Ionut Topala

Dielectric barrier discharge technique in improving the wettability and adhesion properties of polymer surfaces

A dielectric barrier discharge (DBD) in helium at atmospheric pressure was used to improve the polymer surface wettability as a first condition for ensuring a good adhesivity in particular for a subsequent immobilization of selected biological macromolecules (heparin, drugs, enzymes, etc.) on these surfaces. The DBD was analyzed by electrical measurements and optical emission spectroscopy. The polymer surface was characterized by thermodynamic parameters which may predict the adhesion properties, the adhesion work and the surface polarity, and also by its morphology. The results show that the DBD treatments improve the wettability and thus the adhesive properties due to the creation of functional groups and less due to a physical adsorption induced by an expected larger area of the treated surfaces. Dimensions of grains/crystallites are decreased on the treated surface, but a significant and systematic modification of the surface roughness was not observed.

Effect of helium DBD plasma treatment on the surface of wood samples.

Abstract The effects of helium dielectric barrier discharge (He-DBD) plasma treatment has been studied aiming at the preparation of wood for profitable dye covering and impregnation with an antibacterial oil. Electrical and optical emission spectroscopy measurements were performed to characterise the He-DBD discharge. The hydrophilic/hydrophobic properties of the modified surfaces were studied by dynamic contact angle measurements. The spreading area of the wet spots was also evaluated as a function of wetting time. After He-DBD plasma exposure, the adhesion properties are substantially improved and the hydrophilic character of wood surface is enhanced. The behaviour of linseed oil drops on the modified surfaces confirmed the utility of He-DBD treatment.

Effects of air transient spark discharge and helium plasma jet on water, bacteria, cells, and biomolecules

Atmospheric pressure DC-driven self-pulsing transient spark (TS) discharge operated in air and pulse-driven dielectric barrier discharge plasma jet (PJ) operated in helium in contact with water solutions were used for inducing chemical effects in water solutions, and the treatment of bacteria (Escherichia coli), mammalian cells (Vero line normal cells, HeLa line cancerous cells), deoxyribonucleic acid (dsDNA), and protein (bovine serum albumin). Two different methods of water solution supply were used in the TS: water electrode system and water spray system. The effects of both TS systems and the PJ were compared, as well as a direct exposure of the solution to the discharge with an indirect exposure to the discharge activated gas flow. The chemical analysis of water solutions was performed by using colorimetric methods of UV-VIS absorption spectrophotometry. The bactericidal effects of the discharges on bacteria were evaluated by standard microbiological plate count method. Viability, apoptosis and cell cycle were assessed in normal and cancerous cells. Viability of cells was evaluated by trypan blue exclusion test, apoptosis by Annexin V-FITC/propidium iodide assay, and cell cycle progression by propidium iodide/RNase test. The effect of the discharges on deoxyribonucleic acid and protein were evaluated by fluorescence and UV absorption spectroscopy. The results of bacterial and mammalian cell viability, apoptosis, and cell cycle clearly show that cold plasma can inactivate bacteria and selectively target cancerous cells, which is very important for possible future development of new plasma therapeutic strategies in biomedicine. The authors found that all investigated bio-effects were stronger with the air TS discharge than with the He PJ, even in indirect exposure.

Dynamics of the wetting process on dielectric barrier discharge (DBD) treated wood surfaces

Protection and preservation of wood properties in exterior environments can only be ensured if the surface is coated with a paint or varnish. In our experiments a dielectric barrier discharge (DBD) was used as a wood surface pretreatment for improvement of the subsequent deposition of thin paint layers from solutions onto these surfaces. As the adsorption, interfacial interactions and adhesion of paints are strongly dependent on surface wettability, the dynamics of the wetting process were analyzed. The results show that the water contact angle decreases after the DBD treatment, proving a more wettable surface. Additionally, the spreading of paint solution on the DBD-treated surface is more isotropic, showing a lower tendency to elongate along the wood fiber orientation.

Influence of operational parameters on plasma polymerization process at atmospheric pressure

In this paper, a dielectric barrier discharge working at atmospheric pressure has been used in order to investigate the plasma polymerization reactions using styrene vapors. The macroscopic parameters were carefully chosen in order to obtain polymer thin films with high deposition rate and high concentration of activated species consequently. Thus, the plasma polymerization processes can be described considering the dependence of polymer deposition rate by monomer flow rate and discharge power. The domains of plasma polymerization reactions were identified and the optimum operating conditions were obtained at a maximum deposition rate of 3.8 nm/s (discharge power: 7.5 W). Different techniques of analysis were used to identify the chemical composition of plasma polystyrene films and the domains of polymerization reaction. The film thickness was measured by optical interferometry and the chemical composition was analyzed by Fourier-transform infrared spectroscopy, UV spectroscopy, and x-ray photoelectron sp...

