This review will summarize the details for crystallization of modified hectorites along with their characterization and materials applications. Among the several potential uses of these synthetic materials, there are two important applications concerning catalysis and composites. The fate of the template dictates which of these applications is pertinent.
First, if the organic molecule or polymer is used with the intention of acting as templates of pore structure, then the organic template is removed after the modified clay has been crystallized. Upon template removal, the now porous materials are examined for their use as potential catalysts and catalyst supports. We have recently proven a correlation between catalyst pore size in the mesoporous range and the size and concentration of a polymeric template that is used.
Preliminary hydrodesulfurization catalytic results have been obtained using these materials. If, on the other hand, intercalants are allowed to remain as a part of the structure, then a distinctive class of organic-inorganic composites becomes possible.
Work in this area has focused on incorporating polymers at higher than 85 wt. Similar records in OSTI. GOV collections:. GOV Journal Article: Synthetic organo- and polymer- clays : preparation, characterization, and materials applications. Title: Synthetic organo- and polymer- clays : preparation, characterization, and materials applications.
Full Record Other Related Research. After functionalization, tremendous changes in morphology have been observed which basically arises by the introduction of aminophenol Figure 6e and PANI Figure 7f on the RGO surfaces. Scheme of direct grafting of polyaniline on the reduced graphene sheets Reprinted with permission from ref Copyright American Chemical Society. Reprinted with permission from ref Copyright American Chemical Society. Graphene being a two-dimensional 2D structure of carbon atoms own exceptional chemical, thermal, mechanical, and electrical properties and mechanical properties.
Extensive research has shown the potential of graphene or graphene-based sheets to impact a wide range of technologies. In this section, graphene based conducting polymer composites are discussed focusing their use an Electromagnetic interference shielding material [ - ]. Electronic systems have compact with increased the density of electrical components within an instrument.
The operating frequencies of signals in these systems are also increasing and have created a new kind of problem called electromagnetic interference EMI. Unwanted EMI effects occur when sensitive devices receive electromagnetic radiation that is being emitted whether intended or not, by other electric or electronic devices such as microwaves, wireless computers, radios and mobile phones.
As a result, the affected receiving devices may malfunction or fail. The effects of electromagnetic interference are becoming more and more pronounced, caused by the demand for high-speed electronic devices operating at higher frequencies, more intensive use of electronics in computers, communication equipment and the miniaturisation of these electronics. Compact, densely packed electronic components produce more electronic noise. Due to the increase in use of high operating frequency and band width in electronic systems, especially in X-band and broad band frequencies, there are concerns and more chances of deterioration of the radio wave environment.
These trends indicate the need to protect components against electromagnetic interference EMI in order to decrease the chances of these components adversely affecting each other or the outer world. The effects of electromagnetic interference can be reduced or diminished by positioning a shielding material between the source of the electromagnetic field and the sensitive component. Shielding can be specified in the terms of reduction in magnetic and electric field or plane-wave strength caused by shielding.
The effectiveness of a shield and its resulting EMI attenuation are based on the frequency, the distance of the shield from the source, the thickness of the shield and the shield material. With any kind of electromagnetic interference, there are three mechanisms contributing to the effectiveness of a shield. Part of the incident radiation is reflected from the front surface of the shield, part is absorbed within the shield material and part is reflected from the shield rear surface to the front where it can aid or hinder the effectiveness of the shield depending on its phase relationship with the incident wave, as shown in Figure 7.
Therefore, the total shielding effectiveness of a shielding material SE equals the sum of the absorption factor SE A , the reflection factor SE R and the correction factor to account for multiple reflections SE M in thin shields. All the terms in the equation are expressed in dB. In practical calculation, SE M can also be neglected for electric fields and plane waves. Absorption loss SE A , is a function of the physical characteristics of the shield and is independent of the type of source field. Therefore, the absorption term SE A is the same for all three waves. As shown in Figure 8 , when an electromagnetic wave passes through a medium its amplitude decreases exponentially.
Therefore, the absorption term SE A in decibel is given by the expression:. The absorption loss of one skin depth in a shield is approximately 9 dB. 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. The reflection loss is related to the relative mismatch between the incident wave and the surface impedance of the shield.
The computation of refection losses can be greatly simplified by considering shielding effectiveness for incident electric fields as a separate problem from that of electric, magnetic or plane waves. The equations for the three principle fields are given by the expressions. It is usually only important when metals are thin and at low frequencies i. The formulation of factor SE M can be expressed as. Due to their high electrical conductivity, metals are particularly suitable as shielding material against electromagnetic fields.
This can be a self-supporting full metal shielding, but also a sprayed, painted or electro-less applied conducting coating e.
