Laser induced surface modification of polydimethylsiloxane as a super-hydrophobic material

In order to render the surface of polydimethylsiloxane (PDMS) super-hydrophobic without changing its bulk properties, a PDMS film without photosensitizer was exposed to CO₂ pulsed laser, at room temperature, as the excitation source. The modified surfaces have been studied by performing scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDXA) and attenuated total reflectance infrared (ATR-IR) spectroscopy. To evaluate the surface property, the water drop contact angle was measured. The dependence of ---Si---O---Si infrared peak intensity, O/Si ratio and water drop contact angle of the treated PDMS as a function of the number of laser pulses were studied. SEM micrographs and water drop contact angle variations show the uniform porosity and super-hydrophobic nature on the surface of PDMS. ATR-FTIR spectra show that the modified PDMS surface contains carbonate groups which enriched the oxygen content of the surface. EDXA analysis shows a higher percentage of oxygen on the surface of the modified PDMS. The hydrophobicity of the samples was found to depend upon the number of laser pulses, but with significant variation between the treated samples. The bulk mechanical properties of PDMS after being laser-treated did not change as shown by dynamic mechanical thermal analysis (DMTA).     

Comparison of the effect of excimer laser irradiation and RF plasma treatment on polystyrene surface

Polystyrene (PS) samples were treated with excimer laser, argon and oxygen plasmas. The surface of PS was irradiated using ArF excimer pulsed laser (λ=193 nm). Radio frequency glow discharge (RF) was used to generate the argon and oxygen plasmas. The samples were processed at different number of pulses and treatment times. The changes were characterized by atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM) and contact angle measurements. The data from ATR-FTIR spectra showed the induction process of oxygen-based functional group in both PS samples treated with RF plasma and laser. AFM and SEM observations demonstrated that a specific nanostructure was created on the laser-treated PS surface. Contact angle measurement indicated higher wettability of the treated PS with both argon and oxygen plasmas and lesser wettability of laser-treated samples. The data from in vitro assays showed the significant cell attachment and growth onto plasma-treated surfaces in comparison with laser treated samples.     

Effect of CO2 laser radiation on the surface properties of polyethylene terephthalate

The surfaces of polyethylene terephthalate (PET) obtained by irradiation with a CO₂ pulsed laser in air were studied. The complicated microstructures using various laser wavelengths were observed by scanning electron microscopy (SEM). The changes in chemical and physical properties of the irradiated PET surface were investigated by attenuated total reflectance infrared spectroscopy (ATR-FTIR) and contact angle measurements. ATR-IR spectrum showed that the crystallinity in the surface region decreased due to laser irradiation. The water drop contact angle also decreased with increasing of laser pulses. The density of peroxides formed on the irradiated PET surface were determined by iodide method.     

Surface modification of low density polyethylene (LDPE) film by low pressure O2 plasma treatment

In this work, low pressure glow discharge O₂ plasma has been used to increase wettability in a LDPE film in order to improve adhesion properties and make it useful for technical applications. Surface energy values have been estimated using contact angle measurements for different exposure times and different test liquids. In addition, plasma-treated samples have been subjected to an aging process to determine the durability of the plasma treatment. Characterization of the surface changes due to the plasma treatment has been carried out by means of Fourier transformed infrared spectroscopy (FTIR) to determine the presence of polar species such as carbonyl, carboxyl and hydroxyl groups. In addition to this, atomic force microscopy (AFM) analysis has been used to evaluate changes in surface morphology and roughness. Furthermore, and considering the semicrystalline nature of the LDPE film, a calorimetric study using differential scanning calorimetry (DSC) has been carried out to determine changes in crystallinity and degradation temperatures induced by the plasma treatment. The results show that low pressure O₂ plasma improves wettability in LDPE films and no significant changes can be observed at longer exposure times. Nevertheless, we can observe that short exposure times to low pressure O₂ plasma promote the formation of some polar species on the exposed surface and longer exposure times cause slight abrasion on LDPE films as observed by the little increase in surface roughness.     

