Polymeric and Soft Materials

The Polymeric and soft materials section is dedicated to research in fundamental and applied science of polymers, soft materials and polymer based nanocomposites. Three different groups are working under this section on various aspects of material science and nanotechnology with special reference to polymeric materials

(a) Activity: Conducting Polymer based composites: EMI Shielding, Anticorrosion coatings
Activity Leader: Dr. S. K. Dhawan

Reduced graphene oxide/?-Fe2O3/carbon fiber sandwich for excellent electromagnetic interference shielding in the X-band
Composite sheet consisting of a reduced graphene oxide (RGO)/?-Fe2O3/ carbon fiber sandwich has been produced by compression molding. Its electrical conductivity lies in the range 0.48-171.21 S/cm. 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. Thermogravimetric analysis show that the thermal stability of the RGO sandwich depends upon the amount of RGO and phenol resin in the sandwich. Complex parameters, i.e., permittivity (e*=e´-ie?) and permeability (µ*=µ´-iµ?) of RGO/?-Fe2O3/carbon fiber have been calculated from experimental scattering parameters (S11 & S21) using theoretical calculations given in Nicholson-Ross and Weir algorithms. The microwave absorption properties of the paper have been studied in the 8.2-12.4GHz (X-Band) frequency range. The maximum shielding effectiveness observed is 45.26 dB, which strongly depends on dielectric loss and volume fraction of ?- Fe2O3 in RGO matrix.

Figure 1.(a) Schematic representation of preparation of RGO sandwich containing different wt% of ?-Fe2O3 nanoparticles using phenol resin in the organic medium (b) SEM images of RGO and (c) RGO/?-Fe2O3 sheet having 1% carbon fiber and 50wt% of phenol resin showing the pullouts of carbon fibers and the fracture surface of sheet. (AvanishPratap Singh , Parveen Garg, FirozAlam, Kuldeep Singh, R.B. Mathur, R.P. Tandon, Amita Chandra & S.K. Dhawan, Carbon 50 (2012) 3868-3875 (I.F. 5.38)

Synthesis of graphene/Fe3O4 incorporated polyaniline (PGF) composite:
Reduced graphene oxide embedded with ferric oxide nano particles were incorporated into polyaniline matrix by emulsion polymerization which shows nice distribution of nanoferrix oxide particles in RGO matrix. 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. PGF composites have shown excellent frequency stability in the measured frequency range, which was found to increase with increasing GF content (Fig. 2). PGF2 has a higher SEA of 22–26 dB (left black scale) with a SER of 4.7–6.3 dB (right blue scale) as compared to PGF1 (SEA ~ 21 dB and SER ~4.5 dB) in the 12.4–18 GHz range, while polyaniline–Fe3O4 (PF12) has a lower value shielding effectiveness (SEA ~ 7–9 dB and SER ~ 1.5–2.5 dB) in comparison to PGF composites in the same frequency range having a thickness of 2.5 mm.

Fig. 2: Dependence of shielding effectiveness (SEA and SER) of PF12, PGF1 and PGF2 composites as a function of frequency for sample thickness d ~ 2.5 mm and EMI shielding representation. The inset illustrates the variation of microwave conductivity and skin depth with frequency.

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.

Smart Coating of Polyaniline for Corrosion Protection:
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. 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.

Photograph of (a) epoxy coated (b) PANI (at 6 wt.% loading) coated (c) HPSC (at 1.5 wt. % loading) and (d) HPSC (6.0 wt. % loading) mild steel after 35 days of exposure to salt spray test.

(b) Activity: Conjugated polymer composites for Immunosensing applications
Activity Leader: Dr. Rajesh

Impedimetricimmunosensor for cardiac biomarkers
Timely and effective treatment of patients arriving in the emergency department with chest pain requires a prompt and reliable diagnosis. 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. These ZnS(MPA) modified ITO-glass plates were subsequently immobilized with protein antibody, Ab-Mb, through free carboxyl groups available on ZnS(MPA) nanocrystals by using N-(3-dimethylaminopropyl)-N’-ethyl carbodiimide hydrochloride (EDC) / N-hydroxysuccinimide (NHS) approach, for the fabrication of bioelectrode (Ab-Mb(BSA)/ZnS(MPA)/APTES/ITO-glass). The stepwise fabrication of the bioelectrode is shown in scheme 1.

Scheme1. Stepwise fabrication of bioelectrode

Electrochemical impedance response studies of Ab-Mb(BSA)/ZnS(MPA)/APTES/ITO electrode to protein antigen, Ag-Mb, was carried out in 0.1 M KCl solution containing 2 mM [Fe(CN)6]3-/[Fe(CN)6]4- (pH 7.4), at the scanning frequencies from 1.0 to 10,000 Hz. The Nyquist plots of impedance spectra for different concentration of antigen, Ag-Mb, solution at the bioelectrode is shown in Fig. 1a. 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. 1b) demonstrates three distinct regions corresponding to the three types of elements in the equivalent circuit. The double layer capacitance region is in the low frequency range from 50 Hz to 1 kHz, whereas the frequency region below 50 Hz and above 1 KHz corresponds to charge transferresistance and solution resistance, respectively.

Fig. 1.(a)Nyquist plots obtained on Ab-Mb(BSA)/ZnS(MPA)/APTES/ITO electrode for control and different concentration of Ag-Mb in PBS (pH 7.4); (b) Corresponding bode plots.

