Supervisors: Prof Väino Sammelselg, Keemia Instituut Tartu Ülikool and Prof Jüri Tamm, Keemia Instituut Tartu Ülikool
Oponent: Prof Mikhael Levi, Ülikool Bar-Ilan, Israel.
Within the last few decades conducting polymers were intensively investigated as a novel generation of organic materials that have both electrical and optical properties similar to those of metals and inorganic semiconductors, but which also exhibit the attractive properties associated with conventional polymers, such as ease of synthesis and flexibility in processing. These materials have already found applications in a number of advanced technologies, such as chemical sensors, electronic displays, batteries , etc., and are potent for application in a number of growing new technologies, such as soft polymer actuators or, artificial muscles. One popular representative of these conducting polymers is polypyrrole (PPy) - because of its good stability and ease of preparation by electrochemical polymerisation.In recent time interest also in nonconductive PPy films is increased, as they can be used as matrixes for biosensors, membranes, molecular sieves, etc..
PPy type polymers can be obtained by chemical or electrochemical oxidation of the monomer and it is possible to control some of the polymer properties by varying the experimental conditions. The electrochemical polymerisation of Py is a complex process, which includes several electrochemical and chemical reactions. The electronic properties of PPy films can be reversibly electrochemically changed between insulating and conducting states.
As is typical of polymers in general, the exact structure of PPy is difficult to determine. It is well known that experimental variables such as dopant, solvent, applied potential, nature of electrode and etc., have a strong influence on morphology of PPy film. The surface morphology of PPy films synthesised by electrochemical polymerisation is always mainly amorphous. In most cases the bulk PPy film has a "cauliflower" like structure. Differences in roughness and nodule sizes are connected with thickness of PPy film or dopant ion.
The aim of the present work was to investigate the first stage of PPy growth for better understanding the film formation mechanisms and also study of dependences of PPy film morphology on different dopant anions. For these purposes electrochemically polymerised PPy films were used. Morphology of these films were studied by scanning probe microscopy (SPM) methods.
The essential results of these investigations can be listed as follows:
¿ It was shown that the adsorbtion of Py and the ultrathin PPy films could be studied in details with SPM.
¿ AFM measurements of relatively "thick" (up to 1 ¿m) PPy films showed that morphology of the films is strongly influenced from synthesis conditions, dopant ion nature, and thickness of film.
A new simpliest way to produce ultrathin overoxydised PPy films was discovered during the investigations. Such films are applicable in different sensors.