Behavior and surface energies of polybenzoxazines formed by polymerization with argon,oxygen, and hydrogen plasmas

Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF₄ plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004     

Modification,degradation, and stability of polymeric surfaces treated with reactive plasmas

The degradation, modification, and stability of polymeric surfaces exposed to chemically reactive O₂ and H₂O‐vapor plasmas were investigated. Specifically, the effects of these plasmas on etching rate, surface morphology, wetting instability, and fluid‐holding capability were studied. Wetting instability is reflected by hydrophobic recovery and can be examined by the Wilhelmy balance method. Although hydrophobic recovery is usually attributed to surface configuration change, there are actually two types: reversible and permanent. Reversible hydrophobic recovery is caused by surface configuration change, whereas permanent hydrophobic recovery is caused by the creation of oxidized surface oligomers. This study distinguishes the two by identifying differences in the shapes of the corresponding Wilhelmy force loops and in the fluid‐holding parameter. The presence of surface oligomers was most detrimental to wetting stability and fluid‐holding capability but could be controlled via the type of reactive gas, the discharge conditions, and the polymer substrate. In general, polymers most susceptible to O₂‐plasma etching had the least surface oligomers and vice versa, whereas H₂O‐vapor plasma suppressed surface oligomers on polymers less susceptible to etching. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3028–3042, 2000     

Surface modification of poly(tetrafluoroethylene) by a low-temperature cascade arc torch and radio-frequency plasmas

Poly(tetrafluoroethylene) (PTFE) films were treated with a low-temperature cascade arc torch (LTCAT) and radio-frequency (RF) plasmas of argon and hydrogen. The plasma-treatment effect on the PTFE surface was studied with contact-angle measurement and scanning electron spectroscopy (SEM). LTCAT argon plasma, which is recognized as a beam of excited argon neutrals, was very efficient at improving the surface hydrophilicity of PTFE. For both the LTCAT and RF operation, argon plasma was more effective at modifying the surface wettability of PTFE films than hydrogen plasma was. Furthermore, the sample positions (inside or beyond the glow region) had a strong impact on the efficiency of the plasma treatment. SEM surface images indicated that no significant morphology change was induced on the PTFE films exposed to a LTCAT and RF argon plasmas. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4432–4441, 1999     

Nitrogen plasma modification on polyimide films for copper metallization on microelectronic flex substrates

Surface modification of polyimide films Kapton E(N) and Upilex S by nitrogen plasmas were investigated for their enhanced adhesion strength with sputtered coppers. Peel tests demonstrate this improvement, with peel strengths of 7 and 12 N/m for unmodified Kapton E(N) and Upilex S, and 1522 and 1401 N/m for nitrogen plasma‐modified Kapton E(N) and Upilex S at certain plasma conditions. Atomic force microscopy (AFM) and the sessile drop method indicated the surface roughness, and the surface energy of polyimide films were highly increased by nitrogen plasmas. This study shows the enhanced adhesion strengths of polyimide films with sputtered coppers by nitrogen plasmas, and these nitrogen plasmas were strongly affected by the surface characteristics of polyimide films. Electron spectroscopy for chemical analysis (ESCA) observed the increased surface energy on polyimide films by nitrogen plasmas was due to the increased surface composition of O and the increased chemical bond of C? O. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2023–2038, 2005     

Surface modification on thermoplastic olefins by low‐temperature cascade arc discharge‐air plasmas for enhanced adhesion with primer

