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The present paper reports an approach to develop self-supported lightweight thin sheets of polyaniline-carbon fiber (PANi-CF) composite by compression molding using phenolic novolac resin as a binder, for their use in electromagnetic interference (EMI) shielding.
The Polymeric and soft materials section is dedicated to research in fundamental and applied science of polymers, soft materials and polymer based nanocomposites. XRD studies incorporation of amino group in the GO matrix which has also been confirmed by FTIR studies.
GO functionalized amino group polymerized alongwith aniline monomer moiety shows excellent shielding behavior and more studies are being carried out. Tafel polarization behaviour of mild steel in 3.5 % NaCl solution with uncoated, epoxy coated, PANI and HPSC coated mild steel have also been carried out.
Impedimetricimmunosensor for cardiac biomarkers Timely and effective treatment of patients arriving in the emergency department with chest pain requires a prompt and reliable diagnosis.
Similarly, structural and ac impedimetric properties of a biofunctionalized conducting copolymer poly(pyrrole-co-pyrrolepropylic acid) (PPy-PPa) film electrochemically grown onto an indium-tin-oxide (ITO) coated glass plate studies havealso been measured. Polyaniline (PANI)-tetragonal BaTiO3 (TBT) nanocomposites have been prepared by in-situ emulsion polymerization (Figure 1). Figure 1 (a) Schematic representation showing the formation of PANI-BaTiO3 NCs by in-situ polymerization. Beside, these composites also give (Figure 2) shielding effectiveness of -23.3 dB (>99% attenuation). Recently, an initiative has been taken towards the designing and development of efficient EMI shielding and supercapacitor electrode materials based on graphene and its nanocomposites.
Science, Technology and Medicine open access publisher.Publish, read and share novel research. The high loading CPND approach shows promise not only for corrosion-resistance, but also as a technology readily incorporated in a wide variety of coating types. Electroactive polymers or EAPs, are polymers that can change size or shape when stimulated by an external electrical activation mechanism. The global electroactive market is projected to reach USD 4.4 Billion by 2020, signifying firm annualized growth of 7% between 2015 and 2020. North America is the biggest market for EAPs, registering a significant share of 63.9% of the global market in 2014. With respect to the type of EAP used, conductive plastics dominated the global electroactive market by enjoying a share of 80.7% of the overall market in 2014.
This study aims to estimate the market of EAPs in 2015, in terms of volume and value, and further project its demand by 2020. This research report categorizes the market for electroactive polymers on the basis of types, applications, and region. On the basis of type: The global electroactive polymers market is segmented on the basis of types, namely, conductive plastics, inherently conductive polymers, inherently dissipative polymers, ferroelectrets, and dielectric elastomers. On the basis of application: The global electroactive polymers market is segmented on the basis of applications, such as organic light emitting diodes, capacitors, batteries, sensors, actuators, electromagnetic interference (EMI) shielding, electrostatic discharge (ESD) protection, antistatic packaging, electrostatic coatings, and other applications. On the basis of region: The global electroactive polymers market is segmented by region into Asia-Pacific, North America, Europe, and RoW.
Electroactive Polymers (EAPs) change their sizes and shapes when an electric charge or voltage is applied across them.
North America is the global leader in the consumption of electroactive polymers and its dominance is expected to continue till 2020. Conductive plastics is the major type of electroactive polymers with high strength and improved electrical properties. This study estimates the market size, in terms of value for electroactive polymers and projects the same by 2020. PANi-CF composites were synthesized by in-situ chemical oxidative emulsion polymerization of aniline along with carbon fiber, using dodecyl hydrogen sulfate (DHS) as surfactant as well as dopant. IntroductionElectromagnetic radiations are one of the deplorable byproducts of the accelerated growth in the field of electronics and telecommunication, aircraft technology, navigation, wireless systems [1-3]. It is interesting to note that, in PGF composites, the contribution to SE values mainly comes from the absorption rather than refection, as observed in metals. The studies revealed that novel designed polyaniline embedded with epoxy shows excellent corrosion preventive behavior even at a loading of 6 % when exposed to salt spray tests for 35 days under accelerated conditions. The use of cardiac biomarkers continues to play a major role in the diagnosis and management of patients suspected of having myocardial damage.We synthesized ZnS(MPA) nanocrystals and their covalent attachment to self assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APTES) on an indium-tin-oxide (ITO) coated glass plate. The Nyquist plots of impedance spectra for different concentration of antigen, Ag-Mb, solution at the bioelectrode is shown in Fig.
XRD studies and HRTEM micrographs of these nanocomposites revealed the incorporation of TBT nanoparticles in the conducting PANI matrix.
A) Mechanical exfoliation of graphene using scotch tape from HOPG (B) Schematic illustration of the graphene exfoliation process. Pictorial representation for the formation of polyaniline nanocomposite by chemical oxidative polymerization5.4. Dhawan1[1] Polymeric & Soft Material Section, National Physical Laboratory (CSIR), New Delhi –110 012, India[2] Department of Physics, Maharshi Dayanand University Rohtak – 124001, India1.
The mechanism of exfoliation is mainly the sudden expansion of CO or CO2 gases evolved into the spaces between graphene sheets during rapid heating of the graphite oxide. Most of the work is done on PANI as it has good environmental stability, reversible redox activity, and potential applications in sensing, energy conversion and storages and electromagnetic shielding application [109,110-111,115].
The skin depth ? can be expressed as:The absorption loss of one skin depth in a shield is approximately 9 dB.
The major application of EAPs which are showing continuous growth are antistatic and electronic applications. Inherently conductive polymers are the second major type of EAPs used for the manufacturing of organic light emitting diodes (OLEDs). This market research study provides a detailed qualitative and quantitative analysis of the global electroactive polymers market. It also presents a forecast of market growth, while analyzing trends in each of the submarkets. The electroactive polymers market for each type is further described in detail in the report with value forecasts.
