Modification of surface properties of polyamide 6 films with atmospheric pressure plasma

To investigate the effect of the different plasma gases treatment on the surface modification of atmospheric pressure plasma, polyamide 6 films were treated using pure helium (He), He/O₂ and He/CF₄, respectively. Atomic force microscopy (AFM) showed rougher surface, while X-ray photoelectron spectroscopy (XPS) revealed increased oxygen and fluorine contents after the plasma treatments. The plasma treated samples had lower water contact angles and higher T-peel strength than that of the control. The addition of small amount of O₂ or CF₄ to He plasma increases the effectiveness of the plasma treatment in polymer surface modification in terms of surface roughness, surface hydrophilic groups, etching rate, water contact angle and bonding strength.     

Surface modification of a polyamide 6 film by He/CF4 plasma using atmospheric pressure plasma jet

Polyamide 6 (PA 6) films are treated with helium(He)/CF₄ plasma at atmospheric pressure. The samples are treated at different treatment times. The surface modification of the PA 6 films is evaluated by water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The etching rate is used to study the etching effect of He/CF₄ plasma on the PA 6 films. The T-peel strengths of the control and plasma treated films are measured to show the surface adhesion properties of the films. As the treatment time increases, the etching rate decreases steadily, the contact angle decreases initially and then increases, while the T-peel strength increases first and then decreases. AFM analyses show that the surface roughness increases after the plasma treatment. XPS analyses reveal substantial incorporation of fluorine and/or oxygen atoms to the polymer chains on the film surfaces.     

Self-assembled monolayer growth on chemically modified polymer surfaces

We report a study of the self-assembled monolayer (SAM) growth of bis[3(triethoxysilane)propyl]tetrasulfide (Tetrasulfide) on low dielectric constant (low-k) aromatic hydrocarbon SiLK whose surface chemistry was modified using sulfuric acid, He plasma treatment, and N₂ plasma treatment. X-ray photoelectron spectroscopy (XPS) spectra show that there is no detectable growth of Tetrasulfide SAM on untreated SiLK surfaces. After the SiLK surfaces have been treated with sulfuric acid, He plasma, or N₂ plasma, the original chemically inert polymer surfaces are functionalized with polar groups resulting in a significant improvement of their wettability, which is confirmed by their reduction of water droplet contact angles. The introduction of polar functional groups thus facilitates the formation of Tetrasulfide SAM on the polymer surfaces. Atomic force microscopy (AFM) analysis shows an insignificant change in the surface morphology after the growth of Tetrasulfide SAM on the chemically modified SiLK surfaces. Quantitative XPS analysis also showed that Tetrasulfide SAM growth is more prominent on He and N₂ plasma treated surfaces than those treated by sulfuric acid.     

Hydrophobization of epoxy nanocomposite surface with 1H,1H,2H,2H-perfluorooctyltrichlorosilane for superhydrophobic properties

Nature inspires the design of synthetic materials with superhydrophobic properties, which can be used for applications ranging from self-cleaning surfaces to microfluidic devices. Their water repellent properties are due to hierarchical (micrometer- and nanometre-scale) surface morphological structures, either made of hydrophobic substances or hydrophobized by appropriate surface treatment. In this work, the efficiency of two surface treatment procedures, with a hydrophobic fluoropolymer, synthesized and deposited from 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) is investigated. The procedures involved reactions from the gas and liquid phases of the PFOTS/hexane solutions. The hierarchical structure is created in an epoxy nanocomposite surface, by filling the resin with alumina nanoparticles and micron-sized glass beads and subsequent sandblasting with corundum microparticles. The chemical structure of the deposited fluoropolymer was examined using XPS spectroscopy. The topography of the modified surfaces was characterized using scanning electron microscopy (SEM), and atomic force microscopy (AFM). The hydrophobic properties of the modified surfaces were investigated by water contact and sliding angles measurements. The surfaces exhibited water contact angles of above 150° for both modification procedures, however only the gas phase modification provided the non-sticking behaviour of water droplets (sliding angle of 3°). The discrepancy is attributed to extra surface roughness provided by the latter procedure.     

