Chemical‐surface modification of polymers using atmospheric pressure nonequilibrium plasmas and comparisons with vacuum plasmas

We demonstrate that stable microwave‐coupled atmospheric pressure nonequilibrium plasmas (APNEPs) can be formed under a wide variety of gas and flow‐rate conditions. Furthermore, these plasmas can be effectively used to remove surface contamination and chemically modify polymer surfaces. These chemical changes, generally oxidation and crosslinking, enhance the surface properties of the materials such as surface energy. Comparisons between vacuum plasma and atmospheric plasma treatment strongly indicate that much of the vacuum‐plasma literature is pertinent to APNEP, thereby providing assistance with understanding the nature of APNEP‐induced reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 95–109, 2002     

Investigation of laser ablated metal and polymer plasmas in ambient gas using fast photography

We report the studies on interaction of laser ablated Teflon and aluminum plasmas in various ambient atmospheres. Intensified Charge Couple Device (ICCD) was used to image the laser ablated plume. The stratification of plasma at moderate laser intensities in the case of metal as well as polymer was observed. The possible cause of stratification is discussed. The reason for expansion and diffusion within the plasma and shock formation in the presence of ambient gas at different pressures is discussed based on hydrodynamic model.     

Plasma etching of III–V semiconductors in BCl3 chemistries: Part II: InP and related compounds

BCl₃/Ar and BCl₃/N₂ plasma chemistries were compared for patterning of InP, InAs, InSb, InGaAs, InGaAsP, and AlInAs. Under electron cyclotron resonance conditions etch rates in excess of 1 μm/min can be achieved at room temperature with low additional rf chuck power (150 W). The etch rates are similar for both chemistries, with smoother surface morphologies for BCl₃/Ar. However, the surfaces are still approximately an order of magnitude rougher (as quantified by atomic force microscopy) than those obtained under the same conditions with Cl₂/Ar. InP surfaces etched at high BCl₃-to-Ar ratios have measurable concentrations of boron-and chlorine-containing residues.     

Plasma etching of III–V semiconductors in BCl3 chemistries: Part I: GaAs and related compounds

BCl₃/Ar discharges provide rapid, smooth pattern transfer in GaAs, AlGaAs, GaP, and GaSb over a wide range of plasma conditions. At high BCl₃-to-Ar ratio there is significant surface roughening on GaSb, which is correlated with the presence of B- and Cl-containing residues detected by Auger electron spectroscopy. BCl₃/N₂ discharges provide similar etch rates to BCl₃/Ar, but when used with photoresist masks lead to rough morphologies on the semiconductor materials due to enhanced dissociation and redeposition of the resist. Etch rates with electron cyclotron resonance discharges are up to two orders of magnitude higher than for rf-only conditions.     

Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods

Advances in characterization of laser induced plasmas by optical emission spectroscopy are reviewed in this article. The review is focused on the progress achieved in the determination of the physical parameters characteristic of the plasma, such as electron density, temperature and densities of atoms and ions. The experimental issues important for characterization by optical emission spectroscopy, as well as the different measurement methods are discussed. The main assumptions of the methods, namely the optical thin emission of spectral lines and the existence of local thermodynamic equilibrium in the plasma are evaluated. For dense and inhomogeneous sources of radiation such as laser induced plasmas, the characterization methods are classified in terms of the optical depth and the spatial resolution of the emission used for the measurements. The review deals firstly with optically thin spatially integrated measurements. Next, local measurements and characterization in not optically thin conditions are discussed. Two tables are included that provide reference to the works reporting measurements of electron density and temperature of laser induced plasmas generated with diverse samples.     

Characterization of laser-induced plasmas by emission spectroscopy with curve-of-growth measurements. Part II: Effect of the focusing distance and the pulse energy

Laser-induced plasmas generated with different focusing distances and pulse energies have been characterized by a method based in emission spectroscopy that includes the measurement and calculation of curves of growth. An infrared Nd:YAG laser is used to generated the plasmas from Fe–Ni samples placed in air at atmospheric pressure. The characterization method provides a reduced set of plasma parameters (N_e, T, N′l, αA) that describe the line emission in optically thin and optically thick conditions. For a pulse energy of 100 mJ, the plasma parameters for varying focusing distances are obtained. The apparent (population averaged) temperatures for neutral atoms and ions are shown to be different in the plasmas generated with all the focusing distances. For each pulse energy (in the range 20–100 mJ), the plasmas generated with the optimum focusing distance, which corresponds to a constant value of irradiance, have been investigated. In these conditions, simple laws have been obtained for the variation of the plasma parameters with the pulse energy E: the electron density N_e and the apparent temperature T are independent of E while linear relations with E are obtained for the parameters N′l, αA. These simple laws lead to a quadratic dependence on E of the line intensities in the optically thin limit and to a variation of the intersection concentration C_int that characterizes self-absorption as E^− 1.     

