Surface treatment – Polymers

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1. Gonzalez, E., Barankin, M. D., Guschl, P. C., and Hicks, R. F., “Surface activation of polymethyl-methacrylate via remote atmospheric pressure plasma,” Plasma Proc. Polymers, accepted November 9, 2009. Abstract: An atmospheric pressure oxygen and helium plasma was used to activate the surface of poly(methyl methacrylate) (PMMA). The plasma physics and chemistry was investigated by numerical modeling.The numerical modeling of the afterglow and experimental results indicate that oxygen atoms generated in the plasma oxidize the polymer chains.

2. Gonzalez, E., and Hicks, R. F., “Surface Analysis of Polymers Treated by Remote Atmospheric Pressure Plasma,” Langmuir, accepted November 1, 2009. Abstract: The surfaces of high-density polyethylene (HDPE), poly(methyl methacrylate) (PMMA), and polyethersulfone (PES) were treated with a low-temperature, atmospheric pressure oxygen and helium plasma. The polymers were exposed to the downstream afterglow of the plasma, which contained primarily oxygen atoms and metastable oxygen molecules (1Δg O2), and no ions or electrons. X-ray photoelectron spectroscopy (XPS) of HDPE revealed that 20% of the carbon atoms were converted into oxidized functional groups, with about half of these being carboxylic acids. Attenuated total reflection infrared spectroscopy of all three polymers was obtained in order to determine the types of functional groups formed by atmospheric plasma exposure. It was found that the polymers were rapidly oxidized with addition of alcohols, ketones, and carboxylic acids to the carbon backbone. Chain scission occurred on HDPE and PMMA, while on PES the aromatic groups underwent ring-opening and insertion of carboxylic acid.

3. Gonzalez, E., Barankin, M. D., Guschl, P. C., and Hicks, R. F., “Ring Opening of Aromatic Polymers by Remote Atmospheric-Pressure Plasma,” IEEE Trans. Plasma Sci. 37, 823 (2009). Abstract: An atmospheric-pressure oxygen and helium plasma was used to treat the surfaces of polyetheretherketone, polyphenylsulfone, polyethersulfone, and polysulfone. Water-contact-angle measurements, mechanical pull tests, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy were used to analyze the change in polymer properties. Plasma treatment converted all the materials from a hydrophobic to a hydrophilic state in a few tenths of a second. The adhesive bond strength was increased from 1.1 to 3.8 plusmn 1.0 MPa for polyetheretherketone and from 0.6 to 1.3 plusmn 0.2 MPa for polyphenylsulfone. XPS revealed that plasma treatment oxidizes between 7% and 27% of the aromatic carbon atoms on the polymer surfaces and converts them into aldehyde and carboxylic acid groups. The degree of oxidation was highest for polyetheretherketone, where the fraction of surface carbon atoms attributable to carbonyl (ketone and aldehyde) and carboxylic acid groups increased from 5% to 11% and from 0% to 19%, respectively. It is concluded that the O atoms generated in the atmospheric-pressure plasma oxidize and open the aromatic rings available on the polymer chains and that this is responsible for the increased adhesion.

4. Ji, Y .Y., Chang, H. K., Hong ,Y. C., and Lee, S. H., “Water-repellent improvement of polyester fiber via radio frequency plasma treatment with argon hexamethyldisiloxane (HMDSO) at atmospheric pressure,” Curr. Appl Phys. 9, 253 (2009). Abstract: This work reports the formation of water-repellent surface on polyethyleneterephthalate (PET) fiber via plasma polymerization at atmospheric pressure. PET fiber was treated by employing a radio frequency (RF) plasma in a mixture of argon gas and gas-phase hexamethyldisiloxane (HMDSO). The surface morphologies and the chemical functional groups of plasma-treated fibers were characterized by a scanning electron microscopy, a Fourier transform infrared spectrometry, and an energy dispersive spectrometer. The water repellency was also characterized by comparing with American Association of Textile Chemists and Colorists (AATCC) standard spray test chart.

5. Mukhopadhyay, S., and Fangueiro, R., “Physical modification of natural fibers and thermoplastic films for composites – a review,” J.Thermoplast. Compos. Mater. 22, 135(2009). Abstract: Surface characteristics of untreated and microwave-assisted dilute lye (MAL) treated rice straw have been investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Rice straw composition was investigated by lignocelluloses determination. FTIR showed MAL treatment could effectively remove lipophilic extractives from the rice straw surface and break hydrogen bonds in the rice straw, and it was proven that more cellulose was exposed by MAL-treated with SEM. The composition analysis result indicated that the content of cellulose is 46.8% and content of lignin is 8.3% in rice straw with high-fire-power microwave-assisted 1% dilute lye for 1 h, and saccharification rate is 86% with high-fire-power microwave-assisted 1% dilute lye for 2 h.

