Long Term Effects of Air Dielectric Barrier Discharge Treatment on the Surface Properties of Ethylene Vinyl Acetate (EVA)

This paper discusses the long term effects of dielectric barrier discharge (DBD) treatment on the surface properties of ethylene vinyl acetate (EVA) film. The EVA surface was characterised using contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and 180° peel tests. EVA subjected to two different treatment times was compared to as-received and solvent cleaned film. The long term stability of the surface modification induced by the DBD treatment was studied over a period of 466 days. On initial application of DBD treatment to the EVA surface an increased wettability was observed, evident from a decreased water contact angle, improved peel strength when bonded, and an increased level of carbon–oxygen moieties measured using XPS. However, over the storage period of 466 days the material reverted to almost its original state with the contact angle being only ～3° lower than that of as-received EVA compared to a difference ～25° directly after treatment. AFM measurements showed that the treatment had a slight smoothing effect on the surface topography.     

Effect of roughness as determined by atomic force microscopy on the wetting properties of PTFE thin films

The influence of film roughness on the wetting properties of vacuum-deposited polytetrafluorethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (R_q) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150°) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer-size surface asperities on the wetting properties of hydrophobic coating.     

Surface properties and moisture behaviour of pine and heat-treated spruce modified with alkoxysilanes by sol–gel process

The surface morphology and moisture behaviour of pine (Pinus sylvestris) sapwood and heat-treated spruce (Picea abies) deposited with two types of silane-based sol–gel coatings were studied by atomic force microscopy (AFM) and water contact angle measurement. The chemical composition and distribution of sol–gel coatings on wood surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The AFM images revealed that the sol–gel coatings applied by spreading covered the fine structure of the wood substrates. The surface roughness analysis of the AFM topographical images indicated that the sol–gel coatings, especially the one with short aliphatic chain, had a tendency to smooth the wood surface. The XPS results confirmed that the sol–gel coatings had successfully deposited onto pine sapwood and heat-treated spruce changing their surface chemistries. ToF-SIMS images showing Si ion distribution on treated surfaces revealed that the coatings fully covered pine sapwood surfaces. The thin coating layers formed on heat-treated spruce surfaces followed the original wood surface structure. The contact angle measurements indicated that the water repellent properties of both pine and heat-treated spruce were improved to certain extent by the sol–gel coatings.     

Statically non-wetting electrospun perfluorocyclobutyl (PFCB) aryl ether polymer doped with room temperature ionic liquid (RTIL)

A statically non-wetting, electrospun surface of non volatile room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate, (BMIM-PF₆), hosted in a solution-processable, semi-fluorinated perfluorocyclobutyl (BP-PFCB) aryl ether polymer was successfully prepared by electrospinning and compared with a surface prepared by spin casting. The surface properties of undoped and BMIM-PF₆ doped systems were analyzed by water contact angle (WCA) and atomic force microscopy (AFM). BMIM-PF₆ doped BP-PFCB surfaces prepared by spin casting showed a WCA of 90° while non-woven electrospun surfaces with the same BMIM-PF₆ concentration showed high degree of hydrophobicity with a WCA greater than 150°. Morphologies of the electrospun surfaces were characterized by scanning electron microscopy (SEM). The surface composition was analyzed by energy-dispersive X-ray spectroscopy (EDXS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Thermal analysis of the electrospun, non-woven surfaces of the doped and the undoped system of BP-PFCB were done by TGA.     

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     

Deposition of high fluorine content macromolecular thin layers under continuous-flow-system corona discharge conditions

Summary High fluorine content macromolecular layers were deposited on polyethylene (PE) film surfaces under an originally designed, continuos-flow-system plasma reactor conditions. Survey and angle resolution, ESCA data and ATR-FTIR results indicate that the plasma-created films are thin and have a fairly uniform structure. The fluorinated layers have a 60% relative fluorine atomic concentration, and are mainly composed of CF₂-CF, and C-CF₃ groups. AFM images collected from virgin and plasma-exposed PE surfaces show a significantly rougher surface of the plasma-treated substrates. Applications can be envisaged for creating Teflon-like coatings on various polymeric film surfaces using a continuous plasma process. Received: 1 June 1999/Revised version: 1 September 1999/Accepted: 1 September 1999     

Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge

The surface degradation and production of low molecular weight oxidized materials (LMWOM) on biaxially oriented polypropylene (BOPP) and low‐density polyethylene (LDPE) films was investigated and compared for two different dielectric barrier discharge (DBD) treatment types, namely air corona and nitrogen atmospheric pressure glow discharge (N₂ APGD). Contact angle measurements, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) analyses were performed in conjunction with rinsing the treated films in water. It is shown that N₂ APGD treatments of both polyolefins result in much less surface degradation, therefore, allowing for a significantly higher degree of functionalization and better wettability. Hydrophobic recovery of the treated films has also been studied by monitoring their surface energy (γ_s) over a period of time extending up to several months after treatment. Following both surface modification techniques, the treated polyolefin films were both found to undergo hydrophobic recovery; however, for N₂ APGD modified surfaces, γ_s ceases to decrease after a few days and attains a higher stable value than in the case of air corona treated films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1291–1303, 2004     

Preparation and Characterization of Covalently Binding of Rat Anti-human IgG Monolayer on Thiol-Modified Gold Surface

The 16-mercaptohexadecanoic acid (MHA) film and rat anti-human IgG protein monolayer were fabricated on gold substrates using self-assembled monolayer (SAM) method. The surface properties of the bare gold substrate, the MHA film and the protein monolayer were characterized by contact angle measurements, atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) method and X-ray photoelectron spectroscopy, respectively. The contact angles of the MHA film and the protein monolayer were 18° and 12°, respectively, all being hydrophilic. AFM images show dissimilar topographic nanostructures between different surfaces, and the thickness of the MHA film and the protein monolayer was estimated to be 1.51 and 5.53 nm, respectively. The GIXRD 2θ degrees of the MHA film and the protein monolayer ranged from 0° to 15°, significantly smaller than that of the bare gold surface, but the MHA film and the protein monolayer displayed very different profiles and distributions of their diffraction peaks. Moreover, the spectra of binding energy measured from these different surfaces could be well fitted with either Au4f, S2p or N1s, respectively. Taken together, these results indicate that MHA film and protein monolayer were successfully formed with homogeneous surfaces, and thus demonstrate that the SAM method is a reliable technique for fabricating protein monolayer.     

Effects of surface modification by Ar+ irradiation on wettability of surfaces of poly(ethylene terephthalate) films

Surfaces of poly(ethylene terephthalate); PET, films were irradiated with Ar⁺ at 1 keV using various ion doses (ID) from 10¹⁴ to 10¹⁷ ions/cm² (isc) with and without an O₂ environment. The wettability of the modified surfaces of PET was determined by measuring the contact angle between water droplets and the modified surfaces. The modified surfaces were also characterized by AFM (atomic force microscopy) and XPS (X-ray photoelectron spectroscopy) for changes in the surface morphology, and the chemical composition and molecular structure, respectively. The contact angle decreased from 70° for unmodified surfaces to 45° for modified surface with ID = 10¹⁴ isc without O₂ and remained relatively constant with higher ID. The contact angle, however, reached a minimum value of 8° for modified surfaces with ID = 10¹⁶ isc with O₂. The improved wettability may be due to a combination of the formation of hydrophilic groups, chemical and molecular structural changes, physical structural or morphological changes, and increased roughness of the surface. The wettability of the modified surfaces also depended on the time of exposure to air. The wettability worsened with exposure time to air, but was revived by immersing the films into water. Possible mechanisms for the change of the wettability of the modified surfaces are given.     

Dynamics of the wetting process on dielectric barrier discharge (DBD)-treated wood surfaces

Protection and preservation of wood properties in exterior environments can only be ensured if the surface is coated with a paint or varnish. In our experiments a dielectric barrier discharge (DBD) was used as a wood surface pretreatment for improvement of the subsequent deposition of thin paint layers from solutions onto these surfaces. As the adsorption, interfacial interactions and adhesion of paints are strongly dependent on surface wettability, the dynamics of the wetting process were analyzed. The results show that the water contact angle decreases after the DBD treatment, proving a more wettable surface. Additionally, the spreading of paint solution on the DBD-treated surface is more isotropic, showing a lower tendency to elongate along the wood fiber orientation.     