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. The copolymer film was bio-functionalized with myoglobin protein antibody, Ab-cMb, to form a bioelectrode. The ac impedance studies of the PPy-PPa copolymer film show both charge transfer resistance (Ret) and ions diffusion (WR) characteristics, at high and low frequency regions respectively, whereas the bioelectrode (Ab-Mb(BSA)/PPy-PPa/ITO) shows only Ret in a comparatively low ac frequency region with respect to the PPy-PPa copolymer film, indicating a good biocompatibility of the polymer electrode (Fig.1).

Fig. 1. SEM images of (a) PPy-PPa/ITO; (b) Ab-Mb/PPy-PPa/ITO-glass electrode and Bode plots corresponding to Impedance modulus and phase angle diagram vs frequency for PPy-PPa/ITO-glass and Ab-Mb(BSA)/PPy-PPa/ITO-glass electrodes (in between image).

(c) Activity:Conjugated polymer/Graphene based nanocomposites for electrostatic protection, microwave absorbing/EMI shielding and Electrochemical supercapacitors
Activity Leader: Dr. Parveen Saini(pksaini@nplindia.org)

Formation mechanism, electronic properties & microwave shielding by nano-structured polyanilines prepared by template free route using surfactant dopants(Impact Factor: 5.97)

Parveen Saini and ManjuArora, Journal of Materials Chemistry A, 2013; DOI:10.1039/C3TA11086A

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 (Figure 1) 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 dopant whereas

Figure 1: Schematic representation of formation of polyaniline nanorodsvia emulsion polymerization using organic sulfonic acids and their EMI shielding mechanism

The shielding effectiveness (SE) values of PCD, PLS, PCS and PDB samples were -23.6, -38.3, -44.2 and-55.0 dB respectively (Figure 2) which followed the electrical conductivity trend and clearly demonstrate the superiority of DBSA over other dopants. The complex permittivity spectra showed highest value of normalized losses (tanδ=0.71) in PDB while PCD gives lowest value of tanδ i.e. 0.57. This accounted for the observed shielding pattern. These results were further supported by highest microwave conductivity and lowest skin depth value for PDB. Interestingly, SET value of -55.0 dB for PDB represents >99.999 % attenuation and surpasses the shielding criteria of SET ~ -30 to -40 dB for commercial utility.

Figure 2: Frequency dependence of total shielding effectiveness (SET) of polyaniline samples doped with different bulky counter-anion sulfonic acids

High Permittivity Polyaniline/Barium Titanate Nanocomposites with Excellent Electromagnetic Interference Shielding Response (Impact Factor: 6.23)

Parveen Saini, ManjuArora,Govind Gupta, Bipin K. Gupta, V. N. Singh andVeenaChoudhary, Nanoscale, 2013, 5, 4330

Polyaniline (PANI)-tetragonal BaTiO3 (TBT) nanocomposites have been prepared by in-situ emulsion polymerization (Figure 1). XRD studies and HRTEM micrographs of these nanocomposites 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 reduction of doping level of PANI.

Figure 1 (a) Schematic representation showing the formation of PANI-BaTiO3 NCs by in-situ polymerization. (b) XRD patterns of (i) BaTiO3, (ii) PBT11 and (iii) PBT10 showing characteristic diffraction planes.Inset displays the distinct splitting of 45o peak and presence of tetragonal phase of BaTiO3 and (c) DSC curve reflecting tetragonal to cubic phase transition temperature.

The Ku-Band (12.4-18 GHz) network analysis of these composites show exceptional microwave shielding response (Figure 2) with absorption dominated total shielding effectiveness (SET) value of -71.5 dB (blockage of more than 99.99999% of incident radiation) which critically depends on fraction of BaTiO3 is attributed to optimized dielectric and electrical attributes.

Figure2 Variation of (a) SER and SEA, (b) real permittivity (ε’), (c) imaginary permittivity (ε”), and (d) loss tangent (tan δ) with frequency for PANI and its TBT based NCs

Enhanced electromagnetic interference shielding effectiveness of polyaniline functionalized carbon nanotubes filled polystyrene composites (Impact Factor: 3.29)

Parveen Saini and VeenaChoudhary, Journal of Nanoparticle Research 15 (2013) 1415

Multiwall carbon nanotubes (MWCNTs)/polystyrene composites were fabricated by solution processing route using non-covalently functionalized (polyaniline coated) MWCNTs. These composites exhibit an extremely low percolation threshold (0.12 vol % MWCNT) along with micro porosity and are found to have potential applications in the areas of electromagnetic interference(EMI) shielding and electrostatic dissipation (ESD) with an ESD time of 0.78 sec (Figure 1).

Figure 1: Static decay profile of 0.5 vol. % PSPMNT composite and pure PS film (inset)

Beside, these composites also give (Figure 2) shielding effectiveness of -23.3 dB (>99% attenuation). The EMI shielding was found to be dominated by absorption (-18.7 dB) with a nominal contribution from reflection (-4.6 dB) that can explained in terms of multiple internal reflection phenomenon driven by high conductivity and the porous structure

Figure 2: (a) Variation of reflection (SER) & absorption (SEA) losses with MWCNT loading and magnified SEM image (inset) showing dispersed CNTs and voids, (b) Schematic representation of radiation shield interaction & involved multiple internal reflection (MIR) phenomenon

Graphene and its nanocomposites for EMI shielding and Supercapacitors

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. In this direction group has already established facility for synthesis of graphene like sheets via chemical oxidation/reduction route. The initial work in the above direction has yielded encouraging response and the further studies are underway. We welcome the interested groups, academic organization and related industries for possible collaboration in the above areas.

Group Members:

  • Dr. Parveen Saini, Scientist
  • Dr. ManjuArora, Principal Tech. Off.
  • Ms. ChandniPuri, CSIR Diamond Jubilee Research Intern