Improvement of primer adhesion to thermoplastic olefins (TPOs) by surface modification with a low‐temperature cascade arc discharge‐air plasmas was investigated. Air plasma with a low‐temperature cascade arc plasma torch can be used for improving the primer adhesion to TPOs. Tape‐adhesion tests (ASTM 3359‐92a method) demonstrated this improvement with a rating of “0” for untreated TPOs and “5” for air plasma‐modified TPOs at certain plasma conditions even for aging at 60 °C and 80% relative humidity for 5 days. The adhesion to primer for the soft and flexible kind of TPOs (ETA‐3041c and ETA‐3101) was easily enhanced. The adhesion to primer for the hard and brittle TPOs (ETA‐3183) needs to optimize the plasma conditions to pass the wet‐adhesion test using air plasmas. To relate the surface characteristics of air plasma‐modified TPOs to adhesion performance with primer, the wettability and polarity of TPOs were evaluated by the contact‐angle measurements of primer and deionized water to TPOs. TPO surface morphology was evaluated using scanning electron microscopy. The surface composition was characterized with electron spectroscopy for chemical analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 623–637, 2002; DOI 10.1002/polb.10122     

Solid‐state bonding of silicone elastomer to glass by vacuum oxygen plasma,atmospheric plasma,and vacuum ultraviolet light treatment

We experimentally demonstrated that treating a silicone elastomer by a vacuum oxygen plasma, an atmospheric pressure plasma, and vacuum ultraviolet (VUV) radiation resulted in different surface modifications that gave different contact angles, contact angle aging, and bond strengths. The aim of this study was to assess whether high‐throughput surface modification techniques of atmospheric pressure plasma and VUV radiation have the potential to replace conventional oxygen plasma modification. Four silicone elastomers with different hardnesses were used as specimens. The surfaces of all four silicone elastomers were successfully modified from hydrophobic to hydrophilic and they were also bonded to glass surfaces by the three surface modification techniques, although considerable variations were observed in the surface hydrophobicity and the bonding properties. The results clearly reveal that atmospheric pressure plasma and VUV treatment have the potential to replace conventional oxygen plasma treatment. In particular, VUV irradiation produced the most hydrophilic surface that was preserved for a long time. Thus, VUV irradiation is the most promising technique for realizing high‐throughput surface modification and bonding of silicone elastomers. Copyright © 2012 John Wiley & Sons, Ltd.     

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     

Surface modification of ethylene‐co‐tetrafluoroethylene films by remote plasmas

The surface modifications of ethylene‐co‐tetrafluoroethylene (ETFE) surfaces by six plasmas (direct H₂, Ar, and O₂ plasmas and remote H₂, Ar, and O₂ plasmas) were investigated with two questions in mind: (1) what plasma could effectively modify ETFE surfaces and (2) which of the CF₂? CF₂ and CH₂? CH₂ components in ETFE was selectively modified? The plasma exposure led to a weight loss from the ETFE surfaces and changes in the chemical composition on ETFE surfaces. The weight‐loss rate showed a strong dependence on what plasma was used for the modification. The remote H₂ plasma led to the lowest rate of weight loss in the six plasma exposures, and the direct O₂ plasma led to the highest rate of weight loss. During exposure to the plasmas, defluorination occurred, and two new C_1s components [? CH₂? CHF? CH₂? and ? CH₂? CH(O? R)? CF_x? , and ? CH₂? CHF? CF₂? , ? CH₂? C(O)? CF_x? , and ? CF_x? C(O)? O? ] were formed on the modified ETFE surfaces. Defluorination was strongly influenced by what plasma was used for the modification. The remote H₂ and Ar plasmas showed high defluorinations of 55 and 51%, respectively. The remote O₂ plasma showed a low defluorination of only 25%. Conclusively, the remote H₂ and Ar plasma exposure effectively modified ETFE surfaces. With the exposure of these surfaces to the remote H₂ plasma, the CF₂? CF₂ component was predominantly modified, rather than the CH₂? CH₂ component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2871–2882, 2002     

Surface characterization and properties of plasma‐modified cyclic olefin copolymer/layered silicate nanocomposites

