Andrei Choukourov

The influence of pulse parameters on film composition during pulsed plasma polymerization of diaminocyclohexane

Abstract Plasma polymerization of diaminocyclohexane was investigated in order to deposit the amine groups rich plasma polymer films for biomedical applications. The obtained films were characterized by FTIR and XPS in dependence on duty cycle ranging from continuous wave mode (CW) to 0.1 and ton varied from 0.02 to 10 ms. The concentration of primary and secondary amine groups was determined by the derivatization technique using trifluoromethyl benzaldehyde (TFBA) and trifluoroacetic anhydride (TFAA). It has been shown that the concentration of both follows the same curve with the minimum at ton=0.5 ms (duty cycle 0.1). The plasma polymerization process likely differs here from the processes for higher and lower ton. The highest primary amine concentration reached is 8%. The films prepared at ton=0.5 ms are shown to be less stable due to aging by oxidation as shown by XPS on films kept in open air. The FTIR analysis confirms the same dependence of amine groups’ concentration as above. As the deposition rate increases for decreased ton it will be advantageous to prepare the plasma polymer films with the higher amine group concentrations at decreased ton below 0.5 ms.

Vacuum Thermal Degradation of Poly(ethylene oxide)

Thermal degradation of poly(ethylene oxide) (PEO) was studied under vacuum conditions. PEO macromolecules degrade predominantly by random chain scission of a backbone with elimination of oligomer fragments. The reactions include the mechanism of radical termination by disproportionation. The eliminated fragments form thin film deposits which have chemical composition close to the original PEO. Activation of the evaporated flux with a glow discharge leads to further fragmentation and recombination of the released species and can be used to tune the properties of the resulting thin films.

RF sputtering of hydrocarbon polymers and their derivatives

RF sputtering of polymeric targets was discussed from the point of view of history and present status of the field. RF sputtering of polytetrafluorethylene (PTFE) was mentioned in self-sputtering mode, argon, nitrogen and other gases. The emission of fragments from the target observed by means of quadrupole mass spectroscopy and target surface as observed by SEM were described. Columnar morphology of the sputtered films at substrate temperatures below room temperature was mentioned. Deposition rate of sputtered PTFE films was found up to one order of magnitude higher than polyimide (PI) sputtered films. Results of PI sputtering process and films characterization in terms of tribological coatings were reviewed. Polyethylene (PE) and polypropylene (PP) sputtering was found below 100 W power more than three times slower than PTFE sputtering. The films are hydrocarbon plasma polymers containing a lot of oxygen and OH groups. Above 100 W the co-evaporation from the erosion zone of the target took place and deposited films resemble much more the parent target as observed by FTIR. Finally, co-sputtering of metal and polymer that results in nanocomposite metal/plasma polymer films and sputtering of SiO2/PTFE composite target is shortly discussed.

Plasma polymers prepared by RF sputtering of polyethylene

Hydrocarbon plasma polymer thin films were deposited by means of magnetron sputtering of polyethylene (PE) using Ar as the working gas. AFM, ESCA, FTIR techniques were applied to investigate the films properties and composition. The films sputtered at Radio frequency (RF) power up to 100 W have a plasma polymer structure whereas further increase of RF power results in hydrocarbon plasma polymers more resembling conventional PE.

Rf sputtering of composite SiOx/plasma polymer films and their basic properties

Abstract Composite SiOx/PTFE films were deposited by rf sputtering in argon using balanced magnetron equipped with a PTFE/SiO2 target. The composition of deposited films, found by XPS and FTIR, ranged from fluorocarbon plasma polymers with very small SiOx content up to coatings with a greater incorporation of SiOx. The hardness of fluorocarbon polymer films with increased concentration of SiOx was 2400 N/mm2. This is between two to three times higher than in the case of fluorocarbon plasma polymers with very low SiOx content. The static contact angle of water ranges from 112 to 95° and the refractive index from 1.49 to 1.43, when incorporation of SiOx into fluorocarbon plasma polymer matrix decreases.