6. Jiang, Q. R., Li, R. X., Sun, J, Wang, C. X., Peng, S. J., Ji, F., Yao, L., and Qiu, Y. P., “Influence of ethanol pretreatment on effectiveness of atmospheric pressure plasma treatment of polyethylene fibers,” Surf. Coat. Technol. 203, 1604 (2009). Abstract: Unlike low pressure plasmas, atmospheric pressure plasmas can treat materials with adsorbed liquids such as organic solvents used as cleaning agents in preparation of material surfaces for plasma treatments. These solvents may interact with the plasmas to influence the treatment results. This paper studies the influence of ethanol pretreatment on atmospheric pressure plasma jet (APPJ) treatment of ultrahigh molecular weight polyethylene (UHMWPE) fibers when a mixture of helium and 1% of oxygen is used as the treatment gas. The fibers had 0.82% and 0.86% weight gain after soaking in ethanol for 12 and 24 h, respectively. Scanning electron microscopy shows that the surface of fibers soaked in ethanol for 12 h or longer before the plasma treatment does not show any morphological change. X-ray photoelectron spectroscopy shows oxygen content doubled for the plasma treated fibers compared with control but a rather small increase in oxygen content on the surface of the ethanol pretreated UHMWPE fibers compared with the plasma treated fibers without pretreatment. Water contact angle of the ethanol pretreated fibers did not change after the plasma treatment compared with the control fiber. Microbond test shows that the interfacial shear strength values (IFSS) of the fibers to epoxy do not change for the ethanol pretreated fibers while that of the plasma directly treated fibers increases significantly. It is likely that ethanol absorbed into the fiber reacts with the plasma, forming a weakly bonded layer of polymers that reduced plasma etching and IFSS.

7. Gonzalez, E., Barankin, M. D., Guschl, P. C., and Hicks, R. F., “Remote atmospheric-pressure plasma activation of the surfaces of polyethylene terephthalate and polyethylene naphthalate,”Langmuir24, 12636 (2008). Abstract: The surfaces of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were treated with an atmospheric-pressure oxygen and helium plasma. Changes in the energy, adhesion, and chemical composition of the surfaces were determined by contact angle measurements, mechanical pull tests, and X-ray photoelectron spectroscopy (XPS). Surface-energy calculations revealed that after plasma treatment the polarity of PET and PEN increased 6 and 10 times, respectively. In addition, adhesive bond strengths were enhanced by up to 7 times. For PET and PEN, XPS revealed an 18-29% decrease in the area of the C 1s peak at 285 eV, which is attributable to the aromatic carbon atoms. The C 1s peak area due to ester carbon atoms increased by 11 and 24% for PET and PEN, respectively, while the C 1s peak area resulting from C-O species increased by about 5% for both polymers. These results indicate that oxygen atoms generated in the plasma rapidly oxidize the aromatic rings on the polymer chains. The Langmuir adsorption rate constants for oxidizing the polymer surfaces were 15.6 and 4.6 s-1 for PET and PEN, respectively.

8. Vandencasteele, N., Nisol, B., Viville, P., Lazzaroni, R., Castner, D. G., and Reniers, F. A., “Plasma-modified PTFE for biological applications: correlation between protein-resistant properties and surface characteristics,” Plasma Process. Poly. 5, 661 (2008). Abstract: PTFE samples were treated by low-pressure O2 RF plasmas. The adsorption of BSA was used as a probe for the protein-resistant properties. Exposure of PTFE to an O2 plasma leads to an increase in chamber pressure. OES reveals the presence of CO, CO2 and F in the gas phase, indicating a strong etching of the PTFE surface by the plasma. Furthermore, the high-resolution C1s spectra show CF3, CF and C[BOND]CF components. WCA as high as 160° were observed, indicating a super-hydrophobic behavior. AFM images of surfaces treated at high plasma power showed an increase in roughness. Lower amounts of BSA adsorption were detected on high power, O2 plasma-modified PTFE samples compared to low power, oxygen plasma-modified ones.

9. Morent, R., De, Geyter. N., Verschuren, J., De, Clerck. K., Kiekens, P., and Leys, C., “Non-thermal plasma treatment of textiles,” Surf. Coat. Technol. 202, 3427 (2008). Abstract: This article attempts to give an overview of the literature on the treatment of textiles with non-thermal plasmas. Because of the enormous amount of potential uses of non-thermal plasmas for the modification of textile products, categorizing the applications is difficult, and therefore a review is given on plasma treatment effects or results rather than on the textile applications that benefit from the treatment.