In this study, cyclic olefin copolymer (COC)/layered silicate nanocomposites (CLSNs) were prepared by the intercalation of COC polymer into organically‐modified layered silicate through the solution mixing process. Both X‐ray diffraction data and transmission electron microscopy images of CLSNs indicate most of the swellable silicate layers were disorderedly intercalated into the COC matrix. The effect of layered silicate on the mechanical and barrier properties of the fabricated nanocomposites shows significant improvements in the storage modulus and water permeability when compared with that of neat COC matrix. Surfaces of COC and CLSN films were modified by a mixture of oxygen (O₂) and nitrogen (N₂) plasmas with various treated times, system pressures, and radio frequency (RF) powers. The surfaces of plasma‐modified COC and CLSN were investigated using scanning probe microscopy and contact‐angle measurements. The exposure of the COC and CLSN film to the plasmas led to the combination of etching reactions of polymer surface initiated by plasma and the following addition reactions of new functional groups onto polymer surfaces to change the topology of COC film surfaces. The surface roughness was closely related to how high and how long the RF power was input into the system. The plasmas also led to changes in the surface properties of the CLSN surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surface decreases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2745–2753, 2005     

Surface characterization and barrier properties of plasma‐modified polyethersulfone/layered silicate nanocomposites

This study describes the preparation of polyethersulfone (PES)/layered silicate nanocomposites (PLSNs) by mixing PES polymer chain into organically‐modified layered silicate in 1‐methyl‐2‐pyrrolidinone (NMP) solution. Both X‐ray diffraction data and transmission electron microscopy images of PLSNs indicate that the silicate layers were almost exfoliated and randomly distributed into the PES matrix. The mechanical and barrier properties of PLSNs show remarkable enhancement in the storage modulus and water/oxygen permeability when compared with that of neat PES matrix. Surfaces modification of PES and PLSN films with various treated times, system pressures, and radio frequency (RF) powers were performed using a mixture of oxygen (O₂) and nitrogen (N₂) plasmas. The topographical and physical properties of plasma‐modified PES and PLSN surfaces were investigated using scanning probe microscopy (SPM), contact‐angle measurements, and X‐ray photoelectron spectroscopy (XPS). These results indicate that the surface roughness of PLSNs with the same condition of plasma modification is lower than that of neat PES matrix and is probably due to the increase of stiffness with the presence of inorganic layered silicates in PES matrix. The surface properties of the PES and PLSNs are also changed from hydrophobic to hydrophilic. The XPS spectra suggest that the exposure of the PES and PLSNs to the plasmas led to the combination of etching reactions of polymer surface initiated by plasma and the following addition reactions of new oxygen‐ and nitrogen‐containing functional groups onto polymer surfaces to change their surface properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3185–3194, 2006     

A versatile and rapid coating method via a combination of plasma polymerization and surface‐initiated SET‐LRP for the fabrication of low‐fouling surfaces

In this work, we demonstrate the potential of surface‐initiated single electron transfer living radical polymerization for surface modification applications that confer low‐fouling properties. The versatility of the technique, which can be applied to a wide variety of substrates, has been displayed by the successful grafting of a range of monomers after immobilizing a bromine initiator on the surface via plasma polymerization. The thickness of the grafted surfaces can be controlled through variation of reaction parameters such as monomer concentration, reaction time, and the ratio between catalyst and ligand. Furthermore, the low‐fouling properties of the resulting surfaces were demonstrated against fully concentrated serum proteins and adhesive fibroblast cells, via grafting of N‐hydroxyethyl acrylamide (N‐HEA) or [2‐(methacryloyloxy)ethyl]dimethyl‐(3‐sulfopropyl) ammonium hydroxide (SBMA). This rapid and versatile coating technique, which has the ability to be applied to a wide range of substrates, can be performed in aqueous conditions without the exclusion of atmospheric oxygen, and shows excellent potential for the surface modification of biomaterial surfaces that require low‐fouling properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2527–2536     

Atmospheric plasma treatment of pre‐electrospinning polymer solution: A feasible method to improve electrospinnability

