Low-pressure Ammonia Plasma Research Articles

Activation of water in the downstream of low-pressure ammonia plasma discharge

In the present work, we study the physicochemical changes that arise in water named plasma processed water (PPW) when it is exposed to the downstream low-pressure discharge of ammonia (NH3) gas. Optical emission spectroscopy and voltage-current characteristics of NH3 plasma are studied to identify species formed in NH3 plasma along with plasma characterization. A three-way full factorial design of experiment is performed to study the effect of process parameters named applied voltage, post-discharge gas-water interaction time, and NH3 gas pressure on physicochemical properties of PPW. The obtained results are analyzed using analysis of variance, standardized effect estimation, regression analysis, and response surfaces. The optimum values of these properties and PPW process parameters are estimated using MATLAB fmincon solver with experimental constraints. The emission spectrum of NH3 plasma showed strong intensity N2 + lines along with weak intensity N2, NH, and N+ lines. The obtained results showed the post-discharge gas-water interaction time and applied voltage had a significant impact on physicochemical properties and ammonium ions concentration in PPW. The obtained optimum value of voltage and time is 550 V and 15 min with given experimental constraints.

Adhesion of carbon fibers to amine hardened epoxy resin: Influence of ammonia plasma functionalization of carbon fibers

The modification of carbon fiber surface properties represents a powerful tool to improve the adhesion between fibers and polymeric matrix in carbon fiber reinforced polymers. In the presented work the surface of untreated carbon fibers, taken from the production process directly after carbonization, is functionalized by a low pressure ammonia plasma treatment. Compared to the untreated fibers an enhanced concentration of surface nitrogen functionalities and an increased surface energy are observed. This leads to an improved wetting behavior, similar to that of carbon fibers activated by anodic oxidation. No changes of the fiber surface topography on micro- and on nanoscale are induced by the plasma treatment. Compared to the untreated fiber no increase of interfacial fracture toughness between the plasma treated fibers and an amine hardened epoxy resin is detected by single fiber push-out tests. Anodically oxidized fibers, in contrast, show a significant increase of interfacial fracture toughness. The results suggest, that adhesion of carbon fibers to an amine hardened epoxy resin is dominantly enhanced by interactions between surface oxygen functionalities and the components of the resin. In contrast, nitrogen surface functionalities appear to be of minor importance for fiber matrix adhesion in carbon fiber reinforced amine hardened epoxy resin.

Effect of surface modification of poly(lactic acid) by low-pressure ammonia plasma on adsorption of human serum albumin

Abstract The final goal of the study was to promote understanding of mechanisms involved in cell attachment on biomedical polymer poly(lactic acid) (PLA). As the cell attachment on the material surface was preceded by blood protein adsorption which would critically affect subsequent cell adhesion, for the clinic application purpose, human serum albumin (HSA) was used in the investigation on its adsorption on PLA, which was however treated by low-pressure ammonia (NH3) plasma. The NH3-plasma-treated PLA was found to adsorb less HSA than the untreated PLA. The PLA was characterized using various techniques such as atomic force microscopy, contact angle and surface energy analysis and x-ray photoelectron spectroscopy. All of the characterization results indicated that due to NH3-plasma-induced polar groups the PLA enhanced its hydrophilicity which in turn inhibited the HSA adsorption. The decreased HSA adsorption would consequently increase the cell attachment because of the cell adhesion barrier reduced.

Different plasma-based strategies to improve the interaction of anionic dyes with polyester fabrics surface

Low-pressure plasma treatments with subsequent immobilization of functional macromolecules from aqueous solution have gained an increasing popularity for its applications in new industrial processes. In this work, two different strategies to endow polyester fabrics (PET) with accessible primary amino groups are compared.(a) NH2 groups were produced directly using low-pressure ammonia plasma. (b) Negatively charged groups were introduced by low-pressure oxygen plasma to hydrophilize the fabric surfaces and used as anchor groups for the immobilization of water-borne polyelectrolyte copolymers poly(vinyl amine-co-vinyl amide) (PVAm).To study the effects of these surface modifications, a combination of various surface-sensitive characterization techniques such as X-ray photoelectron spectroscopy (XPS), streaming potential measurements and time-dependent contact angle measurements were used. Furthermore, the influence of the pre-treatments on the interaction of PET fabrics with water-soluble dyes was evaluated. For that purpose, color strength and fastness tests were carried out to prove the effectiveness of pre-treatments.

Effect of Surface Modification by Ammonia Plasma on Vascular Graft: PET Film and PET Scaffold

Nowadays, poly (ethylene terephthalate) (PET) textiles, either knitted or woven, are largely used as substitutes for replacement of medium and large calibre (10–40 mm) arteries. Unfortunately, these substitutes do not perform well when they are used to replace small diameter arteries due to thrombogenicity and compliance mismatch issues. Surface treatments were often used as the first step to solve thrombogenicity issues. For example, low pressure ammonia plasma processes can provide modification of the top ≈ 10–50 A of polymer surface without affecting bulk properties of materials. This work compared ammonia plasma surface modifications of PET film (flat surface) and PET scaffolds (porous surface). Plasma treatments lead to a higher amount of nitrogen as well as amino groups on scaffolds compared to films. N/C maximum was reached for PET film and scaffold after plasma treatments of 5 s and 100 s, respectively. Highest amine concentration on films and scaffolds were obtained at short treatment time, specifically 1 s. In addition, high resolution spectra of C 1s confirmed that amino groups were mainly grafted on aromatic rings. Nodule formation was observed after plasma treatment with atomic force microscopy. Their size and shape increased with longer treatment time.

