Highly Hydrophobic Wood Surfaces Prepared by Treatment With Atmospheric Pressure Dielectric Barrier Discharges

Atmospheric dielectric barrier discharge (DBD) treatments of wood were done to attain water repellency on wood surfaces. A specially designed frequency controlled parallel-plate DBD reactor was utilized to produce the discharges. Ethylene, methane, chlorotrifluoroethylene and hexafluoropropylene were used as DBD reagents. Contact angle, water absorption, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements on the modified surfaces were performed. For methane and ethylene, XPS data showed an increased surface atomic concentration of carbon from 72.7% on untreated samples up to 80.7 and 96%, respectively, whereas nearly 50% fluorine concentration was observed with fluorinated reagents. The C_1s spectrum of hexafluoropropylene-DBD-treated wood sample showed that the CF₃ group was introduced in a relative amount of 19%. AFM images showed distinct features for each of the DBD treatments, such as a deposit of a thin uniform film in the case of ethylene-DBD treatment, whereas the hexafluoropropylene-DBD treatment resulted in the nucleation of plasma-derived entities at the fiber surface and the subsequent growth of a film. Under optimized conditions the water contact angle was in the range of 139°–145°. The combination of depositing a low surface energy polymer on an already rough surface gave the surface-treated wood a highly hydrophobic character.     

Wettability assessment of plasma-treated PBO fibers based on thermogravimetric analysis

Changes in the surface wettability of poly(p-phenylene benzobisoxazole) (PBO) fibers were investigated by thermogravimetric analysis (TGA) following an air dielectric barrier discharge (DBD) plasma treatment. The results were then supplemented and confirmed by scanning electron microscopy (SEM), dynamic contact angle analysis (DCAA), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. After exposure to the DBD plasma at a pre-determined power level, TGA analysis showed that the residual rates retained by the PBO composites decreased, which meant an increase in the amount of resin coating the PBO fibers in the composites. Observations by SEM confirmed that there was more resin adhering to the treated PBO fibers and the wetting behavior of resin on the fibers was greatly improved. Meanwhile, DCAA for the treated fibers showed a significant enhancement in fiber surface free energy. XPS and AFM were performed in order to reveal any variations in fiber surface activity and surface morphology resulting from the surface treatment. The resulting data showed that increases in oxygen-containing polar groups and surface roughness on the plasma-treated PBO fibers contributed to the above improved wetting behavior. With comprehensive analyses, it was concluded that TGA could be used as a supporting method assessing the surface wettability of PBO fibers before and after air DBD plasma treatment.     

Effects of environment and heat treatment on an oxygen plasma-treated polyimide surface and its adhesion to a chromium overcoat

—The effects of oxygen plasma treatment time, duration of storage, and heat treatment on the surface chemistry of and Cr adhesion to Dupont RC5878 and Kapton polyimides were investigated using X-ray photoelectron spectroscopy (XPS), and contact angle and peel strength measurements. The XPS results indicate that the initial stage of plasma treatment involves oxygen adsorption with insignificant modification of the surface chemistry. After 5 s of plasma treatment the surface chemistry is modified, as suggested by the changes in the carbonyl and partially oxidized carbon functional groups' contributions to the C(1s) line shape. These modifications resulted in an increase in the peel strength and a decrease in the contact angle of water. Over the first month of storage, the intensity of the carbonyl functional group peak decreased, while the contact angle increased and reached a steady-state value of 30° after 20 days of storage. These changes are mainly attributed to moisture absorption. Importantly, the metal adhesion to polyimide remained fairly constant over the storage period. The aged plasma-treated surface experienced loss of moisture when baked at 150°C for less than 5 min. This was followed by an increase of the partially oxidized carbon at the expense of the plasma-induced carbon-oxygen bonds at higher baking temperatures or longer times.     