Interest of NH3 and N2 plasmas for polymer surface treatment before “electroless” metallization

The electroless metallization of polymers needs an activation of their surface which consists of palladium chemisorption. In this study, the effect of surface treatments of polystyrene and polyamide substrates by reactive gas plasmas (O₂, NH₃, N₂) has been followed by XPS analysis. According to the functional groups grafted on the surface, specific chemisorption reactions can occur. The latter have been highlighted through a comparative investigation of two activation processes, viz. a conventional way using successively SnCl₂ and PdCl₂ solutions and a new procedure, developed by the authors, using only a PdCl₂ solution. This work shows that this simplified process can be extended to any polymer whose surface is grafted with nitrogenated functions.     

An improvement on the adhesion‐strength of laminated ultra‐high‐molecular‐weight polyethylene fabrics: surface‐etching/modification using highly effective helium/oxygen/nitrogen plasma treatment

In this study, helium/oxygen/nitrogen (He/O₂/N₂)‐plasma was used to etch/modify the surface of ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber. After coated with polyurethane (PU), the plasma treated UHMWPE fabrics were laminated. It was found that the values of peeling strength between the laminated UHMWPE fabrics treated with He/O₂/N₂‐plasma were significantly higher (3–4 times) than that between pristine fabrics. The hydrophilic property and the value of the surface roughness of the UHMWPE fibers increased significantly after treated with He/O₂/N₂‐plasma. The mechanism of the oxidation/degradation of the polymers on the surface of the UHMWPE fiber during He/O₂/N₂‐plasma treatment was suggested. In addition, it was found that the higher content of functional groups (carbonyl, aldehyde, and carboxylic acid) on fiber surface and the higher value of surface roughness of the UHMWPE fiber treated with He/O₂/N₂‐plasma could significantly improve the adhesion‐strength of the laminated UHMWPE fabric. Especially, the micro‐aperture on the surface of UHMWPE fiber caused by the strenuous etching of He/O₂/N₂‐plasma treatment was also an important factor on improving the adhesion‐strength between the laminated UHMWPE fabrics. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanism of etching and of surface modification of polyimide in RF and LF SF6-O2 discharges

Etch rates of Kapton H polyimide film in SF₆-O₂ plasmas (0.25 torr) were studied as a function of the input gas mixture, the excitation frequency (25–450 kHz; 13.56 MHz), and the biasing mode. The treated surface was examined by X ray photoelectron spectroscopy (ESCA), scanning electron microscopy (SEM), and contact angle measurement. The ion and neutral species of the plasma were sampled and analyzed by mass spectrometry. Etch rates are found to depend on the positive ion flux and the degree of dissociation of neutral molecules. Plasma-treated surfaces are always covered with a deposited material (C_nH_mO_xF_y) which partially obstructs the etching reaction by a masking effect and causes surface roughness. A proposed kinetic analysis of the etching mechanism is in good agreement with the experimental data.     

LC–QToF–MS method for quantification of ethambutol,isoniazid, pyrazinamide and rifampicin in human plasma and its application

In this research, we developed and validated a liquid chromatography coupled to mass spectrometry (LC–QToF–MS) method for simultaneous quantification of the anti-tuberculosis drugs ethambutol, isoniazid, pyrazinamide and rifampicin in human plasma. Plasma samples spiked with cimetidine (internal standard) were extracted using protein precipitation with acetonitrile containing 1% formic acid. Separation was performed using a C₁₈ column under flow gradient conditions with water and acetonitrile, both containing 5 mm ammonium formate and 0.1% formic acid. The method was validated according to the ANVISA and US Food and Drug Administration guidelines for bioanalytical method validation. The calibration curve was linear over a concentration range of 0.2–5 μg ml⁻¹ for ethambutol, 0.2–7.5 μg ml⁻¹ for isoniazid, 1–40 μg ml⁻¹ for pyrazinamide and 0.25–2 μg ml⁻¹ for rifampicin, all with adequate precision and accuracy. The method was reproducible, selective and free of carryover and matrix effects. The validated LC–QToF–MS method was successfully applied to real samples and shown to be applicable to future therapeutic and pharmacokinetic monitoring studies.     