Surface characterization of poly(L-lactic acid)-methoxy poly(ethylene glycol) diblock copolymers by static and dynamic contact angle measurements, FTIR, and ATR-FTIR

The surface composition and surface free energy properties of two types of amphiphilic and semicrystalline diblock copolymers consisting of poly(L-lactic acid) coupled to (methoxy poly(ethylene glycol) (PLLA-MePEG) having differing block lengths of PEG were investigated by using static and dynamic contact angle measurements, transmission Fourier infrared spectroscopy (FTIR), and attenuated total reflection spectroscopy (ATR-FTIR) and compared with results obtained from PLLA and MePEG homopolymers. The contact angle results were evaluated by using the van Oss-Good method (acid-base method), and it was determined that the Lewis base surface tension coefficient (gamma-) of the copolymers increased with an increase of the PEG molar content at the copolymer surface. This result is in good agreement with the transmission FTIR and ATR-FTIR results but not proportional to them, indicating that the surfaces of the copolymers are highly mobile and that the molecular rearrangement takes place upon contact with a polar liquid drop. The dynamic contact angle measurements showed that the strong acid-base interaction between the oxygen atoms in the copolymer backbone of the relatively more hydrophilic PEG segments with the Lewis acidic groups of the polar and hydrogen-bonding water molecules enabled the surface molecules to restructure (conformational change) at the contact area, so that the PEG segments moved upward, whereas the apolar methyl pendant groups of PLLA segments buried downward.     

氧等离子体改性聚乙烯表面的疏水性过回复机制

用200 W射频容性耦合氧等离子体处理低密度聚乙烯(LDPE)表面1 min, 研究了老化温度及时间对LDPE表面成分、 形貌和润湿性的影响. 扫描电子显微镜结果表明, 等离子体改性LDPE表面出现纳米凸点织构, 在60和90 ℃老化24 h后纳米凸点织构特征基本保持稳定. X射线光电子能谱分析表明, 等离子体改性LDPE表面经60 ℃老化24 h后, C—C含量由76.9%增至83.0%, C—O, CO和O—CO含量分别由16.4%, 2.2%和4.5%降至13.1%, 1.9%和2.0%. 经90 ℃老化24 h后, C—C含量较60 ℃老化表面增至84.1%, C—O含量分别降至10.1%, CO和O—CO含量分别增至3.1%和2.7%. 等离子体改性LDPE表面接触角由97.2°降至42.3°, 经60 ℃老化24 h后接触角增至95.9°, 经90 ℃老化24 h后接触角增至104.2°, 等离子体改性LDPE表面发生“疏水性过回复”. 根据含有粗糙因子的接触角随时间演变模型, 得到了具有纳米凸点织构LDPE表面在不同老化温度下的可移动极性基团所占面积分数(\begin{array}{c}{f}_m^p\end{array})、 固定极性基团所占面积分数(\begin{array}{c}{f}_{\mathit{im}}^p\end{array})和特征时间常数(τ)3个成分重构参数, 解释了“疏水性过回复”现象.     

Influence of polar groups on the wetting properties of vertically aligned multiwalled carbon nanotube surfaces

In this work, we have studied superhydrophilic and superhydrophobic transitions on the vertically aligned multiwalled carbon nanotube (VACNT) surfaces. As-grown, the VACNT surfaces were superhydrophobic. Pure oxygen plasma etching modified the VACNT surfaces to generate superhydrophilic behavior. Irradiating the superhydrophilic VACNT surfaces with a CO₂ laser (up to 50?kW?cm^?2) restored the superhydrophobicity to a level that depended on the laser intensity. Contact angle and surface energy measurements by the sessile drop method were used to examine the VACNT surface wetting. X-ray photoelectron spectroscopy (XPS) showed heavy grafting of the oxygen groups onto the VACNT surfaces after oxygen plasma etching and their gradual removal, which also depended on the CO₂ laser intensity. These results show the great influence of polar groups on the wetting behavior, with a strong correlation between the polar part of the surface energy and the oxygen content on the VACNT surfaces. In addition, the CO₂ laser treatment created an interesting cage-like structure that may be responsible for the permanent superhydrophobic behavior observed on these samples.     