Composite Ag/C:H films prepared by DC planar magnetron deposition

Abstract Composite Ag/C:H films were deposited by means of an unbalanced magnetron operated in a gas mixture of argon and n -hexane. We used a gradual coating (‘poisoning’) of the target by a carbonaceous layer to deposit films with decreasing rate of silver sputtering. Rate of deposition of the films decreases with the covering of the magnetron target. XPS measurements were performed with the aim to study the composition of the films. The surface energy of the films was estimated from static water and formamide contact angles, which were measured using the droplet method. Values of the water contact angle were found to be in the range from 88° to 66°. Absorption spectra in the visible, near UV and IR region were studied as a function of silver concentration. FTIR spectroscopy was employed to investigate the composite films and monitor their aging. CH 2 /CH 3 stretching and deformation bands are present in all infrared spectra of the films. Evolution of the FTIR spectra with aging shows a high influence of concentration and size of the metallic inclusions on the absorption bands of the carboxyl and carbonyl groups.

Deposition of amino-rich thin films by RF magnetron sputtering of nylon

RF magnetron sputtering of a nylon target in different gas mixtures was studied in order to evaluate the capability of this process to deposit amino-rich coatings needed in a wide range of biomedical applications. It has been demonstrated that both the deposition rate of the coatings and the surface density of primary amino groups are strongly linked with working gas mixture composition. From this point of view, a sufficiently high deposition rate as well as the highest amine efficiency reaching a NH2/C value of 18% was observed in the N2/H2 discharge, which leads to the surface exhibiting a high rate of protein adsorption.

Nylon-sputtered nanoparticles: fabrication and basic properties

Nylon-sputtered nanoparticles were prepared using a simple gas aggregation cluster source based on a planar magnetron (Haberland type) and equipped with a nylon target. Plasma polymer particles originated in an aggregation chamber and travelled to a main (deposition) chamber with a gas flow through an orifice. The deposited nanoparticles were observed to have a cauliflower-like structure. The nanoparticles were found to be nitrogen-rich with N/C ratio close to 0.5. An increase in rf power from 60 to 100 W resulted in a decrease in mean particle size from 210 to 168 nm whereas an increase in their residence time in the cluster source from 0.7 to 4.6 s resulted in an increase in the size from 73 to 231 nm.

Nanocomposite Ti/hydrocarbon plasma polymer films from reactive magnetron sputtering as growth support for osteoblast-like and endothelial cells

Nanocomposite Ti/hydrocarbon plasma polymer (Ti/ppCH) films were deposited by DC magnetron sputtering of titanium target in n-hexane, argon, or a mixture of these two gases. The resultant films were heterogeneous, with inorganic regions of nanometer scale distributed within a plasma polymer matrix. The titanium content was controlled by adjusting the argon/n-hexane ratio in the working gas. In the pure n-hexane atmosphere, the Ti concentration was found to be below 1 at %, whereas in pure argon it reached 20 at %, as measured by Rutherford backscattering spectroscopy and elastic recoil detection analysis (RBS/ERDA). A high level of titanium oxidation is detected with TiO(2), substoichiometric titania, and titanium carbide, composing an inorganic phase of the composite films. In addition, high hydrogen content is detected in films rich with titanium. Ti-deficient and Ti-rich films proved equally good substrates for adhesion and growth of cultured human osteoblast-like MG 63 cells. In these cells, the population densities on days 1, 3, and 7 after seeding, spreading area on day 1, formation of talin-containing focal adhesion plaques as well as concentrations of talin and osteocalcin (per mg of protein) were comparable to the values obtained in cells on the reference cell culture materials, represented by microscopic glass coverslips or a polystyrene dish. An interesting finding was made when the Ti/ppCH films were seeded with calf pulmonary artery endothelial cells of the line CPAE. The cell population densities, the spreading area and also the concentration of von Willebrand factor, a marker of endothelial cell maturation, were significantly higher on Ti-rich than on Ti-deficient films. On Ti-rich films, these parameters were also higher or similar in comparison with the reference cell culture materials. Thus, both types of films could be used for coating bone implants, of which the Ti-rich film remains effective in enhancing the endothelialization of blood contacting artificial materials.

Nanocomposite and Nanostructured Carbon-based Films as Growth Substrates for Bone Cells

Lucie Bacakova1, Lubica Grausova1, Jiri Vacik2, Alexander Kromka3, Hynek Biederman4, Andrei Choukourov4 and Vladimir Stary5 1Department of Growth and Differentiation of Cell Populations, Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, 2Nuclear Physics Institute, Academy of Sciences of the Czech Republic & Research Center Rez, 3Institute of Physics, Academy of Sciences of the Czech Republic, Prague, 4Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, Prague, 5Faculty of Mechanical Engineering, Czech Technical University, Prague, Czech Republic