Electrophoretic deposition of semiconducting polymer metal / oxide nanocomposites and characterization of the resulting films Dissertation zur Erlangung des akademischen Grades Doctor rerum naturalium (Dr. rer. nat.) vorgelegt der Fakultät für Mathematik und Naturwissenschaften der Technischen Universität Dresden von M.Sc Vu Quoc Trung geboren am 11. September 1972 in Hanam – Vietnam Gutachter: Prof. Dr. W. Plieth Prof. Dr. B. Voit Prof. Dr. S. Nespurek Eingereicht: 12.11.2005 Tag der Verteidigung: 13.01.2006 Acknowlegement Foremost, I would like to thank Prof. Dr. rer. nat. habil. Waldfried Plieth for giving me a good opportunity to study in the world of the conducting polymers and of the semiconductor electrochemistry. He is a strict but very kind teacher. He trains me to become a competent researcher with the independent thinking. I would like to thank Dr.rer.nat.habil. Ursula Rammelt and Dr. Jiri Pfleger for their valuable discussions and suggestions. They are willing to provide me all supports to undergo this study. Many words are talked to thank Dr. Niels Hebestreit and Dr. Martin Pavlik for introducing me to conducting polymers and methods for characterization. They teach me how to use the devices in the laboratory and help me to overcome the scientific problems. They are my best friends and collaborators. I appreciate the help of Mrs. Ellen Kern for SEM, Mrs. I. Poitz for TGA measurements, Dr. C. Bellmann and Mrs. Cascapi for zeta potential measurements, Dipl.-Chem. Andreas Anders for Raman spectra, Dipl.-Phys. A. Lenk for TEM measurements. My sincere thanks to Dr. rer. nat. habil Andreas Bund, Miss Adriana Ispas and Mr. Ashok Kumar N. for helping me to set up QCM system and for teaching me how it works. I would like to acknowledge all my members of the work group and of the Institute of Physical Chemistry and Electrochemistry (especially Matthias Intelmann and Dr. Hartmut Dietz). They have given me happiness and pleasure in the last three years. I will remember them forever. I deeply appreciate all the teachers in the European Graduate School “Advanced polymeric materials” (720), who teach me about the advanced polymeric materials. This work is financially supported by DFG (Deutsche Forschung Germeinshaft) and the Fonds der chemischen Industrie. Content Abbreviation..........................................................................................................................6 Introduction and aim of the work .......................................................................................8 Part I Theoretical background of conducting polymers and their composites...............9 1.1. Intrinsically conducting polymers....................................................................................9 1.1.1 Brief overview ...............................................................................................................9 1.1.2 Basic properties of conducting polymers.....................................................................10 1.1.2.1 Charge storage and band structure............................................................................10 1.1.2.2 Charge transport........................................................................................................13 1.1.2.3 Stability.....................................................................................................................13 1.1.2.4 Processing possibility................................................................................................14 1.1.2.5 Application................................................................................................................15 1.2. Conducting polymer nanocomposites............................................................................17 1.2.1 Introduction..................................................................................................................17 1.2.2 Chemical process .........................................................................................................17 1.2.2.1 Nanocomposite particles with core-shell structure...................................................17 1.2.2.2 Nanocomposite layers prepared by chemical oxidation ...........................................19 1.2.3 Electrochemical preparation ........................................................................................20 1.2.3.1 Electropolymerization of conducting polymer on metal oxide layer........................20 1.2.3.2 Codeposition of conducting polymer and oxide particles.........................................21 1.2.4 Physical preparation.....................................................................................................22 1.2.5 Other processes ............................................................................................................24 Part II Theoretical background of electrophoretic deposition (EPD) ...........................25 2.1 Introduction.....................................................................................................................25 2.2 Mechanism of electrophoretic deposition.......................................................................28 2.3 Kinetics of electrophoretic deposition ............................................................................32 2.4 Application of electrophoretic deposition.......................................................................36 2.4.1 Coatings .......................................................................................................................36 2.4.2 Fibre reinforced ceramic matrix composites................................................................37 2.4.3 Laminated and graded composites...............................................................................37 2.4.4 Nanomaterials and nanostructures ...............................................................................38 3 Part III Theoretical background of semiconductor electrochemistry ...........................39 3.1 Introduction.....................................................................................................................39 3.2 Fundamentals of semiconductor electrochemistry..........................................................40 3.2.1 Energy bands in solids and charge carrier generation .................................................40 3.2.2 Fermi level and effect of applied potential ..................................................................43 3.2.3 Photoeffect at the semiconductor electrolyte interface................................................45 3.2.4 Determination of flatband potential.............................................................................48 3.2.4.1 Mott-Schottky plot....................................................................................................48 3.2.4.2 Photocurrent onset potential .....................................................................................49 Part IV Experimental procedures .....................................................................................51 4.1 Reagents and solvents.....................................................................................................51 4.1.1 Reagents.......................................................................................................................51 4.1.2 Solvents........................................................................................................................51 4.1.3 Other chemicals ...........................................................................................................51 4.2 Preparation of nanocomposites.......................................................................................51 4.3 Morphology and chemical structure of nanocomposites ................................................52 4.4 Dark conductivity and thermogrametrical measurements ..............................................52 4.5 Properties of suspension .................................................................................................53 4.6 Electrophoretic deposition ..............................................................................................53 4.7 Characterization of resulting films..................................................................................55 4.7.1 UV-VIS spectra............................................................................................................55 4.7.2 Photocurrent measurements.........................................................................................55 4.7.3 Photoelectrical and electrical characteristics ...............................................................56 4.7.4 Cyclic voltammetry......................................................................................................56 4.7.5 Electrochemical impedance spectroscopy ...................................................................56 Part V Results and discussion............................................................................................60 5.1 Morphological and chemical characterization of nanocomposites.................................60 5.1.1 Morphology of nanocomposite particles .....................................................................60 5.1.2 Chemical characterization of nanocomposites.............................................................62 5.2 Electrophoretic deposition ..............................................................................................64 5.2.1 Properties