Surface modification of ethylene copolymers moulded against different mould surfaces-1. Surface enrichment by functional groups

A polymer surface chemical composition can be changed by the influence of different environments. Results presented from this study show that the surface of the mould influences the outermost polymer surface by enriching it with specific functional groups. This was done by moulding random copolymers against polymer films with low and high surface energies. The values presented are interpreted in terms of differences in surface energy between the mould surface and the copolymer. The random copolymers used were poly(ethylene-co-vinylacetate) (EVA) and poly(ethylene-co-acrylic acid) (EAA), both with a different comonomer content. The copolymers were moulded in contact with mould surfaces made of polymer films which were perfluorinated ethylene propylene copolymer (FEP), poly(tetrafluoroethylene) (PTFE), and poly(ethylene terephthalate) (PET). The resultant surfaces were characterized by X-ray photoelectron spectroscopy (XPS or ESCA) and contact angle measurements The surface content of acrylic acid functional groups increased in the case of EAA copolymer moulded against PET, and decreased when moulded against FEP as compared to the bulk concentration. EVA copolymers were found to be enriched in acetate groups when moulded against FEP and deficient when moulded against PET. The contact angle measurements together with the XPS measurements showed significant differences between materials moulded in contact with low and high energy surfaces. A low molecular weight additive (an internal release agent), in an EVA copolymer, was found to be enriched at the moulded polymer surface when a PET film was used as mould surface. A material transfer was also found to occur from the solid polymer films to the moulded polymer surface.     

Improvement of performance of polyamide reverse osmosis membranes using dielectric barrier discharge plasma treatment as a novel surface modification method

In this research, surface modification of aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes was carried out using dielectric barrier discharge (DBD) plasma treatment to improve the performance and fouling resistance of prepared RO membranes. First, polyamide TFC RO membranes were synthesized via interfacial polymerization of m‐phenylenediamine and trimesoyl chloride monomers over microporous polysulfone support membrane. Next, the DBD plasma treatment with 15 s, 30 s, 60 s, and 90 s duration was used for surface modification. The surface properties of RO membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), SEM, AFM, and contact angle measurements. The ATR‐FTIR results indicated that DBD plasma treatment caused hydrogen bonding on the surface of RO membranes. Also, the contact angle measurement showed that the hydrophilicity of the membranes was increased due to DBD plasma treatment. The changes in the membranes surface morphology indicated that the surface roughness of the membranes was increased after surface modification. In addition, it was found that the DBD plasma treatment increased the water permeation flux significantly and enhanced sodium chloride (NaCl) salt rejection slightly. Moreover, the filtration of bovine serum albumin revealed that the antifouling properties of the modified membranes had been improved. POLYM. ENG. SCI., 59:E468–E475, 2019. © 2018 Society of Plastics Engineers     

Polymer Masks Fabrication by Micropatterning Surfaces of Composite Polymer Coatings

Abstract

Micropatterning of surfaces has been demonstrated using composite polymer coatings of PS and PMMA of equal molecular weights in different volume proportions with varying surface topographies on silicon surfaces. The creation of PMMA masks with various surface morphological features has also been demonstrated by removal of PS from the composite coatings using cyclohexane. Atomic force microscopy (AFM) investigations revealed that the surface pattern and the dimensions of these masks significantly changed with the change in the volume proportions of each homopolymer. The composite coatings of 20/80 vol% PS/PMMA, 50/50 vol% PS/PMMA, and 80/20 vol% PS/PMMA resulted in PMMA masks with holes (depth ～300 nm), wrinkles (height ～350 nm) and pillars (height ～600 nm), respectively. Surface compositional analysis carried out using FTIR and XPS investigations confirmed the presence of polymer coatings of PS, PMMA and PS/PMMA. XPS investigations also confirmed the successful removal of PS from the PMMA mask by showing the presence of the silicon substrate on those masks where PS was previously present. The water contact angle of the composite polymer masks ranged from 70 to 90° which increased with the increase of PS vol% in the composite. The wetting behavior of certain PMMA masks showed hydrophobicity with water contact angle values above 90°.     

Atomic force microscopy analysis of cellulose triacetate surface modified in low temperature argon plasma and its adhesion behavior

The surface of cellulose triacetate (CTA) film was modified with gaseous plasma of several discharge power in the presence of Argon (Ar) gas at 0.5 torr pressure. After gas plasma etching, the surface structure of the films is analyzed by atomic force microscopy (AFM) and measured with peel strength. Furthermore, the wetting properties of the CTA film treated with Ar plasma are studied by contact angle measurement. Peel strength after plasma treatment was increased with increasing plasma treatment time. However, treatments of plasma greater than 7 min did not find an additional increase in peel strength, similarly to roughness and morphological changes of AFM. The water contact angle decreased for an initial treatment time due to the improved wettability of the film, but showed an increasing trend for a higher treatment time (7 min). These results show that Ar plasma treatment is a convenient tool for improving the adhesive properties of CTA film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3963–3971, 2006     

Selective surface modification of ethylene-vinyl acetate and ethylene polymer blend by UV–ozone treatment