Each application is further described in detail in the report with value forecasts for the mentioned period. As a part of quantitative analysis, the study segments the market by type, application, and by region. Polyaniline-carbon fiber-novolac (PCN) sheets having thickness of ~0.6 mm were then prepared by hot pressing and thermal annealing, using different amount of novolac resin in order to optimize the thermal, mechanical, electrical and shielding properties. The rapid proliferation of electronic devices has increased the vulnerability to electromagnetic interference (EMI).
Transmission and scanning electron microscopy observations confirm the presence of nano particles of ?- Fe2O3 (~9.8 nm) and carbon fiber (~1 mm) which gives flexural strength to the RGO sandwich. PGF composites have shown excellent frequency stability in the measured frequency range, which was found to increase with increasing GF content (Fig. The inset illustrates the variation of microwave conductivity and skin depth with frequency. EPR and XPS measurements reveal that increase in loading level of BaTiO3 results in reduction of doping level of PANI.
The initial work in the above direction has yielded encouraging response and the further studies are underway. Introduction Carbon the 6th element in the periodic tables has always remains a fascinating material to the researcher and technologist. However, this technique is not so promising as it leads to the structural damage to graphene sheets caused by the release of carbon dioxide [85].
Skin effect is especially important at low frequencies, where the fields experienced are more likely to be predominantly magnetic with lower wave impedance than 377 ?.
EAP materials have high energy density, rapid response time, customizability (shape and performance characteristics), easy controllability, low power consumption, high force output, deflections, combined sensing & actuation functions, and uses relatively low cost raw materials. Among all the EAP applications, the actuator segment is witnessing high R&D activity whereas medical devices and robotics are expected to be the largest applications for EAP actuators. It also provides a comprehensive review of drivers, restraints, and opportunities in this market. Electronic EAPs are generally driven by electric field whereas ionic EAPs are primarily driven by diffusion of ions.
Conductive plastics are the most preferred electroactive polymers that are used in the major applications, namely, protection against electrostatic discharge, LED lamps, and electromagnetic interference (EMI) shielding, among others. EMI consists of any unwanted disturbance that effect a circuit due to many superfluous radiated signals emitted from an external source carrying transient currents [4, 5]. Thermogravimetric analysis show that the thermal stability of the RGO sandwich depends upon the amount of RGO and phenol resin in the sandwich. An increase in the diameter of Nyquist circle was observed with increasing concentration of added antigen, Ag-Mb, indicating an antibody–antigen interaction, at the electrode surface.The impedance modulus bode plot of the bioelectrode (Fig.
We welcome the interested groups, academic organization and related industries for possible collaboration in the above areas. Horn-ultrasonication exfoliates few-layer graphene flakes that are encapsulated by sodium cholate micelles. Diamond, graphite, fullerenes, carbon nanotubes and newly discovered graphene are the most studied allotropes of the carbon family.
Approximately 30% of the mass of the graphite oxide is lost during the exfoliation process, leaving behind lattice defects throughout the sheet [83].
After the reduction of GO with hydrazine, the corresponding composites with CCG can be obtained.
From the absorption loss point of view, a good material for a shield will have high conductivity and high permeability along with a sufficient thickness to achieve the required number of skin depths at the lowest frequency of concern. Some of the major types of EAPs are conductive plastics, inherently conductive polymers, inherently dissipative polymers, ferroelectrets, and dielectric elastomers. Other important EAPs used are inherently dissipative polymers, ferroelectrets, and dielectric elastomers. Secondary sources referred include company websites, encyclopedia, directories, and databases to identify and collect information useful for this extensive study of electroactive polymers.
The segmentation by type includes Conductive Plastics, Inherently Conductive Polymers, Inherently Dissipative Polymers, Ferroelectrets, and Dielectric Elastomers. Dhawan, Self-Supported Lightweight Polyaniline Thin Sheets for Electromagnetic Interference Shielding with Improved Thermal and Mechanical Properties, American Journal of Polymer Science, Vol. The source of the emitted radiation may have frequency ranging from the lower power frequencies to the microwave region. 1b) demonstrates three distinct regions corresponding to the three types of elements in the equivalent circuit.
These results were further supported by highest microwave conductivity and lowest skin depth value for PDB. The key point to note here is that, the polymerization must be carried out in an acidic medium (pH ~ 1) for producing high-quality PANI. The primary sources such as experts from related industry, were interviewed to verify and collect critical information, as well as assess the future prospects of the global electroactive polymers market.
In terms of application, the electroactive polymers market is segmented into Organic Light Emitting Diodes, Capacitors, Batteries, Sensors, Actuators, Electromagnetic Interference (EMI) Shielding, Electrostatic Discharge (ESD) Protection, Antistatic Packaging, Electrostatic Coatings, and Other applications.
So this work develops a methodology to fabricate lightweight self-supported conducting PCN sheets having good thermal, mechanical and electrical behavior and can be used to design shields of electronic equipments for protection of electromagnetic interference. The disturbances created by EMI may interrupt, obstruct or otherwise can cause unacceptable degradation of system or equipment performance in terms of partial or total loss of data. After the flood of publications on graphite intercalated [1], fullerenes (1985) [2], and carbon nanotubes (1991) [3], graphene have been the subject of countless publications since 2004 [4,5].