Atmospheric pressure plasma jet—Living tissue interface: Electrical, optical, and spectral characterization

The atmospheric pressure plasma jet is studied as potential plasma source for medical applications in direct contact with living tissues. Plasma bullets are generated in the region of the high voltage electrode and propagate towards the tissue surface. The presence of a localized plasma structure on tissues, played here by a human fingertip, is experimentally revealed. It was found that this plasma structure is sustained by a current flowing through the tissue, with the magnitude dependent on the distance from the discharge tube. The characteristic time span of the plasma at the interface is up to 20 μs and the diameter up to 5 mm. These parameters were studied using the two independent techniques: ultra-fast imaging and photomultiplier measurements. Generation of supplementary reactive species at the interface, the NO molecules, was proved by optical emission spectroscopy.The atmospheric pressure plasma jet is studied as potential plasma source for medical applications in direct contact with living tissues. Plasma bullets are generated in the region of the high voltage electrode and propagate towards the tissue surface. The presence of a localized plasma structure on tissues, played here by a human fingertip, is experimentally revealed. It was found that this plasma structure is sustained by a current flowing through the tissue, with the magnitude dependent on the distance from the discharge tube. The characteristic time span of the plasma at the interface is up to 20 μs and the diameter up to 5 mm. These parameters were studied using the two independent techniques: ultra-fast imaging and photomultiplier measurements. Generation of supplementary reactive species at the interface, the NO molecules, was proved by optical emission spectroscopy.

Hydrophobic Coatings Obtained in Atmospheric Pressure Plasma

Plasma polymerization at atmospheric pressure is used to obtain stable hydrophobic coatings onto various substrates. Plasma is generated in a dielectric barrier discharge configuration using a mixture of helium gas and styrene vapors. The discharge is characterized by means of electrical measurements and optical emission spectroscopy. Since the styrene vapors introduced in plasma provide a significant decrease of the discharge current, we established the optimum parameters (voltage waveform, gap length, and gas flow rates) for plasma polymerization, assuring a maximum discharge current. The plasma-polymerized films (polystyrene), deposited onto the glass or silicon substrates, are analyzed by contact angle measurements, ellipsometry, IR spectroscopy, and atomic force microscopy (AFM). The film thickness is measured by light interferometry and confirmed by AFM analysis. The water contact angles are higher than 130deg, proving the hydrophobic characteristics of the film, and the refractive index is around 1.5, corresponding to the values of commercial polystyrene.

Properties of some azo-copolyimide thin films used in the formation of photoinduced surface relief gratings

Thin free standing films have been obtained by casting from dimethylacetamide solutions of some azo-copolyimides. The dynamo-mechanical and dielectric properties, and the effect of the chemical structure of polymers on the physical properties are investigated. The incorporation of substituted azobenzene groups and hexafluoroisopropylidene units in the macromolecular chain allowed the patterning of the materials under different irradiation conditions. The azo-copolyimide thin films showed high thermal stability, low dielectric constant, good dynamo-mechanical characteristics and uniform surface relief gratings.

Atmospheric pressure plasma polymers for tuned QCM detection of protein adhesion.

Our efforts have been concentrated in preparing plasma polymeric thin layers at atmospheric pressure grown on Quartz Crystal Microbalance-QCM electrodes for which the non-specific absorption of proteins can be efficiently modulated, tuned and used for QCM biosensing and quantification. Plasma polymerization reaction at atmospheric pressure has been used as a simple and viable method for the preparation of QCM bioactive surfaces, featuring variable protein binding properties. Polyethyleneglycol (ppEG), polystyrene (ppST) and poly(ethyleneglycol-styrene) (ppST-EG) thin-layers have been grown on QCM electrodes. These layers were characterized by Atomic Force Microscopy (AFM), Contact angle measurements, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The plasma ppST QCM electrodes present a higher adsorption of Concanavalin A (ConA) and Bovine Serum Albumin (BSA) proteins when compared with the commercial coated polystyrene (ppST) ones. The minimum adsorption was found for ppEG, surface, known by their protein anti-fouling properties. The amount of adsorbed proteins can be tuned by the introduction of PEG precursors in the plasma discharge during the preparation of ppST polymers.

Thermal behavior of bovine serum albumin after exposure to barrier discharge helium plasma jet

Non-thermal plasma jets at atmospheric pressure are useful tools nowadays in plasma medicine. Various applications are tested such as cauterization, coagulation, wound healing, natural and artificial surfaces decontamination, and sterilization. In order to know more about the effects of gas plasma on biological supramolecules, we exposed protein powders to a barrier discharge helium plasma jet. Then, spectroscopic investigations were carried out in order to obtain information on protein secondary, tertiary, and quaternary structures. We obtained a reduction of the protein alpha-helix content after the plasma exposure and a different behavior, for both thermal denaturation/renaturation kinetics and thermal aggregation process.