Asian Program

Japanese

Data

Former Fellows

Dissertation Abstracts

India

Name	Shilpa Nandkishor SAWANT
Position	Scientific Officer (E) Chemistry Division, Bhabha Atomic Research Centre
Japanese Advisor	Toshiaki ENOKI Professor,Tokyo Institute of Technology

  This thesis involves studies on physical properties of two categories of organic conductors, namely, conducting polymers and charge transfer complexes. These organic conductors are paving the way for 'all-organic' electronics-microelectronics devices and chips. Though these materials have a large potential for application, they have not been utilized to full extent due to practical difficulties. Many of these material lack important properties required for practical application such as high conductivity, stability, processability etc. The present thesis is an attempt to study some of the factors, which will help in improving physical properties of these materials. The thesis consists of a general introduction, a chapter on experimental details, followed by Chapters 3 to 6 describing the results, concluding with a summary in chapter 7.

  Polyaniline (PANI), a conducting polymer, has immense potential for application in new generation electronic devices. Thus evaluation of the environmental stability of polyaniline becomes an important issue so as to fabricate long lasting devices. The influence of aromatic sulphonate anions on the redox behavior and stability of polyaniline was investigated. Among the aromatic sulphonate anions studied, naphthalene sulphonic acid gave highest stability to polyaniline against degradation due to hydrolysis. Molecular modeling studies were conducted inorder to rationalize the experimental observations. In particular, the redox peak positions were correlated with the interaction energies.

  Organic-inorganic hybrid materials are designed to combine the properties of the inorganic part with the advantages of organic part. An organic-inorganic hybrid material composed of a conducting polyaniline (PANI) matrix and redox active Prussian blue (PB) network was synthesized, the latter formed in situ in the polymer matrix. The aim was to add the physical property of 'magnetism' to a conducting polymer. PB is known to exhibit magnetic ordering and it is electroactive in the potential range where polyaniline is conducting. The hybrid material showed ferromagnetic ordering with a Tc of - 6 K.

  Conductivity of conducting polymers can be improved by reducing defects in the long polymer chains, which can be achieved by preparing ordered or crystalline films. The monomer phenosafranine (PS) was arranged in the form of a well-ordered Langmuir-Blodgett (LB) film and then polymerized to obtain an ordered two-dimensional polymer. The film showed higher in-plane conductivity as compared to conductivity across the layer structure.

  Charge Transfer (CT) salts are usually synthesized as single crystals by electrocrystallisation technique. But for practical application in devices, generally it is required to use these materials in thin film form. Thin films of charge transfer salt of an ethylenedithiatetrathiafulvalne (EDT) derivative were prepared using the LB technique. The electrical conductivity of the 25 layer LB film was found to increase by two orders of magnitude on doping with iodine.

  Nanomaterials have received considerable attention in recent years since they can offer highly promising and novel options for a wide range of applications. Preparation of conducting polymer in the form of colloidal nanoparticles helps in improving its processability as these nanoparticles can be easily dispersed in water. An attempt was made to prepare colloidal nanoparticles of polyaniline using surfactant as microreactor to control the size and shape of the particles.

  Control over the spatial orientation and arrangement of nanoparticles is important for assembling and pattering nano-building blocks to fabricate future devices that are extremely fast, efficient and small. The Langmuir-Blodgett (LB) is a well-established tool, which allows supramolecular organization of different molecules at interfaces. Surfactant encapsulated molecular magnetic nanoparticles were synthesized and their LB film was deposited. The above strategy can be extended for fabrication of thin film of conducting polymer nanoparticles or other technologically important material.

  To summarize, the primary goal of this thesis was to study some of the important physical properties of organic conductors from the point of view of enhancing them for potential application. Various strategies were implemented for this purpose. Judicious selection of the dopant anion helped in improving the stability of polyaniline. Preparation of organic-inorganic hybrid helped in adding extra functionality (e.g. magnetism in the present case) to polyaniline. Polymerisation of monomer in its LB film helped in preparing an ordered film of the polymer with higher conductivity. The processability of polyaniline could be increased by preparing its colloidal nanoparticles. Magnetic nanoparticles based on Prussian blue analogue were synthesized and its LB films were prepared. LB technique helped in preparation of thin film of an EDT derivative (donor), which could be doped with iodine to give a conducting charge transfer salt.