10. Lewis, G. T., and Cohen, Y., “Controlled nitric oxide-mediated styrene surface graft polymerization with atmospheric plasma surface activation,” Langmuir 24, 13102 (2008).

11. Ji, Y. Y., Chang, H. K., Hong, Y. C., and Lee, S. H., “Formation of hydrophobic and water-repellent surface on polyester fibers using Ar/hexamethyldisiloxane plasma at atmospheric pressure,” Jap. J. Appl. Phys. 47, 4687 (2008). Abstract: In this study, surface modification of polyester fibers with high water repellency was obtained by plasma treatment. Polyester fibers with water repellency were treated with atmospheric pressure middle-frequency (MF) plasma system using Ar and hexamethyldisiloxane (HMDSO). Ar gas has been used as the carrier gas. The surface morphologies of plasma-treated fibers were characterized by scanning electron microscopy (SEM). The Fourier transform infrared (FTIR) spectrometry was carried out to analyze the chemical composition of the polymer surface.

12. Ji, Y. Y., Hong, Y. C., Lee, S. H., Kim, S. D., and Kim, S., “Formation of super-hydrophobic and water-repellency surface with hexamethyldisiloxane (HMDSO) coating on polyethylene terephthalate fiber by atmospheric pressure plasma polymerization,” Surf. Coat. Technol. 202, 5663 (2008). Abstract: We investigated the effects of deposition plasma power on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of hexamethyldisiloxane and 3,3-dimethy-1-butene as the precursor, which are referred to as plasma polymerized hexamethyldisiloxane:3,3-dimethy-1-butene (PPHMDSO:DMB) films. As the deposition plasma power was increased from 15 to 60 W, the relative dielectric constants k of PPHMDSO:DMB films, increased from 2.67 to 3.19. After annealing at 450 degrees C, the films deposited at a deposition plasma power of 15-60 W showed k values of 2.27-2.64. With increased deposition plasma power, the as-deposited and annealed films showed increased values of hardness and Young’s modulus. For as-deposited films, deposited at a plasma power of 15-60 W, showed a hardness of 0.13-2.0 GPa and a modulus of 2.25-17.27 GPa. Annealed films, deposited at a plasma power of 15-60 W, showed a hardness of 0.05-2.07 GPa and a modulus of 1.66-14.4 GPa. The change in the k value and hardness of plasma polymer films as a function of deposition plasma power was correlated with fourier transform infrared (FT-IR) absorption peaks of C-H-x, Si-CH3, and Si-O related groups. The as-deposited and annealed PPHMDSO:DMB films showed decreased intensities of C-H-x, and Si-CH3 peaks as the deposition plasma power increased. The reduction in the dielectric constant after annealing is mainly due to hydrocarbon removal in the film. Deconvolution of Si-CH3 bending peaks of PPHMDSO:DMB films was performed to relate mechanical properties to chemical structures. The relative oxygen content in the O-Si-(CH3)(x) structure is analyzed in detail. Improvements in hardness and modulus of our films are attributed to an increased amount of O3Si-(CH3) in the Si-CH3 structure.

13. Zhu, L., Teng, W. H., Xu, H. L., Liu, Y., Jiang, Q. R., Wang, C. X., and Qiu, Y. P., “Effect of absorbed moisture on the atmospheric plasma etching of polyamide fibers,” Surf.Coat.Technol. 202, 1966 (2008). Abstract: Effect of absorbed moisture on the atmospheric plasma etching of polyamide fibers|atmospheric pressure plasma; plasma etching; moisture regain; polyamide; SEM|A potential problem for the atmospheric pressure plasma treatment is that the moisture absorbed by the substrate may influence plasma surface modification processes. This study evaluated the effect of moisture regain on the surface morphology change of polyamide fibers by plasma etching. Polyamide 6, poly(p-phenylene terephthalamide) (PPTA, aromatic polyamide), wool (polyamide 2), and ultrahigh modulus polyethylene (UHMPE, polyamide infinity) fibers, were selected to represent various polyamide molecular structures. The fibers were plasma treated at three moisture regains corresponding to three different relative humidity levels (10, 65, and 100%). Scanning electron microscope (SEM) showed that no apparent morphology change was observed on the surface of UHMPE and PPTA fibers. Under the nano-scale surface analysis of atomic force microscopy (AFM), however, rougher surface of UHMPE and PPTA fibers appeared with elevated relative humidity or higher moisture regain. In terms of polyamide 6 and wool, SEM images revealed that compared to the slight plasma etching effect of fibers with the lowest moisture regain, a thin surface layer of the treated fibers with higher moisture regain was partially or completely peeled off. It may be concluded that fiber moisture regain plays an important role in atmospheric pressure plasma etching of polyamide fibers, which may be mainly due to the interaction between the absorbed water and the polymer molecules. It can be concluded that the etching rate of atmospheric pressure plasma for a polymer depends on its moisture regain, intermolecular forces, crystallinity, and molecular structure.

