XPS study of dimethylolurea polymers and hollow fibers modified by these polymers. I. XPS study of dimethylolurea polymers

Polycondensation of dimethylolurea leads to the formation of a gel or a film according to the experimental conditions. Both forms of the polymer would be characterized by a specific chemical structure, i.e., dimethylene ether or diaminomethylene, respectively. We studied both forms of dimethylolurea polymer by XPS and have shown that it is possible to distinguish them using this technique. The study of the carbon peak shape attributed mainly a dimethylene ether structure to the gel and a diaminomethylene structure to the film. © 1994 John Wiley & Sons, Inc.     

Electroless plating of polymers: XPS study of the initiation mechanisms

This paper deals with polymer metallization by the electroless process. Previous studies in the authors' laboratory have shown the interest of plasma surface treatments of polymers before chemical metallization and the significant role they play towards the chemisorption of a catalyst (Pd2+ ions). Three different processes are used to activate the polymer surface for electroless deposition: namely, the one-step process using a mixed SnCl2–PdCl2 solution, the conventional two-step process using SnCl2, then PdCl2, and a new simplified process (using only PdCl2), previously proposed by the authors. According to the process utilized a variable initiation time is observed before metal deposition takes place in the metallization bath. The surface phenomena occurring on the polymer during this initiation time are studied by XPS through the chemical form of palladium adsorbed on the surface and through changes in the Pd surface concentration. A reaction mechanism relative to the initiation of the metallic ion reduction is proposed.     

Reversible mechanochemical systems based on stimuli-responsive polymers. I. Fundamental aspects

Polymer gels can be used to prepare mechanical systems that convert chemical free energy into mechanical work. These gels have characteristics that cause shape changes or generate tensile stress that can lead to mobility.

The polymer gel network can be produced by several physical and chemical methods. The principle of reversible contraction and dilatation is based on different mechanisms that depend on the type of stimuli applied.

The kinetics of gel swelling has been studied and understood as a combination of two consecutive processes: the collective diffusion and the relaxation process. The response time of gel depends on the thermodynamic quality of the solvent. Gels based on “intelligent” polymers have many interesting applications. Hence, these gels can form the basis of future “soft, wet” technology.     

An XPS study of argon ion beam and oxygen RIE modified BPDA-PDA polyimide as related to adhesion

Modification of polymer surfaces by changing the chemical structure, surface energy, and bonding characteristics has considerable technological importance in the area of adhesion. Reactive ion etching (RIE) and ion beam (IB) bombardment were employed to modify the surfaces of fully imidized 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride-p-diaminophenyl (BPDA-PDA)-based polyimide (PI) films. These modification techniques affect only a shallow surface region, approximately 10-20 nm, and the bulk properties of the polymer are unaffected. The angle-resolved X-ray photoelectron spectroscopy (XPS) technique was used to characterize the PI surfaces modified by argon IB bombardment or oxygen RIE treatment. On the argon ion-bombarded surfaces, the XPS spectra indicate that the carbonyl and imide groups are decreased. Oxygen RIE treatment resulted in an increase in the atomic concentration of oxygen. To understand the surface aging effect, the freshly modified PI surfaces were exposed to laboratory air for 1 and 2 days. The changes in composition as a function of the depth of the modified surface region right after treatment and after aging were determined by the angle-resolved XPS technique (ARXPS). Contact angle measurements were used to determine the polar and dispersion components, the sum of which is the surface free energy. The polar component of the surface free energy shows the greatest change, with an increase of 8.0-9.4 times for both the oxygen RIE and ion beam treatments as compared with the as-cured PI surface. Aging of these modified surfaces resulted in a decrease of surface free energy as compared with the just-modified surfaces. In the case of oxygen RIE treatment, the dispersion component of the surface free energy showed little or no change from the as-cured sample. Adhesion of chromium/copper/chromium (Cr/Cu/Cr) films on PI was determined by peel strength measurements. Significant increases in peel strength, by a factor of 10-80, were shown for the modified surfaces. A good correlation between the peel strength and the experimentally determined polar component of surface energy was shown.     

Microcapillary oxidation-reduction polymers

“Replica gel” polymers, characterized by their extremely high specific surface area, have not previously been prepared in “redox” form. Some illustrative syntheses are described, and the capability of these materials to oxidize acetic acid and to epoxidize oleic acid and cyclohexene is demonstrated.     

