniline. The research on the structures and properties of the composites showed the individual or aggregated silver nanoparticles are dispersed in the matrix of polyaniline. The composites possess a higher degradation temperature than polyaniline alone, and their electrical conductivity are raised morethan 200 times. The cyclic voltammetry and impedance spectroscopy results showed that the polyaniline/Ag film exhibits considerably higher electroactivity compared with polyaniline film without Ag particles. POLYM. COMPOS., 31:1662–1668, 2010. © 2009 Society of Plastics Engineers     

Didecyl ester of 4‐sulfophthalic acid as a plast dopant and emulsifier in the chemical polymerization of aniline into polyaniline salt

Polyaniline salt was synthesized through the chemical oxidation of aniline with sodium persulfate as the oxidant and didecyl ester of 4‐sulfophthalic acid via three different polymerization pathways (aqueous, emulsion, and interfacial). In these polymerization processes, the ester acted as a novel plast dopant and as an emulsifier. The yield, conductivity, and number of ester units present in the polyaniline salts were determined. A polyaniline salt prepared by emulsion polymerization was soluble in chloroform and showed excellent solution‐processing properties. Polyaniline samples prepared by aqueous or interfacial polymerization were not soluble in chloroform. A soluble polyaniline salt was successfully synthesized through the washing of an organic layer containing the polyaniline salt with water in emulsion polymerization. X‐ray diffraction spectra of polyaniline salts prepared by the three different methods showed an ordered, layer‐type supramolecular structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of polyaniline derivative and silver nanoparticle composites

BACKGROUND: There has been a recent surge of interest in the synthesis and applications of electroactive polymers with incorporated metal nanoparticles. These hybrid systems are expected to display synergistic properties between the conjugated polymers and the metal nanoparticles, making them potential candidates for applications in sensors and electronic devices. RESULTS: Composites of polyaniline derivatives—polyaniline, poly(2,5‐dimethoxyaniline) and poly(aniline‐2,5‐dimethoxyaniline)—and silver nanoparticles were prepared through simultaneous polymerization of aniline derivative and reduction of AgNO₃ in the presence of poly(styrene sulfonic acid) (PSS). We used AgNO₃ as one of the initial components (1) to form the silver nanoparticles and (2) as an oxidizing agent for initiation of the polymerization reaction. UV‐visible spectra of the synthesized nanocomposites reveal the synchronized formation of silver nanoparticles and polymer matrix. The morphology of the silver nanoparticles and degree of their dispersion in the nanocomposites were characterized by transmission electron microscopy. Thermogravimetric analysis and differential scanning calorimetry results indicate an enhancement of the thermal stability of the nanocomposites compared to the pure polymers. The electrical conductivity of the nanocomposites is in the range 10^?4 to 10^?2 S cm^?1. CONCLUSION: A single‐step process for the synthesis of silver nanoparticle–polyaniline derivative nanocomposites doped with PSS has been demonstrated. The approach in which silver nanoparticles are formed simultaneously during the polymerization process results in a good dispersion of the nanoparticles in the conductive polymer matrix. Copyright © 2008 Society of Chemical Industry     

The mechanism of the oxidative polymerization of aniline and the formation of supramolecular polyaniline structures

Polyaniline is one of the most important conducting and responsive polymers. A molecular mechanism for the oxidation of aniline is proposed. This mechanism explains the specific features of aniline oligomerization and polymerization in various acidity ranges. The formation of polyaniline precipitates, colloids and thin films is reviewed and discussed on the basis of the chemistry of aniline oxidation. The generation of nanostructures, i.e. granules, nanotubes, nanowires and microspheres, is also considered. Oligomers containing phenazine constitutional units play an important role in self‐assembly to form templates. Polyaniline chains then grow from these templates and produce the various individual morphologies. Copyright © 2008 Society of Chemical Industry     