14. Ren, Y., Hong, Y. Y., Sun, J., and Qiu, Y. P., “Influence of treatment duration on hydrophobic recovery of plasma-treated ultrahigh modulus polyethylene fiber surfaces ,” J. Appl. Polym. Sci.110, 995 (2008). Abstract: One of the major disadvantages of ultrahigh modulus polyethylene (UHMPE) fibers is their low surface energy which makes them difficult to adhere to most of the resins used in composites. Therefore, UHMPE fibers are often treated with plasmas to improve their surface properties. However, aging of plasma treatment effect is a major concern for plasma-treated fibers. In this study, UHMPE fibers were treated for 30, 60, 90, and 120 s with Ar/O2 plasma on a dielectric barrier discharge device. The change of the surface properties and adhesion characteristics of the fibers were investigated immediately after and 30 days after the plasma treatments using X-ray photoelectron spectroscopy, contact angle measurement, scanning electron microscopy, and micro-bond tests. Results show that aging of the plasma treatment effect was suppressed by increasing the plasma treatment duration. The interfacial shear strengths were increased from 4 MPa to 5.9, 7.8, 9.2, and 7.6 MPa for the 30, 60, 90, and 120 s treatment groups, respectively. After 30 days’ aging, the IFSS for the 30, 60, 90, and 120 s treatment groups lowered 24, 22, 10, and 9%, respectively. Increasing the plasma treatment time will increase the thickness and saturation degree of the oxidized layer on the polymer surfaces, which might hinder the migration of the hydrophobic polar functional groups from the surface to the bulk of the polymer after the plasma treatment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

15. Wang, C. X., Xu, H. L., Liu, Y., and Qiu, Y. P., “Influence of twist and filament location in a yarn on effectiveness of atmospheric pressure plasma jet treatment of filament yarns,” Surf. Coat. Technol. 202, 2775 (2008). Abstract: A twist free polyethylene terephthalate (PET) filament tow and ultrahigh modulus polyethylene (UHMPE) filament tows with 0, 1, 2, and 3 twist/cm are used as model systems to investigate the penetration of atmospheric pressure plasma jet modification effects through a single yarn. The change in surface wettability is determined using static contact angle measurements. Morphological and chemical changes on the fiber surface are characterized by scanning electron microscopy and X-ray photoelectron microscopy. The adhesion improvement is analyzed by micro-bond pullout test. For the PET filament tow, the fibers from the middle layer tend to have poorer treatment effect than those from the top and the bottom layers in terms of surface roughness, wettability and surface chemical composition change. For the UHMPE yarns, as the twist level increases, the plasma treatment is less effective in improving the fiber surface chemical composition, wettability and interfacial shear strength to epoxy due to the tightened yarn structure.

16. Ren, Y., Wang, C., and Qiu, Y. P., “Aging of surface properties of ultra high modulus polyethylene fibers treated with He/O2 atmospheric pressure plasma jet,” Surf. Coat. Technol. 202, 2670 (2008). Abstract: To investigate the relationship between aging of the treatment effect and the gas composition of atmospheric pressure plasma treatment, ultra high modulus polyethylene (UHMPE) fibers were selected as a model fiber to study the aging behavior of fiber surface treated by atmospheric pressure plasma jet (APPJ) with pure helium, helium+1% oxygen, and helium+2% oxygen. Atomic force microscopy showed increased surface roughness, while X-ray photoelectron spectroscopy revealed increased oxygen contents after the plasma treatments. The plasma treated fibers had lower contact angles and higher interfacial shear strengths to epoxy than those of the control fiber. Adding 1% of O2 to helium increased effectiveness of the plasma in polymer surface modification and suppressed aging after the treatment, while adding 2% of O2 had a negative effect on the APPJ modification results and accelerated aging. In addition, no significant difference in single fiber tensile strength was observed between the control and the plasma treated fibers.

17. Wang, C. X., Liu, Y., Xu, H. L,, Ren, Y., and Qiu, Y. P., “Influence of atmospheric pressure plasma treatment time on penetration depth of surface modification into fabric,” Appl. Surf. Sci. 254, 2499 (2008). Abstract: In order to determine the relationship between the treatment duration of atmospheric pressure plasma jet (APPJ) and the penetration depth of the surface modification into textile structures, a four-layer stack of polyester woven fabrics was exposed to helium/oxygen APPJ for different treatment durations. The water-absorption time for the top and the bottom sides of each fabric layer was reduced from 200s to almost 0s. The capillary flow height for all fabric layers in the stack increased linearly with the treatment duration but the rate of increasing reduced linearly with the fabric layer number. A model for the capillary flow height as a function of treatment duration and the layer number was established based on the experimental data and the maximum penetration depth of the APPJ was predicted for the polyester fabric. The improved wettability of the fabrics was attributed to the enhanced surface roughness due to plasma etching and the surface chemical composition change due to plasma-induced chemical reaction as detected by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The surface roughness and the surface chemical composition change diminished as the fabric layer number increased.

