**4.1 Fourier transform infra Red (FTIR) spectroscopy**

Fig.2 shows the Fourier Transform Infra Red (FTIR) spectroscopy of the pristine cuticle. The samples were first annealed at 350K for 12 hrs before measurement. The wide band at 3348 cm-1 which has been observed in many other cuticular membranes (Bykov, 2008) is assigned to O-H stretching vibration. It is caused by presence of alcoholic and phenolic hydroxyl groups involved in hydrogen bonds. Methylene is the most repeated structural unit in the cutin biopolyester (Jose, et al., 2004) and these shows up in the spectra band around 2300 cm-1. The band at 2916 cm is assigned to C-H asymmetric and symmetric stretching vibrations of methoxyl groups. Absorption around 1604 cm-1 and 1427 cm-1 are assigned to the stretching of C*=*C bonds and the stretching of benzenoid rings. Absorption bands in the range 1300-1150 cm-1 are related to asymmetric vibration of C-O-C linkages in ester to esters or phenolic groups. Fig. 3 show the infra red (IR) spectra of cuticle compared with the spectra of other biopolymers.

Fig. 1. Thin and translucent cuticle attached to the Nandi flame seed

Charge Transport and Electrical Switching in Composite Biopolymers 233

Fig. 4. AFM topographic scans showing surface structure of the cuticle; (a) is a map from the scan on a larger area of about 3×105 square pixels (b) is a scan on a single pixel of about 2.5×106 nm2. Doted lines on (a) represents the region shown by (b). Scale bars ∼ 0.5nm.Taken

This section discusses electrical characteristics of the cuticle samples. Current-voltage (I-V) data measured as a function of annealing temperature, irradiation and pooling temperature was used in analyzing the electrical characteristics .Samples were separately annealed and irradiated before electrode coating was done. When annealing, cuticles were placed inside a temperature-controlled furnace, which was fitted inside an electrical shielded cage of a Lindberg/Blue Tube Furnace of model TF55035C. Samples were annealed at various temperatures of 320K, 350K and 400K for a constant period of 12hrs each. Irradiation of the sample was done with He-Ne laser beam of wavelength 632.8nm in a dark room each for a different period of 10minutes, 30minutes, and 60minutes. Electrode coating on the film of pristine, pre-annealed and pre-irradiated samples was done by using quick drying and highly conducting Flash-Dry silver paint obtained from SPI Supplies (USA). A mask of a circular aperture of 0.56 cm diameter was used while coating to ensure uniformity in size of coated surface. Circular aluminum foil of the same diameter was placed on freshly coated surface such that the sample was sandwiched between two aluminum electrodes. These metal-sample-metal sandwiches were left to dry at room temperature for a period of 24hrs to ensure that there was good ohmic contacts between aluminum electrode and the sample. The same Flash-Dry Silver paint was used to connect thin wires onto the aluminum electrodes. When measuring I-V at different temperatures, a sample sandwiched between aluminium electrodes was placed inside the Lindbarg/Blue Tube Furnace and temperature varied in steps of 5K between 350K and 500K at constant electric fields of 0.75V/cm,

Fig. 5(a) shows the I-V characteristics of pristine and annealed samples. These indicate clearly that there was electrical switching and memory effect in the cuticle samples. At

**5. Electrical characterization and charge transport mechanism** 

from (Kipnusu et al., 2009).

1.50V/cm 2.25V/cm, 3.00V/cm, and 3.75V/cm.

Fig. 2. FT-IR spectrum of pristine cuticle

Fig. 3. Comparison of IR spectrum of Nandi flame cuticle with those of other biopolymers

#### **4.2 Atomic force microscopy (AFM)**

The AFM scans (Fig. 4) shows that NFSC has a highly oriented surface topography. The AFM permits measurement of the distance variations in the surface of the sample by use of two pairs of cursors. The cursors can be made to scale the surface in nanometer (nm) or micrometer (μm).

The interstitial region between the ridges represented in the dark area in Fig. 4 represents cavities in the membrane with a diameter of about 0.5nm. It is important to note that molecular basal spacing (cavities) in the range of 0.4-0.5nm has also been observed from molecular dynamic simulations of a cutin oligomer (Domnguez et al., 2011) and is attributed to the distance between the methylene groups of oligomeric chain. The presence of such cavities is a typical property of amorphous cross-linked polymers and may be important in explaining the interaction between cutin and endogenic low-molecular weight compounds such as phenolics and flavonoids.

2291.3 2615.3

2916.2

3348.2

3000.0 2000.0 1500.0 1000.0 500.0 CUTICLE PURE 1/cm

Fig. 3. Comparison of IR spectrum of Nandi flame cuticle with those of other biopolymers

The AFM scans (Fig. 4) shows that NFSC has a highly oriented surface topography. The AFM permits measurement of the distance variations in the surface of the sample by use of two pairs of cursors. The cursors can be made to scale the surface in nanometer (nm) or

The interstitial region between the ridges represented in the dark area in Fig. 4 represents cavities in the membrane with a diameter of about 0.5nm. It is important to note that molecular basal spacing (cavities) in the range of 0.4-0.5nm has also been observed from molecular dynamic simulations of a cutin oligomer (Domnguez et al., 2011) and is attributed to the distance between the methylene groups of oligomeric chain. The presence of such cavities is a typical property of amorphous cross-linked polymers and may be important in explaining the interaction between cutin and endogenic low-molecular weight

1427.2 1604.7

478.3

1033.8

1319.21157.2

0.0

Fig. 2. FT-IR spectrum of pristine cuticle

**4.2 Atomic force microscopy (AFM)** 

compounds such as phenolics and flavonoids.

micrometer (μm).

20.0

%T

40.0

Fig. 4. AFM topographic scans showing surface structure of the cuticle; (a) is a map from the scan on a larger area of about 3×105 square pixels (b) is a scan on a single pixel of about 2.5×106 nm2. Doted lines on (a) represents the region shown by (b). Scale bars ∼ 0.5nm.Taken from (Kipnusu et al., 2009).
