Surface Treatment Of Polymers Research Articles

Studying electron-beam-irradiated PET surface wetting and free energy

In this article, a comparative study has been made to evaluate the adhesion properties of poly (ethylene terephthalate) film irradiated with electron beam. The wetting behavior of the treated polymer surface is studied by employing the contact angle method and the surface free energy analysis. The contact angle is found to be dependable on the surface layer properties which in turn affected by the radiation dose and the measuring liquid polarity. Also, three different methods are used to calculate work of adhesion and surface free energy of that film. The comparison between these methods shows differences which are mainly due to the intermolecular interaction in the liquid/polymer system. The assessment of the surface free energy permits to control a large number of physicochemical properties of polymer surface and its reactivity.

Activation of PET Using an RF Atmospheric Plasma System

The plasma treatment of polymer surfaces is routinely used to enhance surface properties prior to adhesive bonding or biomolecule interaction. This study investigates the influence of plasma treatment conditions on the surface activation of polyethylene terephthalate (PET) using the SurFx Atomflo™ 400L plasma source. In this study the effect of applied plasma power, processing speed, gas composition and plasma applicator nozzle to substrate distance were examined. The level of polymer surface activation was evaluated based on changes to the water contact angle (WCA) of PET samples after plasma treatment. PET surface properties were also monitored using surface energy and X-ray photoelectron spectroscopy (XPS) analysis. The heating effect of the plasma was monitored using thermal imaging and optical emission spectroscopy (OES) techniques. OES was also used as a diagnostic tool to monitor the change in atomic and molecular species intensity with changes in experimental conditions in both time and space. XPS analysis of the PET samples treated at different plasma powers indicated that increased oxygen content on samples surfaces accounted for the decreases observed in WCAs. For the first time a direct correlation was obtained between polymer WCA changes and the OES measurement of the atomic hydrogen Balmer Hα and molecular OH line emission intensities.

Surface Treatment of Glass by Microplasma

Microplasma technology was used in many applications from biomedical to surface treatment of polymers. A new application could be the surface treatment of glass panels for the electronic industry in order to improve the surface wettability. The remote microplasma method is proposed for the surface treatment of glass. It can be easily applied as an industrial process due to the relatively low discharge voltage around 1 kV and small size of the reactor. This paper presents the surface treatment of glass by microplasma using Ar and mixtures of Ar with N2 and O2. A microplasma process was analyzed by the emission spectroscopy method. A Marx generator with MOSFET switches, a neon transformer, and a pulsed power supply were used to energize the electrodes. The emission spectrum was measured by an intensified charge-coupled device camera and a spectrometer. An optic fiber was used to have an accurate measurement of a small part of the microplasma discharge. Surface wettability of glass was confirmed, measuring the contact angle before and after the microplasma treatment. The surface of glass was modified due to the action of the radicals and active species generated by microplasma. The emission spectrum of the microplasma discharge in Ar and mixtures of Ar with and showed ArI peaks, OH peaks, second positive band system peaks, and first positive band system peaks.

Simultaneous treatment of polymer surface by EUV radiation and ionized nitrogen

In this paper chemical modification of a poly(vinylidene fluoride) surface by extreme ultraviolet (EUV) irradiation in a presence of ionized nitrogen was demonstrated for the first time. Nitrogen gas, injected into an interaction region, was ionized and excited by the EUV radiation from a laser-plasma source. The ionization degree and excited states of nitrogen were investigated using EUV spectrometry and the corresponding spectra are presented. Chemical modification of polymer after combined EUV and ionized nitrogen treatment was investigated using X-ray photoelectron spectroscopy. A significant contribution of nitrogen atoms in near-surface layer of the polymer after the treatment was demonstrated.