18. Wang, T., Wang, C., and Qiu, Y. P., “Surface modification of ultra high modulus polyethylene fibers by an atmospheric pressure plasma jet,” J. Appl. Poly. Sci. 108, 25 (2008). Abstract: To improve their adhesion properties, ultra high modulus polyethylene (UHMPE) fibers were treated by an atmospheric pressure helium plasma jet (APPJ), which was operated at radio frequency (13.56 MHz). The surface properties of the fibers were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurement. The surface dyeability improvement after plasma treatments was investigated using laser scanning confocal microscopy (LSCM). The adhesion strengths of the fibers with epoxy were evaluated by microbond tests. In addition, the influence of operational parameters of the plasma treatment including power input and treatment temperature was studied. XPS analysis showed a significant increase in the surface oxygen content. LSCM results showed that the plasma treatments greatly increased fluorescence dye concentrations on the surface and higher diffusion rate to the fiber center. The tensile strength of UHMPE fiber either remained unchanged or decreased by 10–13.6% after plasma treatment. The contact angle exhibited a characteristic increase in wettability, due to the polar groups introduced by plasma treatment. The microbond test showed that the interfacial shear strengths (IFSS) increase significantly (57–139%) after plasma treatment for all groups and the optimum activation is obtained at 100°C and 5 W power input. SEM analysis showed roughened surfaces after the plasma treatments.

19. Zhu, L., Teng, W., Xu, H., Liu, Y., Jiang, Q., Wang, C., and Qiu. Y. P., “Effect of absorbed moisture on the atmospheric plasma etching of polyamide fibers,” Surf. Coat. Technol. 202, 1966 (2008). Abstract: A potential problem for the atmospheric pressure plasma treatment is that the moisture absorbed by the substrate may influence plasma surface modification processes. This study evaluated the effect of moisture regain on the surface morphology change of polyamide fibers by plasma etching. Polyamide 6, poly(p-phenylene terephthalamide) (PPTA, aromatic polyamide), wool (polyamide 2), and ultrahigh modulus polyethylene (UHMPE, polyamide infinity) fibers, were selected to represent various polyamide molecular structures. The fibers were plasma treated at three moisture regains corresponding to three different relative humidity levels (10, 65, and 100%). Scanning electron microscope (SEM) showed that no apparent morphology change was observed on the surface of UHMPE and PPTA fibers. Under the nano-scale surface analysis of atomic force microscopy (AFM), however, rougher surface of UHMPE and PPTA fibers appeared with elevated relative humidity or higher moisture regain. In terms of polyamide 6 and wool, SEM images revealed that compared to the slight plasma etching effect of fibers with the lowest moisture regain, a thin surface layer of the treated fibers with higher moisture regain was partially or completely peeled off. It may be concluded that fiber moisture regain plays an important role in atmospheric pressure plasma etching of polyamide fibers, which may be mainly due to the interaction between the absorbed water and the polymer molecules. It can be concluded that the etching rate of atmospheric pressure plasma for a polymer depends on its moisture regain, intermolecular forces, crystallinity, and molecular structure.

20. Ren, Y., Wang, C., and Qiu, Y. P., “Influence of aramid fiber moisture regain during atmospheric plasma treatment on aging of treatment effects on surface wettability and bonding strength to epoxy,” Appl. Surf. Sci. 253, 9283 (2007). Abstract: One of the main differences between a low-pressure plasma treatment and an atmospheric pressure plasma treatment is that in atmosphere, the substrate material may absorb significant amount of water which may potentially influence the plasma treatment effects. This paper investigates how the moisture absorbed by aramid fibers during the atmospheric pressure plasma treatment influences the aging behavior of the modified surfaces. Kevlar 49 fibers with different moisture regains (MR) (0.5, 3.5 and 5.5%, respectively) are treated with atmospheric pressure plasma jet (APPJ) with helium as the carrier gas and oxygen as the treatment gas. Surface wettability and chemical compositions, and interfacial shear strengths (IFSS) to epoxy for the aramid fibers in all groups are determined using water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and micro-bond pull out tests, respectively. Immediately after the plasma treatment, the treated fibers have substantially lower water contact angles, higher surface oxygen and nitrogen contents, and larger IFSS to epoxy than those of the control group. At the end of 30 day aging period, the fibers treated with 5.5% moisture regain had a lower water contact angle and more polar groups on the fiber surface, leading to 75% improvement of IFSS over the control fibers, while those for the 0.5 and 3.5% moisture regain groups were only 30%.