A ToF-SIMS study of the deuterium—hydrogen exchange induced by ammonia plasma treatment of polyolefins

ToF-SIMS has been used to study the surface functionalization of polypropylene and polyethylene samples by exposure to low-pressure ammonia plasma. Static secondary ion mass spectrometry is an appropriate tool to determine hydrogen isotopes as elements and in fragment ions with high sensitivity and selectivity. Specifically the exchange of hydrogen isotopes and the incorporation of N-containing moieties in the near-surface layer of the polyolefins have been studied in ND3 plasma experiments with conventional polypropylene (h-PP) and polyethylene (h-PE) and NH3 plasma experiments with deuterated polyethylene (d-PE). Considering the exchange of hydrogen between the plasma and the polymer surface studied by using deuterated ammonia and polyolefin samples the conclusion has been derived that polypropylene with its side chain methyl groups is more susceptible to hydrogen exchange reactions. For ND3 plasma treatment of polyethylene and polypropylene similar N-containing fragments were obtained and the measured semi-quantitative ToF-SIMS N-uptake data are rather similar. The observation of a wide range of characteristic mixed CkNlHmDn+ secondary fragment ions suggests complex and manifold reaction pathways at the polymer–plasma interface besides simple grafting of –ND2 or –NH2 moieties formed by ammonia fragmentation in the plasma. Finally, indications of an isotopic effect for hydrogen isotopes in the plasma process have been observed by comparison of ND3/h-PE results with those of NH3/d-PE.

A new approach to biofunctionalisation and micropatterning of multi-well plates

Biomolecule attachment and lateral micropatterning of biomolecular layers are essential techniques to provide in advanced biochemical and cell culture assays. For that purpose, we introduced a versatile, simple and robust method to functionalise standard polystyrene well plates. Free amino groups were generated on the polystyrene surface by low pressure ammonia plasma treatment. Subsequently, thin films of different maleic anhydride copolymers were covalently attached to the surfaces. The distinct physicochemical properties of the coupled maleic anhydride copolymers provided a broad range of possible attachment schemes of proteins and polysaccharides. Micrometer-sized lateral patterns of these functional coatings were created by plasma etching through silicon masks and subsequent chemical conversion of the etched areas using poly(ethylene glycol). The approach facilitates a wide variety of cell culture experiments allowing a combination of biomolecule coupling and micropatterning within the multi-well plate technology.

Functionalization of Poly(dimethylsiloxane) Surfaces with Maleic Anhydride Copolymer Films

Combining advantageous bulk properties of polymeric materials with surface-selective chemical conversions is required in numerous advanced technologies. For that aim, we investigate strategies to graft maleic anhydride (MA) copolymer films onto poly(dimethylsiloxane) (PDMS) precoatings. Amino groups allowing the covalent attachment of the MA copolymer films to the PDMS (Sylgard 184) surface were introduced either by low-pressure ammonia plasma treatment, or by attachment of 3-aminopropyltriethoxysilane (APTES) onto air plasma-treated PDMS. The resultant coatings were extensively characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), contact angle measurements, and atomic force microscopy (AFM). The results show that the impact of the plasma treatment on the physical properties on the topmost surface of the PDMS is critically important for the characteristics of the layered coatings.

Determination of Amine and Aldehyde Surface Densities: Application to the Study of Aged Plasma Treated Polyethylene Films

The aim of this work was to test and to compare different methods reported in the literature to quantify amine and aldehyde functions on the surface of polyethylene (PE) films treated by ammonia plasma and to specify their stability against time. A low pressure ammonia plasma reactor was used to functionalize PE films with amine groups, which could be subsequently used for further immobilization of biomolecules. In order to determine the density of amine groups on the surface of treated films, various molecule probes and spectrophotometric analytical methods have been investigated. Two methods using (i) sulfosuccinimidyl 6-[3'-(2-pyridyldithio)-propionamido] hexanoate (sulfo-LC-SPDP) and (ii) 2-iminothiolane (ITL) associated with bicinchoninic acid (BCA) have been proved to be reliable and sensitive enough to estimate the surface concentration of primary amine functions. The amount of primary amino groups on the functionalized polyethylene films was found to be between 1.2 and 1.4 molecules/nm2. In a second step, the surface concentration of glutaraldehyde (GA), which is currently used as a spacer arm before immobilization of biomolecules, has been assessed: two methods were used to determine the surface density of available aldehyde functions, after the reaction of GA with the aminated polyethylene film. The concentration of GA was found to be in the same range as primary amine concentration. The influence of aging time on the density of available amino and aldehyde groups on the surfaces were evaluated under different storage conditions. The results showed that 50% of the initial density of primary amine functions remained available after storage during 6 days of the PE samples in PBS (pH 7.6) at 4 degrees C. In the case of aldehyde groups, the same percentage of the initial density (50%) remained active after storage in air at RT over a longer period, i.e., 15 days.