Surface treatment of polymers for the fabrication of all-polymer MEMS devices

Polymer microelectromechanical systems (MEMS) have received considerable attention due to their low cost, remarkable biocompatibility, and high flexibility when compared to glass and silicon devices. However, the fabrication process of all-polymer MEMS devices can be complicated and often requires a special group of techniques. In particular, different types of polymers possess different properties in terms of surface chemistry and hydrophilicity, making device assembly a challenging task. In this paper, we demonstrate the fabrication of an all-polymer microfluidic device through the investigation of the essential surface treatment methods. An SU-8–SU-8-polydimethylsiloxane (PDMS) sandwiched structure is used in this research because SU-8 enables alignment capabilities during the fabrication process. It can also be easily extended to other lithography-compatible processes. Both untreated SU-8 and PDMS are hydrophobic and they have different surface chemistry properties, so surface modifications are necessary. Three critical surface treatment steps are used in our process. The first step is to treat the first SU-8 layer with low-power (10W) oxygen plasma, making its surface hydrophilic. This step enables the uniform coating of the second SU-8 layer. The next surface treatment is on the second SU-8 layer. Both oxygen plasma (40W) etching and diluted 3-aminopropyltriethoxysilane (APTES, a silane solution) coating are needed. APTES introduces amine (SiNH2) groups on the surface. The last treatment step is to introduce silanol (SiOH) groups on PDMS using oxygen plasma. These surface treatment steps are critical in the fabrication process and can determine the quality of the final device. The knowledge obtained from this research can enable the development of novel all-polymer MEMS devices for biomedical applications.

Modification of polyethylene terephthalate by atmospheric pressure dielectric barrier discharge (DBD) in view of improving the polymer wetting properties

Surface treatment of polymers by discharge plasmas has increasingly found industrial applications due to its capability of modifying uniformly the surface without changing the material bulk properties. This work deals with surface modification of polyethylene terephthalate (PET) by a dielectric barrier discharge (DBD) at atmospheric pressure. The treatments were conducted in air, nitrogen or argon plasma. The polymer surface was characterized by contact angle measurement, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results show that the plasma treatment introduces oxygen- and nitrogen- related polar groups on the polymer surface and promotes the surface roughening. Both plasma-induced surface modifications contribute to the enhancement of the polymer wettability.

Control of the interfacial properties of ultrahigh-molecular-weight polyethylene/magnesium hybrid composites through use of atmospheric plasma treatment

This work aims to explore the use of lightweight magnesium alloys as an advanced composite material in conjunction with lightweight thermoplastic materials, such as ultrahigh-molecular-weight polyethylene (UHMWPE). High throughput, environmentally friendly, atmospheric plasma treatment methods were used to control the interfacial properties and improve the adhesion behavior of metallic/UHMWPE composites. Helium-oxygen dielectric barrier discharges were used, and the plasma-activated UHMWPE surfaces were characterized through analytical and mechanical characterization methods. Oxygen content on the treated polymer surfaces increased 18.1–36.0%. A reduction in silicon content combined with characterization through microscopy reveal a preference for the attack of the matrix over the polyethylene fibers. Wetting angles for the treated samples decreased as much as 53.7%. Treated UHMWPE/Mg hybrid samples exhibited lap shear strengths up to 113.7% greater than the control. Both the plasma-induced surface functionalization with oxygen-containing polar groups (carboxyl, carbonyl, and hydroxyl groups) and the preferential mild etching of the polymer matrix over the fibers lead to the improvement in adhesion. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers

Tribological effects of polymer surface modification through plastic deformation

The efficacy of using polymers in cylindrical applications depends closely on its surface friction and wear characteristics. In this regard, a surface modification technique through plastic deformation has been implemented. Roller burnishing is commonly used to improve the surface quality of non-ferrous surfaces, but no work showed concern about roller burnishing as a polymer surface treatment process. The objective of the present work is to investigate the influence of burnishing force and burnishing speed on the friction and wear performance of acetal homopolymer and polyurethane under dry and lubricated sliding conditions. The results reveal that the coefficient of friction and wear rate decreased to a minimum value and then increased as higher burnishing force and speed were applied. It was shown that roller burnishing had favourable prospective to be utilized as a valuable polymer surface treatment technique.

Emission Spectroscopy of Pulsed Powered Microplasma for Surface Treatment of PEN Film

Microplasma can be found in many applications. The technology is also used for surface treatment of polymers. The process of surface treatment by microplasma is environmental friendly, and it could be realized at low cost due to the relatively low discharge voltage (around 1 kV) even under atmospheric pressure and the small size of the power supply and reactor. This paper presents the surface treatment by microplasma of polyethylene naphthalate (PEN) film using Ar gas and mixtures of Ar with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The microplasma process was analyzed by the emission spectroscopy method. An experimental Marx generator with MOSFET switches was used as a pulsed high-voltage power supply. The emission spectra were measured by an intensified charge coupled device camera, a spectrometer, and a photomultiplier tube. Surface wettability of the PEN film was confirmed by measuring the contact angle before and after the microplasma surface treatment. It was observed that the contact angle of the PEN film decreased, especially with the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar mixture. The analysis using an X-ray photoelectron spectrometer showed the decrease of C1s, which correspond to the C-H bond. The emission spectrum of the microplasma discharge in the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar mixture showed Ar peaks, OH peaks, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> second positive band system peaks (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SPS), N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> first positive band system peaks ( N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FPS), and decrease in the peak intensities of ArI and OH for microplasma discharge in the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar mixture. The lifetime emission signals for the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SPS for the microplasma discharge in 0.25% N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in Ar were around 1 μs. The calculation of the microplasma rotational and electron temperatures shows low rotational and high electron temperatures.