Inverted emulsion polymerization route to polyaniline‐3D nanofiber network using sulfonated‐p‐cresol as novel dopant

Sulfonated‐p‐cresol (SPC) was used as novel dopant for the first time in the synthesis of polyaniline in 3D nanofiber networks (PANI‐3D). Polyaniline in 3D nanofiber network was prepared using organic solvent soluble benzoyl peroxide as oxidizing agent in presence of SPC and sodium lauryl sulfate (SLS) surfactant via inverted emulsion polymerization pathway. The influence of synthesis conditions such as the concentration of the reactants, stirring/static condition, and temperature etc., on the properties and formation of polyaniline nanofiber network were investigated. Polyaniline in 3D nanofiber network with 40–160 nm (diameter), high yield (134 wt % with respect to aniline used), and reasonably good conductivity (0.1 S/cm) was obtained in 24 h time. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Catalytic oxidization polymerization of aniline in an H2O2?Fe2+ system

Polyaniline is prepared by chemical polymerization of aniline in an acidic solution using H₂O₂ as an oxidant and ferrous chloride as a catalyst. A wide variety of synthesis parameters are studied, such as the amount of the catalyst, reaction temperature, reaction time, initial molar ratio of oxidant, monomer and catalyst, and aniline and HCl concentrations. The polymerization of aniline can be initiated by a very small amount of catalyst. The yield and the conductivity of product depend on the initial molar ratio of the oxidant and monomer. The polyaniline with a conductivity of about 10° S/cm and a yield of 60% is prepared under optimum conditions. The process of polymerization was studied by in situ ultraviolet–visible spectroscopy and open‐circuit potential technology. Compared to the polymerization process in a (NH₄)₂S₂O₈ system, the features of the H₂O₂ Fe²⁺ system are pointed out, and the chain growth mechanism is proposed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1077–1084, 1999     

Characterization and AC conductivity of polyaniline–montmorillonite nanocomposites synthesized by mechanical/chemical reaction

Polyaniline–clay nanocomposites were prepared by solid state polymerization of aniline chloride in the interlayer of montmorillonite through the use of persulfate of ammonium as oxidant. The proportion of aniline to clay and the molar ratio of oxidant to aniline are being varied. The analyse of UV visible and FTIR spectroscopy demonstrated that aniline has been polymerized to polyaniline (PANI) in its conducting emeraldine form. The conformation adopted by PANI chains in the clay interlayer depended on the molar ratio of aniline to montmorillonite. Thermogravimetric analysis of the nanocomposites suggested that polyaniline chains are more thermally stable than those of free polyaniline prepared by solid–solid reaction. The AC conductivity data of different synthesized nanocomposites were analyzed as a function of frequency. Low frequency conductivities of polyaniline/montmorillonite nanocomposites materials ranges from 0.18 to 5.6 × 10^?3 S/cm. All characterization data were compared to those of free polyaniline that was synthesized using a solid–solid reaction.     

Synthesis of a Graphite Oxide Polyaniline Nano‐Composite by an Electrochemical Method

In order to produce a polyaniline graphite oxide nano‐composite, electro‐polymerization of aniline was performed within the graphite oxide layers via electrochemical treatment of aniline‐intercalated graphite oxide in the supporting electrolyte. It was found that graphite oxide has special electro‐active properties. Therefore, electrochemical polymerization of aniline was performed on a Pt substrate in the presence of graphite oxide that had been dispersed in the electrolyte solution by the cyclic voltammetric method. Formation of polyaniline within the layers of graphite oxide occurred during electro‐polymerization. This mechanism affects the polyaniline morphology and leads to the formation of well‐defined concrete microstructures differing from the pure graphite oxide. Moreover, the results of the thermogravimetric analysis showed that graphite oxide and the polyaniline graphite oxide nano‐composite electrodeposited on the Pt substrate have different weight loss behaviors. This confirms that intercalation of the polyaniline improved the oxidation stability of graphite oxide, along with the fact that the polyaniline graphite oxide nano‐composite was successfully synthesized by an electrochemical method.     