An alternative way is to exfoliate graphite oxide in the liquid phase, which enables the exfoliation of graphene sheets with large lateral sizes [86]. Increase in the consumption of electroactive polymers has been observed in the Asia-Pacific region due to rapid industrialization and subsequent growth of the electronics, medical, and automotive sector. By region, the report segments the market into North America, Asia-Pacific, Europe, and Rest of the world (RoW). The compatibility of an equipment function in close proximity of other equipment is called as electromagnetic compatibility (EMC).
The maximum shielding effectiveness observed is 45.26 dB, which strongly depends on dielectric loss and volume fraction of ?- Fe2O3 in RGO matrix. Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, completely conjugated sp2 hybridized planar structure and is a basic building block for graphitic materials of all other dimensionalities (Figure 1). Further as a part of qualitative analysis, the research study provides a comprehensive review of the major market drivers, restraints, opportunities, challenges, and key issues in the market. These twin problems of EMI and EMC must be attended, otherwise, that can cause severe damage to communication system and safety operation of many devices.
A graphene oxide-polypyrrole composite was also prepared by in situ polymerization in water in the presence of a surfactant [116-120] although graphene oxide was not converted to CCG, the composite exhibited a higher electrical conductivity than pure PPy. In fact, EMI shielding represents a way towards the enhancement of the electromagnetic compatibility. In 2004, Geim and co-workers at Manchester University successfully identi?ed single layers of graphene in a simple tabletop experiment and added a revolutionary discovery in the ?eld of nano science and nanotechnology.
Graphene has a tendency of aggregation and shows poor solubility, is the dominant factor for limiting the application of this technique.
Now shielding of EMI is getting increasing attention in digital electronics and communication systems because of devices becoming increasingly sensitive, dense and ample. In this case, special care should be taken to avoid the precipitation of CCG, especially when oxidant was added. In addition, EMI shielding is of critical use due to the health concerns, such as symptoms of languidness, insomnia, nervousness, headache etc. One of the most remarkable properties of graphene is that its charge carriers behave as massless relativistic particles or Dirac fermions, and under ambient conditions they can move with little scattering. In addition to annealing temperature, annealing atmosphere is important for the thermal annealing reduction of GO. Since the etching of oxygen will be dramatically increased at high temperatures, oxygen gas should be excluded during annealing.
Corrosion is another major drawback of metallic materials which reduces the SE of the shields, especially in joints [8]. First, graphene is a zero-band gap 2D semiconductor with a tiny overlap between valence and conduction bands.
Another approach to overcome the problems of weight and corrosion, came to existence is the use of various types of conducting composites comprising a non-conducting polymer matrix and conducting fillers such as metal particulates, metal fillers, carbon black and carbon fibers (CF).
Second, it exhibits a strong ambipolar electric field effect so that the charge carrier concentrations of up to 1013 cm-2 and room-temperature mobility of ?10000 cm-2s-1 are measured.
Chemical reductionChemical reduction has been evaluated as one of the most efficient methods for low-cost, large-scale production of Graphene. However, the solubility or dispersibility of CPs can be improved by chemical modifications or fabricating them into nanostructures.


The major advantages of the polymer composites are their low fabrication cost and high strength to weight ratio. Third, an unusual half-integer quantum Hall effect (QHE) for both electron and hole carriers in graphene has been observed by adjusting the chemical potential using the electric field effect [5,6].
Another advantage of chemical reduction methods is that the produced GNS in the form of a monolayer can be conveniently deposited on any substrate with simple processing. But these conventional polymer composites could not offer desired value of SE, especially in microwave range.
It has high thermal conductivity with a value of ? 5000 WmK?1 for a single-layer sheet at room temperature.
The chemical reduction method involves graphite oxidation by a strong oxidant to create graphene oxide, which is subsequently reduced by reducing agents [90-94] thermal [94], solvo-thermal [95-98], or electrochemical [99] methods to produce chemically modi?ed graphene.
The strong ? –? interaction between the CPE chains and the basal planes of CCG sheets enables the composites to form stable dispersions. CF and metal filled polyethylene composites are reported to have poor performance of EMI shielding [9].
In addition, graphene is highly transparent, with absorption of ? 2.3% towards visible light [7, 8]. Among these reduction processes, hydrazine reduction and solvo-thermal reduction can create process able colloidal dispersions of reduced graphene oxide, which may be used in a wide range of applications. Narrow ribbons of graphene with a thickness of 1-2 nm are, however, semiconductors with a distinct band gap, and these can be used to produce transistors [9-11].
Chemical reduction using hydrazine is one of the most effective methods for converting graphene oxide to chemically converted graphene (CCG).
Now a days intrinsically conducting polymers (ICPs) and their composites along with their wide spread applications in organic light emitting diodes [11], polymer solar cells [12], antistatic coatings [13], and electrochromic devices[14] are also finding their application as shielding materials for electromagnetic radiations in low as well as high frequency range [2, 14, 15]. Figure 1.Different allotropes of carbon viz Graphite, Diamond, Fullerene, and Carbon nanotube In last couples of years, graphene has been used as alternative carbon-based nano?ller in the preparation of polymer nanocomposites and have shown improved mechanical, thermal, and electrical properties [12-19].
Chung at al [100] has report a simple and effective method for reducing and functionalizing graphene oxide into chemically converted graphene by solvo-thermal reduction of a graphene oxide suspension in N-methyl-2-pyrrolidone (NMP). A lot of work has been reported based on the preparation and shielding properties of ICPs, their blends and composites. The recent advances have shown that it can replace brittle and chemically unstable indium tin oxide in ?exible displays and touch screens [20-21].
NMP is a powerful solvent for dispersing SWCNT and graphene and high boiling point (~202 ?C) of NMP facilitates the use of NMP as a solvent for solvo-thermal reduction in open systems.