Gas permselectivity properties of high free volume polymers modified by a low molecular weight additive

The permselectivity properties of mixtures of the highly substituted polymers tetramethylhexafluoro polysulfone (TMHFPSF) and tetramethylhexafluoro bisphenol A t-butyl isophthalate (TMHFBPA-tBIA) with a low molecular weight glassy additive Kenflex A (denoted here as KXA) were measured for different gases and compared with the permselectivity properties shown by the base, unsubstituted polymers polysulfone (PSF) and bisphenol A t-butyl isophthalate (BPA-tBIA). The results show that the selectivity-permeability balance of polymer membranes may be appropriately tailored by a combination of chemical and physical alterations of the base polymer. The addition of modest amounts of KXA (ca. 20 wt %) into TMHFPSF or TMHFBPA-tBIA leads to materials whose permeability/selectivity combination is better than that of the unsubstituted materials, PSF or BPA-tBIA. The polymer TMHFPSF responds more beneficially to the incorporation of KXA than TMHFBPA-tBIA. At the same level of permeability, mixtures based on TMHFPSF have higher selectivity factors for H₂/CH₄ and CO₂/CH₄ than those based on TMHFBPA-tBIA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 403–415, 1998     

Porosity and pore size determination in polysulfone hollow fibers

Average pore sizes and effective porosity of microporous polysulfone hollow fibers were determined by the gas permeability method. Surface structure and porosity were determined by scanning electron microscopy. The values of effective porosity ε/q² (porosity/tortuosity factor) are approximately one order of magnitude lower than those reported previously for flat sheet porous membrane. These lower values are a direct outcome of a higher polymer concentration in the spinning dope. Correlations between the wall void volume, equivalent pore size, and hydraulic permeabilities of the hollow fibers have been determined. Rather low values of ε/q² have been calculated compared to those of the void volume; these effective porosity values indicate either a very high tortuosity factor or a large number of “dead end” pores. Exposure of the fibers to elevated temperature (110°C) for a short period of time drastically reduces the surface pore size and narrows the pore size distributions, whereas overall fiber dimensions are reduced only by 1%, and 85% of the fiber's hydraulic permeability is retained. The scanning electron microscopy study reveals the formation of a relatively dense skin in some spun fibers. For such “skinned” fibers, kinetic (permeability) evaluation of static structure such as mean pore size is not realistic and is further generalized to the term “equivalent pore size.”     

Removal of calcium and magnesium using polyaniline and derivatives modified PVDF cation-exchange membranes by Donnan dialysis

In this work, polyaniline (PAni), poly-n-ethylaniline, poly-n-methylaniline and poly-o-anisidine were prepared by chemical polymerization. 1,3 (6 or 7)-napthalenetrisulfonic acid was used for the first time in the literature as a dopant to increase the solubility of the polymers in methanol solution. The structure and properties of these conducting polymers were characterized by FTIR, UV–Vis, elemental analysis and conductivity measurements. Poly(vinylidene fluoride) (PVDF) membranes were modified by PAni and its derivatives and used as cation-exchange membranes. Poly-n-ethylaniline, poly-n-methylaniline and poly-o-anisidine were also used for the first time for this purpose in the literature. Ion-exchange capacity, water uptake and fixed group concentration of the polymer modified PVDF membranes were investigated. The changes in the surface morphologies of non-modified and polymer modified PVDF membrane was investigated by AFM and SEM. The polymer modified membranes were used for the removal of calcium (II) and magnesium (II) ions from water samples with Donnan dialysis (DD) experiments. The modified membranes show excellent stability during 120 days.     

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.     

XPS study of the PET film surface modified by CO2 plasma: effects of the plasma parameters and ageing

Chemical modification of the PET surface by carbon dioxide plasma treatment has been studied using X-ray photoelectron spectroscopy (XPS). The plasma process results mainly in the formation of carbonyl, carboxyl, and carbonate groups at the PET surface. Under rather mild treatment conditions (low plasma power combined with a short treatment time), the formation of C-O bonds was found to be dominant, whereas the formation of highly oxidized carbon or double-bonded oxygen-containing groups required a high plasma power or a relatively long treatment time. The treatments performed under excessive conditions frequently led to degradation at the polymer surface. Angle-resolved XPS analyses performed on a freshly modified PET film showed a slight decrease in the O/C atomic ratio when the take-off angle (TOA) increased, indicating a relatively uniform distribution of oxygen within the sampling depth (estimated to be about 8 nm at 80° TOA). The chemical composition of the plasma-modified surface was found to be relatively stable on extended storage in air under ambient conditions. The decrease in oxygen-containing groups at the carbon dioxide-plasma-treated PET surface upon ageing is mainly ascribed to the surface rearrangement of macromolecular segments, the loss of oxygen-containing moieties introduced by the plasma treatment, and the possible migration of non-affected PET chains from the bulk to the surface region.     

