G. Danev

Polyimide coatings containing azo-chromophores as structural units

Results are presented on the vacuum deposition of polyimide layers containing azochromophore as structural unit. The imidization process of the polymer thin films was studied by FT-IR and optical spectroscopy. After microwave and thermal treatment the, polyimide layers are E-diastereomers only, with a homogeneous smooth surface devoid of cracks. The technique used is suitable for preparing polyimide coatings containing chromophores with tailored properties.

VACUUM DEPOSITED COPPER PHTHALOCYANINE THIN FILMS-STRUCTURE AND SURFACE MORPHOLOGY

Abstract The surface morphology and the structure has been studied of vacuum deposited copper phthalocyanine (CuPc) thin films formed by vapour deposition of CuPc on fixed substrates at room temperature. Scanning electron microscopy revealed a grain surface morphology. Subsequent annealing, increase in layer thickness and the angle and the rate of deposition raised the average grain size. The electron diffraction pattern and optical transmission spectra showed an α polycrystalline structure. The most fine-grained 10 nm and homogeneous layers had thicknesses below 250 nm and a growth rate of 0.2–0.8 nm\s. The study was directed towards the potential application of the vacuum deposited CuPc layers in gas sensors.

Properties of vacuum-deposited polyimide films

Abstract Vacuum-deposited polyimide (PI) thin films have been prepared by co-deposition of precursor pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) followed by thermal treatment. The dependency of the optical and electrical properties, chemical resistivity and mechanical stability on the composition (ODA:PMDA) and the degree of imidization of the PI layers have been investigated and discussed. The experimental results have yielded possibilities to microstructure the vacuum-deposited PI films by excimer laser irradiation or reactive ion etching in gas mixture CF 4 /O 2 .

Excimer laser structuring of bulk polyimide material

Abstract A bulk polyimide system prepared by pressing of the precursor monomers 4,4′-oxidianiline (ODA) and 1,2,4,5-benzenetetracarboxylic or pyromellitic dianhydride (PMDA) mixtures has been investigated. The synthesized bulk polyimide is formed as a result of a polycondensation reaction of monomers in solid state phase. A change of the monomers polycrystalline structure to an amorphous one of the bulk polyimide after imidization is established. The possibility for excimer laser microstructuring by drilling at various diameters and depths is demonstrated. The scanning electron microscopic observations reveal alterations in the so formed blind holes as a consequence of the laser action parameters variation. The changes observed and the dependencies obtained are discussed.

Chemical and Physical Properties of Polyimides: Biomedical and Engineering Applications

© 2012 Georgiev et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Chemical and Physical Properties of Polyimides: Biomedical and Engineering Applications

Preparation of Polyimide Thin Films by Vapour Deposition and Solid State Reactions

In this chapter we describe the preparation of polyimide thin films by physical vapour deposition and comment on their potential application as a pure material or a thin layer matrix for producing nanocomposite layers. Their superb properties, such as a low dielectric constant, high thermaland photo-stability, high chemical resistance and high optical transmittance predetermine their widespread applications as a casts and layers used as insulators, protective or capsulation layers, mechanical or diffusion barriers, in optoand microelectronics. The bulk properties of the polyimide allowed the preparation of nanocomposite materials with organic chromophores as a “guest” (the embedded in the matrix nanosized particles). Moreover, some of the “guest” could bind to the polyimide chain. There are numbers of aromatic polyimides which are broadly used as thin layers in nanotechnology. Vapour deposition of the precursors and solid state reactions of imidization are of a greater priority than the spin coating and dipping methods. These as-deposited films by the vacuum deposition process consist of a dianhydride and diamine mixture, which by solid state reactions is converted to polyimide by thermal treatments or by combined microwave and thermal treatments. The physical vapour deposition as a “dry” method provides high purity for producing thin polymer films of controlled thickness, ratio of precursors and composition control of the so prepared layers. In this chapter we suggest possibilities for the practical application of vapour deposition of precursors and the following solid state reactions. By the used spectral methodFourier Transform Infrared Spectroscopy for analysis of the investigated kinetics of imidization reactions and microstructure of the layers are studied. The relationship between vapour deposition conditions and the presence of regular chains leading to the appearance of infrared bands is discussed. Polymers are also capable of forming a range of conformations depending on the backbone structure. The conditions for preparation by physical vapour deposition and solid state reaction of polyimide or nanocomposite polyimide layers are discussed.

Polyimide-matrix-based composite materials

A polycondensation solid-state-reaction-based polyimide (PI) matrix has been used for composite material formation. Two types of PI matrix have been employed – a bulk PI system prepared by pressing a mixture of the powdered precursors (4, 4′-oxidianiline (ODA) and pyromellitic dianhydride (PMDA)) and a thin-film matrix formed by vapor co-deposition of the same precursors, PI monomers. A variety of different “guests” (trimethylaminalan, phthalocyanine, carbon) and the methods for their incorporation into the PI matrix are presented. The influence of the “guest” concentration and the thermal-treatment conditions on the surface morphology are shown and discussed.

Synthesis of “Main – Chain” Type Polyimide Matrix with a Chemically Bound Azo Group

A method for obtaining thin vacuum deposited azopolyimide layers is established. On the basis of the thermogravimetric and differential thermal analyses, the chemical reaction in the solid state between the initial precursors - 4,4’-diaminoazobenzene and pyromellitic dianhydride is discussed. Also, the preparation parameters allowing for a condensation of films of desired composition are determined. Fourier Transform Infrared Spectroscopy analyses confirm that the azo group is chemically bound in a thin polyimide layer matrix. This is a solution to the task of preparing a “Main – Chain” type polyimide matrix with a chemically bound azo- group.

Vacuum deposited composite polyimide – phthalocyanine films☆

Abstract Polyimide (PI) – phthalocyanine (Pc) composite films prepared by means of simultaneous vacuum deposition of vapours of PI precursors — oxydianiline (ODA) and pyromellitic dianhydride (PMDA), and Pc — metal-free — or copper phthalocyanine, were investigated. Thermal treatment regimes for imidization of ODA and PMDA to PI without essential changes in the chromophore concentration and in the surface morphology of the layers have been determined. The changes observed in the optical transmission and adsorption of the films, and in the optical density of the irradiated areas have been discussed as resulting from the different composition of the layers. Also laser modification and structuring in different film depths were accomplished. The threshold energies of excimer laser irradiation necessary for these purposes were determined. The obtained results render the possibilities for the study of the layers’ properties in optical element formation.

Vacuum deposited polyimide\carbon composite layers

Abstract Composite layers, 500–1000 nm thick, consisting of a polyimide matrix and a guest of embedded carbon particles were investigated. The layers were obtained by a simultaneous deposition of the monomers—pyromellitic dianhydride and oxydianiline. Carbon particles were intermittently incorporated by means of quasi-arc evaporation and erosion of the graphite electrode in the course of the organic layer growth. The so obtained layers were thermally treated aiming at an imidization of the matrix and its transformation into a polyimide. The electron microscopy observations show that the layer surfaces are devoid of visible structure and cracks at carbon concentration up to 4 vol.%. The average size of the embedded carbon particles is x = 18.5 nm and the size dispersion is 6.3 nm [2] . The optical density, transmittance and reflectance, as well as the conductivity are considerably dependent on the carbon amount. The measured conductivity of the composite layers is several orders of magnitude higher than the one of the vacuum deposited polyimide films.