Surface chemistry of atmospheric plasma modified polycarbonate substrates

Surface of polycarbonate substrates were activated by atmospheric plasma torch using different gas pressure, distance from the substrates, velocity of the torch and number of treatments. The modifications were analyzed by contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-vis spectrophotometry. Plasma treatment caused the surface characteristics to become more hydrophilic as measured by the water contact angle, which decreased from 88° to 18°. The decrease in contact angle was mainly due to oxidation of the surface groups, leading to formation of polar groups with hydrophilic property. XPS results showed an increase in the intensity of -(C-O)- groups and also introduction of new functional groups i.e. -(O-CO)- after the treatment process. AFM topographic images demonstrated an increase in the rms roughness of the surface from 2.0 nm to 4.0 nm caused by the treatment. Increase in rms roughness of the surface caused relevant decrease in transmission up to ∼2-5%.     

Surface modifications of ITO electrodes for polymer light-emitting devices

Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.     

The influence of sulfonated polyethersulfone (SPES) on surface nano-morphology and performance of polyethersulfone (PES) membrane

In this research, firstly sulfonation of polyethersulfone (PES) was carried out and then polyethersulfone (PES)/sulfonated polyethersulfone (SPES) blend membranes were prepared with phase inversion induced by immersion precipitation technique. polyvinylpyrrolidone (PVP, 2 wt% concentration) was added in the casting solution as pore former. SPES was characterized by FT-IR and UV-visible spectra, ion exchange capacity and swelling ratio. The characterization of SPES polymer indicates that the sulfonic acid groups were produced on PES polymer. Also, the prepared PES/SPES blend membranes were characterized by contact angle, AFM, SEM and cross-flow filtration for milk concentration. The contact angle measurements indicate that the hydrophilicity of PES membrane is enhanced by increasing the SPES content in the casting solution. The SEM and AFM images show that the addition of SPES in the casting solution results in a membrane with larger surface pore size and higher sub-layer porosity. The mean pore size of the membrane increased from 98 nm for PES membrane to 240 and 910 nm for 50/50 and 0/100 PES/SPES blend membranes, respectively. The pure water flux and milk water permeation through the prepared membranes are increased by blending PES with SPES. Moreover, the protein rejection of PES/SPES blend membranes was lower than PES membrane.     

Modification of surface properties of polypropylene (PP) film using DC glow discharge air plasma

The industrial use of polypropylene (PP) films is limited because of undesirable properties such as poor adhesion and printability. In the present study, a DC glow discharge plasma has been used to improve the surface properties of PP films and make it useful for technical applications. The change in hydrophilicity of modified PP film surface was investigated by contact angle (CA) and surface energy measurements as a function of exposure time. In addition, plasma-treated PP films have been subjected to an ageing process to determine the durability of the plasma treatment. Changes in morphological and chemical composition of PP films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap shear strength. The results show that the surface hydrophilicity has been improved due to the increase in the roughness and the introduction of oxygen-containing polar groups. The AFM observation on PP film shows that the roughness of the surface increased due to plasma treatment. Analysis of chemical binding states and surface chemical composition by XPS showed an increase in the formation of polar functional groups and the concentration of oxygen content on the plasma-processed PP film surfaces. T-peel and lap shear test for adhesion strength measurement showed that the adhesion strength of the plasma-modified PP films increased compared with untreated films surface.     