Surface-modified polysulfone hollow fibers. IV. Chloromethylated fibers and their derivatives

A chloromethylated reaction was performed on the surfaces of polysulfone ultrafiltration hollow fibers and their derivative membranes, i.e., triethylaminated, ethylenediaminated, and acethylated fibers, were prepared. The modified fibers have a 30–60% insoluble region in chloroform, whereas nonmodified fibers can be dissolved in the chloroform. It is suggested that the insoluble parts of the fibers are highly cross-linked due to the high degree of chloromethylation. The modified fibers showed a 50–98% rejection of polyethylene glycol 6000 at a feed concentration of 0.5 wt %, except for the triethylaminated fibers, which gave a negative rejection from ?91 to ?96%. It was found that the modified segments significantly influenced the rejection behavior of the solutes. Absorption of bovine serum albumin on the ethylenediaminated fibers at pH 7.1 was estimated from permeation measurements to be less than that of the other modified and nonmodified fibers. This effect is attributed to the hydrophilic surface of the ethylenediaminated fibers.     

Studies of polymeric systems for absorbing airborne sound

Sound absorption properties of polymer systems were investigated as functions of temperature, frequency, and chemical composition. Viscoelastic polymers were mixed with rigid polymers to obtain improved acoustical performance. In the case of foamed polymers, it was found that the chemical nature of the polymer is the most important factor controlling sound attenuation if the thin membranes of the closed-cell foams are “acoustically transparent.” Polyurethane-based polymer foams have been developed which possess excellent sound absorption characteristics. The foams are closed-cell, leathery, and “dead,” and can absorb as much as 96% of the normal incident sound energy at 1250 Hz (foam thickness 25 mm). The temperature-dependent acoustical properties of various polymer systems are discussed in terms of viscoelastic theory of polymers.     

XPS and SEM study of UV laser surface modification of polymers

Several commercial polymers—poly(ethylene) (PE), poly(propylene) (PP), poly(vinylidene fluoride) (PVF₂), poly(vinyl chloride) (PVC) and polystyrene (PS)—were treated in air with an argon-fluorine UV excimer laser (λ = 193 nm). The polymer etch rate was investigated by two methods: quartz crystal microbalance (QCM) and piercing of films. X-ray photoelectron spectroscopy (XPS) analysis was performed on the modified surfaces after laser exposure at various fluences. Samples were subsequently analysed by scanning electron microscopy (SEM). From our results, polymers may be classified into two categories concerning their reactivity towards UV laser light. — the weakly absorbing polymers (e.g. PE, PP, PVF₂) where a photothermal process (thermal degradation) dominates the interaction. — the strongly absorbing polymers (e.g. PVC, PS) where a photochemical process (photoablation) dominates the interaction.     

Streaming potential of microporous membranes made from homogeneously functionalized polysulfone

Microporous membranes were prepared from chemically modified polysulfone. The substitution of the polysulfone was performed in solution using reactions known from polymer modification such as halomethylation, aminomethylation, and lithiation. Membranes can be prepared directly from halomethylated polysulfones which are consecutively converted heterogeneously in a second step to the final functionalized form. Sometimes, two-step reactions are necessary to yield the polymers from which the membranes were cast. In those cases where the reactions change the charge of the polymer, the success of the reaction can be demonstrated by streaming potential measurements. The advantage of this analytical method lies in the fact that the intact membrane is investigated.     

Characterisation of flame retardant plasma polymer deposited BOPP film

Abstract

Flame retardancy of polypropylene films was studied by plasma polymerisation technique. The surface of BOPP film was modified by boron containing plasma polymers at different plasma conditions. Plasma polymer coated polypropylene films were examined by flame retardancy test (limiting oxygen index, LOI) and TGA. Boron containing plasma polymer deposition on the film surface showed an improvement of flame retardancy. Furthermore, TGA thermograms pointed out that the first degradation temperature of treated polypropylene film was increased from 331 to 396°C, and the second degradation temperature was shifted from 401 to 455°C. Also, the plasma polymers were characterised by FTIR spectroscopy and XPS. According to XPS results, the BOPP surfaces treated with TMB showed significant difference in the composition with respect to the untreated sample. The FTIR spectra of plasma polymers obtained indicated that when the treatment time was increased to 60 min with a constant discharge power at 80 W, the absorption intensities of all the functional groups increased. As a result, boron containing plasma polymer treatment was found to be an effective method in enhancing the flame retardancy of BOPP film.     

