Nicoleta Dumitrascu

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.

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...

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.

Atmospheric-Pressure Dielectric Barrier Discharge for Surface Processing of Polymer Films and Fibers

This paper presents results on surface processing of polymeric materials using a particular plasma reactor configuration. An atmospheric-pressure plasma beam is used to create a surface discharge with an axially symmetric profile. The exposure to He and mixtures of He with reactive gases allows combined functionalization and cross linking on polymers in film and fiber forms.

Control of the Blood-Polymer Interface by Plasma Treatment

Plasma that is generated using dielectric barrier discharge is used to modify the surface properties of polymers used in medicine, at atmospheric pressure. Treatments are performed on films of polyamide-6, high density polyethylene, polymethylmetacrylate, and polytetrafluorethylene, selected for their medical applications. The plasma treatment conditions are discussed, in relation with relevant parameters for the adhesion properties, like the surface energy components, interfacial tension, surface topography, structural changes, and chemical composition. The interface properties are analyzed using the most important fluids implicated in the interfacial events related to the coagulation process at the interface of blood-polymer surface, respectively, water, whole blood, fibrinogen, and albumin. The physical and chemical modification of the surface is theoretically favorable to the interaction of the polymer with the blood and its components, by means of interfacial tension reduction, polarity increase, cleaning, ordering of molecular chains, functionalization, and stabilization effects.

A 980 nm driven photothermal ablation of virulent and antibiotic resistant Gram-positive and Gram-negative bacteria strains using Prussian blue nanoparticles

A 980nm laser-driven antimicrobial photothermal therapy using poly(vinylpyrrolidone) -coated Prussian Blue nanoparticles (PVP/PB NPs) is demonstrated. This approach allows an efficient eradication of a virulent strain of Gram-negative Escherichia coli (E. coli) associated with urinary tract infection as well as for the ablation of antibiotic resistant pathogens such as methicillin resistant Staphylococcus aureus (MRSA) and extended spectrum β-lactamase (ESBL) E. coli. Interestingly the 980nm irradiation exhibits minimal effect on mammalian cells up to a PVP/PB NPs concentration of 50μgmL(-1), while at this concentration bacteria are completely eradicated. This feature is certainly very promising for the selective targeting of bacteria over mammalian cells.

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.

Particle-based photodynamic therapy based on indocyanine green modified plasmonic nanostructures for inactivation of a Crohn's disease-associated Escherichia coli strain

Particle-based photodynamic therapy (PPDT) holds great promise in theranostic applications. Herein, we demonstrate that PPDT based on gold nanorods coated with an indocyanine green (ICG)-loaded silica shell allows for the inactivation of the Crohns disease-associated adherent-invasive Escherichia coli strain LF82 (E. coli LF82) under pulsed laser light irradiation at 810 nm. Fine-tuning of the plasmonic structures together with maximizing the photosensitizer loading onto the nanostructures allowed optimizing the singlet oxygen generation capability and the PPDT efficiency. Using a nanoparticle concentration low enough to suppress photothermal heating effects, 6 log10 reduction in E. coli LF82 viability could be achieved using gold nanostructures displaying a plasmonic band at 900 nm. An additional modality of nanoparticle-based photoinactivation of E. coli is partly observed, with 3 log10 reduction of bacterial viability using Au NRs@SiO2 without ICG, due to the two-photon induced formation of reactive oxygen species. Interaction of the particles with the bacterial surface, responsible for the disruption of the bacterial integrity, together with the generation of moderate quantities of singlet oxygen could account for this behavior.