Covalent Grafting of polyaniline on graphene sheetRecently Kumar et al [126] has reported the covalent functionalization of amine-protected 4-aminophenol to acylated graphene oxide and simultaneously reduced and in-situ polymerized in the presence of aniline monomer and produces a highly conducting networks. It is well established that the superior properties of graphene are associated with its single-layer. In this the oxygen containing functional groups on the surface of graphene oxide make it easily dispersible in aqueous solution and act as nucleation sites for producing PANI on its surfaces. These composites of conducting polymer have prolonged their sphere and currently finding their application in EMI shielding technology [2, 14, 15]. The fabrication of PANI-grafted RGO (PANI-g-RGO was carried out in three steps as shown in Figure 5.First the GO was synthesized by modified Hummers method and acylated in the presence of excess SOCl2 and then reacted with amine-protected 4-aminophenol. ICPs are becoming increasingly available, but they are not common and tend to be poor in their processability, fabrication and mechanical properties. If the sheets are not well separated from each other than graphene sheets with a high surface area tend to form irreversible agglomerates and restacks to form graphite through p–p stacking and Vander Waals interactions [22,23]. Futher, deprotection of N-(tert-butoxycarbonyl) groups by hydrolysis with trifluoroacetic acid. Although, ICPs may be used with or without filler for providing shielding for commercial application, yet, in the presence of conductive filler, an electrically conducting polymer matrix has the added advantage of being able to electrically connect the filler units that do not touch one another, thereby enhancing the connectivity and so improve the conductivity. Aggregation can be reduced by the attachment of other small molecules or polymers to the graphene sheets. However, the electrical conductivity of free-standing paper of graphene prepared by ?ltration was very low i.e. PANI-g-RGO was prepared from in-situ oxidative polymerization of aniline in the presence of an oxidant and amine-terminated RGO (RGO-NH2) as an initiator. In order for a conductive filler to be highly effective, it preferably should have a small unit size, a high conductivity (for shielding by reflection) and a high aspect ratio (for connectivity). The presence of hydrophilic or hydrophobic groups prevents aggregation of graphene sheets by strong polar-polar interactions or by their bulky size [24].
The attachment of functional groups to graphene also aids in dispersion in a hydrophilic or hydrophobic media, as well as in the organic polymer. Therefore, an ef?cient approach to the production of surface-functionalized graphene sheets in large quantities has been a major focus of many researchers. Instead of reducing the graphene oxide using hydrazine at high temperature (80–100 ?C) excess amounts of hydrazine were used. Polyaniline exists in four different forms namely leucoemeraldine, pernigraniline, emeraldine and conductive emeraldine salt. Methods of Graphene Synthesis There have been continuous efforts to develop high quality graphene in large quantities for both research purposes and with a view to possible applications. The methods of preparation for graphene can be divided into two categories, top-down and bottom-up ones. The key to achieve highly dispersed RGO is performing the hydrazine reduction of graphene oxide at low temperature, which minimizes the formation of irreversible RGO aggregates [102].
This shows that oxidant play an important role in controlling the structure and electrical properties which can be tailored according to the application. Notably, the electrical conductivity of the hydrazine reduced graphene (HRGs) was sharply and inversely proportional to the dispersibility in DMF.
The use of strong oxidizing agent like ammonium peroxydisulfate (APS) and potassium dichromate resulted in high yield, conductivity and viscosity of polyaniline [23]. While the bottom-up methods include (1) epitaxial growth on SiC and other substrates, (2) Chemical vapor deposition, and (3) arc discharging methods. Conducting Polymer-graphene composite Nanocomposites have been investigated since 1950, but industrial importance of the nanocomposites came nearly forty years later following a report from researchers at Toyota Motor Corporation that demonstrated large mechanical property enhancement using montmorillonite as filler in a Nylon-6 matrix and new applications of polymers. Anionic surfactants may act as counter ions for conducting-polymer polycations, and the hydrophobic part of the surfactant molecules may adsorb on the produced conducting polymer, a surfactant thus becoming a part of the resulting material. A nanocomposite is defined as a material with more than one solid phase, metal ceramic, or polymer, compositionally or structurally where at least one dimension falls in the nanometers range. The presence of surfactants improves the colloidal solubility of conducting polymers in organic solvents [26] and, consequently, also the processability [27].
Most of the composite materials are composed of just two phases; one is termed the matrix, which is continuous and surrounds the other phase, often called the dispersed phase and their properties are a function of properties of the constituent phases, their relative amounts, and the geometry of the dispersed phase. It had been reported in the literature that the introduction of a surfactant during the preparation of ICP leads to an increase in the conductivity also [14, 15, 25]. The combination of the nanomaterial with polymer is very attractive not only to reinforce polymer but also to introduce new electronic properties based on the morphological modification or electronic interaction between the two components. Various types of composites consisted of such anionic surfactant doped PANi have been widely developed and used for various applications. Depending on the nature of the components used and the method of preparation, significant differences in composite properties may be obtained. Mechanical exfoliationThe “perfect” graphene, necessary for the fundamental studies can be obtained by the mechanical exfoliation and epitaxial methods, but these methods have a limit for scale up. Nanocomposites of conducting polymers have been prepared by various methods such as colloidal dispersions, electrochemical encapsulation coating of inorganic polymers, and insitu polymerization with nanoparticles and have opened new avenues for material synthesis [103-105].
Mechanical exfoliation is a simple peeling process where a dried highly oriented pyrolytic graphite (HOPG) sheet are etched in oxygen plasma and then it is stuck onto a photo resist and peeled off layers by a scotch tape (Figure 2a).
Moreover, little work has been reported for the fabrication of PANi composites in the form of thin sheets. The thin flakes left on the photo resist were washed off in acetone and transferred to a silicon wafer.