Influence of O2 Plasma on Surface Properties of PC-TiO2 Nanocomposite Film

In this work, polycarbonate-TiO₂ nanocomposite films were prepared with different percentages. The aim was to consider the effect of O₂ LF plasma (50 Hz) on the hydrophilicity, surface energy, and surface morphology of polycarbonate and polycarbonate-TiO₂ nanocomposite. Structure of samples was determined by using X-ray diffraction analysis. In comparison with the reference sample, the samples’ structure did not change after plasma treatment. Surface properties of polycarbonate and polycarbonate-TiO₂ nanocomposite films were studied by X-ray photoelectron spectroscopy (XPS), contact angle measurement, atomic force microscopy (AFM), and Vickers microhardness tester. XPS analysis showed that the surface of samples became more oxidized due to plasma treatment. The water contact angle significantly decreased from 88° to 15° after plasma treatment. It was observed that the hardness of the nanocomposite films was not modified after plasma treatment.     

Plasma surface modification of poly (l-lactic acid) and poly (lactic-co-glycolic acid) films for improvement of nerve cells adhesion

Radio frequency (RF) plasma treatment in O₂ was applied to modify the surface of poly (l-lactic acid) (PLLA) and poly (d,l-lactic acid-coglycolic acid) (PLGA) as biodegradable polymers. The surface structure, morphology, wettability and surface chemistry of treated films were characterized by water drop contact angle measurement, scanning electron microscope (SEM), optical invert microscope, differential scanning calorimetry (DSC) and ATIR–FTIR spectroscopy. The cell affinity of the oxygen plasma treated film was evaluated by nervous tissue B65 cell culture in stationary conditions. The results showed that the hydrophilicity increased greatly after O₂ plasma treatment. The results showed that improved cell adhesion was attributed to the combination of surface chemistry and surface wettability during plasma treatment. Cell culture results showed that B65 nervous cell attachment and growth on the plasma treated PLLA was much higher than an unmodified sample and PLGA. Surface hydrophilicity and chemical functional groups with high polar component play an important role in enhancing cell attachment and growth.     

LDPE Transformation by Exposure to Sequential Low-Pressure Plasma and TiO2/UV Photocatalysis

Low-density polyethylene (LDPE) sheets (3.0 ± 0.1 cm) received sequential treatment, first by the action of direct-current low-pressure plasma (DC-LPP) with a 100% oxygen partial pressure, 3.0 × 10⁻² mbar pressure, 600 V DC tension, 5.6 cm distance, 6-min treatment. Then, sheets were submitted to TiO₂ photocatalysis at UV radiation at 254 nm (TiO₂/UV) with a pH value of 4.5 ± 0.2 and a TiO₂ concentration of 1 gL⁻¹. We achieved a complementary effect on the transformation of LDPE films. With the first treatment, ablation was generated, which increased hydrophilicity. With the second treatment, the cavities appeared. The changes in the LDPE sheets’ hydrophobicity were measured using the static contact angle (SCA) technique. The photocatalytic degradation curve at 400 h revealed that the DC-LPP photocatalysis sequential process decreased SCA by 82°. This was achieved by the incorporation of polar groups, which increased hydrophilicity, roughness, and rigidity by 12 and 38%, respectively. These sequential processes could be employed for LDPE and other material biodegradation pretreatment.     

Surface modification of an ethylene-acrylic acid copolymer film: grafting amine-terminated linear and branched architectures

Polymer films can be tailored for a specific application by modifying their surface properties. In this study, linear and branched architectures were grafted to ethylene-acrylic acid (EAA) copolymer films using the so-called grafting from approach. Dicyclohexylcarbodiimide was used to activate the carboxylic acid functionality on the surface of the EAA copolymer film before reacting it with selected di- and tri-amine compounds. The carboxylic acid functionality was subsequently regenerated by reacting the amine-grafted film with succinic anhydride. These reaction steps were then repeated to create the linear and branched architectures on the EAA film surface. The film surface resulting from each reaction step was analyzed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and contact angle measurements. A systematic analysis of the ATR-FTIR results was performed to estimate the average conversion of the reaction schemes and to explain the observed contact angle results. A significant reduction in water contact angle for the EAA film grafted with a branched architecture was observed. The EAA film grafted with a linear architecture showed a marginal reduction in water contact angle when ethanol was used as a solvent for ethylenediamine. When the solvent for ethylenediamine was changed to water, the contact angle decreased noticeably. However, analysis of control films showed that the reduction in the contact angles was due to the solvent treatment. In the case of branched architectures, such reduction in contact angle due to the solvent treatment was not observed. Several control experiments were performed to ensure that the reduction in the contact angles was in fact due to the grafted species and not due to exposure to various solvents used in the reaction scheme.     