Cytocompatibility of polymers grafted by activated carbon nano-particles

Carbon nano-structures find their application in bio-medicine. In this work we functionalized carbon nano-particles (CNPs) with nitrogen (amine) groups. The CNPs were then chemically grafted onto the surface of polyethyleneterephthalate (PET) and high density polyethylene (HDPE) previously treated (activated) in argon plasma. Transmission electron microscopy (TEM) was used for investigation of the size and form of reactivated CNPs. Chemical composition of the modified polymer surfaces was determined by Raman and X-ray photoelectron (XPS) spectroscopies and by an electrokinetic analysis (zeta potential) as well. Surface contact angle was measured by goniometry. Surface roughness and morphology of polymers grafted with CNPs was studied using atomic force microscopy (AFM). Adhesion and proliferation of vascular smooth muscle cells (VSMC) on CNPs grafted HDPE and PET surfaces were studied in vitro. TEM results show that CNPs aggregate in water solution. Successful grafting of CNPs on the HDPE and PET surfaces was proved by XPS and Raman spectroscopies (amorphous carbon in the form of sp² hybridization) and by AFM. CNPs grafting of polymer surfaces leads to a decrease of contact angle and also to a change in surface zeta potential. Grafting with CNPs has a positive effect on adhesion and proliferation of VSMC on polymers’ surface.     

Corrosion protection by ultrathin films of conducting polymers

A new experimental model based on the electrochemical impedance spectroscopy for investigating the reactions taking place in a film of intrinsically conducting polymers formed on iron or steel substrate is developed, in which the reaction at the injured surface area of the coated iron and reaction of polymer could be studied separately. It is evident that a combination of adhesion promoting self assembling monolayer and a film of conducting polymer gives the protection against the delamination, but the catalytic action of the conducting polymer for the oxygen reduction and for the metal passivation is not found.     

XPS study of reductively and non-reductively modified coals

Two demineralised coals: Mequinenza and Illinois No. 6 have been subjected to reduction and reductive methylation in the potassium/liquid ammonia system and to non-reductive methylation by the Liotta method. The initial coals and the products obtained have been analysed by classical chemical methods and by the X-ray photoelectron spectroscopy (XPS) method. The coal surface has been found susceptible to oxidation by atmospheric oxygen, but the differences in the elemental composition between the surface and the bulk sample proved small. Deconvolution of the XPS spectrum has shown that the dominant form of oxygen in all samples is ether and hydroxyl oxygen and the dominant form of nitrogen is pyrrolic nitrogen. It has also been shown that the main sulphur species in the initial Mequinenza coal is sulphidic sulphur, while Illinois No. 6 is richer in thiophenic systems. The results have confirmed an earlier finding that modification of coals in the potassium/liquid ammonia system leads to elimination of sulphur from some thiophene compounds.     

Electron beam effects on polymers. II. Surface modification of bis-GMA substrates by functionalized siloxane oligomers

Surface modification of polymer films via electron beam irradiation was studied using the methacrylic acid derivative of the diglycidyl ether of bisphenol A, commonly called bis-GMA, as a curable substrate. Functionalized polydimethylsiloxane (PDMS) oligomers were utilized as surface modifiers. Considerable changes in the wetting characteristics were observed for the siloxane modified bis-GMA surfaces by critical surface tension measurement. For dosages up to 5 Mrads, the dosage level strongly affects the critical surface tension of the polymer. This result implies differences in the concentration of the attached PDMS oligomers to the bis-GMA substrate. The methacrylate-terminated PDMS was observed to be more effective in lowering the critical surface tension than a similar vinyl-terminated PDMS. Higher molecular weight and multifunctional PDMS coatings resulted in somewhat lower critical surface tensions in the dosage range applied in this study. The surface thickness of the functionalized PDMS coatings which were bonded to the substrate surface depended on the molecular weight of the surface modifiers as obtained by XPS analysis. Peel tests of the uncoated and PDMS coated bis-GMA clearly resulted in agreement with the critical surface tension data. Chemical inertness and poor wettability of PDMS provided the PDMS coatings with enhanced resistance to chemical degradation caused by a 24-h exposure to aqueous nitric and acetic acid.     

Direct introduction of phosphonate by the surface modification of polymers enhances biocompatibility

A novel chemical method for the modification of polystyrene and nylon polymers by the reaction of diaryl carbenes permits the direct and efficient introduction of phosphonate residues upon the polymer surface. The method is simple to execute, involving solution coating to adsorb the reactive coating agent, followed by drying and thermolysis at temperatures not greater than 150 °C. This material can be further modified to the calcium phosphonate derivative, by treatment with aqueous calcium hydroxide. The modified polymers show enhanced biocompatibility of the modified polymer, as evidenced by the improved growth of MG63 human osteosarcoma cell line on the surface. This method is of significance since it offers a simple chemical protocol for the tailoring of the surface properties of materials, it avoids the need to construct ab initio new polymers for a given application, it provides an alternative to existing surface modification protocols, and it extends the range of polymers suitable as biocompatible materials .