For example, In case of electromagnetic interference shielding application, the combination of magnetic nanoparticles with conducting polymer leads to form a ferromagnetic conducting polymer composite possessing unique combination of both electrical and magnetic properties.
In the present work PANi-CF composites were synthesized by in-situ emulsion polymerization using acidified sodium dodecyl sulphate (DHS) as surfactant as well as dopant and much attention has been paid to make self-supported resin based thin sheets (~0.6 mm thickness) of PANi-CF composite by thermal annealing during compression moulding technique using different amount of phenolic novolac resin as a binder. This type of materials can effectively shield electromagnetic waves generated from an electric source. The composite sheets have shown good mechanical strength and thermal stability with sufficient SE values for their potential use in microwave shielding.2. Chemical exfoliation and intercalation of small molecules: The first graphite intercalation compound (GIC), commonly known as expandable graphite was prepared by Schafhautl in 1841, while analyzing crystal flake of graphite in sulfuric acid solution.
When conducting polymers are combined with carbons material like CNT graphite and graphene they show good thermal and electrical properties as electronic conduction occurs at long range. The intercalation of graphite by atoms or molecules such as alkali metals or mineral acids increases its interlayer spacing, weakening the interlayer interactions and facilitating the exfoliation of GIC by mechanical or thermal methods (Figure 2b& 2c) [25]. In last couples of years, a variety of processing routes have been reported for dispersing the graphene based and it derivative as fillers in the polymer matrices. The intercalation of graphite by a mixture of sulfuric and nitric acid produces a higher-stage GIC that can be exfoliated by rapid heating or microwave treatment of the dried down powder, producing a material commonly referred to as expanded graphite [26].
Many of these procedures are similar to those used for other nanocomposite systems but some are different and unique and have enhanced the bonding interaction at the interface between the filler and matrix significantly. Reagent-grade sodium dodecyl sulphate (SDS, Himedia, India), ammonium peroxydisulfate (APS, Merck, India) and hydrochloric acid (Merck, India) were used as received. It retained a layered structure but has slightly increased interlayer spacing relative to graphite and has been investigated as a composite ?ller [27-28]. Most of the dispersion methods produce composites by non-covalent assemblies where the polymer matrix and the filler interact through relatively weak dispersive forces.
Polyacrylonitrile based carbon fibers (Toray-T-300-Japan) were chopped to get fiber size of 5-6 mm prior to use. However its effectiveness in enhancing the properties as compared to graphene oxide (GO) derived fliers is limited by its layered structure and relatively low speci?c surface area. However, there is a growing research focus on introducing covalent linkages between graphene-based filler and the supporting polymer to promote stronger interfacial bonding.
To produce a higher surface area material, expanded graphite can be further exfoliated by various techniques to yield graphene nanoplates (GNPs) down to 5 nm thickness[29-30]. It is well known that most of the ?-conjugated conducting polymers (CPs) are quite different from classical insulating polymers. In-situ synthesis of PANi-CF CompositeSynthesis of PANi-CF composite has been carried out by In-situ chemical oxidative emulsion polymerization. It has also been reported that sulfuric acid intercalated expanded graphite can be co-intercalated with tetrabutyl ammonium hydroxide. They have conjugated backbones, which provide them with unique electrical and optical properties.
A monolayer like graphene can be obtained by sonicating the GIC in N,N-dimethylformamide (DMF) in the presence of a surfactant like poly(ethylene glycol)-modified phospholipid. These polymers are conductive in their doped states while insulating in their neutral states. To convert SDS to DHS, 0.1 M HCL is added to this aqueous solution of SDS until pH was maintained at 2-3.
Furthermore they are usually brittle, weak in mechanical strengths and usually insoluble, intractable and decompose before melting, having poor processability [104]. Such approach utilizes the similar surface energy of N-methyl-pyrrolidone and graphene that facilitates the exfoliation.
The incorporation of CCG into conducting polymer is attractive for combining the properties of both components or improving the properties of resulting composites based on synergy effects.
Appropriate amount of aniline (0.1M) was added to the above solution and homogenized again for 1 h to form micelles (emulsion) of aniline-CF with DHS. However, the disadvantage of this process is the high cost of the solvent and the high boiling point of the solvent that makes the graphene deposition difficult. The major forerunner of conducting polymer family are polyaniline (PANI), polypyrrole (PPy), polythiophene and poly(3,4-ethylenedioxythiophene) PEDOT and most of the research work has been done on them, polyaniline [105,106-111], PPy [112], poly(3-hexylthiophene) (P3HT) [113], PEDOT [1114] have been hybridized with CCG to form composites.
The emulsion so formed was transferred to two walled stainless steel reactor and polymerized at -3? through chemical oxidative polymerization by drop wise addition of 0.1M APS and continuous stirring. Lotya and coworkers have used a surfactant (sodium dodecyl benzene sulfonate, SDBS) to exfoliate graphite in water to produce graphene. The graphene monolayers are stabilized against aggregation by a relatively large potential barrier caused by the Coulomb repulsion between surfactant-coated sheets. The polymer composite so formed was filtered by means of buchner funnel of G-4 specification and washed repeatedly with distilled water to remove any amount of interior left out & then dried at 60-70?. The dispersions are reasonably stable with larger flakes precipitating out over more than 6 weeks [33]. In this composite PANi act as a conducting matrix and CF act as a reinforcement or filler material to improve mechanical as well as electrical properties. The CVD processes generally utilize transition metal surfaces for growth of Graphene nanosheets (GNS) using hydrocarbon gases as GNS precursors at the deposition temperature of about 1000 ?C. By the similar route pristine PANi doped with DHS was also synthesized for comparative study.