21. Liu, Y., Xu, H., Ge, L., Wang, C., Han, L., Yu, H., and Qiu, Y. P., “Influence of environmental moisture on atmospheric pressure plasma jet treatment of ultrahigh-modulus polyethylene fibers,” J. Adhes. Sci. Technol. 21, 663 (2007). Abstract: One of the main differences between low-pressure and atmospheric-pressure plasma treatments is that there is little moisture involved in the low-pressure plasma treatment, although moisture could exist at the wall of the vacuum chamber or react with the substrate after plasma treatment, while in the atmospheric-pressure plasma treatment moisture exists not only in the environment but also in any hygroscopic substrate. In order to investigate the influence of environmental moisture on the effect of atmospheric pressure plasma treatment, ultra-high-modulus polyethylene (UHMPE) fibers were treated using an atmospheric-pressure plasma jet (APPJ) with 10 l/min helium gas-flow rate, treatment nozzle temperature of 100°C and 5 W output power. The plasma treatments were carried out at three different relative humidity levels, namely 5, 59 and 100%. After the plasma treatments, the surface roughness increased while the water-contact angle decreased with increasing relative humidity. The number of oxygen containing groups increased as the environmental moisture content increased. The interfacial shear strength of the UHMPE fiber/epoxy system was significantly increased after the plasma treatments, but the moisture level in the APPJ environment did not have a significant influence on the adhesion properties. In addition, no significant difference in single fiber tensile strength was observed after the plasma treatments at all moisture levels. Therefore, it was concluded that the environmental moisture did not significantly influence the effect of atmospheric-pressure plasma treatment in improving interfacial bonding between the fiber and epoxy. The improvement of the interfacial shear strength for the plasma-treated samples at all moisture levels was mainly due to the increased surface roughness and increased surface oxygen and nitrogen contents due to the plasma etching and surface modification effect.

22. Wang, C. X., and Qiu, Y. P., “Two sided modification of wool fabrics by atmospheric pressure plasma jet: Influence of processing parameters on plasma penetration,” Plasma Sources Sci. Technol. 201, 6273 (2007). Abstract: Atmospheric pressure plasma jet can treat fabrics from one side and therefore the penetration of the plasmas to the other side of the fabric is critical for the successful treatment of the fabric which needs to be treated on both sides. In this study a wool fabric was treated under various treatment conditions such as different output power, different nozzle to substrate distance, different substrate moving speed and different treatment time to see how these processing parameters influenced the penetration of plasma through the fabric. After the plasma treatments, scanning electron microscopy analysis showed that the fiber surface morphological change occurred on both sides of the fabric; Fourier transform infrared spectrometry analysis showed an increase in number of polar groups on the fiber surface for both sides; the water absorption time was also greatly reduced. The treatment effects were enhanced when the output power and the treatment time were increased. When the fabric was too close (≤ 1 mm) or too far (≥ 6 mm) from the nozzle, the treatment was not effective to either side of the fabric. The treatment on both sides was most effective when the fabric was 2–3 mm away from the nozzle. The substrate moving speed did not affect the treatment results. Therefore adequate plasma processing parameters have to be carefully selected for the best results for treating both sides of the fabric.

23. Thurston, R. M., Clay, J. D., and Schulte, M. D., “Effect of atmospheric plasma treatment on polymer surface energy and adhesion,” J. Plast. Film Sheeting. 23, 63 (2007). Abstract: This study describes experiments to quantify polymer surface energy changes after exposure to atmospheric plasma. Atmospheric plasma treatment permits surface functionalization at near-ambient temperatures. Polyethylene and polystyrene are treated with an atmospheric plasma unit. The increased surface energy and improved wetting characteristics lead to a significant adhesion improvement with adhesives that cannot be used without surface treatment.

24. Wang, C. X., Ren, Y., and Qiu, Y. P., “Penetration depth of atmospheric pressure plasma surface modification into multiple layers of polyester fabrics,” Surf.Coat.Technol. 202, 77 (2007). Abstract: Penetration depth of plasma surface modification of polyester fabrics was investigated. An eight-layer stack of woven polyester fabrics was exposed to a helium/oxygen atmospheric pressure plasma jet. Water-absorption time was used to evaluate surface hydrophilicity on the top and the bottom sides of each fabric layer and water capillary rise height was recorded as a measure of modification effectiveness for each fabric layer. Surface morphology and chemical compositions of each fabric layer in the stack were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). After atmospheric pressure plasma jet treatment, the top side of the polyester fabric became more hydrophilic. The penetration of plasma surface modification into the fabric layers was deeper for fabrics with larger average pore sizes. It was found that helium/oxygen atmospheric pressure plasma jet was able to penetrate 8 layers of polyester fabrics with pore sizes of 200 μm.

