Characterization of Surface Modification of Polyethersulfone Membrane

Surface modification of polyethersulfone (PES) membrane surfaces using UV/ozone pretreatment with subsequent grafting and interfacial polymerization on membrane surface was investigated in order to improve the resistance of membrane surface to protein adsorption. The surface modifications were evaluated in terms of hydrophilicity, chemical composition of the surface and static protein adsorption. In both methods, poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG) and chitosan were chosen as hydrophilic polymers to chemically modify the commercial virgin PES membrane to render it more hydrophilic as these materials have excellent hydrophilic property. Modified PES membranes were characterized by contact angle and XPS. Contact angles of modified PES membranes were reduced by 19 to 58% of that of the virgin PES membrane. PES membrane modified with PEG shows higher wettability than other hydrophilic materials with the highest contact angle reduction shown for UV/ozone pretreated, PEG grafted PES membrane surface. In general, XPS spectra supported that the PES membranes were successfully modified by both grafting with UV/ozone pretreatment and interfacial polymerization methods. The results of the static protein adsorption experiments showed all surface modifications led to reduction in protein adsorption on PES membranes; the highest protein adsorption reduction occurred with membrane modified by UV/ozone pretreatment followed by PES grafting, which corresponded to the highest contact angle reduction. However, there seems to be no clear correlation between contact angle reduction and reduction in protein adsorption in the case that involved chitosan. Nevertheless, membranes modified with chitosan do show higher reduction in protein adsorption than membranes modified with other materials under the same conditions.     

Surface characterization of polymers modified by keV and MeV ion beams

The present work deals with two different surface modification techniques for altering the surface properties of polymers: plasma treatment and ion implantation. Polymer foils were exposed in an inductively-coupled r.f. (13.56 MHz) plasma system with and without applying a negative high voltage pulse to the sample stage. The influence of low pressure plasmas of oxygen, nitrogen, or argon on the chemical composition, topography, and wettability of polymer surfaces was studied in detail. Etch rates of poly(ethylene terephthalate) for different plasma parameters were monitored. The polymer surface was also modified by a high energy ion beam process. Polyimide films were implanted with different ion species such as Ar⁺, N⁺, C⁺, He⁺, and O⁺ at doses from 1 × 10¹⁵ to 1 × 10¹⁷ ion/cm². Ion energy was varied from 10 to 60 keV for the plasma source ion implantation (PSII) experiment. Polyimide samples were also implanted with 1 MeV hydrogen, carbon, and oxygen ions at a dose of 1 × 10¹⁴ ion/cm². Depending on the ion energy, dose, and ion species, the surface resistivity of the film was reduced by several orders of magnitude. A study on the plasma-treated and ion beam-treated polymer surfaces was performed using TOF-SIMS, XPS, SEM, AFM, and water contact angle measurements.     

Surface modification of polymers and improvement of the adhesion between evaporated copper metal film and a polymer. I. Chemical modification of PET

To improve the interfacial adhesion between evaporated copper film and poly(ethylene terephthalate) (PET), the surface of PET films was modified by treating with hydrazine monohydrate. The effect of the treatment time in the range of 5-20 min with 80 wt% hydrazine monohydrate at 60 °C on the number of polar groups created on PET was investigated. The surface topography of and water contact angle on the PET film surface, the mechanical properties of the PET film, and the adhesion strength of evaporated copper metal film to the PET film surface were also investigated. The introduction of polar groups on the modified PET film surface was examined by FT-IR and ESCA analyses. The amount of polar groups increased to the maximum value with increasing treatment time to 10 min, and thereafter it decreased markedly. The surface roughness increased with increasing treatment time up to 10 min and cracks occurred after 20 min. The water contact angle and tensile properties decreased with increasing treatment time. Using the scratch test, the adhesion between Cu film and PET was found to increase with increasing treatment time up to 10 min and thereafter there was a remarkable decrease in adhesion. From these results, it was concluded that the optimum treatment time with hydrazine monohydrate (80 wt%) at 60°C was about 10 min to improve copper-PET adhesion.     