Modification of Polyimide in Barrier Discharge Air-Plasmas: Chemical and Morphological Effects

Chemical and physical modifications of polyimide (PI) surfaces caused by an air plasma have been studied. The plasma-induced surface changes of PI were investigated by using a local dielectric barrier discharge (DBD) in air at atmospheric pressure and room temperature as a function of the plasma exposure time and plasma power, while the excitation frequency was kept constant at about 130 kHz. The first results obtained in this work suggest that DBDs operating in air at atmospheric pressure can be an efficient alternative plasma source for surface treatment of polymers: a short time air plasma treatment of few seconds leads to chemical and physical changes including the rise of wettability, surface oxidation, and enhancement of surface roughness. Therefore, this simple kind of dry surface treatment seems to be an effective, low cost method for production of well-adhering subsequent layers such as metal films, paints, glues, etc. on DBD pretreated polymers.     

Effects of oxygen plasma treatment on the surface of bisphenol A polycarbonate: a study using SIMS,principal component analysis,ellipsometry, XPS and AFM nanoindentation

The effects of oxygen plasma treatment and the subsequent air exposure on the surface composition and properties of bisphenol A polycarbonate (BPA‐PC) were analysed by X‐ray photoelectron spectroscopy (XPS), ellipsometry, static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) with principal component analysis (PCA) and nanoindentation using an atomic force microscope (AFM). PCA showed systematic changes in the film chemistry after short treatment times (0.1 s), with the main sites of attack being the carbonate and aromatic ring structure. On the basis of this multitechnique analysis, it was unambiguously determined that extended oxygen plasma treatment times resulted in the formation of low‐molecular‐weight material (LMWM) within the first 50 nm on the surface, and not in a cross‐linked skin as has been proposed by other researchers. The study shows that controlled surface modification of BPA‐PC polymers is possible, allowing surface oxygen incorporation without degradation of the polymer structure. This result is relevant for improved adhesion of coatings applied to BPA‐PC polymers. Copyright © 2006 John Wiley & Sons, Ltd.     

Preparation of inorganic materials,surface treatment,and etching in low pressure plasmas: Present status and future trends

The present status and future trends in the chemistry of nonisothermal plasmas of glow and dielectric barrier discharges are summarized. Particular attention is devoted to the surface treatment, plasma etching, and to the plasma-induced and-assisted chemical vapor deposition. Several open problems which deserve exploratory research are addressed.     

Reactions of polyethylene surfaces with the downstream products of an air plasma: Gas phase and surface spectroscopic studies

The gas phase downstream products of an air glow discharge have been measured, using absorption and emission spectroscopies, as a function of plasma power, air flow rate, and distance from the plasma. In addition, the reaction of these products with a linear low density polyethylene (LLDPE) polymer surface has been followed using x-ray photoelectron spectroscopy (XPS). At higher air flow rates (>300 sccm), the primary reactive species is confirmed to be O(³P) atomic oxygen. Some O(³P) is generated in the plasma itself, but more appears to be formed in the downstream region, because of dissociation of molecules in their excited states. At low flow rates, the concentration of O(³P) is strongly depleted at the sample position, but other atomic oxygen states become more prominent. O(⁵S) and O(³S) are two states which are identified. XPS studies of the polyethylene surface reacted at high flow rates shows oxygen functionalities that are likely the result of an initiation by hydrogen abstraction. At low flow rates, the products suggest initiation by oxygen insertion. Thus, changes in flow rate can result in major changes to the polymer surface chemistry. © 1996 John Wiley & Sons, Inc.     

Electrostatic interaction between a charge-regulated particle and a solid surface in electrolyte solution: effect of cationic electrolytes

The effect of cations on the electrostatic interaction between a negative charge-regulated particle and a solid surface of constant negative potential in electrolyte solution is analyzed. Here, we assume that the rate of approach of a particle to a solid surface is faster than that of the dissociation of the ionogenic groups on the surface of particle. In other words, the effect of the time-dependent dissociation of ionogenic groups on the surface of a particle is taken into account. The result of the present study reveals that, although the solid surface is negatively charged, the presence of cations in the suspension medium has a negative effect on the rate of adhesion. The qualitative behaviors in the variation of the interaction force between a particle and a solid surface as a function of separation distance between them predicted by a kinetic model and the corresponding equilibrium model and constant charge density model are entirely different. The rate of approach of a particle to a solid surface is on the order (constant charge density model)>(kinetic model)>(equilibrium model).     