Ethylene-vinyl acetate (EVA) copolymers intended for sport sole manufacturing may contain noticeable amounts of polyethylene (LDPE) for improving abrasion resistance and decrease cost; however, this blend (EVA–PE) had low polarity and showed poor adhesion. In this study an effective environmentally friendly and fast surface treatment based on UV–ozone has been used to increase the wettability, polarity and roughness of EVA–PE material. Both the length of the UV–ozone treatment and the distance between the material surface and the UV-radiation source were tested. The UV–ozone treated EVA–PE material was characterized by ATR-IR spectroscopy using Ge prism, water contact angle measurements, X-Ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adhesion properties were obtained from T peel tests of as-received and UV–ozone treated EVA–PE/polyurethane adhesive/leather joints.The more extended length of treatment and the shorter UV source–substrate distance increased the wettability of the EVA–PE material. Oxidation of the EVA–PE surface was produced by UV–ozone treatment creating new carbonyl groups mainly, and the amounts of hydroxyl and carboxylic groups were increased. The UV–ozone treatment produced ablation and etching of the EVA–PE material surface, mainly in the vinyl acetate, creating a particular roughness consisting on ruffles with deep crevices; this topography was also produced by heating produced during UV–ozone treatment. For low length of UV treatment or high UV source–material distance, the modifications of the EVA–PE material were mainly produced in the ethylene causing the selective removal of vinyl acetate, whereas more aggressive conditions produced strong oxidation in the EVA–PE material. Finally, adhesive strength was noticeably increased in the UV–ozone treated EVA–PE/polyurethane adhesive joints, and a cohesive failure in the leather was obtained.     

Surface modifications on eva treated with sulphuric acid

In this study, treatment with sulphuric acid was used to increase the adhesion of an ethylene-vinyl acetate copolymer containing 20 wt% vinyl acetate (EVA20). The treatment with sulphuric acid improved the wettability of EVA20 due to thecreation of different oxygen and sulphonic acid moieties on the surface. The treatment also created cracks and heterogeneities on the EVA20 surface, and enhanced T-peel strength values of EVA20/polychloroprene adhesive+5 wt% isocyanate joints were obtained. The loci of failure of the joints were mixed, i.e. , adhesional and cohesive in the adhesive. Peel strength values of both as-received and sulphuric acid-treated EVA20/polychloroprene adhesive joints increased after ageing at 50°C and 95 wt% relative humidity for 72 because the complete cure of the adhesive was thereby was produced. The durability of the EVA20 treated with sulphuric acid was monitored between 15 min and 5 years. High peel strength values were obtained for times up to 61 days; the joints produced with the treated EVA20 five years after treatment showed lower peel strength value due to the creation of a weak boundary layer produced by reaction of the residual sulphuric acid on the surface with EVA20. On the other hand, different experimental variables in the treatment of EVA20 with sulphuric acid were considered. The optimum treatment conditions for EVA20 were obtained by immersion in highly concentrated sulphuric acid (96 wt%) for one minute followed by neutralisation with ammonium hydroxide.     

Surface modification of polyimide film by coupling reaction for copper metallization

In this study, Upilex-S [poly(biphenyl dianhydride-p-phenylene diamine)], one of polyimide films, was modified by coupling reactions with N,N-carbonyldiimidazole (CDI) to increase adhesion to copper for flexible copper clad laminate (FCCL). Imidazole groups show strong interaction with copper metal to make charge transfer complexes. Because polyimide film did not have active site with coupling agent, the film surfaces were modified by aqueous KOH solutions and reacted with dilute HCl solutions.Surface modified Upilex-S was analyzed by X-ray photoelectron spectroscopy (XPS) to examine the surface chemical composition and film morphology and investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Changes in the wettability were evaluated by measuring contact angle with the sessile drop method. After deposition of copper on surface modified Upilx-S, the adhesion strength of the copper/polyimide system was measured by a 90° peel test using the Instron tensile strength tester. The peel strength of the copper/polyimide system increased from 0.25 to 0.86 kg_f/cm by surface modification. This result confirmed that the CDI coupling reaction is an effective treatment method for the improvement of the adhesion property between copper metal and polyimide film.     