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Another option is the incorporation of metal stainless steel powder or fibres as conducting filler in a plastic matrix. However, there are a certain draw backs to use metal as a shielding material. In order to produce metal coatings, at least two processing techniques have to be applied one for the support and one for the coating, which can be costly. It will also be difficult to apply these coatings onto complicated shaped objects. In addition, the long-term adhesion of the coating to the support has to be reliable.
To solve the EMI problems, spinel-type ferrites, metallic magnetic materials, and carbon nanotube CNT composites [ - ] have been extensively studied. To achieve higher SE and to overcome the drawbacks of the metal-based art, polymer material with appropriate conductive fillers can be shaped into an EMI shielding substrate, which exhibit improved EMI shielding and absorption properties.
The conductive composites in the form of coatings, strips or molded materials have been prepared by the addition of highly conductive fillers or powders to non-conductive polymer substrates. It is observed that the high conductivity and dielectric constant of the materials contribute to high EMI shielding efficiency SE. The combination of conducting polymer with nanostructured ferrite along with graphene offers potentials to fight with EM pollution.
Recently Dhawan et al have reported that if magnetic particles of barium ferrite or Fe 2 O 3 are incorporated in the polymer matrix they improve the magnetic and dielectric properties of host materials [ - ]. Therefore, conjugated polymers combined with magnetic nanoparticles to form ferromagnetic nanocomposites provide an exciting system to investigate the possibility of exhibiting novel functionality. The unique properties of nanostructured ferrite offer excellent prospects for designing a new kind of shielding materials.
The designing of ferrite based conducting polymer nanocomposites increases the shielding effectiveness. Conducting and magnetic properties of conducing polymer-ferrite nanocomposites can be tuned by suitable selection of polymerization conditions and controlled addition of ferrite nanoparticles.
The dependence of SE A on magnetic permeability and conductivity demonstrates that better absorption value has been obtained for material with higher conductivity and magnetization. Therefore, it has been concluded that the incorporation of magnetic and dielectric fillers in the polymer matrix lead to better absorbing material which make them futuristic radar absorbing material. There are many methods for the preparation of conducting polyaniline PANI like chemical or electrochemical oxidation of a monomer where the polymerization reaction is stoichiometric in electrons.
However, number of methods such as photochemical polymerization, pyrolysis, metal-catalyzed polymerization, solid-state polymerization, plasma polymerization, ring-forming condensation, step-growth polymerization, and soluble precursor polymer preparation, have been reported in literature for synthesis of conjugated polymers. However, as discussed earlier good quality of polymer graphene composite can synthesized in-situ polymerization technique [ ].
Mesoporous Zeolites: Preparation, Characterization and Applications
The Oxidative polymerization of aniline in aqueous acidic media using ammonium persulfate as an oxidant is the most common and widely used method [ ]. However by taking cationic or anionic surfactant one can easily controlled the morphology of the polymer. Therefore, emulsion polymerization is an appropriate method as the polymerization reaction takes place in a large number of loci dispersed in a continuous external phase. In a typical synthesis process, functional protonic acid such as dodecyl benzene sulfonic acid DBSA is used which being a bulky molecule, can act both as a surfactant and as dopant.
The polymerization of aniline monomer in the presence DBSA dodecyl benzene sulfonic acid leads to the formation of emeraldine salt form of polyaniline.
When the graphene nanosheets are dispersed and homogenized with DBSA in aqueous solution, micelles are formed over the graphene sheets. Anilinium cations sit between the individual DBSA molecules near the shell of the micelle complexed with sulfonate ion.
Pictorial representation for the formation of polyaniline-graphene composite is shown in figure 8. The same methodology can be used to prepare ferromagnetic conducting polymer graphene composite. Here key to synthesized good quality of polymer composite is the weight ratio of ferrite and graphene to monomer. In this process, water is the continuous phase and DBSA is a surfactant that acts as discontinuous phase. Monomer aniline is emulsified to form the micro micelles of oil in water type. The shape of a micelle is a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH and ionic strength.
Addition of the APS to the aniline monomer leads to the formation of cation radicals which combine with another monomer moiety to form a dimer, which on further oxidation and combination with another cation radical forms a termer and ultimately to a long chain of polymer. Recently our group has synthesized the graphene oxide coated Fe 2 O 3 nanoparticles and prepared polyaniline GO- Fe 2 O 3 PGF nanocomposite by the same procedure as depicted in scheme Figure 9 and reports the SE and dielectric measurement.
Pictorial representation for the formation of polyaniline nanocomposite by chemical oxidative polymerization.