The electrospinnability of polyethylene oxide (PEO) was manipulated by atmospheric plasma treatment of pre‐electrospinning solutions. Conductivity, viscosity, and surface tension of PEO solutions increased after plasma treatment, and the plasma effect remained longer when the solution concentrate increased. Both untreated and treated solutions were then electrospun, and the morphology of the resultant nanofibers was observed by SEM. Atmospheric plasma treatment improved the electrospinnability of PEO solutions and led to less beads and finer diameter distribution in the resultant nanofibers. Additionally, plasma treatment of the pre‐electrospinning solutions affected the crystal structure of resultant nanofibers. These results suggest that atmospheric plasma treatment is a feasible approach to improve the electrospinnability of polymer solutions and can used to control the structure of electrospun nanofibers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Modification of porous poly(ether sulfone) membranes by low‐temperature CO2‐plasma treatment

A general method of modifying the entire cross section of porous poly(ether sulfone) membranes with a low‐temperature CO₂‐plasma treatment is reported. Both surfaces of the membranes are highly hydrophilic, with a water drop on the surface disappearing in less than 1 s, even 6 months after plasma treatment. This high hydrophilicity of both membrane surfaces results from the incorporation of hydrophilic functionalities, as evidenced by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The incorporation of these hydrophilic functionalities takes place primarily during plasma treatment, with some incorporation of atmospheric oxygen and nitrogen immediately upon exposure to air. Scanning electron microscopy shows that the membrane surface is covered by a thin, white layer that is likely the result of etching and redeposition of sputtered surface fragments. An increase in the water bubble point and glass‐transition temperature is also observed for CO₂‐plasma‐treated membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2473–2488, 2002     

Fluorine-based plasmas: Main features and application in micro-and nanotechnology and in surface treatment

Fluorine cold plasmas produced by an electrical discharge in SF₆, CF₄, CHF₃ or C₄F₈ gases, principally, have two main fields of application. The first and historical application is etching of materials for microelectronics and later for micro- and nanotechnology. The second concerns the modification of surface properties, mostly in terms of reflectance and wettability. After an introduction to cold plasmas and plasma–surface interaction principles, the article aims at presenting successively the evolution of fluorine plasma etching processes since the origin with respect to other halogen-based routes in microelectronics, the important and raising application in deep etching and microtechnology, and finally some examples in surface treatment.     

Surface characterization of plasma‐modified poly(ethylene terephthalate) film surfaces

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O₂), hydrogen (H₂), nitrogen (N₂), and ammonia (NH₃) plasmas, and the plasma‐modified PET surfaces were investigated with scanning probe microscopy, contact‐angle measurements, and X‐ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O₂ plasma > H₂ plasma > N₂ plasma > Ar plasma > NH₃ plasma, and the surface roughness was in the order of NH₃ plasma > N₂ plasma > H₂ plasma > Ar plasma > O₂ plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O₂, Ar, H₂, and N₂ plasmas modified mainly CH₂ or phenyl rings rather than ester groups in the PET polymer chains to form C? O groups. On the other hand, the NH₃ plasma modified ester groups to form C? O groups. Aging effects of the plasma‐modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of C?O groups in ester residues toward the topmost layer and to the movement of C? O groups away from the topmost layer. Such movement of the C?O groups could occur within at least 3 nm from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3727–3740, 2004     

Enhancement of polymer hydrophobicity by SF6 plasma treatment and argon plasma immersion ion implantation

In this study sulphur hexafluoride (SF₆) plasmas and argon plasma immersion ion implantation (ArPIII) techniques have been applied to improve the hydrophobicity of poly(tetrafluoroethylene) (PTFE), polyurethane and silicone surfaces. As evaluated by water contact angle measurements, all the treatments resulted in a significant enhancement in the hydrophobicity of the polymers. However, exposure of the treated samples to air induced a strong variation in their hydrophobicity as a consequence of post‐plasma reactions between atmospheric species and remnant surface free radicals. X‐ray photoelectron spectroscopy results strongly suggest that for polyurethane and silicone the surface fluorination by SF₆ plasmas and the creation of new carbon bonds and radicals are the main agents for hydrophobicity enhancement. The PTFE exposed to ArPIII revealed increases in the contact angles after exposure to air. A significant incorporation of oxygen and the formation of new carbon bonds were revealed by XPS measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