Investigation of the hydrophobic recovery of various polymeric biomaterials after 172 nm UV treatment using contact angle, surface free energy and XPS measurements

Surface modification as a route to improving the performance of polymeric biomaterials is an area of much topical interest. Ultraviolet (UV) light treatment has received much attention, but polymers so treated revert to their original surface condition over a period of time—an effect known as hydrophobic recovery. It is important to develop an understanding of the underlying processes contributing to the effect, since it has an impact on the applicability of UV treatment. In this work a number of polymeric biomaterials were surface-modified using 172 nm UV light from an excimer lamp. The modified polymers were characterised using contact angle, surface free energy (SFE) measurements and X-Ray Photoelectron Spectroscopy (XPS) techniques. The wettability, variation in surface free energy and chemical functionality changes were analysed on the surfaces immediately after UV treatment and subsequently over a period of 28 days. It was noted that hydrophobic recovery proceeds at a different rate for each polymer, is generally a two-phase process and that surfaces are still more hydrophilic after 28 days than the original untreated state. XPS analysis reveals that particular chemical configurations move from the surface at a faster rate than others which may contribute to the two-phase nature of the process.     

Stability of atmospheric-pressure plasma induced changes on polycarbonate surfaces

Polycarbonate films are subjected to plasma treatment in a number of applications such as improving adhesion between polycarbonate and silicon alloy in protective and optical coatings. The surfaces that undergo changes in surface properties due to plasma treatment have a tendency to revert back to their original states. Thus, the stability of the plasma induced changes on polymer surfaces over a desired time period is an important issue. The objective of this study was to examine the effect of ageing on atmospheric-pressure helium-plasma treated polycarbonate (PC) sample as a function of treatment time. The ageing effects were studied over a period of 10 days. The samples were plasma treated for 0.5, 2, 5 and 10 min. Contact angle made by water droplet on polymer surfaces were measured to study surface energy changes. Modification of surface chemical structure was examined using X-ray photoelectron spectroscopy (XPS). Contact angle decreased from 93° for untreated samples to 30° for samples treated with plasma for 10 min. After 10 days the contact angle for the 10 min plasma treated sample increased to 67°, but it never reverted back to that of the untreated surface. Similarly, the oxygen-carbon (O:C) ratio increased from 0.136 for untreated samples to 0.321 for 10 min plasma-treated samples, indicating an increase in surface energy.     

Effect of contact angle on the morphology of nanostructures produced by solution wetting of anodized aluminum oxide templates

Template-assisted nanofabrication is a simple and effective method to produce various nanostructure morphologies by controlling the polymer, solvent, and template characteristics. In this study, the importance of the surface interactions between the solution and the template in controlling the morphology of the nanostructures has been highlighted. Contact angles between various polymer solutions and anodized aluminum oxide (AAO) templates have been determined. The morphology of the resultant nanostructures has been correlated with the measured contact angles between solution and template. It is generally observed that nanorods (diameter of 100–350 nm) are produced at low contact angles, whereas nanotubes (diameter of 200–400 nm) tend to form at high contact angles. Therefore, desired nanostructure morphology for a given application can be obtained by controlling the initial wetting interaction between solution and template.     

The Controllable Surface Morphology of Polyimide (PI) Electrospun Fibers

Electrospun materials have been proposed for application for gas filtration, drug carriers, and tissue engineering. The surface morphology of electrospun fibers is the key for consideration for the above applications, such as pore size on the fiber surface, surface area, and roughness. In this work, we investigated the influence of polymer/solvent properties on soluble polyimide (PI) fibers. The studied PIs included three fluorinated aromatic polyimides containing naphthalene pendant groups. By using various solvents we adjusted the size, shape, and structure of the fibers. As a result, PI electrospun fibers could be achieved with width around 10 μm. The rough and smooth surface morphologies were studied by scanning electron microscopy (SEM). Surface wettability of the electrospun fiber membranes were characterized by contact angle measurement. The contact angles on the electrospun PI fiber mats for water and glycerol were in the range of 137.6°–144.5° and 139.1°–143.6°, respectively. Moreover, the rough fiber surface could make the electrospun fiber membrane possess good adhesive force for liquids. The results suggest that we could widen the application of electrospun membranes through controlling the fiber morphology.     