Preparation of Self-Supported Thin Sheets of PANi-CF CompositeSelf-supported free standing thin sheets of PANi-CF composite were prepared by compression moulding using novolac as a binder.
As obtained films are predominantly single-layer GNS with a small percentage (less than 5%) of the area having few layers, and continuous across copper surface steps and grain boundaries. For this, first PANi-CF composite powder was mixed and grinded with novolac powder for 2 h using Retsch “PM-400” planetary-ball mill in tungsten carbide jars.
Further to increase the homogeneity of this mixture, it was dispersed in ethanol (10% by wt. Recently, Bae and coworkers reported a roll-to-roll production of 30 inch (Figure 3) graphene films using the CVD approach [41]. After that the solvent, ethanol was evaporated at 50? and the sample was then dried at 70?. It is a very promising method for the synthesis of uniform, wafer-size graphene nano layers, in which single crystal SiC substrates are heated in vacuum to high temperatures in the range of 1200–1600 ?C.
Thin sheets of PANi-CF composite were prepared by compression moulding at 100? temperature and contact pressure which results in crosslinking of novolac resin in the polymer matrix and excess of resin squeezed out after doing its action.
Since the sublimation rate of silicon is higher than that of carbon, excess carbon is left behind on the surface, which rearranges to form GNS[42-44] More recently Bao et al has reported an interesting route for the preparation of GNS that employed commercial polycrystalline SiC granules instead of single-crystal SiC [45] to formulate high-quality freestanding single-layer GNS. After getting the post curing temperature of 150? for 2 h, PCN sheets having thickness ~0.6 mm were then ejected out from the mould upon cooling up to room temperature. Chemically converted Graphene At present, the most viable method to afford graphene single sheets in considerable quantities is chemical conversion of graphite to graphene oxide followed by successive reduction [46-48]. Further loading of Phenolic novolac resin have been avoided because the conductivity and SE start lessening. Materials CharacterizationThe morphology of PCN composites were examined by scanning electron microscope (SEM, Zeiss EVO MA-10).


UV-vis absorption studies were carried out on Shimadzu 1601 Spectrophotometer in the wavelength range of 200-1100 nm (see supporting information).
Synthesis of graphene oxide and its reductionIn 1859, Brodie was first to prepared graphite oxide by the oxidation of graphite with fuming nitric acid and potassium chlorate under cooling [49], In 1898, Staudenmaier improved this protocol by using concentrated sulfuric acid as well as fuming nitric acid and adding the chlorate in multiple aliquots over the course of the reaction. Fourier transform infrared (FTIR) spectras were recorded on Nicolet 5700 in the wavenumber range of 4000-500 cm-1. This small change in the procedure made the production of highly oxidized GO in a single reaction vessel [50]. The specimens having length (l) = 70 mm, width (b) = 20 mm and thickness (t) ~ 0.6 mm were taken to measure this three-point test. In this test the failure occur at the center of the specimen span since this is the location of maximum stresses. The specimen was placed centrally with its long axis perpendicular to the loading nose and supports and load was applied until the specimen breaks. This technique greatly increased the efficiency of oxidizing graphite to GO and also prevented the formation of toxic gases, such as NO2 and N2O4. The record of mid-span maximum deflection and the maximum applied load F on the specimen were used to calculate the flexural strength (?) which represents the highest stress experienced within the material at the moment of its rupture and was calculated in Megapascal (MPa) by using the following equation:(1)Where, F is the maximum load (in Newton), L is the span length (in mm), b is the width of the specimen (in mm), t is the thickness of the specimen (in mm). The graphene oxide prepared by this method is more oxidized than that prepared by Hummer’s method and also possesses a more regular structure. Graphite can also be oxidized by benzoyl peroxide (BPO) at 110 C for 10 min in an opened system (Caution!
Room temperature conductivity of the PCN samples was measured by a standard four-probe technique using Keithley programmable current source (model 6221). Four contacts were made on the cut out samples of press moulded PCN samples using conducting silver paste. Compared to pristine graphite, GO is heavily oxygenated bearing hydroxyl and epoxy groups on sp3 hybridized carbon on the basal plane, in addition to carbonyl and carboxyl groups located the sheet edges on sp2 hybridized carbon.
Hence, GO is highly hydrophilic and readily exfoliated in water, yielding stable dispersion consisting mostly of single layered sheets (graphene oxide). It is important to note that although graphite oxide and graphene oxide share similar chemical properties (i.e. Mechanism for the Formation of PANi-CF Composites Synthesis of PANi-CF composite was carried out by in-situ chemical oxidative emulsion polymerization at -3?. The overall reaction process for the formation of PANi-CF composite by the emulsion polymerization pathway using SDS as surfactant as well as dopant is shown in Fig. Sufficiently dilute colloidal suspension of graphene oxide prepared by sonication are clear, homogeneous and stable indefinitely. In the first step SDS surfactant is converted to DHS by treating with equimolar HCl (0.1M) solution.
Second step involves the addition of chopped CF, and then upon high speed homogenization DHS surfactant formed emulsion in water system. The pristine graphite sheet is atomically flat with the Vander Waals thickness of 0.34 nm, graphene oxide sheets are thicker due to the displacement of sp3 hybridized carbon atoms slightly above and below the original graphene plane and presence of covalently bound oxygen atoms.
The micelles containing CF formed at critical micelle concentration, in which the polar head group of the DHS on the outer surface of the micelles stabilizes the system where micro micelles are also absorbed on the polar surface of the CF.
A similar degree of exfoliation of GO was also attained for N,N-dimethylformamide (DMF), tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP) and ethylene glycol [54].
The incorporation of CF into DHS emulsion strongly affects the micelle aggregation number and second critical micelle concentration. The shape of a micelle is the function of molecular geometry of the surfactant molecules and solution conditions such as surfactant concentration, temperature, pH and ionic strength [32].
