V. S. Panwar

Low‐frequency ac conduction in lightly doped polypyrrole films

The total measured ac conductivity σ(ω)m of lightly doped polypyrrole films has been measured in the frequency range 100 Hz–10 MHz and in the temperature range 77–350 K. In the low‐temperature region the measured ac conductivity is almost independent of temperature but shows a strong dependence on frequency and can be described by a relation σ(ω) = Aωs where the exponent s has been observed to be less than unity. In the high‐temperature region the frequency dependence becomes weak at low frequencies but remains strongly frequency dependent at high frequencies. The weak frequency dependence is due to the contribution of dc conductivity to the measured ac conductivity. A clear Debye‐type loss peak is observed by substracting the contribution of dc conductivity. The frequency dependence of conductivity remains less than quadratic at low frequencies indicating thereby some distribution of relaxation times. This is confirmed by the measurement of dielectric constant as a function of frequency and temperature. ...

Growth kinetics of polypyrrole, poly (N-methyl pyrrole) and their copolymer, poly (N-methyl pyrrole-pyrrole) : effect of annealing on conductivity and surface structure

Abstract Films of polypyrrole, poly ( N -methyl pyrrole) and their copolymer, poly ( N -methyl pyrrole-pyrrole), are prepared by an electrochemical polymerization technique using a planar electrode configuration. Scanning electron microscopy (SEM) studies reveal a cauliflower morphology for these films which is attributed to the 3D-type nodular growth in these polymers. The effect of annealing on the surface morphology and the conductivity of these films are examined.

Origin of d.c. conduction and dielectric relaxation in lightly doped polypyrrole films

We discuss the basic mechanism of transport in lightly doped PPY films. An attempt has been made to establish a correlation between dielectric relaxation and d.c. conductivity, both of which originate from the same conduction process

Low-frequency ac conduction and dielectric relaxation in vinyl chloride:vinyl acetate copolymers

ac conductivity σ(ω), dielectric constant e’, and loss e‘ of vinyl chloride:vinyl acetate (VC:VAc) copolymers having 3%, 10%, and 17% VAc content (by weight) have been measured in the temperature range 77–410 K and in the frequency range 50 Hz–100 kHz. At low temperatures up to 250 K, the ac conductivity can be expressed by σ(ω)=Aωs, where the slope s is close to unity and its value decreases with the increase in temperature. The dielectric constant in this temperature region shows a very weak frequency and temperature dependence. At temperatures above 300 K, the ac conductivity shows a strong temperature dependence; however, in this temperature region the dielectric constant shows a strong frequency dispersion. The measured dielectric loss as a function of temperature reveals the β1, the β2, and the α relaxations. The β1 relaxation is associated with the movement of the more flexible side group dipoles and the β2 relaxation is due to the movement of rigidly attached side group dipoles, whereas the α rela...

Hoppijg Transport and Relaxation Phenoiena in Poly(Vinyl Chloride: Vinyl Acetate: Vinyl Alcohol) Terpolymer

Dielectric measurements have been made on poly(vinyl chloride: vinyl acetate: vinyl al cohol) in the frequency range 30 Hz to 100 kHz and in the temperature range 77 to 410 K. A frequencydependent conductivity described by ¿(w) = Aws is observed, where s<1 and is independent of temperature up to 250 K but decreases at higher temperatures. Two relaxations, the ¿- and the ß-relaxation, are observed having activation energies ¿0.92 and ¿0.42 eV, respectively. The ¿-relaxation is attributed to the segmental motion of the main chain consisting of the constituent groups of the terpolymer under dipole-dipole interaction and the ß-relaxation is due to the C-Cl dipoles in the amorphous phase of the terpolymer.

Low temperature relaxation in polypyrrole

The loss tangent and dc conductivity of electrochemically polymerized BF−4 doped polypyrrole films have been measured in the temperature range 77–300 K. The low temperature relaxation has been observed which shows decrease of relaxation frequency with increase in temperature. The dc conductivity data has been described by a hopping model.