紫铜为基材用化学复合镀法制备Ni-P-聚四氟乙烯疏水性膜

采用化学复合镀的方法,以紫铜为基材,制备复合材料Ni-P-聚四氟乙烯(PTFE)疏水性膜;控制镀液的组成和条件,可获得具有良好疏水性的复合材料Ni-P-PTFE膜,其与蒸馏水接触角为128.6°;原子力显微镜扫描图像表明,表面微粒分布均匀,表面由许多微小的结构覆盖;XPS光电子能谱分析结果表明镀层组成Ni,P,PTFE质量分数约为52.68%。     

介质阻挡放电等离子体处理芳纶的表面性能研究

采用介质阻挡放电(DBD)装置对芳纶1414表面进行改性处理,探讨低温等离子体处理对纤维表面性能的影响。结果表明:经过DBD等离子体处理后,芳纶1414纤维表面粗糙程度加剧,粘结性能和浸润性能有了明显的改善;当DBD等离子体处理功率为200～300 W,时间为60 s,氩气流量为2～3 L/min时,芳纶1414的界面剪切强度从处理前的11.9 MPa上升到14.2 MPa,接触角由处理前的85.0°下降到了60.6°。     

Long‐term stable hydrophilic surface modification of poly(ether ether ketone) via the multilayered chemical grafting method

The aging phenomena of a poly(ether ether keton) (PEEK) surface hydrophilically modified via various protocols was investigated. The use of plasma treatment or chemical etching methods offers a relatively convenient surface modification route. However, the effects of hydrophilic treatment quickly disappeared and its original surface property was recovered within a few hours or a few days when stored at ambient conditions. Surface treatment based on a single‐layered chemical grafting method rendered an excellent hydrophilic surface with an initial contact angle of <15° and an improved retardation of surface aging. However, the contact angle of the modified PEEK specimen gradually increased with time and eventually reached ～50° after 23 days. A new method for the long‐term stable hydrophilic surface treatment of PEEK using a multilayered chemical grafting strategy was also developed. With this regard, aging of the modified surface could be significantly retarded over ～90 days. It was believed that the effectiveness of the surface modification and the retarded aging phenomena via the multilayered hydrophilic treatment could be attributed to mechanical and chemical stability of the covalently bonded active surface groups on the grafted polymer networks. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46042.     

Controlling the surface wettability of poly(sulfone) films by UV‐assisted treatment: benefits in relation to plasma treatment

Hydrophilic and superhydrophilic surfaces of poly(sulfone) (PSU) thin films were prepared by UV irradiation in the presence of O₂ or acrylic acid (AA) vapor. Treated surfaces were then investigated by water contact angle measurements, Fourier transformed IR spectroscopy in attenuated total reflectance mode (FTIR‐ATR), X‐ray photoelectron spectroscopy (XPS), near‐edge X‐ray absorption fine structure (NEXAFS) and AFM. Water contact angle values of treated PSU films using either O₂ or AA vapor as the reactive atmosphere reached about 6° after more than 120 min of irradiation. FTIR‐ATR, XPS and NEXAFS analysis showed incorporation of oxygenated groups onto the surface that led to its hydrophilic characteristics. In addition, when AA vapor was used as the reactive atmosphere, a photopolymerization process of poly(acrylic acid) onto the surface of the PSU was observed. AFM analysis showed a very low level of roughness after the treatments. A comparison of UV‐assisted surface modifications of PSU films with traditional plasma treatments showed excellent qualitative agreement between the two techniques. Our results show that UV‐assisted treatments in the presence of AA vapor or O₂ are efficient ways of controlling the surface wettability and functionalities grafted on the surface of PSU films. This treatment can be considered as a permanent dry grafting method that resists aging and uses a simple experimental setup. © 2012 Society of Chemical Industry     

Surface analysis and printability studies on electron beam-irradiated thermoplastic elastomeric films from LDPE and EVA blends

The electron beam-initiated surface modification of films prepared from various blends of low-density polyethylene (LDPE), ethylene vinyl acetate (EVA), and ditrimethylol propane tetraacrylate (DTMPTA) was carried out over a range of radiation doses (20-500 kGy) and concentrations of DTMPTA. The films were characterized by Fourier transform infrared-attenuated total reflectance (FT-ATR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact angle measurements, and peel adhesion. The printability of the films was also measured. FT-ATR and XPS revealed that the surface polarity of the films made from a 50 : 50 blend of LDPE and EVA increased up to a radiation dose of 100 kGy, compared with the unirradiated sample. The polarity decreased after 100 kGy radiation. Surface pitting and roughness were observed in the SEM photomicrographs of the same films, irradiated at higher radiation doses. Higher values of the surface energy were obtained at 100 kGy for the samples without DTMPTA and for the samples containing 3 wt% DTMPTA. Excellent printability was observed for all the films irradiated above an irradiation dose of 20 kGy. The data on the printability and peel adhesion of the irradiated films could be explained by surface energy, XPS, and SEM results.     