Plasma Surface Modification of PMMA for Optical Applications

Optical surfaces with antireflective structures show excellent optical properties for a wide range of light incidence angles. Suitable structures can be generated on PMMA by an optimized plasma etching process. The chemical composition of PMMA modified using plasma was studied with infrared reflection absorption spectroscopy (IRRAS). The investigations indicate a change of chemical composition even during the first few seconds of plasma etching. It is assumed that the modified surface layer is essentially involved in the structure formation process.     

Surface modification of polypropylene film using N2O-containing flames

Contact-angle measurements and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize polypropylene (PP) films that were exposed to laminar premixed air: natural gas flames containing small quantities of nitrous oxide. During combustion, the nitrous oxide generates gas-phase nitrogen oxides that lead to the affixation of nitrogen-containing functional groups to the PP surfaces. Treatment of PP in nitrous oxide-containing flames also leads to an increase in surface oxidation and markedly improves wettability when compared with standard flame treatments. The chemical form of the nitrogen affixed to the PP surface is strongly dependent on the flame equivalence ratio. Fuel-lean flames tend to affix highly oxidized forms of nitrogen such as nitrate and nitro groups, while fuel-rich flames tend to affix less-oxidized nitrogen groups such as nitroso, oxime, amide, and amine. A computational model, SPIN, was used to elucidate the chemistry of the flame as it impinges upon the cooled PP surface. The SPIN modeling indicates that the principal reactive gas-phase species at or near the PP surface are O₂, OH, H, NO, NO₂, HNO, and N₂O. A number of possible reactions between these species and the PP can account for the formation of the various nitrogen functional groups observed.     

The Do's and Don'ts of Wettability Characterization in Textiles

Surface treatments introduce chemical modifications to the fiber surface that affect the surface free energy (SFE). This is done either with the obvious aim to change the wetting behavior, or to affect related properties, such as, e.g., adhesion phenomenon, surface conductivity, adsorption of proteins, etc. On planar substrates, the measurement of contact angles of specific liquids and making use of formalisms such as Neumann or Owens–Wendt equations is a commonly used approach to determine the surface free energy. It is to be observed that this direct approach is often and lightheartedly applied to porous and textured samples, such as textiles, too. The geometry of a textile is extremely complex and defined by the topography of the fiber, the construction of the yarn, and the construction of the fabric. In addition, polymer fibers may be porous and take up water from the environment. Accordingly, wetting is the result of simultaneous spreading on a rough surface, penetration, and capillary motion in the multi-porous system. Therefore, the critical consideration of any analytical method for wettability measurements cannot be overemphasized, and the present paper is meant to critically discuss the pros and cons of various methods common to the textile researcher. It can be summarized that contact angles can be useful for comparative measurements on hydrophobic samples, while the established drop penetration tests characterize the effects of fabric finishing, fiber surface modifications, etc. with limited quantification. By no means can these test be used to derive the SFE, and in all cases it is essential to avoid accidental distortions of the fabric. The single fiber micro-Wilhelmy method can be regarded as the only reliable method to obtain advancing and receding contact angles.     

Atmospheric-Pressure Plasma Amination of Polymer Surfaces

Using dielectric barrier discharges (DBDs) in suitable gas atmospheres, appreciable densities of amino groups can be generated on polymer surfaces. After the introduction and a few remarks on analytical methods for the determination of functional groups densities, this paper presents a short summary of recent studies on the mechanism of the polymer surface amination from nitrogen and nitrogen/hydrogen mixtures, and possible relevant precursor species. Combination of chemical derivatization with quantitative FT-IR spectroscopy was employed for the determination of primary amino groups densities introduced on polyolefin surfaces in DBD afterglows in N₂ and N₂ + H₂ mixtures. Owing to the possibility to generate atmospheric-pressure plasmas in sub-mm³ volumes, DBD plasmas can be used to modify polymer surfaces area selectively: a new process termed 'plasma printing' can be applied for the achievement of micropatterned surface modifications, such as hydrophilization/hydrophobization or chemical functionalization. Direct-patterning polymer surface modification processes are of interest for biochemical/biomedical applications as well as for polymer electronics. Two examples are presented in more detail: ? the area-selective plasma amination of carbon-filled polypropylene minidiscs to manufacture microarrays with peptide libraries utilizing parallel combinatorial chemical synthesis, and ?the continuous treatment of polymer foils by means of reel-to-reel patterned plasma amination for the subsequent electroless copper metallization, leading to a fast and highly efficient process for the manufacture of structured metallizations for flexible printed circuits or RFID antennas.     