Optical emission diagnostics in cascade arc plasma polymerization and surface modification processes

Optical Emission Spectroscopy (OES) was used to identify reactive species and their excitation states in low-temperature cascade arc plasmas of N₂, CF₄, C₂F₄, CH₄, and CH₃OH. In a cascade arc plasma, the plasma gas (argon or helium) was excited in the cascade arc generator and injected into a reactor in vacuum. A reactive gas was injected into the cascade arc torch (CAT) that was expanding in the reactor. What kind of species of a reactive gas, for example, nitrogen, are created in the reactor is dependent on the electronic energy levels of the plasma gas in the cascade arc plasma jet. OES revealed that no ion of nitrogen was found when argon was used as the plasma gas of which metastable species had energy less than the ionization energy of nitrogen. When helium was used, ions of nitrogen were found. While OES is a powerful tool to identify the products of the cascade arc generation (activation process), it is less useful to identify the reactive species that are responsible for surface modification of polymers and also for plasma polymerization. The plasma surface modification and plasma polymerization are deactivation processes that cannot be identified by photoemission, which is also a deactivation process. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1583–1592, 1998     

Improvement of PBO fiber surface and PBO/PPESK composite interface properties with air DBD plasma treatment

The interface of fibrous composites is a key factor to the whole properties of the composites. In this study, the effects of air dielectric barrier discharge (DBD) plasma discharge power density on surface properties of poly(p‐phenylene benzobisoxazole) (PBO) fiber and the interfacial adhesion of PBO fiber reinforced poly(phthalazinone ether sulfone ketone) (PPESK) composite were investigated by several characterization methods, including XPS, SEM, signal fiber tensile strength, interlaminar shear strength, and water absorption. After the air DBD plasma treatment at a power density of 41.4 W/cm³, XPS analysis showed that some polar functional groups were introduced on the PBO fiber surface, especially the emergence of a new oxygen‐containing group (?O–C = O group). SEM observations revealed that the air DBD plasma treatment had a great influence on surface morphologies of the PBO fiber, while the signal fiber tensile strength results showed only a small decline of 5.9% for the plasma‐treated fiber. Meanwhile, interlaminar shear strength value of PBO/PPESK composite was increased to 44.71 MPa by 34.5% and water absorption of the composite decreased from 0.46% for the untreated specimen to 0.27%. The results showed that the air DBD plasma treatment can effectively improve the properties of the PBO fiber surface and the PBO/PPESK composite interface. Results obtained from the above analyses also showed that both the fiber surface and the composite interface performance would be reduced when an undue plasma discharge power density was applied. Copyright © 2011 John Wiley & Sons, Ltd.     

On the correlation of surface charge and energy in non‐thermal plasma‐treated polyethylene

Non‐thermal non‐equilibrium oxidative air 40‐kHz frequency, 13.56‐MHz radiofrequency and 2.46‐GHz microwave discharge plasma treatment were used for modifying low‐density polyethylene foils. The untreated and treated samples were chemically characterised by X‐ray photoelectron spectroscopy. In order to estimate the extent of the plasma sources at distinct treatment times, surface charge and energy were determined by zeta potential (ζ) and surface tension measurements. In addition, the isoelectric points (IEPs) of the studied samples were ascertained, and surface property variations were appraised by ageing time. The overall outcome indicated that ζ‐potential and surface energy progressively changed after each treatment, as well as the influences of ageing on surface features, the IEP shifting to lower pH values and how all of these changes are associated with the new surface chemistry. This contribution seeks to shed light on topics related to polymer science and plasma‐based strategies for surface modification. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a new polypropylene-based suture: plasma grafting, surface treatment, characterization, and biocompatibility studies

Polypropylene sutures (PP) are already used in surgery. Because microbial infection leads to complications, we developed antimicrobial PP suture by plasma-induced graft polymerization of acrylic acid followed by chitosan binding on the remaining carboxyl groups. Mechanical properties and surface morphologies were analyzed on these sutures. Tetracycline hydrochloride (TC) or nanosilver (NS) was then immobilized to PP. The resulting PP sutures evidenced drug release properties and antimicrobial activity in vitro. PP implanted in vivo for 30 days in the muscle of rats showed the absence of adverse effects and a tissue organization. This new polypropylene suture with suitable antimicrobial features appears to be a promising macromolecular material for clinical and cosmetic applications.