The third step is the addition of aniline monomer in to the emulsion system, followed by slow addition of APS initiator (oxidant) in the fourth step. The most attractive property of GO is that it can be reduced to graphene-like sheets by removing the oxygen-containing groups with the recovery of a conjugated structure.
Here a spherical micelle phase has been formed via cooperative interaction of aqueous APS solution and DHS in water.
The reduced GO (RGO) sheets are usually considered as one kind of chemically derived graphene (CCG). Aniline and APS molecules due to their hydrophobic nature diffused in to the micelles and surrounded by hydrophilic sulfonate, –SO3H unit. It is a very promising candidate for many applications such as electronic devices [56,57], polymer composites [58-61], energy conversion, storage materials [62,63], and sensors [64]. Addition of oxidant APS leads to the formation of cationic free radicals, which combines with second monomer to form dimer, which on further oxidation and combination with another cation radical forms a termer and ultimately to a long chain of polymer.
The most desirable goal of any reduction procedure is produce graphene-like materials similar to the pristine graphene.
The properties of polymer composites depends on various factors like method of preparation, type & amount of oxidant and dopant used.
Slow addition of oxidant at low temperature controls the chain linearity and internal defects in the polymer structure. Residual functional groups and defects dramatically alter the structure of the carbon plane and affect its conductivity which mainly depend on the long-range conjugated network of the graphitic lattice [65,66].
The final structure of PANi in scheme 1 is showing that the surfactant molecules have become a part of the resulting material due to ionic interaction between the polymer and the surfactant. In this way PANi-CF composite having spherical shaped PANi has been prepared whose morphology is shown further in SEM images. The most obvious changes can be directly observed or measured to judge the reducing effect of different reduction processes. Since a reduction process can dramatically improve the electrical conductivity of GO, the increased charge carrier concentration and mobility will improve the re?ection to incident light, and color changes to brown to black as shown in Figure 4.
The variation of electrical conductivity of RGO can be a direct criterion to judge the effect of different reduction methods.
In addition to these other tools like Raman spectroscopy, solid-state FT-NMR spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM), are most promising tools to show the structural changes of GO after reduction. There are several routes to reduce the graphene oxide like thermal annealing, microwave and photo reduction, and chemical reduction (Chemical reagent reduction, Solvo-thermal reduction, Multi-step reduction, Electrochemical reduction, Photocatalyst reduction).
Thermal AnalysisThe thermogravimetric analysis (TGA) of the PANi, PANi-CF composite and PCN sheet was carried out in order to see the effect of CF and novolac on the thermal stability of PCN sheets.
It is generally known that three weight-loss steps are observed in the TGA curve of PANi [25]. The second stage observed within the temperature range of 182–300°C should be related to removal of dopant molecules from the polymer structure [29]. The weight-loss observed after the removal of the dopant molecules should correspond to the complete degradation and decomposition of the polymer main chain [25, 36]. From 300-900 °C there is continuous weight loss of 28.90% which may be due to degradation of polymer backbone. On comparing the thermal behavior of PANi with the thermal behavior of PANi-CF composite (Fig. Initial weight loss of 2.6% is observed up to 110°C which may be due to the loss of water molecules entrapped in the polymer matrix. From 210°C to 300°C, weight loss observed is 27.41%, which is accounted due to the loss dopant from the polymer composite. 3a), it is observed that the thermal stability of the composite sheet has been increased up to 230°C. Initial weight loss due to loss of water molecules in this case is very less that is 0.6% because the sheet was already thermally cured at 150°C.
Further the weight loss from 230-300°C is 16.37% which is due to partial leaching of the dopant from the polymer composite matrix. A very less weight loss due to removal of dopant in this case (as compared to thermogram of pristine PANi) showed that novolac has made some kind of ionic interaction with the PANi structure. From 300-900°C a weight loss of 29.19% is observed due to degradation of polymer backbone as well as due to removal of novolac resin from the composite sheet. The weight loss observed nearly from 480-650°C is due to partial leaching of novolac resin from the polymer composite matrix. 3a showed that thermal stability of polymer is enhanced due to incorporation of CF as filler and further increased due to novolac resin used as binder. Fourier-Transform Infrared Spectroscopy (FTIR)A typical infrared spectrum of PANi-CF composite powder is shown in Figure 3b. It shows major characteristic peaks (vibrational bands) at 1560, 1470, 1290, 1110 and 791 cm?1, which are similar to the standard PANi reported in the literature [37] the bands at 1560 and 1470 cm?1 are due to ring stretching of quinoid and benzenoid, respectively.
For PANi, a strong band characteristically appears at 1110 cm?1, which has been explained as an electronic band or a vibrational band of nitrogen quinine. The small shift in the peak position and the intensity might be due to the different dopant levels of the resulting PANI. In addition to these normal bands of PANi, the presence of bands at 2920 cm?1 and 2850 cm?1 are related to asymmetric and symmetric aliphatic C-H stretching vibrations, respectively [38], indicates the existence of alkyl substituent of DHS in the polyaniline chain, which is used as dopant as well as surfactant in the polymerization reaction. Furthermore, in the cases PANI prepared in SDS, the presence of SO3? group is confirmed by appearance of a band around 570 cm?1 attributed to degenerate bending mode of the SO3? group [34] Comparison of spectra of PANi-CF, with spectra of PCN5, PCN15 and PCN25 sheet samples (Fig. The slight shift in the main peaks of sheets was observed due to some ionic interaction between novolac resin and PANi chains. Mechanical Strength, Conductivity Measurement and Shielding MeasurementPANi-CF composite mixed with novolac resin when compression moulded leads to the formation of free standing PCN composite sheets which have better mechanical, electrical and shielding properties. Electrical Conductivity and Mechanical StrengthOn comparing the properties of the pristine PANi with its different composite sheets shown in Table 1, it was observed that incorporation of carbon fiber in the polymer matrix during polymerization dramatically increases the electrical conductivity of PANi-CF composite.