Surface effects on the diagnostic of carbon/nitrogen low‐pressure plasmas studied by differentially pumped mass spectrometry

In this work, the characterization of the species produced in reactive plasmas by differentially pumped mass spectrometry is addressed. A H₂/CH₄/N₂ mixture (90 : 5 : 5) was fed into a direct current glow discharge and analysed by conventional and cryo‐trap assisted mass spectrometry. The gaseous mixture was chosen because of its particular relevance in the inhibition of tritium‐rich carbon film deposition in fusion plasmas (scavenger technique) and in the deposition of amorphous hydrogenated carbon films by plasma‐assisted chemical vapour deposition. Important changes in the composition of the detected species upon surface modification of the reactor walls (stainless steel or covered by an amorphous hydrogenated carbon layer) or in the way they are sampled (length and spatial configuration of the stainless steel duct) were detected. They are analysed in terms of radical formation and recombination on the reactor walls or into the sampling duct, thus providing some insight into the underlying chemistry. In general, when the reactor walls are covered by an amorphous hydrogenated carbon layer, more hydrocarbons are produced, but the radical production is lower and seem to be less reactive than in stainless steel. Also, two sources of oxygen contamination in the plasma have been identified, from the native oxide layer in stainless steel and from unintended water contamination in the chamber, which modify considerably the detected species. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface immobilization of poly(ethylene oxide): Structure and properties

We covalently immobilized poly(ethylene oxide) (PEO) chains onto a fluorinated ethylene propylene copolymer (FEP) surface. On the FEP surface, aldehyde groups were first deposited by plasma polymerization of acetaldehyde or acrolein. Then, amino‐PEO chains were immobilized through Schiff base formation, which was followed by reduction stabilization with sodium cyanoborohydride. The PEO‐grafted polymer surfaces thus prepared were characterized by X‐ray photoelectron spectroscopy (XPS), atomic force microscopy, contact‐angle measurements, and protein adsorption. The dramatic increase in the C O intensity of the high‐resolution XPS C 1s spectrum, together with an overall increase in oxygen content, indicated the successful attachment of PEO chains onto the acetaldehyde plasma surfaces. The amount of grafted PEO chains depended on the superfacial density of the plasma‐generated aldehyde groups. The grafted monoamino‐PEO chains formed a brushlike structure on the polymer surface, whereas the bisamino‐PEO chains predominately adopted a looplike conformation. The PEO surface had a regular morphology with greater roughness than the aldehyde surface underneath. Surface hydrophilicity increased with the grafting of PEO. Also, the bisamino‐PEO‐grafted surface had slightly higher surface hydrophilicity than its monoamino‐PEO counterpart. These PEO coatings reduced fibrinogen adsorption by 43% compared with the substrate FEP surface. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2323–2332, 2000     

Methane plasma polymerization by low‐temperature cascade arc discharge for enhanced adhesion of primer to thermoplastic olefins

Improvement of primer adhesion to thermoplastic olefins (TPOs) by methane plasma polymerization with a low‐temperature cascade arc discharge was investigated. Methane plasma with a low‐temperature cascade arc plasma torch can be used for improving the primer adhesion to TPOs. Tape‐adhesion tests (ASTM 3359‐92a method) demonstrated this improvement, with a rating of 0 for untreated TPOs and 5 for methane plasma‐polymerized TPOs at certain plasma conditions even for aging at 60 °C and 80% relative humidity for 5 days. The adhesion to primer for the soft, flexible TPOs (ETA‐3041c and ETA‐3101) was easily enhanced. The adhesion to primer for the hard and brittle TPOs (ETA‐3183) needs to optimize the plasma conditions to pass the dry‐ and wet‐adhesion test with methane plasmas. To relate the surface characteristics of methane plasma‐polymerized TPOs to adhesion performance with primer, the wettability and polarity of TPOs were evaluated by the contact‐angle measurements of primer and deionized water to TPOs. TPO surface morphology was evaluated with scanning electron microscopy. The surface composition was characterized with electron spectroscopy for chemical analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2004–2021, 2003