Preparation and characterization of thin organosilicon films deposited on SPR chip

The paper reports on the preparation and characterization of organosilicon thin polymer films deposited on glass slides coated with 5 nm adhesion layer of titanium and 50 nm of gold. The polymer was obtained by the decomposition of 1,1,3,3-tetramethyldisiloxane precursor (TMDSO) premixed with oxygen induced in a N₂ plasma afterglow using remote plasma-enhanced chemical vapor deposition (PECVD) technique. The film thickness was controlled by laser interferometry and was 9 nm. The chemical stability of the gold substrate coated with the organosilicon polymer film (p-TMDSO) was studied in different acidic and basic solutions (pH 1-14). While the gold/polymer interface showed a high stability in acidic media, the film was almost completely removed in basic solutions. The resulting surfaces were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle measurements, cyclic voltammetry, and surface plasmon resonance (SPR).     

Reversible Photocontrol of Wood-Surface Wettability Between Superhydrophilicity and Superhydrophobicity Based on a TiO2 Film

The reversible photocontrol of wood-surface wettability between superhydrophilicity and superhydrophobicity based on a TiO₂ film modified with octadecyl trichlorosilane (OTS) was achieved via a facile hydrothermal method at low temperature. Under UV illumination, the wood surface became superhydrophilic with a water contact angle (WCA) of approximately 0°. However, when placed in the dark, a superhydrophobic wood surface with a WCA of approximately 152° was achieved. The mechanism of the reversible photocontrol of wood-surface wettability is discussed in this article. This photocontrolled wood surface may have potential for wood self-cleaning or manipulation in response to indoor humidity.     

Study of nisin adsorption on plasma-treated polymer surfaces for setting up materials with antibacterial properties

Setting up antibacterial materials by nisin adsorption on surfaces depends mainly on the surface properties and the surface treatments allowing the modification of such properties. In order to investigate the factors affecting such adsorption, the native low density polyethylene (LDPE) was modified using Argon/Oxygen (Ar/O₂) plasma, nitrogen (N₂) plasma and plasma-induced grafting of acrylic acid (AA). The films were studied by various characterization techniques. The chemical surface modification was confirmed by X-ray photoelectron spectroscopy (XPS), the wettability of the surfaces was evaluated by contact angle measurements, the surface charge was determined by the zeta potential measurements, and the changes in surface topography and roughness were revealed by atomic force microscopy (AFM). Nisin was adsorbed on the native and the modified surfaces. The antibacterial activity, the nisin adsorbed amount, and the peptide distribution were compared for the four nisin-functionalized films. The highest antibacterial activity was recorded on the Ar/O₂ followed by AA then by N₂ treated films and the lowest activity was on the native film. The observed antibacterial activity was correlated to the type of the surface, hydrophobic and hydrophilic interactions, surface charge, surface topography, nisin adsorbed amount, and nisin distribution on the surfaces.     

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     

Application of polymer nanoparticle coating for tuning the hydrophobicity of cellulosic substrates

Nanoparticles of partially imidized poly(styrene–maleic anhydride) were applied from an aqueous dispersion as a one- or two-layer coating onto paper substrates, for controlling the paper surface hydrophobicity and improving the water barrier resistance. The effect of deposition conditions and thermal treatments on the topography and properties of the coating was studied by scanning electron microscopy, atomic force microscopy (AFM), contact angle measurements, and friction measurements. The wettability of paper surfaces with adsorbed nanoparticles can be controlled by tuning the chemical and topographical surface parameters: the water contact angles were found to increase at higher imide content as determined by Raman spectroscopy (depending on synthesis and thermal treatment), and higher average surface roughness determined by AFM (depending on the deposition method). The present technique may serve as a unique replacement for chemical treatments hydrophobizing fibrous substrates.     