Introduction of CF facilitate the charge transfer process between the two components of the composite and thereby enhances the conductivity by formation of conductive network.
Some reports are also there in the literature where improved mechanical and electrical properties has been achieved by incorporation of carbon nanotubes and carbon fiber in the conjugated polymer matrix [17]. In the present work CF loading in the polymer matrix is fixed (20% by wt.) and novolac percentage is varied in the PANi-CF composite to get self-supported thin sheets having better mechanical strength, sufficient electrical conductivity and shielding effectiveness.
On comparing the absolute values of conductivity (Table 1), it is concluded that electrical conductivity decreases when PANi-CF composite was physically blended with novolac resin because the insulating novolac resin hinders the free flow of electrons in the conducting polymer composite. 3c showed that conductivity keeps on decreasing with increasing the novolac percentage in the composite.
When PCN composites were transformed in the form of thin sheets electrical conductivity again increases (See supporting information) as the novolac resin make some kind of ionic interaction with carbon fibers and binds the fillers tightly with the polymer matrix, thereby enhancing the connectivity of fillers and matrix. Moreover, during the thermal curing of the sheets at 150? for 2 h in compression moulding, the excess of novolac resin squeezed out after doing its action.Table 1. As up to this limit the electrical conductivity and EMI shielding properties of PANi-CF composite sheets have been start decreasing significantly due to the insulating character of novolac resin. Our coworkers have also reported the effect of phenolic novolac resin on mechanical, electrical and shielding properties of grapheme oxide composite with higher loading of resin [19].
Electromagnetic ShieldingThe EMI shielding effectiveness of a material is defined as the ratio of transmitted power to the incident power and is given by(4)Where, PT and Po are the transmitted and incident EM powers, respectively. The total EMI shielding effectiveness (SET) is the sum of contributions from absorption (SEA), reflection (SER), and transmission or multiple reflection (SEM), which can be simply quoted as (5)Where, SER, SEA, and SEM are due to reflection, absorption, and multiple reflections, respectively. In two port network, S-parameters S11 (S22), S12 (S21) represent the reflection and the transmission coefficients given as [7](6)(7)and absorption coefficient, A is,(8)Here, it is noted that the absorption coefficient is given with respect to the power of the incident EM wave. If the effect of multiple reflections between both interfaces of the material is negligible, then the relative intensity of the effective incident EM wave inside the material after reflection is based on the quantity . After 15 wt% phenolic novolac resin loading the transmittance coefficient is observed more than 0.09 as shown in Figure 5a.
In other words, due to higher absorption coefficient (A) and reflection coefficient (R) coefficients, more EM wave is consumed by the PCN sheets, which leads to more significant decrease of the T values.
These plots show that the trend of the R depends on the amount of phenolic resin in the sheets and the frequency. When the PCN composite were compression moulded in the form of thin sheets, it is observed (Fig. It has been observed that for conducting PANi-CF sheets SE is contributed by absorption and reflection. This is due to the improved interfacial interaction between resin and reinforcement phase of composite upon thermal curing of the sheets at 150°C temperature. In contrast, the SE of PCN sheets were found very low after 25 wt % loading, near about 5-6 dB, regardless of phenolic novolac resin content, and only marginally higher than about ~2 dB of the neat phenolic novolac resin sheet. The insulating nature of phenolic novolac resin resulted in insulating sheets with little potential for EMI shielding.
Earlier reports were there on electromagnetic shielding and microwave absorption properties of conducting polymer filled with CF & some other magnetic particles, but thick samples are required to achieve high SE. As SE is dependent on multiple factors specially SEA directly proportional to thickness (from Eq. Therefore It is observed that the thickness of the shield has a great influence on the microwave shielding properties as shown in Fig.
ConclusionsSelf-supported thin sheets of PANi-CF have been successfully prepared by compression moulding, using novolac resin as binder.
Dispersion of conducting filler in the polyaniline matrix improves the mechanical as well as electrical properties of sheets. By improving the filler matrix interaction, novolac resin has improved the mechanical properties of PCN sheets without affecting the shielding properties significantly.
In addition, multiple PCN sheets have shown SE up to 35dB at a critical thickness of 3.0 mm. It is believe that the polymer composite sheets could be promising candidate for next generation building block material in microwave shielding with vast utility in aerospace applications due to their lightweight, good thermal and mechanical properties.ACKNOWLEDGEMENTSThe authors wish to thank Prof. Pratibha, Chairperson, Department of Chemistry, DCRUST for their keen interest in the work. Sood for recording SEM micrograph.AppendixSupporting Material Document1 UV-vis spectroscopyUV-vis absorption spectrum of PANi, PANi-CF and PCN25 composites were shown in fig. The study was carried out by preparing the samples in N-methyl pyrolidone as solvent, which changes the polymer in deprotonated (undoped) form. To make the polymer again protonated (doped) 1N HCl is added to the samples up to color changes from blue to green (doped PANi). Doped PANi shows three characteristic absorption bands at 320–360, 400–420 and 740–800 nm wavelengths.
The second and third absorption bands are related to doping level and formation of polaron, respectively. But position of the bands depends on the dopant and nature of alkali or solvent in which UV study is carried out. In the acidic region, three distinct absorption bands of the green protonated polyaniline are observed at 350, 430 and 810 nm.Figure S1.



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