Polyaniline‐supported acid catalyst: Esterification of cinnamic acid with alcohols

Polyaniline‐supported acid salts such as polyaniline‐hydrochloride, polyaniline‐sulfate, and polyaniline‐nitrate were prepared by oxidation of aniline using benzoyl peroxide and ammonium persulfate as oxidizing agents. Polyaniline salts were used as catalysts in the esterification of cinnamic acid with alcohols. Polyaniline‐sulfate salt was found to be the best catalyst for the esterification of cinnamic acid. The reusability, handling, and recovery of the catalyst were found to be good. The yield of the ester depended on the type of the polyaniline salt, amount of the catalyst, amount of alcohol, and both the time and the temperature of the reaction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1584–1590, 2005     

Electrochemical behaviors of polyaniline–poly(styrene‐sulfonic acid) complexes and related films

This research focuses on the syntheses of polyaniline with poly(styrenesulfonic acid) and their electrochemical behavior, including absorbance behavior and electrochemical response time of polyaniline‐poly(styrenesulfonic acid) [PANI–PSSA]. The complexes PANI–PSSA were prepared by electrochemical polymerization of monomer (aniline) with PSSA, using indium‐tin oxide (ITO) as working electrode in 1M HCl solution. Polyaniline (PANI), poly(o‐phenetidine)–poly(styrenesulfonic acid) [POP–PSSA], and poly(2‐ethylaniline)–poly(styrenesulfonic acid) [P2E‐PSSA] also were prepared by electrochemical polymerization and to be the reference samples. The products were characterized by IR, VIS, EPR, water solubility, elemental analysis, conductivity, SEM, and TEM. IR spectral studies shows that the structure of PANI–PSSA complexes is similar to that of polyaniline. EPR and visible spectra indicate the formation of polarons. The morphology of the blend were investigated by SEM and TEM, which indicate the conducting component and electrically conductive property of the polymer complexes. Elemental analysis results show that PANI–PSSA has a nitrogen to sulfur ratio (N/S) of 38%, lower than that for POP–PSSA (52%) and P2E–PSSA (41%). Conductivity of the complexes are around 10^?2 S/cm, solubility of PANI–PSSA in water is 3.1 g/L. The UV‐Vis. absorbance spectra of the hybrid organic/inorganic complementary electro‐chromic device (ECD), comprising a polyaniline–poly(styrenesulfonic acid) [PANI–PSSA] complexes and tungsten oxide (WO₃) thin film coupled in combination with a polymer electrolyte poly(2‐acrylamido‐2‐methyl‐propane‐sulfonic acid) [PAMPSA]. PANI–PSSA microstructure surface images have been studied by AFM. By applying a potential of ～3.0 V across the two external ITO contacts, we are able to modulate the light absorption also in the UV‐Vis region (200–900 nm) wavelength region. For example, the absorption changes from 1.20 to 0.6 at 720 nm. The complexes PANI–PSSA, POP–PSSA, and P2E–PSSA were prepared by electrochemical polymerization of monomer (aniline, o‐phenetidine, or 2‐ethylaniline) with poly(styrenesulfonic acid), using ITO as working electrode in 1M HCl solution, respectively. UV‐Vis spectra measurements shows the evidences for the dopped polyaniline system to be a highly electrochemical response time, recorded at the temperature 298 K, and the results were further analyzed on the basis of the color‐ discolor model, which is a typical of protontation systems. Under the reaction time (3 s) and monomer (aniline, o‐phenetidine, 2‐ethylaniline) concentration (0.6M) with PSSA (0.15M), the best electrochemical color and discolor time of the PANI–PSSA is slower than POP–PSSA complexes (125/125 ms; thickness, 3.00 μm) and P2E–PSSA complexes. Under the same thickness (10 μm), the best electrochemical color and discolor time of the PANI–PSSA complexes is 1500/750 ms, that is much slower than P2E–PSSA complexes (750/500 ms) and POP–PSSA complexes (500/250 ms). In film growing rate, the PANI–PSSA complexes (0.54 μm/s) are slower than P2E–PSSA complexes (0.79 μm/s) and POP–PSSA complexes (1.00 μm/s), it can be attributed to the substituted polyaniline that presence of electro‐donating (? OC₂H₅ or ? C₂H₅₎ group present in aniline monomer. The EPR spectra of the samples were recorded both at 298 K and 77 K, and were further analyzed on the basis of the polaron–bipolaron model. The narrower line‐width of the substituted polyaniline complexes arises due to polarons; i.e., it is proposed that charge transport take place through both polarons and bipolarons, compared to their salts can be attributed to the lower degree of structural disorder, the oxygen absorption on the polymeric molecular complexes, and due to presence of electro‐donating (? OC₂H₅ or ? C₂H₅) group present in aniline monomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4023–4044, 2006     