光固化环氧全氟辛酸酯聚氨酯的研究

以环氧树脂、全氟辛酸、聚乙二醇、异佛尔酮二异氰酸酯(IPDI)和甲基丙烯酸羟乙酯为原料,通过四步反应合成了一种新型的可光固化的聚氨酯大分子单体。利用1H-NMR、IR、接触角、XPS、DSC、TGA、TEM等分析测试手段对单体的结构以及含氟聚合物的表面特性,热性能和断面形貌进行了研究。接触角和XPS的结果表明由于含氟聚合物中的全氟链段容易向表面迁移,使得固化膜表面对H2O和CH2I2的接触角可以达到108.9°和92.3°,具有低的表面自由能,能够有效地改善涂膜的耐水、耐油等性能;热性能以及断面形态分析发现该聚合物表现出较好的热性能和柔韧性。     

Grafting of acrylic acid onto corona-treated polyethylene surfaces

Peroxides formed on the surface by corona treatment of low-density polyethylene film can be used to initiate grafting of polar vinyl monomers such as acrylic acid. Different types of peroxides are probably formed on the surface, but at least hydroperoxides could be detected by XPS analysis. The grafting reaction was carried out directly after corona treatment, by placing the corona-treated film above a solution of acrylic acid heated to 100°C. The grafting reaction takes place in a vapor phase of the monomer. After extracting the reacted films with hot methanol and drying, surface analysis by XPS, IR, and contact angle measurements were carried out. Effect of degree of corona treatment and reaction time have been studied. The conclusion from this work is that acrylic acid in vapor phase can successfully be grafted onto corona-treated polyethylene film by this method. © 1992 John Wiley & Sons, Inc.     

Combined XPS and contact angle studies of flat and rough ethylene‐vinyl acetate copolymer films

Flat and rough thin films were prepared by dip coating using LDPE, PVAc, and EVA polymers containing 12–40% VA contents. Surface free energy of flat films was determined by measuring contact angles. Surface atomic composition was investigated by XPS at 0° and 60° take‐off angles. XPS results show that hydrophobic PE component was found to enrich at the near‐surface region for all EVA samples for a depth of ～ 5 nm for both flat and rough surfaces, whereas hydrophilic VA component was enriched on the surface when VA < 18% for only at 10 nm depth. The difference between the XPS results of the flat and rough surfaces was not significant for EVA samples except EVA‐33 surface where the atomic oxygen content decreased 15–20% for rough surfaces. Contact angle hysteresis values for the rough samples were much larger than that of the flat samples for LDPE and EVA‐12 surfaces due to the presence of partial trapping of air pockets on these rough surfaces. A good agreement was obtained between surface concentration of atomic oxygen in the 5 nm outermost layer and γ surface free energy component especially for the samples having high VA contents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The TPB Properties of Plasma-Treated Carbon Fiber-Reinforced Polystyrene Composites

Dielectric barrier discharges (DBD) in ambient air are used on carbon fiber to improve the fiber surface activity. Carbon fibers with length of 75 µm are placed into the plasma configuration. The interaction between modified carbon fibers and polystyrene was studied by the three-point bending (TPB) test. The chemical and physical changes induced by the treatments on carbon fiber surface are examined using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Contact angles of the plasma-treated carbon fiber and XPS results reveal that the carbon fibers modified with the DBD at an atmospheric pressure show a significant increase in oxygen and nitrogen concentration. These results demonstrate that the surfaces of the carbon fiber are more active, hydrophilic after plasma treatments using a DBD operating in ambient air.     

Surface modification and degradation of poly(lactic acid) films by Ar-plasma

Surface modification of poly(lactic acid) (PLA) film surface by Ar-plasma was investigated by contact angle measurements and XPS in order to answer the following two questions. (1) Could the Ar-plasma modify the PLA film surfaces? (2) What chemical reactions occurred on the film surfaces during the Ar-plasma treatment? The Ar-plasma treatment did not lead to hydrophilic modification of the PLA film surface, but to degradation reactions of the PLA film. Poor modification may be due to instability of the carbon radicals formed from C—O bond scission in the PLA chains by the Ar-plasma.