Large-area fabrication of stochastic nano-structures on polymer webs by ion- and plasma treatment

Self-organized nano-structures can be created on polymer surfaces by applying a plasma or ion treatment [1]. This technology may be used for anti-reflection (AR) applications in plastic optical devices, e.g. for aspheric lenses in mobile phone cameras. Compared to conventional AR-coatings, the nano-structures exhibit a large potential for reduction of cost and increase of optical performance. The technology described in [1] was developed in a batch-coater and successful used to achieve AR-properties to polymer sheets and optical devices.This paper describes the transfer of this technology from a batch coater to an in-line machine for continuous surface treatment. A suited ion source to being installed in reel-to-reel equipment is chosen. The best properties for the described approach were observed by polymer surface treatment by a glow discharge created with a dual magnetron system with fully poisoned (oxidized) target surface. The process was installed and optimized in a pilot-scale reel-to-reel coating machine with a process width of 600mm. Stochastic nano-structures were created on PET, TAC and ETFE substrates. The relevant process parameters for plasma treatment are discussed. The process was transferred to industrial equipment with 2100mm process width.

Plasma modification of PET foils with different crystallinity

Polymers are commonly used in industry for packaging applications and as protective coatings but are sometimes unsuitable to use due to their low surface energies. For these latter applications, surface modification is usually necessary to improve wettability, printability and adhesive properties. In the past decades, plasma surface treatment of polymers has been extensively studied and different treatment conditions have been investigated. However, the influence of polymer crystallinity on plasma treatment effects is not well-known and therefore this study focuses on plasma treatment of PET foils with different degrees of crystallinity. The different PET foils are treated with a DBD discharge operating in air at medium pressure and the effect of polymer crystallinity on the treatment efficiency is studied in detail using contact angle measurements and atomic force microscopy (AFM). Also the ageing behavior of the different types of plasma-treated samples is investigated in this work. Results clearly show that the crystallinity of the PET foil influences both the plasma treatment effect as well as the ageing process of the samples. AFM analysis indicated that the DBD plasma homogeneously etches the surface of the amorphous PET foil resulting in smoother surfaces after plasma treatment, while for the more crystalline PET foil the etching effect is more randomly leading to rougher surfaces. As a result, amorphous polymer regions are most likely more prone to plasma etching than crystalline regions.

Surface Treatment of Polyethylene Terephthalate Films Using DBD Excited by Repetitive Unipolar Nanosecond Pulses in Air at Atmospheric Pressure

Dielectric barrier discharge (DBD) is proved to be an effective method for surface treatment of polymers over the past 20 years and is now widely used in the fields of surface modification. In this paper, surface treatment of polyethylene terephthalate (PET) films for improving the hydrophilicity using DBD excited by unipolar nanosecond pulses is presented. Two typical discharges exhibiting homogeneous and filamentary modes are obtained under certain experimental conditions, and then, they are used to modify the surface of PET films. The microstructure and properties of the film surface before and after treatment are characterized with water contact angle measurement, scanning electron microscope, atomic force microscope, and X-ray photoelectron spectroscope. The results show that, with the treatment power density of 192 and 158 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in filamentary and homogeneous modes, respectively, surface morphology and property after treatment are significantly changed, and the physical etching and introduction of oxygen-containing polar functional groups account for the decease of surface contact angle and the increase of surface roughness. Compared with the filamentary DBD treatment, the homogeneous DBD (HDBD) is more effective in surface treatment, such as lower contact angle, higher roughness, and more oxygen-containing function groups after treatment. It is attributed to the fact that the HDBD can achieve a uniform treatment and can make the physical and chemical interaction much sufficient.