Hydrogen bonding and its temperature dependence in vinyl chloride-vinyl acetate-vinyl alcohol terpolymer: A study using the IR absorption technique

Abstract IR absorption studies have been made on vinyl chloride-vinyl acetate-vinyl alcohol terpolymer in the range 4000–400cm −1 at temperatures of 298, 323, 348, 373 and 398 K. It shows a broad—OH band at about 3460 cm −1 with a kink at its shoulder on the higher frequency side at about 3580 cm −1 at 298K. The IR spectra of the films treated at 323 and 348K show a decrease in the magnitude of the band at about 3460 cm −1 with a slight increase in the magnitude of the band at about 3580cm −1 while the IR spectra of films treated at 373 and 398K show, besides a shift in the sharp band (about 3580 cm −1 ) towards the higher frequency side, an increase in its magnitude, whereas the broad band (about 3460 cm −1 ) continues to decrease in magnitude with rise in temperature. The analysis of these bands and their temperature dependence are reported in the present paper.

A Model for AC Conduction of Conducting Polymers

Conducting polymers have been a subject of extensive investigations1–3 but little has been done to understand the mechanism of conduction and dielectric relaxation behaviour perhaps due to the fact that the main interest was to enhance the conductivity by doping.Polypyrrole (PPY) has been investigated by several workers1–3 for its electrical and optical properties. It has been argued that soliton antisoliton pairs in the form of polarons and bipolarons3,4 can be stable in polymeric conductors with slightly nondegenerate ground states. Kivelson5 has applied the intersoliton hopping model to explain the electrical conductivity of trans polyacetylene (trans-PA).However, several doubts have been raised4 on the procedure adopted by Kivelson5 in formulating his model. It has been concluded’ that none of the existing models of ac and dc conduction are satisfactory for lightly doped trans-PA. The present investigation is an attempt to provide the exhaustive conductivity data and to propose a model based on polaronic hopping conduction1,6. The observed frequency and temperature dependence of ac conductivity of PPY can be explained satisfactorily by the proposed model which considers the contribution from two mechanisms one giving a linear dependence of conductivity on frequency and the other having distribution of relaxation times giving rise to a broad dielectric loss peak.

Temperature dependence of -OH band in vinyl chloride:vinyl acetate:vinyl alcohol terpolymer

IR absorption studies of vinyl chloride:vinyl acetate:vinyl alcohol (VC:VAc:VA) terpolymers in the range 4000-400 cm/sup -1/ at temperatures of 298, 323, 348, 373 and 398 K show a broad -OH band at approximately 3460 cm/sup -1/ with a kink at its shoulder on the higher frequency side at approximately 3580 cm/sup -1/. The IR spectra of the films treated at 323 and 348 K show a decrease in the magnitude of the band at approximately 3460 cm/sup -1/ with a slight increase in the magnitude of the band at approximately 3580 cm/sup -1/. The IR spectra of films treated at 373 and 398 K show, besides a shift in the sharp band toward the higher frequency side, an increase in its magnitude, whereas the broad band (at approximately 3460 cm/sup -1/) continues to decrease in magnitude with the rise of temperature. The analysis of these bands and their temperature dependence are reported.<<ETX>>

Hopping transport and relaxation phenomena in poly (vinyl chloride: vinyl acetate: Vinyl alcohol) terpolymer

Dielectric measurements have been made on poly (vinyl chloride: vinyl acetate: vinyl alcohol) in the frequency range 30 Hz-100 KHz and in the temperature range 77–410 K. A frequency dependent conductivity described by σ(ω) = A ω^s, is observed where S < 1 and is independent of temperature upto 250 K but with further increase in temperature it decreases. Two relaxations, the α-and the β-relaxation, are observed having activation energies ∼ 0.92 and 0.42 eV, respectively. The α-relaxation is attributed to the segmental motion of the main chain consisting of the constituent groups of the terpolymer under dipole-dipole interaction and the β-relaxation is due to the C-C1 dipoles in the amorphous phase of the terpolymer.