Surface properties of polymers treated with tetrafluoromethane plasma

Polymer films of poly(ethylene terephthalate), polypropylene, and cellophane were surface treated with tetrafluoromethane plasma under different time, power, and pressure conditions. Contact angles for water and methylene iodide and surface energy were analyzed with a dynamic contact angle analyzer. The stability of the treated surfaces was investigated by washing them with water or acetone, followed by contact angle measurements. The plasma treatments decreased the surface energies to 2–20 mJ/m² and consequently enhanced the hydrophobicity and oleophobicity of the materials. The treated surfaces were only moderately affected after washing with water and acetone, indicating stable surface treatments. The chemical composition of the material surfaces was analyzed with X-ray photoelectron spectroscopy (XPS) and revealed the incorporation of about 35–60 atomic % fluorine atoms in the surfaces after the treatments. The relative chemical composition of the C ls spectra's showed the incorporation of —CHF— groups and highly nonpolar —CF₂— and —CF₃ groups in the surfaces and also —CH₂—CF₂— groups in the surface of polypropylene. The hydrophobicity and oleophobicity improved with increased content of nonpolar —CF₂—, —CF₃, and —CH₂—CF₂— groups in the surfaces. For polyester and polypropylene, all major changes in chemical composition, advancing contact angle, and surface energy are attained after plasma treatment for one minute, while longer treatment time is required for cellophane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1591–1601, 1997     

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     

Simultaneous graft copolymerization of 2‐hydroxyethyl methacrylate and acrylic acid onto polydimethylsiloxane surfaces using a two‐step plasma treatment

Acrylic acid (AAc) and 2‐hydroxyethyl methacrylate (HEMA) mixtures were simultaneously grafted onto the surfaces of polydimethylsiloxane (PDMS) films using a two‐step oxygen plasma treatment (TSPT). The first step of this method includes: oxygen plasma pretreatment of the PDMS films, immersion in HEMA/AAc mixtures, removal from the mixtures, and drying. The second step was carried out by plasma copolymerization of preadsorbed reactive monomers on the surfaces of dried pretreated films. The effects of pretreatment and polymerization time length, monomer concentration, and ratio on peroxide formation and graft amount were studied. The films were characterized by attenuated total reflection Furrier transformer infrared (ATR‐FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), zeta potential, surface tension, and water contact angle measurements. The ATR‐FTIR spectrum of the modified film after alkaline treatment showed the two new characteristic bands of PHEMA and PAAc. Both increase the polar part of surface tension (γ_p) after grafting and the evaluation of surface charge at pH 1.8, 7, and 12 confirmed the presence of polar groups on the surface of grafted films with a mixture of HEMA/AAc. Morphological studies using both AFM and SEM evaluation illustrated various amounts of grafted copolymer on the surface of PDMS films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Fabrication of fluorine-terminated diamond-like carbon thin film using a hyperthermal atomic fluorine beam

Surface modification of diamond-like carbon (DLC) film was performed using a hyperthermal atomic fluorine beam on the purpose of production of hydrophobic surface by maintaining the high hardness of DLC film. By the irradiation of atomic fluorine beam of a 1.0 × 10²⁰ atoms/cm², the contact angle of a water drop against the DLC surface increased from 73° to 111°. The formation of CF₃, CF₂ and CF bonding on the modified DLC surface was confirmed from the measurements of X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectra. Irradiation of hyperthermal atomic fluorine beam was concluded to produce insulator fluorine-terminated DLC film, which has high F content on the surface, by the taking of the use of neutral atomic beam as a fluorine source.     

Friction force microscopy study of diamond films modified by a glow discharge treatment

A glow discharge treatment technique has been developed which enables control of the surface roughness and morphology of diamond films for applications in optical and electrical components. A conventional hot filament chemical vapour deposition (CVD) system was used to deposit the diamond films onto silicon substrates via a three-step sequential process: (i) deposition under normal conditions; (ii) exposure to either a pure hydrogen plasma or 3% methane in an excess of hydrogen using DC-bias; and (iii) diamond deposition for a further 2 h under standard conditions. The frictional characteristics and roughness of the film surfaces were investigated by atomic force microscopy (AFM) and the morphology and the growth rates determined from scanning electron microscope images. Lateral force microscopy (LFM) has revealed significant differences in frictional behaviour between the high quality diamond films and those modified by a glow discharge treatment. Friction forces on the diamond films were very low, with coefficients ∼0.01 against silicon nitride probe tips in air. However, friction forces and coefficients were significantly greater on the DC-biased films indicating the presence of a mechanically weaker material such as an amorphous carbon layer. A combination of growth rate and frictional data indicated that the exposure to the H₂ plasma etched the diamond surface whereas exposure to CH₄/H₂ plasma resulted in film growth. Re-Nucleation of diamond was possible (stage iii) after exposure to either plasma treatment. The resultant friction forces on these films were as low as on the standard diamond film.