Interfacial polymerization of morphologically modified polyaniline: from hollow microspheres to nanowires

BACKGROUND: Polyaniline (PANI) has attracted much attention in many fields due to its chemical and physical properties, and different nanostructures of PANI changing from one‐dimensional to three‐dimensional have been obtained. By changing the concentration of cetyltrimethylammonium bromide (CTAB), the morphology of hydrochloric acid‐doped polyaniline could be changed from one‐dimensional nanoneedles or nanowires with a network structure (50–100 nm in diameter) to three‐dimensional hollow microspheres (ca 400 nm in outer diameter) via combining interfacial polymerization and self‐assembly process. RESULTS These different nanostructures of PANI were proved using scanning electron and transmission electron microscopies. A plausible mechanism of the formation of the changeable nanostructures of PANI may be different from that of interfacial polymerization without surfactant or a traditional homogenous reaction system using CTAB as surfactant. CONCLUSION The results obtained from Fourier transform infrared spectrometry, X‐ray diffraction and the four‐probe method showed that the molecular structure of PANI does not change with increasing CTAB concentration, but crystallinity and conductivity of PANI increase with surfactant concentration. Copyright © 2007 Society of Chemical Industry     

Preparation of Polyaniline/Mesoporous Silica Hybrid and Its Electrochemical Properties

Polyaniline/mesoporous silica hybrids were prepared by chemical modification with aniline and their capacitances were examined for application to electrode of electrochemical capacitor. The chemical modification was performed by two kinds of processes, polymer insertion into pores and in-situ polymerization within pores. In the case of the polymer insertion process, since the mean pore sizes of the hybrid did not change, polyaniline molecules were not inserted. On the other hand, in the case of the in-situ polymerization process, the mean pore sizes decreased from that of mesoporous silica, while the XRD patterns became broad. Therefore, aniline molecules polymerized in the inside of pores, however, the mesoporous silica collapsed in part. Maximum capacitance measured in 1 mol/l H₂SO₄ aqueous solution was around 226 F per unit mass of polyaniline.     

Rapid polymerization initiated by redox initiator for the synthesis of polyaniline nanofibers

High quality polyaniline nanofibers have been synthesized by a rapid polymerization of aniline using ammonium peroxydisulfate (APS)/Fe²⁺ redox initiator as the oxidant without any hard or soft templates. The addition of Fe²⁺ in conventional polymerization system plays an important role in changing the bulk morphologies of polyaniline from irregular particle agglomerates to nanofibers. Open-circuit potential measurements indicate that the rate of polymerization of aniline with the aid of Fe²⁺ ions has a substantial increase. The influences of synthetic parameters, such as the concentrations of aniline, dopant, and redox initiator, and reaction time, on the sizes and morphologies of polyaniline nanostructures have been investigated for elucidating the formation of polyaniline nanofibers. Fourier transform infrared spectrum, UV-vis spectrum, and cyclic voltammograms reveal that the molecular structures and electrochemical properties of polyaniline nanofibers do not differ significantly from that of conventional polyaniline.     