Plasma-induced grafting of polydimethylsiloxane onto polyurethane surface: Characterization and in vitro assay

Plasma-induced grafting of polydimethylsiloxane (PDMS) onto the surface of polyurethane (PU) film. The virgin, plasma treated, and PDMS grafted PU films were characterized by means of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, water drop contact angle measurements, and scanning electron microscopy (SEM). The ATR-FTIR spectrogram of the grafted film showed the new characteristic peaks of PDMS. These grafted surfaces exhibited higher hydrophobicity and homogenous morphology. In vitro cell culture study showed that modified surfaces as well as virgin film were compatible with fibroblast cells. The formation of graft polymers combines the biostability of silicone with excellent physical and mechanical properties of PU.     

Biaxially Oriented Polypropylene (BOPP) Surface Modification by Nitrogen Atmospheric Pressure Glow Discharge (APGD) and by Air Corona

We compare two surface treatments of biaxially-oriented polypropylene (BOPP), which are carried out in the same dielectric barrier discharge (DBD) apparatus, namely air corona, and N₂ atmospheric pressure glow discharge (APGD). Changes in the surface energy and chemistry are investigated by contact angle measurements, by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance infrared spectroscopy (ATR-FTIR). It is shown that N₂ APGD treatment leads to a higher surface energy than air corona treatment, and to the formation of mostly amine, amide, and hydroxyl functional groups at the polypropylene surface. Finally, hydrophobic recovery of the treated film is studied; for both treatment types, the increased surface energy is found to decay in a similar manner with increasing storage time after treatment.     

Enhancement of wettability in low density polyethylene films using low pressure glow discharge N2 plasma

Low pressure glow discharge nitrogen plasma has been used to improve wettability in a low density polyethylene (LDPE) film for technical applications. The plasma treatment was carried out at a power of 300 W for different exposure times in the 1–20 min range. Wettability changes were analyzed using contact angle measurements. In addition to this, plasma‐treated samples were subjected to an aging process to determine the durability of the plasma treatment. X‐ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy were used for surface characterization. The nitrogen plasma treatment considerably reduced contact angle values thus indicating an increase in surface wettability. The spectroscopic study showed presence of oxygen‐based species on the plasma‐treated samples, which are mainly generated after the plasma treatment as a consequence of air exposure. These polar species contribute to improve surface functionalization, but this is almost lost during aging due to the hydrophobic recovery process. Microscopic studies revealed that also small changes in surface roughness occurred during the plasma treatment but these are very low compared to surface activation. The results confirmed that low pressure nitrogen can be considered as an environmentally efficient process to improve wettability in low density polyethylene films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2390–2399, 2007     

Visible light-induced thione-ene cycloaddition reaction for the surface modification of polymeric materials

A feasible method for the surface modification of polymeric materials with LDPE films as model substrates based on visible light-induced thione-ene cycloaddition reaction is proposed.     

木粉/聚乙烯复合材料的等离子体表面处理——等离子体处理时间对复合材料表面特性的影响

为改善木粉/聚乙烯复合材料的表面粘接性,实现木粉/聚乙烯复合材料的无缝连接,利用低温等离子体处理技术,对木粉/聚乙烯复合材料进行了表面处理.采用接触角测试、傅立叶变换红外光谱分析(FTIR)以及X射线光电子能谱分析(XPS)研究了等离子体处理前后复合材料表面性能的变化.试验结果表明,经等离子体处理后,复合材料表面的接触角减小,表面润湿性得以改善;FTIR分析结果表明,经等离子体处理后,复合材料表面有—OH、—C=O和—O—C=O基团生成;XPS分析表明,经等离子体处理后,复合材料表面含氧基团的含量增加,在较短的时间内表面氧元素含量增加会达到平衡,且生成大量的—O—C=O基团。     

