Parveen Saini

High permittivity polyaniline–barium titanate nanocomposites with excellent electromagnetic interference shielding response

Organic conductive polymers are at the forefront of materials science research because of their diverse applications built around their interesting and unique properties. This work reports for the first time a correlation between the structural, electrical, and electromagnetic properties of polyaniline (PANI)-tetragonal BaTiO3 (TBT) nanocomposites prepared by in-situ emulsion polymerization. XRD studies and HRTEM micrographs of these nanocomposites clearly revealed the incorporation of TBT nanoparticles in the conducting PANI matrix. EPR and XPS measurements reveal that increase in loading level of BaTiO3 results in a reduction of the doping level of PANI. The Ku-Band (12.4-18 GHz) network analysis of these composites shows exceptional microwave shielding response with absorption dominated total shielding effectiveness (SET) value of -71.5 dB (blockage of more than 99.99999% of incident radiation) which is the highest value reported in the literature. Such a high attenuation level, which critically depends on the fraction of BaTiO3 is attributed to optimized dielectric and electrical attributes. This demonstrates the possibility of using these materials in stealth technology and for making futuristic radar absorbing materials (RAMs).

Improved Electromagnetic Interference Shielding Properties of MWCNT-PMMA Composites Using Layered Structures.

Electromagnetic interference (EMI) shielding effectiveness (SE) of multi-walled carbon nanotubes–polymethyl methacrylate (MWCNT–PMMA) composites prepared by two different techniques was measured. EMI SE up to 40 dB in the frequency range 8.2–12.4 GHz (X-band) was achieved by stacking seven layers of 0.3-mm thick MWCNT–PMMA composite films compared with 30 dB achieved by stacking two layers of 1.1-mm thick MWCNT–PMMA bulk composite. The characteristic EMI SE graphs of the composites and the mechanism of shielding have been discussed. SE in this frequency range is found to be dominated by absorption. The mechanical properties (tensile, flexural strength and modulus) of the composites were found to be comparable or better than the pure polymer. The studies therefore show that the composite can be used as structurally strong EMI shielding material.

Effective improvement of the properties of light weight carbon foam by decoration with multi-wall carbon nanotubes

In the present investigation, carbon foam (CF) has been decorated with multi-wall carbon nanotubes (MWCNTs) by two different routes to improve its electromagnetic interference (EMI) shielding effectiveness (SE) and mechanical properties. In the first case, a MWCNTs incorporated carbon precursor was used for the development of CF whereas in the other case, MWCNTs were directly grown over CF by a chemical vapor deposition (CVD) technique. These foams were characterized by scanning electron microscopy, Raman spectroscopy, X-ray diffraction and vector network analyzer for its EMI-SE. It was observed that, EMI-SE was dominated by reflection phenomena and it increased with an increasing MWCNTs content. The MWCNTs incorporated CF demonstrated a maximum EMI-SE value of −72 dB at 1 wt% MWCNTs. In comparison, MWCNTs directly grown on CF gives a maximum EMI-SE of −85 dB at only 0.5 wt% MWCNTs. The higher extent of improvement in EMI-SE in MWCNTs decorated CF was due to the increase in surface area and surface conductivity. The specific shielding effectiveness was 163 dB cm3 g−1 for MWCNTs decorated carbon foam of thickness 2.75 mm. This is the highest value reported in the open literature for CF in the X-band (8.2 to 12.4 GHz) frequency region. Moreover, besides EMI-SE improvement, compressive strength and thermal conductivity were increased by 66 and 75% respectively.

Microwave Absorption and EMI Shielding Behavior of Nanocomposites Based on Intrinsically Conducting Polymers, Graphene and Carbon Nanotubes

© 2012 Saini and Arora, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Microwave Absorption and EMI Shielding Behavior of Nanocomposites Based on Intrinsically Conducting Polymers, Graphene and Carbon Nanotubes

Formation mechanism, electronic properties & microwave shielding by nano-structured polyanilines prepared by template free route using surfactant dopants

Conducting polymers are at the forefront of nanomaterials research but the fundamental mechanisms that govern the formation of functional nanostructures and control their electromagnetic (EM) properties are still unknown. Herein, we report for the first time a detailed correlation between acquired morphology, structural, spectral, electrical and EM properties of the polyaniline (PANI) nanostructures synthesized by a template free route using surfactant dopants as structure directing agents. Aniline has been emulsion polymerized in the presence of different sulfonic acids viz. dodecylbenzenesulfonic acid, camphorsulfonic acid, ligninsulfonic acid & cardanolazophenylsulfonic acid and the formed PANIs have been designated as PDB, PCS, PLS and PCD, respectively. The SEM investigations revealed that the morphology is critically dependent on the nature of the dopant, while FTIR, XRD, EPR and UV-visible studies revealed that doping level follows the order PCD 99.999% of incident EM radiation) demonstrate the potential of these materials for making future microwave shields.