Surface modification of bioceramics by grafting of tailored allyl phosphonic acid

Abstract

A new route to interfacial bonding between ceramic and matrix in biocomposites is identified. A tailored allyl phosphonic acid is used as a coupling agent bound to the surface of a bioceramic to form a 'grafted' calcium phosphate (CAP). The allyl phosphonic acid coupling agent is synthesised by reaction of allyl halide and trialkyl phosphite. Successful synthesis was confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopy (FTIR). The allyl phosphonic acid was incorporated onto calcium phosphate using a wet chemical coprecipitation synthesis route. The resulting 'grafted' CAP was characterised using FTIR coupled with photoacoustic sampling, and Fourier transform Raman spectroscopy (FTR). The spectroscopic data suggest an interaction between the allyl phosphonic acid and calcium phosphate resulting from observed reductions in intensity of the hydroxyl (3570 cm^?1) and phosphate ν ₃ (1030 cm^?1) peaks. The continued presence of C=C functionality on the surface of the grafted CAP was indicated by FTIR and FTR spectra (peaks at 1650 and 1635 cm^?1 respectively) and confirmed by X-ray photoelectron spectroscopy (XPS). On the basis of these results, it is concluded that grafted CAP may be used to produce a chemically bonded composite with superior mechanical properties.     

Surface modification of films of various high temperature resistant thermoplastics

The influence of different surface treatments on the physical and chemical surface properties of poly(etheretherketone) (PEEK), poly(phenylenesulfide) (PPS) and a liquid crystal polymer (LCP) was studied. For all the three polymers, the adhesion strength of an adhesively-bonded copper foil could be increased significantly by a chemical etching process using chromic sulphuric acid or a low pressure air-plasma treatment. However, for LCP the enhancement of adhesion by the surface treatments was lower than for the other polymers. Peel tests were employed for determining the adhesion strength of the copper foil. The physical surface properties were investigated by laser scanning microscopy (LSM). Contact-angle measurements and X-ray photoelectron spectroscopy (XPS) provided detailed information on the chemical surface properties. The detailed XPS analyses revealed different chemical mechanisms of the surface treatments depending on the polymer investigated. In all cases an incorporation of oxygen containing groups by the surface treatments was found to be responsible for a better adhesion of the copper foil on the treated polymer films compared to the untreated.     

Surface modification of PET films by a combination of vinylphthalimide deposition and Ar plasma irradiation

A new surface modification technique for PET films is proposed. This technique, called VPI modification technique, is a combination of two processes: The first step involves the deposition of vinylphthalimide (VPI) on the PET film surfaces, followed by Ar plasma irradiation of the VPI-covered film surfaces. The VPI modification technique led to large increases in the N/C atom ratio on the PET film surfaces. On the VPI-modified PET film surface, a new N_ls peak containing two components due to amide groups as well as imide groups appeared. The C_ls signal for the VPI-modified PET film surface also showed a new component due to ketone groups. These changes indicate that VPI reacted with the PET film surfaces to form nitrogen-containing groups. VPI modification made PET film surfaces hydrophilic. The VPI-modified film surfaces showed a decrease in water contact angle from 73 degrees to 48–56 degrees.     

Surface modification of glass by oligomeric fluoroalkylating agents having oxime-blocked isocyanate groups

A new type of oligomeric fluoroalkylating agent with oxime-blocked isocyanate groups was synthesized and the modification of a glass surface using this oligomer was studied. Based on contact angle measurements, the surface free energy of the modified glass was calculated. The results show that the glass surface was effectively fluoroalkylated, the surface free energy was lowered enough and the glass surface became both water- and oil-repellent. The longer the chain length of the fluoroalkyl group (R _f) is, the lower is the surface free energy of the modified glass. There existed a good relationship between the surface free energy and the F 1s /Si 2 p peak area ratio measured by XPS. The surface free energies decreased with an increase of this peak area ratio and above a ratio of 2, they became constant. The effects of modification by fluoroalkyl end-capped oligomers having oxime-blocked isocyanate groups and fluoroalkyl end-capped silanes were interpreted in terms of the structure of the modified layer, i.e. in terms of the monolayer interphase and network interphase models, respectively.     