The formation of sub-10 nm nanohole array on block copolymer thin films on gold surface using surface neutralization based on O2 plasma treatment and self-assembled monolayer

Blockcopolymer (BCP) lithography is an emerging nanolithography technique for fabrications of various nanoscale devices and materials. In this study, self-assembled BCP thin films having cylindrical nanoholes were prepared on gold by surface neutralization using self-assembled monolayer (SAM). Oxygen plasma treatment was investigated as a way to enhance the functionality of Au surface toward SAM formation. After surface neutralization, well-ordered nanoholes with 9 to 20 nm diameters were formed inside BCP thin films on Au surfaces through microphase separation. The effects of oxygen plasma treatment on the formation of BCP nanopattern were investigated using surface analysis techniques including X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Au nanodot arrays were fabricated on gold film by utilizing the BCP nanotemplate and investigated by atomic force microscopy (AFM).     

Nano-structuring of PTFE surface by plasma treatment,etching, and sputtering with gold

Properties of pristine, plasma modified, and etched (by water and methanol) polytetrafluoroethylene (PTFE) were studied. Gold nanolayers sputtered on this modified PTFE have been also investigated. Contact angle, measured by goniometry, was studied as a function of plasma exposure and post-exposure aging times. Degradation of polymer chains was examined by etching of plasma modified PTFE in water or methanol. The amount of ablated and etched layer was measured by gravimetry. In the next step the pristine, plasma modified, and etched PTFE was sputtered with gold. Changes in surface morphology were observed using atomic force microscopy. Chemical structure of modified polymers was characterized by X-ray photoelectron spectroscopy (XPS). Surface chemistry of the samples was investigated by electrokinetic analysis. Sheet resistance of the gold layers was measured by two-point technique. The contact angle of the plasma modified PTFE decreases with increasing exposure time. The PTFE amount, ablated by the plasma treatment, increases with the plasma exposure time. XPS measurements proved that during the plasma treatment the PTFE macromolecular chains are degraded and oxidized and new –C–O–C–, –C=O, and –O–C=O groups are created in modified surface layer. Surface of the plasma modified PTFE is weakly soluble in methanol and intensively soluble in water. Zeta potential and XPS shown dramatic changes in PTFE surface chemistry after the plasma exposure, water etching, and gold deposition. When continuous gold layer is formed a rapid decrease of the sheet resistance of the gold layer is observed.     

Effect of different solid matrixes on surface free energy of EGDMA and TRIM polymers

Advancing and receding contact angles of water, formamide, glycerol and diiodometane were measured on the two polymers; EGDMA (dimethacrylate of ethylene glycol) and TRIM (trimethacrylate-1,1,1-trihydroksymethylopropane) which were polymerized next to glass, silanized glass, stainless steel, mica and silicon surfaces as the matrices. Then from the contact angle hystereses (CAH) and van Oss, Good, Chaudhury (LWAB) approaches the apparent surface free energies were evaluated. The measured contact angles not only depend solely on the polymer chemical structure but also, to some extent, on the solid matrix next to whose surface the sample has polymerized. Surface free energy of the polymer samples calculated from the LWAB approach shows that they interact mainly by dispersive forces. The apparent surface free energy of the polymers calculated from the diiodomethane contact angles hysteresis is practically the same irrespective of the kind of the matrix used. Therefore it can be concluded that the observed weak polar interactions in the surface free energy of the samples depend on the polymer surface preparation. The AFM images show that the obtained surfaces are of different roughness. The RMS values of roughness range between 3.7-90.2 nm for EDGMA, and 5.3-124.5 nm for TRIM. However, as reported in literature, rather protrusions bigger than 1 μm may significantly affect the contact angles, especially the receding ones.     

