Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Biophysical Sciences 225ing the electronic transport properties of these nanowires.A Rahman, MK Sanyal, R Gangopadhyay, Amitabha DeCSD6.1.8.4 Characterization and dielectric properties of polyanilineTiO 2 nanocompositesNanocomposites of polyaniline (PANI)titanium dioxide (PANITiO 2 ) are prepared from a colloidalsol of TiO 2 nanoparticles. The dc and ac conductivities of samples with different concentrationsof PANI have been investigated as a function of frequency and temperature. The dc conductivityfollows three-dimensional variable range hopping. The ac conductivity has been interpreted as apower law of frequency. The temperature variation of the frequency exponent suggests a correlatedbarrier hopping conduction process in the nanocomposites. A very large dielectric constant ofabout 3700 at room temperature has been observed. An electric modulus presentation is used tointerpret the dielectric spectra. The interface between polyaniline and TiO 2 plays an importantrole in yielding a large dielectric constant in the nanocomposite.SK De, Ashis Dey, Amitabha DeCSD6.1.8.5 Evidence of a Rachet effect in nanowires of a conducting polymerRachet effect, which has been observed in many systems ranging from a living organism to anartificially designed device, is a manifestation of motion in asymmetric potentials. A conductivitystudy of polypyrrole nanowires was carried out where the Rachet effect was observed. The nanowireswere prepared by a simple method that generates a variation of doping concentration along thelength of the wires. This variation gives rise to a Rachet effect that hinders the symmetry of thehopping process of charges and hence the value of measured resistance of the nanowires becomessensitive to the direction of current flow. The asymmetry in resistance was found to increasewith decreasing nanowire diameter and increasing temperature. The observed phenomenon couldbe explained with the assumption that the spatial extension of the localized state involved in thehopping process is reduced as the doping concentration is reduced along the length of the nanowires.The temperature dependence of the static dielectric constant (ǫ ∼T −β ) gave a value of β as 1.4instead of 1.0 perhaps due to dipole rotation being hindered in nanowires, and this would explainthe observed reduction in rachet effect with lowering temperature.A Rahman, R Gangopadhyay, I Das, A De, MK SanyalSP/CSD6.1.8.6 Preparation, Characterization and Transport Properties of Polyaniline-a-Zirconium Phosphate Intercalated Conducting NanocompositeThe synthesis of conducting composite involving polyaniline in the layered zirconium phosphate[a-Zr(HPO4)2 H2O] and its subsequent characterization and dielectric properties were studied.Aniline monomer was introduced into the interlayer space of a-ZrP by adsorption. The encapsulatedaniline was then polymerized by chemical oxidative method by adding appropriate amount ofammonium peroxodisulphate (APS) solution. X-ray diffraction patterns showed that the polyaniline