臭氧氧化炭黑表面改性的研究

在固定床反应器中对不同条件下臭氧氧化炭黑表面改性进行了实验研究.结果表明,普通炭黑经过臭氧氧化处理后其挥发份提高,pH值由8.25变为3-4.臭氧氧化炭黑表面改性的优化条件为:温度为常温;反应时间为60-90 min;臭氧产生量为2.45 g/h;气量为0.4 m3/h.     

Aging of fluorocarbon thin films deposited on polystyrene from hyperthermal C3F+5 and CF+3 ion beams

Fluorocarbon films grown on polystyrene (PS) in vacuum from 25-100 eV CF⁺ ₃ and C₃F⁺ ₅ ions are aged by exposure to atmosphere for 4 and 8 weeks, then analyzed by X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle measurements. These fluorocarbon films oxidize with time, showing an increase in their oxygen/ carbon ratio and a decrease in their fluorine/carbon ratio. The decrease in fluorine/carbon ratio with aging is due not only to increased oxygen content, but also to surface restructuring and release of low molecular weight oxidized material from the surface. The higher oxidation and surface restructuring observed upon aging for 100 eV C₃F⁺ ₅ and 50 eV CF⁺ ₃ ion-modified PS can be additionally attributed to higher surface bond breakage and active site formation. 100 eV C₃F⁺ ₅ and 50 eV CF⁺ ₃ ion-modified PS surfaces are rougher than the 50 eV C₃F⁺ ₅ ion-modified PS. Overall, the aging process of these ion-deposited films appears similar to that of plasma-deposited films.     

Electrokinetic and solvatochromic studies of functionalized silica particles

Zeta potential plots, Kamlet-Taft's α (hydrogen bond-donating, HBD), β (hydrogen bond-accepting, HBA), and π* (dipolarity/polarizability) parameters as well as Gutmann's DN (donor numbers) are presented for 12 differently functionalized (i.e. alkyl, cyanoalkyl, aminoalkyl, and imidazolidine) silica particles. The pH-dependent zeta potential plots were measured in aqueous solution, whereas the solvatochromic studies were performed in 1,2-dichloroethane and cyclohexane as solvents using a special UV/visible spectroscopic technique. For the determination of the solvatochromic polarity parameters, a set of carefully characterized polarity indicators was employed: Cu(tmen)(acac)⁺B(C₆H₅)₄ ^- for β and DN; dicyano-bis(1,10-phenanthroline)iron(II) for α; 4,4′-bis(N,N-dimethylamino)benzophenone for π*; and an aminobenzofuranone derivative {3-(4-amino-3-methylphenyl)-7-phenyl-benzo[1,2b : 4,5b′]difuran-2,6-dione} (ABF) for α, β, and π*. The calculation of the polarity parameters was carried out via linear solvation energy (LSE) correlation equations using the Kamlet-Taft solvent parameters as a reference system. A linear correlation between the electrokinetically determined value of the isoelectric point and the β parameter of the functionalized silicas is demonstrated.     

Surface modification of poly(tetrafluoroethylene) films by graft copolymerization for adhesion enhancement with electrolessly deposited copper

The surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) films via UV-induced graft copolymerization with either 3-(trimethoxysilyl)propyl methacrylate (TM-SPMA) or glycidyl methacrylate (GMA) was carried out to enhance their adhesion to electrolessly deposited copper. The surface compositions of the PTFE films at various stages of surface modification and electroless plating were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the graft-copolymerized PTFE film to the electrolessly deposited copper was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment time after graft copolymerization, and the extent of thermal post-treatment after metallization. The maximum T-peel strength achieved between the electrolessly deposited copper and the GMA graft-copolymerized PTFE film was about 11 N/cm. This adhesion strength represented a more than 20-fold increase over what could be achieved when the PTFE film was treated by Ar plasma alone. The mechanisms of the adhesion strength enhancement and the failure mode in the metal-polymer laminates were also investigated. It was found that the failure was cohesive in nature within the PTFE film.     