Polymer Surface Treatment with SO2 -Containing Plasmas

Polymer Surface Treatment with SO₂ -Containing Plasmas

The use of a micro-cavity discharge array at atmospheric pressure to investigate the spatial modification of polymer surfaces

A micro-cavity discharge array (2500 cavities of 50 µm 2 size) was operated in neon at atmospheric pressure to modify polystyrene (PS), fluorinated ethylene–propylene co-polymer (FEP) and polytetrafluoroethylene (PTFE) polymer surfaces and, with the injection of a polymerisable monomer (acrylic acid), to deposit patterned, thin polymeric coatings. The aim of this study was to investigate the utility of these micro-discharge sources in the surface treatment of polymers and for the patterned deposition of polymeric material. The influence of the driving frequency, treatment time and sample-array distance on polymer surface treatment was investigated. X-ray photoelectron spectroscopy (XPS) was used to explore the surface chemistry of the treated polymer surfaces and of the polymer deposits . It was found that increasing the micro-cavity discharge source driving frequency and/or treatment time and decreasing the sample-array distance all led to a significant decrease in surface energy as determined by water contact angle measurements. For a period of time, post treatment surface hydrophilicity degraded due to the well known “ageing effect” but stabilized after two days. Finally, it was demonstrated that the device could be used for the localized, array sized, deposition of acrylic acid. High resolution XPS analysis of the deposit registered a C 1s spectra typical of poly(acrylic acid) with a prominent peak centred at approximately 289.3 eV indicating a relatively high level retention of the original monomer functionality. These results demonstrate that micro-cavity discharges, operated at or near atmospheric pressure, can be used to both modify and locally deposit polymeric material.

Surface Treatment of Hydrophobic Polymers by Atmospheric-Pressure Plasma

Surfaces of hydrophobic polymers were treated by atmospheric pressure plasma. The plasma system used was a newly developed damage-free dielectric barrier glow discharge. Ar was mainly used as a carrier gas. The treated polymer surfaces were mainly analyzed with contact angle measurement and X-ray photoelectron spectroscopy (XPS). In the treatment of high-density polyethylene (HDPE), atmospheric Ar plasma was found to alter the surface very hydrophilic, which is comparable to low-pressure O2 plasma. The addition of O2 in the plasma gas hardly improved the hydrophilicity. In the treatment of polytetrafluoroethylene (PTFE), atmospheric H2 (0.1%) plasma showed the greatest hydrophilicity but it was not as good as the treatment by low-pressure H2 plasma.

Surface Plasma Modification of LLDPE for Biomedical Applications

Linear low density polyethylene (LLDPE) surface was modified by water plasma treatment to functionalized with oxygen-containing functional groups and to improve wettability. The LLDPE surface was treated at 10 and 20 W discharge power at various exposure times. A laboratory scale Megatherm radio frequency (RF) plasma apparatus that operates at 27 MHz was used to generate the water plasmas. Comparative studies were also made on LLDPE by using Argon plasma discharge followed by exposure to oxygen. The changes in chemical structure of the LLDPE polymeric chain upon plasma treatment were characterized by FTIR and XPS techniques. The selectivity of trifluoroacetic anhydride (TFAA) toward hydroxyl groups is used to quantify the hydroxyl groups formed on the polymer surface upon plasma treatment. The surface wettability of the samples was evaluated by measuring water contact angle of the samples before and after modification. In an attempt to understand the effect of surface modification of polymers on organopolysiloxane coating, selected samples were coated with SIGMACOTE. After exposition to the plasma discharge a decline in water contact angle were observed. FTIR and XPS measurements indicate an oxidation of degraded polymeric chains and creation of hydroxyl, carbonyl, ether, ester and carboxyl groups. Chemical derivatization with TFAA of water plasma treated polymer surfaces has shown that under the conditions employed, a very small (less than 5%) of the oxygen introduced by the water plasma treatment was present as hydroxyl group. The XPS results revealed that, under the plasma condition utilized, the surface modification of LLDPE using water plasma improves the wetting of polysiloxane onto the LLDPE surface.

Durable anti-fogging effect and adhesion improvement on polymer surfaces

The hydrophobic properties of polymeric surfaces may cause fogging in transparent packaging and poor adhesion to printing colours and coatings. Novel plasma processes for durable functionalization of polypropylene and polyethylene terephthalate substrates were developed and analysed using optical emission spectroscopy. A worm-like nano pattern was created on the polypropylene surface prior to the deposition of thin polar plasma polymerised layers. For both substrates, highly polar surfaces exhibiting a surface tension of up to 69 mN/m and a water contact angle of about 10° were produced - providing the anti-fogging effect. The deposition of thin plasma polymerised layers protects the increased surface areas and enables to tailoring the surface energy of the substrate in a wide range. Wetting characteristics were determined by dynamic contact angle measurements. Investigations of the chemical composition of several layers using X-ray photoelectron spectroscopy and FT-infrared spectroscopy were correlated with functional testing. The surface topography was investigated using atomic force microscopy. The weldability and peeling-off characteristics of the plasma treated polymer films could be adjusted by varying the process parameters. Global and specific migration analyses were undertaken in order to ensure the manufacturing of plasma treated polymer surfaces for direct food contact purposes.