Nanostructures of oligoaniline and polyaniline and their properties

A conductive polymer, polyaniline, has been synthesized in the form of nanoparticles of different morphology: globules with a size of 100 nm, nanotubes with an outer diameter of 200 nm and a wall thickness of 50 nm, microspheres with a diameter of 2 μm, and hierarchical structures consisting of fibers with a diameter of 10 nm. All types of nanostructures have been prepared by single-stage oxidation of aniline under different synthesis conditions. The properties of nanostructures of polyaniline and the possibilities of their practical application have been discussed.     

Bioinspired synthesis of novel teeth‐like hierarchical architecture polyaniline/lead tungstate nanocomposites with photoluminescence property

Large‐scale one‐step synthesis of novel teeth‐like hierarchical architecture polyaniline (PANI)/lead tungstate (PbWO4) nanocomposites has been achieved from aqueous solution by in situ polymerization at room temperature. The reaction conditions, such as pH value and the molar ratio, are found to play a crucial role in controlling the size and morphology of the products. The model of “nucleation‐growth‐assembly” is proposed to explain formation mechanism of the teeth‐like PANI/PbWO₄ nanocomposites. Interestingly, the larger size and higher crystallinity are beneficial to the improvement of photoluminescence (PL) intensity. POLYM. COMPOS., 35:516–522, 2014. © 2013 Society of Plastics Engineers     

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte. The mechanochemical oxidation polymerization was believed to be related to the strong Lewis acid characteristic of FeCl₃ and the Lewis base characteristic of aniline. The growth mechanism of the hierarchical structured nanofibers was also discussed. After functionalization with the nanostructured polyaniline, the hybrid polyaniline/CNF composite showed an enhanced specific capacitance, which might be related to its hierarchical nanostructure and the interaction between the aromatic polyaniline molecules and the CNFs.     

Conducting IPN Based on Polyaniline and Crosslinked Cellulose

Polyaniline/crosslinked cellulose conductive interpenetrating polymer networks (IPNs) were prepared by oxidative polymerization of aniline within the self-synthesized cellulose network using ammonium persulphate as oxidant. The conductivity of the IPN increases and then decreases with decrease in the aniline/(NH₄)₂S₂O₈ ratio, with increase in the HCl/aniline ratio, with increase in aniline content, as well as with increase in reaction time. In addition, the conductivity of the films strongly depends on the amount of tetraethyl orthosilicate crosslinker. In comparison with polyaniline/cellulose acetate composites, the conductivity increases by an order of one to two magnitudes in spite of the lower polyaniline content in this work. © of SCI.     

A comparative study of water dispersible polyaniline nanocomposites prepared by laccase‐catalyzed and chemical methods

A comparative study of chemical and enzymatic methods of aniline polymerization was carried out. Fungal laccase from Trametes hirsuta was used in the synthesis of polyaniline nanoparticles made with poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) (PAMPS). Template polymerization of aniline was carried out in aqueous buffer. It was shown that the laccase had high long‐term and operating stabilities under acidic condition favorable for synthesis of conducting polyaniline. UV‐vis, FTIR spectroscopy, and cyclic voltammetry analysis are used for the characterization of the polyelectrolyte complexes of polyaniline and PAMPS. The incorporation of the polymeric acid in polyaniline has been demonstrated by atomic force microscopy. The size and morphology of the nanoparticles of the polyaniline–PAMPS complexes depended on the method of the synthesis. A comparison of some physical and chemical properties of water dispersible conducting polyaniline–PAMPS was performed under production by enzymatic and chemical methods. It was found a difference in structures and some physicochemical properties of polyaniline colloids prepared by chemical and laccase‐catalyzed methods. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010