Investigation on the oxidation of surface layers of polyolefins treated with corona discharge

The results of an X-ray photoelectron spectroscopic investigation of the oxidation of surface layers of low-density polyethylene (LDPE) and biaxially oriented polypropylene (BOPP) films are presented. The analysis was performed using different take-off angles, namely 10°, 30°, and 90°; thus, the depths of the examined layers were 0.6, 1.9, and 3.7 nm, respectively. It was found that the course of the oxidation process in the surface layers was similar for both polymer films. However, for treatment energies lower than 5 kJ/m², the extent of the oxidation was higher for the LDPE film, whereas for energies above this value, the BOPP film was more oxidized. As detected by X-ray photoelectron spectroscopy (XPS), desorption of oxygen from the film surface occurs for both polymers during the treatment.     

Surface Modification of Polycarbonate by Ultraviolet Radiation and Ozone

The effect of ultraviolet (UV) radiation in the presence of ozone as a surface treatment for polycarbonate is examined in regards to changes in the wettability, adhesion, and surface mechanical properties. Standalone, 175-µm-thick films of a commercially available polycarbonate were exposed to UV radiation from sources of different power with various treatment times in the presence of supplemental ozone. Significant decreases in the water contact angle were observed after exposure to UV radiation in the presence of ozone. After several variations in the experimental setup, it was determined that the change in water contact angle is a function of the UV irradiance and the work of adhesion follows a master curve versus UV irradiance. Nanoindentation experiments revealed that the modulus of the top 500 nm of the surface is increased following UV exposure, attributable to surface cross-linking. Adhesion tests to the surface (conducted by a pneumatic adhesion tensile test instrument) showed little change as a function of UV exposure. Analysis of adhesion test failure surfaces with X-ray Photoelectron Spectroscopy (XPS) showed the locus of bond failure lay within the bulk polycarbonate and the measured bond strength is limited by the bulk properties of the polycarbonate and/or the creation of a weak boundary layer within the polymer.     

Spatial Patterns of Microbial Retention on Polymer Surfaces

Microbial adhesion and retention on surfaces are complex phenomena, critical to the formation and development of biofilms. Recently, the focus of research has been more and more on the importance of retention of bacteria under fluctuating high shear forces in biofilm formation. The aim of the present work was to carry out a comparative study of the retention process of different bacterial and yeast species using: (1) a range of surfaces with different surface free energy properties and (2) a number of different bacterial cell physiological states. It was found for the first time that once a threshold cell number is retained on the surface, microbial retention patterns are formed following a power law, i.e., not stochastic. Our results demonstrated that the overall spatial patterns of microbial retention observed for the different substrates are similar for the all investigated cell types and that the drastic modification of the surface free energy does not affect this spatial organization. On the other hand, the microbial retention patterns appear to be significantly affected by the physiological state of the cells. Finally, the experimental retention patterns have been well simulated by a general agent-based model, confirming that the typical fractal distribution of retained cells is the result of a self-organization process.     

等离子体表面改性在高聚物中的应用进展

阐述了等离子体表面改性技术的作用原理,总结了等离子体对高聚物表面作用的多种理论。清除表面杂质、表面刻蚀、表面交联和形成具有新化学结构的表面是4种主要作用形式。等离子体技术正以其优越性在高聚物材料表面改性方面得到越来越广泛的应用。     

Surface Modification of Some Fluorine Polymer Films by Glow Discharges

Extensive study has been made of the effects of various types of glow discharge plasmas on the changes of the surface properties of some fluorine polymers. The properties were investigated as a function of such factors as the exposing period, aging after exposure, type of plasma, and so on.

It was found that the wettability and the critical surface tensions were changed considerably with plasma exposure and that periods of several tens of seconds are long enough to cause changes. The extents of change were not so prominent for fluorine polymers as for polyethylene, and this fact may show the important role of the fluorine atom in the surface properties even after the plasma treatments.