Grafting onto poly(ethylene terephthalate) driven by 172 nm UV light

The reactivity of the surface of poly(ethylene terephthalate) (PET) film under 172 nm UV irradiation (xenon excimer lamp) towards nitrogen-borne 1-octene, n-nonane and heptafluorodecene vapor was investigated. Materials receiving from 0 to 24 J/cm² of UV were examined by X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF/SIMS), water and mineral oil contact angle measurement and atomic force microscopy (AFM). A uniform nanoscale layer developed on PET surface attributed to the grafting reaction between photolytically-produced polymer radicals and vapor phase molecules.     

Fluorination of polymethylmethaacrylate with tetrafluoroethane using DC glow discharge plasma

Fluorination of polymer surfaces has technological applications in various fields such as microelectronics, biomaterials, textile, packing, etc. In this study PMMA surfaces were fluorinated using DC glow discharge plasma. Tetrafluoroethane was used as the fluorinating agent. On the fluorinated PMMA surface, static water contact angle, surface energy, optical transmittance (UV-vis), XPS and AFM analyses were carried out. After the fluorination PMMA surface becomes hydrophobic with water contact angle of 107° without losing optical transparency. Surface energy of fluorine plasma-treated PMMA decreased from 35 mJ/cm² to 21.2 mJ/cm². RMS roughness of the fluorinated surface was 4.01 nm and XPS studies revealed the formation of C-CF_x and CF₃ groups on the PMMA surface.     

Surface wettability of atmospheric dielectric barrier discharge processed Armos fibers

Wettability of Armos fibers has been investigated after exposed to dielectric barrier discharge (DBD) plasma, which was performed at atmospheric pressure in air while varying the sample treatment time between 9 and 27 s. Contact angles and surface free energy of the original and plasma-treated fibers were measured with dynamic contact angle analysis (DCAA) to reveal the correlation between the fiber wettability and the surface treatment, including surface composition and topography modifications, which were evaluated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. It was found by XPS analysis that the O/C atomic ratio on Armos fiber surface can be increased from 0.134 to 0.248 after the 18 s exposure to the plasma and many polar functional groups were proved to be incorporated into the surface, which aided good wetting. In addition, AFM observations revealed the changes of fiber surface microstructure, showing significant enhancement of the surface roughness after the treatment, which could also bring the fiber better wettability. What's more, the impacts of fiber surface treatment on its tensile properties were characterized by single fiber tensile strength (SFTS) testing. Results showed that Armos fibers exhibited only slight reductions in their tensile strengths with the great enhancement in fiber surface free energy.     

Preparation and characterization of thin films by plasma polymerization of glycidoxypropyltrimethoxysilane at different plasma powers and exposure times

This study aims to form a functional film on the glass substrates by plasma polymerization of glycidoxypropyltrimethoxysilane (γ-GPS). Low frequency plasma generator was used to prepare plasma polymer thin films of γ-GPS (PlzP-γ-GPS) on glass substrates at different plasma powers (30, 60 and 90 W) and exposure times (5, 15 and 30 min). XPS analyses were utilized to reveal the presence of functional groups in plasma polymer films. When higher plasma powers are applied, relative amount of Si-C bonds decreases and the amount of Si-O bonds increases. Contact angle measurements were performed to evaluate surface characteristics. Atomic force microscopy (AFM) studies were carried out to elucidate morphological changes. From AFM observations, it was obtained that the surface roughness slightly increased with the increase of plasma power from 30 to 90 W.     

Study on hydrophilicity of polymer surfaces improved by plasma treatment

Surface properties of polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET) samples treated by microwave-induced argon plasma have been studied with contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanned electron microscopy (SEM). It is found that plasma treatment modified the surfaces both in composition and roughness. Modification of composition makes polymer surfaces tend to be highly hydrophilic, which mainly depended on the increase of ratio of oxygen-containing group as same as other papers reported. And this experiment further revealed that CO bond is the key factor to the improvement of the hydrophilicity of polymer surfaces. Our SEM observation on PET shown that the roughness of the surface has also been improved in micron scale and it has influence on the surface hydrophilicity.