Surface modification of poly(hydroxybutyrate) films to control cell–matrix adhesion

Tailoring surface properties of degradable polymer scaffolds is key to progress in various tissue engineering strategies. Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) thin films were modified by low pressure ammonia plasma, low pressure water vapour plasma, or immersion in a sodium hydroxide solution to elaborate means to control the cell-matrix adhesion of human umbilical cord vein endothelial cells grown on these materials. Fibronectin (FN) heteroexchange and cell adhesion were correlated to the physicochemical characteristics of the modified polymer surfaces which were investigated by X-ray photoelectron spectroscopy (XPS), scanning force microscopy (SFM), electrokinetic measurements, and contact angle measurements. All treatments increased the hydrophilicity of the polymer samples, which could be accounted to newly created amine or carboxyl functionalities for ammonia plasma or water vapour plasma treatments, respectively, and ester hydrolysis for treatments with alkaline aqueous solutions. Main features of cell adhesion and FN reorganisation-evaluated after 1h and after 5 days-could be attributed to the anchorage strength of pre-coated FN layers at the polymer surface, which was, in turn found to be triggered by the type of modification applied. In line with earlier studies referring to different materials cell adhesion and matrix reorganisation were shown to be sensitively controlled through the physicochemical profile of poly(hydroxybutyrate) surfaces.

Transience of plasma surface modification as an adhesion promoter for polychlorotrifluorethylene

Poly(chlorotrifluoroethylene) (PCTFE) and other fluoropolymers are increasingly used as inner layer dielectrics. However, these polymers have low surface energies and correspondingly poor adhesive properties. Results are presented on the use of a low-pressure ammonia plasma to enhance the surface bondability of PCTFE. The plasma modified PCTFE film surfaces were characterized by x-ray photoelectron spectroscopy and contact angle measurements. Surface modified films exhibited improved adhesion to electroless copper deposits (180° peel test) compared to coated PCTFE controls and that underwent no plasma exposure. Annealing studies were conducted between 30 and 100 °C to examine the stability of the plasma-modified surfaces. For samples annealed below Tg, contact angle measurements indicated that the plasma-introduced groups remained bound on the surface for four weeks. For specimens annealed above Tg, the surface functionalities were absorbed within the bulk and surface rearrangement occurred within 10 h of...

Polyelectrolyte adsorption on NH3-Plasma-Treated poly(tetrafluoroethylene-co-hexafluoropropylene)

A two-step procedure for a permanently hydrophilic surface modification of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP, fluorinated ethylene propylene) was studied. In the first step a cationic polymer surface was created by low-pressure ammonia plasma treatment introducing nitrogen-containing functional groups. Afterwards, the anionic poly(sodium 4-styrenesulfonate) was adsorbed onto the plasma-treated FEP surface. The adsorption was assumed to be controlled by ionic interactions. The modification effects and their long-term behavior were evaluated by means of water contact angle goniometry. Furthermore, electrokinetic measurements and X-ray photoelectron spectroscopy were used for surface characterization.

Damage induced by carrier injection in 8 nm thick oxides and nitrided oxides

Charge trapping and interface trap creation phenomena observed in 8 nm thick thermally grown oxides and oxides nitrided by low pressure ammonia plasma are reported. These phenomena are observed for samples subjected to uniform high-field current injection. It is demonstrated that trap creation is limited to the generation of interface states. No electron trapping and no positive charge generation are observed for injected fluences ranging from 10 −6 − 10 2 C/cm 2 at oxide fields in the range 8–11 MV/cm. Quite similar trap creation rates and kinetics are observed in both samples, which demonstrates the good reliability performance of the nitrided oxide. Results are discussed in terms of impact ionization and trap creation by hydrogen-related species models.

Modification of Cotton by Radiofrequency Plasma of Ammonia

Cotton printcloth was treated with low-temperature, low-pressure ammonia plasma created by passing ammonia gas through a radiofrequency (rf) electric field of 13.56 MHz. Fabrics were exposed to the plasma for 3600 s. Pressure was maintained at 150 μm Hg and rf power at 40 W. Samples located between the electrodes lost additional weight over that caused by removal of moisture under reduced pressure. Material that was insoluble in cupriethylenediamine was formed in the cotton fibers. Cross sections of these fibers resembled those of conventionally crosslinked cotton cellulose in that they resisted layering. Electron spectroscopy for chemical analysis (ESCA) and multiple internal-reflectance spectroscopy (MIR) showed addition of nitrogen and suggested an amide structure. Free radical sites that produced chemiluminescence were formed. Comparison of ESR spectra with those obtained previously with rf plasmas led to the conclusion that glucoside bonds were broken to form activated carbonyls. The irradiated fabric exhibited a modest increase in conditioned wrinkle recovery with no change in wet recovery.