25. Zhu, L., Wang, C., and Qiu, Y. P., “Influence of the amount of absorbed moisture in nylon fibers on atmospheric pressure plasma processing,” Surf. Coat. Technol. 201, 7453 (2007). Abstract: During atmospheric pressure plasma treatment, the existence of moisture in the substrate material may have a potential influence on the treatment effect. In this study, nylon 6 fibers with three different moisture regains (1.23, 5.19 and 9.70%) were treated by atmospheric pressure plasma jet were investigated to improve the wettability and dyeing properties of fibers. The scanning electron microscope showed that at 9.70% moisture regain, the surface layer of the fibers was partially peeled off after plasma treatment. X-ray photoelectron spectroscopy analysis indicated that the plasma-treated fibers had higher oxygen concentration than the control fibers. In dynamic contact angle measurement, the advancing contact angles of all three treated groups decreased about 12°, while the groups with 5.19 and 9.70% moisture regains had lower receding contact angles than the group with 1.23% moisture regain. Using acid dye and dispersive dye, respectively, greater dye uptake was observed in treated fibers whereas the dye depths of the two dyes in nylon fibers were not affected by plasma treatment. The dyeability of the treated fibers with 1.23% moisture regain was a little better than that of the other two treated groups. In addition, no significant difference in single fiber tensile strength was found among control and treated fibers.

26. Lewis G. T., Nowling G. R., Hicks R. F., and Cohen Y., “Inorganic surface nanostructuring by atmospheric pressure plasma-induced graft polymerization,”  Abstract: Surface graft polymerization of 1-vinyl-2-pyrrolidone onto a silicon surface was accomplished by atmospheric pressure (AP) hydrogen plasma surface activation followed by graft polymerization in both N-methyl-2-pyrrolidone (NMP) and in an NMP/water solvent mixture. The formation of initiation sites was controlled by the plasma exposure period, radio frequency (rf) power, and adsorbed surface water. The surface number density of active sites was critically dependent on the presence of adsorbed surface water with a maximum observed at approximately a monolayer surface water coverage. The surface topology and morphology of the grafted polymer layer depended on the solvent mixture composition, initial monomer concentration, reaction temperature, and reaction time. Grafted polymer surfaces prepared in pure NMP resulted in a polymer feature spacing of as low as 5-10 nm (average feature diameter of about 17 nm), an rms surface roughness range of 0.18-0.72 nm, and a maximum grafted polymer layer thickness of 5.5 nm. Graft polymerization in an NMP/water solvent mixture, however, resulted in polymer feature sizes that increased up to a maximum average feature diameter of about 90 nm at [NMP] = 60% (v/v) with polymer feature spacing in the range of 10-50 nm. The surface topology of the polymer-modified silicon surfaces grafted in an NMP/water solvent mixture exhibited a bimodal feature height distribution. In constrast, graft polymerization in pure NMP resulted in a narrow feature height distribution of smaller-diameter surface features with smaller surface spacing. The results demonstrated that, with the present approach, the topology of the grafted polymer surface was tunable by adjusting the NMP/water ratio. The present surface graft polymerization method, which is carried out under AP conditions, is particularly advantageous for polymer surface structuring via radical polymerization and can, in principle, be scaled to large surfaces.

27. Hicks, R. F., Babayan, S. E., Penelon, J., Truong, Q., Cheng, S. F., Le, V. V., Ghilarducci, J., Hsieh, A. G., Deitzel, J. M., and Gillespie, J. W., “Atmospheric plasma treatment of polyetheretherketone composites for improved adhesion,” SAMPE Fall Technical Conference Proceedings: Global Advances in Materials and Process Engineering, Dallas, TX, CD-ROM pp. 9 (2006). Abstract: A handheld atmospheric plasma has been developed to treat polyetheretherketone (PEEK) composites. The instrument produces a plasma beam that covers a circular area 2.5 cm in diameter. The plasma is fed with 30 L/min of helium and 0.45 L/min of oxygen, and is supplied with 80 W of radio frequency power (13.56 MHz). The plasma beam was swept over the composite surface to activate it for bonding. Following treatment, 3M AF-563 adhesive film was applied to 2.5 x 17.8 cm2 strips of PEEK. The strips were joined together and cured, and a series of lap shear tests (ASTM D-3165) were performed. Plasma treated samples failed cohesively and showed average lap shear strengths of 43.2¡Ó0.6 MPa, whereas the untreated samples failed adhesively at much lower shear strengths. Environmental testing revealed that the plasma-exposed surfaces could sit for at least 8 hours at 49 ¢XC and 90% relative humidity prior to applying the adhesive with no loss of bond strength. The handheld plasma tool is safe, easy to use, environmentally friendly, and well suited for treating large, 3-dimensional PEEK panels.