Increasing the Hydrophobicity of a PP Film Using a Helium/CF<Subscript>4</Subscript> DBD Treatment at Atmospheric Pressure

Plasma surface modification is widely used to tailor the surface properties of polymeric materials. Most treatments are performed using low pressure plasma systems, but recently, atmospheric dielectric barrier discharges (DBDs) have appeared as interesting alternatives. Therefore, in this paper, an atmospheric He + CF₄ DBD is used to increase the hydrophobicity of a polypropylene (PP) film. The surface characterization of the PP film is performed using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results show that the hydrophobic properties of the polymer films are greatly enhanced after plasma treatment as evidenced by an increased contact angle. The incorporation of fluorine on the surface is significant (45 at%), demonstrating the ability of the used DBD set-up to generate fluorine-containing functional groups on the PP surface.     

Introduction of Primary Amino Groups on Poly(ethylene terephthalate) Surfaces by Ammonia and a Mix of Nitrogen and Hydrogen Plasma

With the aim of introducing primary amino groups on the surface of poly(ethylene terephthalate) (PET), two methods were compared—the use of ammonia or a combination of nitrogen and hydrogen low-pressure microwave plasma. Several plasma parameters were optimized on the reactor to increase the –NH₂ surface density, which was estimated by colorimetric titration and X-ray photoelectron spectroscopy (XPS). These techniques show that whatever the plasma treatment, almost 2 –NH₂/nm2 are incorporated on PET films. Emission spectroscopy highlighted a correlation between the density of primary amino groups and the ratio between an NH peak intensity and an Ar peak intensity (I_NH/I_Ar). Variation in surface hydrophilicity with aging in air after plasma treatment was monitored with contact angle measurements and showed a hydrophobic recovery. This was confirmed by XPS, which suggests also that surfaces treated by NH₃ plasma are more stable than surfaces treated by N₂/H₂.     

In Situ ATR-FTIR and UV-Visible Spectroscopy Study of Photocatalytic Oxidation of Ethanol over TiO2 Nanotubes

The photocatalytic oxidation of ethanol over TiO₂ nanotubes (NTs) was investigated by in situ attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR) and ultraviolet (UV)-visible spectroscopy. In the ATR-FTIR study, the TiO₂ NTs were spread in a ZnSe crystal trough that was used as the reactor. The evolution of the reaction under UV irradiation was investigated by in situ monitoring of changes in the species at the surface of the TiO₂ NTs. Ethanol adsorbed on the TiO₂ NTs surface, forming alkoxide and hydroxide groups, which were then attacked by ^?OH, with the formation of a vinyl alcohol intermediate that was finally transformed to acetic acid. In addition, the species changes in the reaction solution were also investigated by in situ UV-visible spectroscopy using a small volume flow-through cell. The UV-visible data further confirmed the oxidation mechanism of ethanol on TiO₂ NTs elucidated by ATR-FTIR data.     

Surface changes brought about by corona discharge treatment of polyethylene film and the effect on subsequent microbial colonisation

Microbial colonisation of synthetic plastic films is normally slow, which affects the total period of biodegradation. Correlation between the modified surface condition and the ability for microorganisms to colonise low-density polyethylene (LDPE) film was studied. Corona discharge treatment was applied to obtain enriched and activated surface condition of LDPE film. It was found from water contact angle and FTIR spectrum evaluations that surface energy was significantly increased due to production of free radicals. Stabilised oxidised LDPE surface was also obtained by further exposure to the corona which gave more suitable condition for subsequent colonisation. Results were compared with UV irradiated (photo-oxidised) LDPE films. Colonisation of corona discharged and UV treated LDPE films were tested in the laboratory environment using known fungal isolates and in a natural compost environment. More active microbial colonisation was observed in all cases for corona discharged and UV treated LDPE films. Far longer UV exposure was required to have the same physicochemical and biological effect as the corona discharge treatment.