The maximum shielding effectiveness due to absorption SE A max has been ca. For the reflection part, the SE R max has been ca. The higher values of SE A strongly suggest that the microwave absorption in the PGF nanocomposites results mainly from the absorption loss rather than the reflection loss. Moreover, with the change in the frequency in 12—18 GHz, the variation in the SE A value is very small, showing high bandwidth, which is commercially important for wide band absorbers.
Clearly, compared to the other carbon coated magnetic nanoparticle as reported by Zhang et al.
Molecular Materials: Preparation, Characterization, and Applications
This increase in the absorption of microwave is due to the fact that in PG21 only dielectric losses contributes to the SE A whereas in PGF11 both dielectric and magnetic losses contributes to the absorption of microwaves. The dependence of SE on complex permittivity and permeability can be expressed as [ ]. Dependence of SE A and SE R on conductivity and permeability revel that the material having higher conductivity and magnetic permeability can achieve better absorption properties. The dielectric performance of the material depends on ionic, electronic, orientational and space charge polarization.
The contribution to the space charge polarization appears due to the heterogeneity of the material. With the increase in frequency, the dipoles present in the system cannot reorient themselves along with the applied electric field as a result of this dielectric constant decreases. Variation of real and imaginary part of magnetic permeability of PGF11 and PGF12 composites as a function of frequency. The magnetic loss caused by the time lag of magnetization vector M behind the magnetic field vector.
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The change in magnetization vector generally brought about by the rotation of magnetization and the domain wall displacement. The rotation of domain of magnetic nanoparticles might become difficult due to the effective anisotropy magneto-crystalline anisotropy and shape anisotropy. The surface area, number of atoms with dangling bonds and unsaturated coordination on the surface of polymer matrix are all enhanced [ - ]. These variations lead to the interface polarization and multiple scattering, which is useful for the absorption of large number of microwaves.
Therefore we can conclude that, incorporation of graphene along with ferrite nanoparticles in the polyaniline matrix by in-situ emulsion polymerization. The high value of shielding effectiveness due to absorption The dependence of SE A on magnetic permeability and ac conductivity shows that better absorption value can be obtained for a material having higher conductivity and magnetization. In another article, Basavaraja et al [ ] has synthesized polyaniline-gold-GO nanocomposite by an in situ polymerization and reports the microwave absorption property in the 2 —12 GHz frequency range.
The presence of GNPs is shown by the absorption peak at — nm. These particles had a diameter between 25 and 45 nm. The variation of the electromagnetic interference EMI shielding effectiveness SE as a function of frequency measured in the 2. This range of values is very high compared with other carbon-based materials [ ]. Figure 14b shows the SE values variation with the thickness at 9.
The SE values increase with increasing thickness of the sheets. This probably would overcome the poor cycling life, processability and solubility of the homo-polymer. Reprinted from ref Copyright , with permission from Elsevier. GO provides an exciting platform to study engineering, physics, chemistry, and materials science of unique 2D systems as well as offers a route towards realizing conducting polymer graphene composite.
Now there is a need to form Graphene polymer composite paint that can be easily coat over the electronic encloser. Therefore, from the present studies, it can be concluded that the incorporation of magnetic and dielectric fillers in the polymer matrix lead to better absorbing material which make them futuristic radar absorbing material. In spite of these interesting developments, a lot remains to be done with regard to both fundamental understanding and the much needed improvement of the method of the designing of electromagnetic shielding materials to operate at higher frequencies for their application.
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Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Introduction Carbon the 6 th element in the periodic tables has always remains a fascinating material to the researcher and technologist. 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.
Chemical exfoliation and intercalation of small molecules: The first graphite intercalation compound GIC , commonly known as expandable graphite was prepared by Schafhautl in , while analyzing crystal flake of graphite in sulfuric acid solution. 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 ].
Synthesis of graphene oxide and its reduction In , Brodie was first to prepared graphite oxide by the oxidation of graphite with fuming nitric acid and potassium chlorate under cooling [ 49 ], In , 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.
Chemical reduction Chemical reduction has been evaluated as one of the most efficient methods for low-cost, large-scale production of Graphene. Conducting Polymer-graphene composite Nanocomposites have been investigated since , 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.
Covalent Grafting of polyaniline on graphene sheet Recently Kumar et al [ ] 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. Application of conducting polymer graphene composites in EMI shielding Graphene being a two-dimensional 2D structure of carbon atoms own exceptional chemical, thermal, mechanical, and electrical properties and mechanical properties.
Absorption Loss Absorption loss SE A , is a function of the physical characteristics of the shield and is independent of the type of source field. Reflection Loss The reflection loss is related to the relative mismatch between the incident wave and the surface impedance of the shield. More Print chapter. How to cite and reference Link to this chapter Copy to clipboard.
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