Jobin Varghese

Self assembled polyaniline nanofibers with enhanced electromagnetic shielding properties

Polyaniline nanofibers have been synthesized by simple chemical polymerization method without using any structure directing agents and organic solvents. The effects of various reaction conditions on the morphology and electromagnetic interference (EMI) shielding properties of the polyaniline nanofibers were investigated. The detailed study of various reaction conditions indicates that stable surfactant free, room temperature oxidation of aniline hydrochloride by ammonium persulfate at low oxidant to monomer ratio in acidic media yields self-assembled uniform polyaniline nanofibers. The nanofibers have excellent EMI shielding efficiency of about 71–77 dB in the frequency range of 8.2–18 GHz.

A facile formulation and excellent electromagnetic absorption of room temperature curable polyaniline nanofiber based inks

A facile formulation of room temperature curable polyaniline nanofiber based absorbing inks has been developed. The polyaniline nanofiber and polyaniline nanofiber–graphite composite of 1 mm thickness exhibit average EMI shielding effectiveness of 74 and 87 dB, respectively, in the frequency range 8.2–18 GHz which corresponds to about 100% of electromagnetic attenuation. The polyaniline nanofiber based screen printed layer with a thickness of 50 µm shows an EMI shielding effectiveness (EMI SE) of above 13 dB. The screen printed pattern formulated using the graphite incorporated polyaniline nanofiber exhibits an EMI SE of about 17 dB which will prevent 98% of electromagnetic radiation in the microwave frequency range. The dominant shielding mechanism of polyaniline nanofiber based materials is found to be absorption. The polyaniline nanofiber based screen printed pattern exhibits a faster curing time along with the excellent absorption shielding properties.

Room temperature curable silica ink

A facile formulation of room temperature curable silica ink screen printed on flexible and rigid substrate for printed electronic applications is presented. The colloidal stability and room temperature curability of the developed ink is controlled by optimizing the solvent, filler, dispersant and binder compositions. The printed ink has a porous microstructure with average surface roughness of 370 nm, and dielectric characterization of printed silica ink on BoPET film reveals relative permittivity (er) of 3.2 and dielectric loss (tan δ) of 0.02 at 1 MHz, and values of the above parameters at microwave frequencies of 8.2–18 GHz vary from 2.4 to 2.3 and from 0.003 to 0.006, respectively, which is suitable for printed electronics. These findings suggest that the newly developed dielectric silica ink is cost effective and is curable at room temperature, which enables printing and curing of flexible electronic circuits in ambient conditions.

Room temperature curable zirconium silicate dielectric ink for electronic applications

A facile formulation of room temperature curable and screen printable zirconium silicate (ZrSiO4) ink has been developed. The ZrSiO4 ink printed on the flexible BoPET (biaxially-oriented polyethylene terephthalate) substrate showed a surface roughness of ∼160 nm for a printed layer thickness of 25 μm. The screen printed ZrSiO4 layer on the BoPET substrate has a relative permittivity of 3.01 and a dielectric loss of 0.0058 at 10 GHz. It showed a temperature coefficient of relative permittivity of 55 ppm per °C in the temperature range of 25–60 °C at 15 GHz. The room temperature curability, low dielectric loss, low relative permittivity, mechanical and temperature stability of microwave dielectric properties of the printed ZrSiO4 layer make it suitable for printed microwave applications.

SOL‐GEL DERIVED TiSiO4 CERAMICS FOR HIGH‐k GATE DIELECTRIC APPLICATIONS

Homogeneous and stable titanium silicate sols and gels were prepared via the sol‐gel process. TiSiO4 ceramic calcined at 800 °C and sintered at 1275 °C exhibited er = 17.75 and tanδ = 0.042. in the radiofrequency range. The variation of relative permittivity in the operating temperature range (−20 to 70 °C) and thermodynamic stability of the TiSiO4 ceramic with Si powder is also investigated.

A NOVEL DIELECTRIC CERAMIC FOR MICROWAVE PASSIVE CIRCUITS

The tetragonal Ca9Nd2W4O24 (CNW) ceramic was prepared by the conventional solid state ceramic route and their dielectric properties were investigated in the radio and microwave frequencies. The CNW ceramics sintered at 1450 °C for 4 h showed a densification 92 % with er = 16 and tanδ = 0.004 at 15.1 GHz. The thermal conductivity of ceramic at room temperature was found to be 1.6 W m−1K−1 and coefficent of thermal expansion of CNW ceramics was 4.2 ppm/°C measured in the range of 25 to 600 °C. The dielectric and thermal properties of CNW ceramic are reported for the first time.