• S Sindhu

      Articles written in Bulletin of Materials Science

    • Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

      M R Anantharaman K A Malini S Sindhu E M Mohammed S K Date S D Kulkarni P A Joy Philip Kurian

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      Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.

    • Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

      S Sindhu M R Anantharaman Bindu P Thampi K A Malini Philip Kurian

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      The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni1–𝑥Zn𝑥Fe2O4, as well as the filler (Ni1–𝑥Zn𝑥Fe2O4) incorporated rubber ferrite composites (RFCs). Ni1–𝑥Zn𝑥Fe2O4 (where 𝑥 varies from 0 to 1 in steps of 0.2) were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (𝜎a.c.) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10–3 S/m. Analysis of the results shows that 𝜎a.c. increases with increase of frequency and the change is same for both ceramic Ni1–𝑥Zn𝑥Fe2O4 and RFCs. 𝜎a.c. increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of 𝜎a.c. on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples.

    • Comparison of performance parameters of poly(3,4 ethylenedioxythiophene) (PEDOT) based electrochromic device on glass with and without counter electrode

      S Sindhu K Narasimha Rao E S R Gopal

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      Conjugated polymers are promising materials for electrochromic device technology. Aqueous dispersions of poly(3,4-ethylenedioxythiophene)-(PEDOT) were spin coated onto transparent conducting oxide (TCO) coated glass substrates. A seven-layer electrochromic device was fabricated with the following configuration: glass/transparent conducting oxide (TCO)/PEDOT (main electrochromic layer)/gel electrolyte/prussian blue (counter electrode)/TCO/glass. The device fabricated with counter electrode (Prussian blue) showed a contrast of 18% and without counter electrode showed visible contrast of 5% at 632 nm at a voltage of 1.9 V. The comparison of the device is done in terms of the colouration efficiency of the devices with and without counter electrode.

    • Optical, electrochemical and morphological investigations of poly (3,4-propylenedioxythiophene)–sultone (PProDOT–S) thin films

      S Sindhu C R Siju S K Sharma K N Rao E S R Gopal

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      In this paper, we have carried out thin film characterization of poly(3,4-propylenedioxythiophene)–sultone (PProDOT–S), a derivative of electrochromic poly(3,4-propylenedioxythiophene) (PProDOT). PProDOT–S was deposited onto transparent conducting oxide coated glass substrates by solution casting method. Single wavelength spectrophotometry is used to monitor the switching speed and contrast ratio at maximum wavelength (𝜆max). The percentage transmittance at the 𝜆max of the neutral polymer is monitored as a function of time when the polymer film is repeatedly switched. This experiment gives a quantitative measure of the speed with which a film is able to switch between the two states i.e. the coloured and the bleached states. PProDOT–S films were switched at a voltage of 1.9 V with a switching speed of 2 s at 𝜆max of 565 nm and showed a contrast of ∼37%. Cyclic voltammetry performed at different scan rates have shown the characteristic anodic and cathodic peaks. The structural investigations of PProDOT–S films by IR spectra were in good agreement with previously reported results. Raman spectra of PProDOT–S showed a strong Raman peak at 1509 cm-1 and a weak peak at 1410 cm-1 due to the C = C asymmetric and symmetric stretching vibrations of thiophene rings. The morphological investigations carried out by using scanning electron microscope (SEM) of polymer films have shown that these polymers are found to be arranged in dense packed clusters with non-uniform distribution having an average width and length of 95 nm and 160 nm, respectively.

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