28. Vandencasteele, N., Fairbrother, H., and Reniers, F. A., “Selected Effect of the Ions and the Neutrals in the Plasma Treatment of PTFE Surfaces: An OES-AFM-contact angle and XPS study,” Plasma Process. Polym. 2, 493 (2005). Abstract: Polytetrafluoroethylene (PTFE) surfaces were treated by oxygen and nitrogen species generated either in a remote (filtered) RF plasma or in an ion gun. In the first case, the majority of the species reaching the surface are neutral molecules, whereas in the second case, ions are the reactive agent. In this paper, we show that ions alone do not lead to a significant grafting of new functions on the PTFE surface. The XPS analysis of the treated surface show identical behaviour with oxygen and nitrogen ion treatment, and the evolution of the C1s peak shape suggest a progressive sputtering, leading to defluorination of the surface. The nitrogen plasma treatment lead to a subsequent grafting that is attributed mostly to the “excited neutrals”, but we suggest here that the ions could play a significant role in the activation process of the surface. The exposure of PTFE to an oxygen plasma lead to chemical etching of the surface, different from the physical sputtering induced by the ion treatment, that lead to a super-hydrophobic behavior of the surface attributed to an increase in the surface roughness.

29. Vandencasteele, N., and Reniers, F. A., “Surface characterization of plasma-treated PTFE surfaces: an OES, XPS and contact angle study,” Surf. Interface Anal. 36, 1027 (2004). Abstract: PTFE surfaces have been exposed to neutral atoms and molecules, and to electrons originating from a modified RF nitrogen plasma, able to filter out the cations. The changes in surface energy of the modified polymer, determined by the water contact angle, are linearly related to the increase of the nitrogen concentration at the surface, determined by XPS. The deconvolution of the spectral envelope of the C 1s photoelectron peak shows a strong modification of the nature of the chemical groups on the surface, depending on the treatment time and on the plasma power. Electrons are postulated to be mainly responsible for the appearance of the CF3 group, while the major functions induced by nitrogen seem to be C[DOUBLE BOND]N, C[BOND]N and a possible F[BOND]C[BOND]N group.

30. Wagner, A. J., Fairbrother, D. H., and Reniers, F. A., “Comparison of PE surfaces modified by plasma generated neutral nitrogen species and nitrogen Ions,” Plasmas and Polymers. 8, 2 (2003). Abstract: The surface modification of polyethylene (PE) by neutral nitrogen species (ground and excited state N2 as well as atomic N; modified nitrogen plasma treatment) has been compared to the effect of nitrogen ion bombardment using X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements. XPS results indicate that a greater nitrogen concentration was grafted during the modified nitrogen plasma treatment of PE, an effect that was attributed to surface sputtering during ion beam modification. The distribution of nitrogen-containing functionalities was strongly dependent upon the treatment strategy; the modified nitrogen plasma treatment lead predominantly to imine groups being formed at the PE surface, while amine groups were the dominant species produced during ion beam modification. The presence of electron irradiation during the modified nitrogen plasma treatment of PE did not modify the rate of nitrogen incorporation or change the nature of N-containing functional groups produced but did lead to a systematic decrease in contact angle.

31. Toshifuji, J., Katsumata, T., Takikawa, H., Sakakibara, T., and Shimizu, I., “Cold arc-plasma jet under atmospheric pressure for surface modification,” Surf. Coat. Technol. 171, 302 (2003). Abstract: A relatively cold arc-plasma jet under atmospheric pressure was developed using a pulse power supply, called a Plasma Energized (PEN)-Jet. A needle electrode was placed in a glass tube, and a cap electrode with a center-hole (3 mm diameter) was placed at the tube end. The electric arc was discharged between the electrodes by applying intermittent bipolar pulse power. By introducing dry air, nitrogen, or oxygen gas into the tube from the other end, the plasma gas of the arc was spewed out from the center-holed cap electrode, and a plasma jet was formed. The length and temperature of this plasma jet was measured as a function of pulse frequency (10–30 kHz). Both were found to increase with the increase in pulse frequency, not being very dependent on the type of gas under present experimental conditions. Maximum jet length was approximately 15 mm at 30 kHz, and maximum temperature at 5 mm from the cap electrode was 250 8C. Various metals and polymers were treated by PEN-Jet. The water contact-angle of these materials was found to decrease.

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