Improved electromagnetic interference shielding effectiveness of light weight carbon foam by ferrocene accumulation

The influence of nanosized iron particles (NSIP) derived from an organometallic compound, i.e. ferrocene, on the properties of light weight carbon foam (CF) derived from coal tar pitch was investigated. It was observed that NSIP acts as a catalyst, resulting in an improved degree of graphitization of CF with increasing NSIP content and hence, higher electrical and thermal conductivity values. The higher value of conductivity has a positive effect on the electromagnetic interference (EMI) shielding effectiveness (SE) of the CF. The EMI SE increased with increasing NSIP content in CF. The specific SE of the light weight CF was 130 dB.cm3/g at 10 wt% of ferrocene in CF, which is the highest value reported so far for CF, particularly at such a low thickness (2.75 mm). Besides, it was thermally stable up to 600 °C in an oxidizing atmosphere and exhibits high specific thermal conductivity up to 121 W cm3 g−1 m−1 K−1.

Designing of epoxy composites reinforced with carbon nanotubes grown carbon fiber fabric for improved electromagnetic interference shielding

In this letter, we report preparation of strongly anchored multiwall carbon nanotubes (MWCNTs) carbon fiber (CF) fabric preforms. These preforms were reinforced in epoxy resin to make multi scale composites for microwave absorption in the X-band (8.2-12.4GHz). The incorporation of MWCNTs on the carbon fabric produced a significant enhancement in the electromagnetic interference shielding effectiveness (EMI-SE) from −29.4 dB for CF/epoxy-composite to −51.1 dB for CF-MWCNT/epoxy multiscale composites of 2 mm thickness. In addition to enhanced EMI-SE, interlaminar shear strength improved from 23 MPa for CF/epoxy-composites to 50 MPa for multiscale composites indicating their usefulness for making structurally strong microwave shields.

Nanostructured polyaniline incorporated ultrafiltration membrane for desalination of brackish water

A novel salt rejecting ultrafiltration (UF) membrane was prepared by a facile, scalable route involving in situ incorporation of negatively charged polyaniline (PANI) nanoparticles within polysulfone (PSF). The incorporated PANI acts as a porogen and charge inducing agent, improving the porosity, permeability, hydrophilicity as well as the surface charge, leading to an enhancement of the permeate flux and improvement of the salt rejection capability. Specifically, 2 wt% PANI loading leads to a 25 times increase in the molecular weight cut-off (from 0.2 to 4.8 kDa). Also, there is improvement in porosity (from 20% to 64%), and a 2-fold increase in permeability (from 8 × 10−12 to 16 × 10−12 m3 m−2 Pa−1 s−1). Surface hydrophilicity (reduction of the contact angle from 82° to 69°) was enhanced as well. All of these effects ultimately lead to a 2.5 times enhancement in the permeate flux (from 21 l m−2 h−1 to 38 l m−2 h−1 at 690 kPa transmembrane pressure, TMP and 20 l h−1 cross flow rate, CFR). This reflects the change in membrane behavior from nanofiltration (NF) to UF. An increase in zeta potential (from −4 mV to −28 mV at pH 7) results in salt rejection between 40–53%, equivalent to the NF performance. Developed UF membranes match the desalination performance of NF membranes showing a higher flux and lower energy requirement. Advantageously, these membranes are also found to be fouling resistant during salt solution filtration, requiring no extensive regeneration. Desalination performance of these membranes is also demonstrated using artificially synthesized seawater. These UF membranes may be exploited as a pretreatment for inlet load reduction to reverse osmosis or for the production of industrial process water. It is believed these charged membranes lay the foundation for the development of next generation desalination membranes possessing high flux and fouling resistant characteristics.

Permittivity and Electromagnetic Interference Shielding Investigations of Activated Charcoal Loaded Acrylic Coating Compositions

Acrylic resin (AR) based electromagnetic interference (EMI) shielding composites have been prepared by incorporation of up to 30 wt% activated charcoal (AC) in AR matrix. These composites have been characterized by XRD, Raman spectroscopy, scanning electron microscopy, dielectric, and EMI shielding measurement techniques. XRD patterns and Raman studies confirm the incorporation of AC particles inside AR matrix and suggest possible interactions between phases. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites especially the formation of porous structure. The dielectric measurements show that 30 wt% AC loading composite display higher relative permittivity value (~79) compared to pristine AR (~5). Further, the porous structure, electrical conductivity, and permittivity value contribute towards EMI shielding effectiveness value of −36 dB (attenuation of >99.9% of incident radiation) for these composites, thereby demonstrating their suitability for making efficient EMI shielding coatings.

Carbon Nanotube-Based Polymer Composites: Synthesis, Properties and Applications

The present chapter covers the designing, development, properties and applications of carbon nanotube-loaded polymer composites. The first section will provide a brief overview of carbon nanotubes (CNTs), their synthesis, properties and functionalization routes. The second section will shed light on the CNT/polymer composites, their types, synthesis routes and characterization. The last section will illustrate the various applications of CNT/polymer composites; important properties, parameters and performance indices backed by comprehensive literature account of the same. The chapter concludes with the current challenges and future aspects.