Plasma surface treatment of polymers with inductivity-coupled RF plasmas driven by low-inductance antenna units

Plasma surface treatment of polymers has been carried out with argon/oxygen mixture plasmas driven by multiple low-inductance antenna units. Kinetic energy distribution of argon ions from the argon/oxygen mixture plasmas onto polymers showed considerable suppression of ion energies sufficiently less than 10 eV. Polyethyleneterephthalate (PET) films were exposed to argon/oxygen mixture plasma for 1–5 min on a water-cooled substrate holder. The etching depth of PET surface increased with increasing plasma-exposure time and the etching rate was 118 nm/min. Surface roughness of PET surface (root-mean-square value) increased from 0.5 nm to 2.7 nm with increasing plasma-exposure time from 0 min (original sample) to 5 min. Hard X-ray photoelectron spectroscopy (HXPES) was carried out for analysis of chemical bonding states of the PET surface. The HXPES analyses exhibited nano-surface modification of the PET surface without suffering degradation of molecular structures beneath.

Effect of electron energy probability function on plasma CVD/modification in a 13.56 MHz hollow cathode discharge

Langmuir probe diagnostics is done on a RF hollow cathode discharge system (13.56 MHz, 200 W) by inserting a single cylindrical probe in the remote region (50 mm away from the primary argon plasma) and at a distance of 10 mm above the substrate holder. The effects of argon gas pressure, the injection of helium in the remote zone and the substrate bias on the measurements of the electron energy probability function (EEPF) and on the plasma parameters (electron density (ne), effective electron temperature (Teff), plasma potential (Vp) and floating potential (Vf)) have been investigated. The EEPFs and plasma parameters obtained have been used to control two remote plasma processes. The first is the remote plasma enhanced chemical vapour deposition (PE-CVD) of thin films, on silicon wafers, from a hexamethyldisiloxane precursor diluted in the remote Ar–He plasma, where the relative thicknesses of the deposited films were investigated by the ex situ Rutherford back-scattering (RBS) technique. The second is the pure argon remote plasma treatment of a polymethylmethacrylate polymer surface, where the reflectance of the modified surface was measured and compared with the untreated one. It is revealed that by varying the gas mixture/pressure and substrate bias, one can engineer the EEPFs to enhance the desired plasma chemical gas phase reactions thus controlling the plasma CVD and plasma surface modification processes. Auxiliary optical emission spectroscopy diagnostics are discussed as well.

Study of carboxylic functionalization of polypropylene surface using the underwater plasma technique

Non-equilibrium solution plasma treatment of polymer surfaces in water offers the possibility of more dense and selective polymer surface functionalization in comparison to the well-known and frequently used low-pressure oxygen plasma. Functional groups are introduced when the polymer surface contacts the plasma moderated solution especially water solutions. The emission of ions, electrons, energy-rich neutrals and complexes, produced by the ion avalanche are limited by quenching, with the aid of the ambient water phase. The UV-radiation produced in plasma formation also helps to moderate the reaction solution further by producing additional excited, ionized/dissociated molecules. Thus, monotype functional groups equipped polymer surfaces, preferably OH groups, originating from the dissociated water molecules, could be produced more selectively. An interesting feature of the technique is its flexibility to use a wide variety of additives in the water phase. Another way to modify polymer surfaces is the deposition of plasma polymers carrying functional groups as carboxylic groups used in this work. Acetic acid, acrylic acid, maleic and itaconic acid were used as additive monomers. Acetic acid is not a chemically polymerizing monomer but it could polymerize by monomer/molecular fragmentation and recombination to a cross linked layer. The other monomers form preferably water-soluble polymers on a chemical way. Only the fragmented fraction of these monomers could form an insoluble coating by cross linking to substrate. The XPS analysis was used to track the alterations in –O-CO- bond percentage on the PP surface. To identify the -COOH groups on substrate surface unambiguously, which have survived the plasma polymerization process, the derivatization with trifluoroethanol was performed.