MST-Department of Physics

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Browsing MST-Department of Physics by Subject "Biopolymers"

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    Structural and electrical characteristics of Nandi flame seed cuticle- A biopolymer
    (2013-07-09) Kipnusu, Wycliffe Kiprop; Katana, G.; Rathore, I. V. S.; Migwi, C. M.
    Improved understanding of material properties allows for the design of new materials that have enhanced physical properties and that make more efficient use of resources. Atomic Force Microscopy and Fourier Transform Infrared (FTIR) spectroscopy have been used to characterize Nandi flame Seed Cuticles (NFSC). The FTIR has shown that Pectin and Cellulose molecules are some of the components of NFSC. The surface analysis using Atomic Force Microscopy (AFM) has shown that the cuticles are porous with average pore size of 0.5nm. The cuticles also have highly oriented topography with pores concentrated within cavities that are spaced at regular intervals. Isochronal and Isothermal loss plots of Dielectric Spectroscopy (DS) studies displayed two dynamical molecular processes that are strongly dependent on temperature and frequency. Dynamics of primary structures obeyed arrheniuous relations while cooperative dynamics obeyed Vogel- Fulcher- Tamman (VFT) scaling law from which glass transition temperature Tg was obtained as 54°C. Differential Scanning Calorimetry (DSC) gave a Tg of 54.5°C and crystallization temperature, (Tg) of 352.4 °C. The cuticles were found to be resistant to common organic solvents. CurrentVoltage (I-V) characteristics of Nandi Flame Seed Cuticles (NFSC) have been studied as a function of irradiation, annealing and poling temperature. The cuticles showed electrical threshold switching and memory effect which results from the fact that after switching, NFSC remains in the low impedance state even when the voltage decreases or withdrawn. The threshold voltage Vth is 5V (1.25x104 V/cm) which is greater than Vth observed in most synthetic polymers. The threshold Voltage Vth increases to 6-8 V after irradiation and annealing depending on the duration of annealing or irradiation. After switching, the conductivity increased by a factor of 10. In reverse bias, increase of the current was observed and the hysteresis loop was at higher conductivity than at the time of switching. This effect was minimized at a poling temperature of 370K. The conduction mechanism in this reverse regime could be explained by Fowler-Nordheim quantum mechanical tunneling. The potential barrier height at the AI/NFSC junction was found to be 11.28 eV and 1.13 eV for pure and annealed (400K) samples respectively. Variable range hoping (VRH) is the main current transport mechanism in the sample at the temperature range of 330-440K. The VRH mechanism has been analyzed basing on Mott theory and the Mott parameters; the fall-off length of wave functions near the Fermi -level is about á~ z 10-10 cm 1, hoping distance R ~ 10 "1° cm while the hopping energy (W) is in the range of 0.13 eV - 0.18 eV.