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- Plasma polymerization (28) (entfernen)
In contrast to most of the existing literature on plasma polymerization of acrylic acid (AA), not only the chemical structure and film thickness of the deposits were studied, but also a new way to obtain COOH-rich surfaces. This is an important aspect when applying the obtained coatings for biomedical and electronics applications. Therefore, acrylic acid/CO2 polymer films with a thickness of ca. 150 nm were deposited in the pulsed plasma regime onto polyethylene and aluminium as organic and inorganic substrates. Their structure–property relationships were studied in dependence on the mixture ratio of acrylic acid monomer and CO2 gas. The influence of the CO2 gas on the regularity and functionality of plasma deposited poly(acrylic acid) (PAA) was studied in detail using bulk-sensitive (dielectric spectroscopy and Fourier transforms infrared spectroscopy) as well as surface-sensitive methods such as X-ray photoelectron spectroscopy. For a clear identification of the functionality of the deposited films, the COOH groups were estimated after derivatization with trifluoroethanol by XPS measurement as well as by the quantitative analysis of the FTIR data. Results show, in presence of a small amount of CO2 gas within the acrylic acid plasma, a structure of poly(acrylic acid) with high concentration of COOH groups was obtained. However, the excess of CO2 gas in the plasma chamber leads to fragmentation of the monomer or/and degradation of the layer which is already deposited. A polymer network is obtained with an increasing abundance of branched groups for AA/CO2 with increasing CO2 gas in the mixture.
The adhesion of thick poly(allylamine)-polyphosphate layers (1 µm) deposited by the wet-chemical layer-by-layer technique (LbL) onto polyethylene or polystyrene (each 100 µm) was very low. To promote the adhesion of these LbL layers the polyolefin substrates were oxidized at the surface by short exposure to the oxygen plasma (2 or 5 s) and subsequently coated with an interlayer of plasma-deposited poly(allylamine) or poly(allyl alcohol) (100 nm). The plasma polymer interlayers have improved strongly the adhesion between polyolefin substrates and polyphosphate coatings. Such phosphate coatings are interesting for life sciences (nucleotide formation) but also for fire retardancy in combination with N-rich compounds such as melamine.
The intention was to prefer chemical and hydrogen bonds for adhesion promoting because of their high binding energy. Therefore, the introduced oxygen-containing groups at the polyolefin surface could interact with the OH or NH2 groups of the adhesion-promoting plasma polymer interlayer. These groups were also able to interact strongly with the poly(allylamine)-polyphosphate topcoating.
The coated polyolefins were investigated using Fourier Transform Infrared Spectroscopy in Attenuated Total Reflectance mode (FTIR-ATR), X-ray Photoelectron Spectroscopy (XPS), Thermo-Gravimetric Analyses (TGA) and Atomic Force Spectroscopy (AFM) and 90° peel test.
Nitrogen- and oxygen-based plasma polymer films are materials with a complex and partially elusive surface chemistry. We present an overview of innovative and established X-ray photoelectron spectroscopy (XPS)-based analysis strategies developed to elucidate the surface chemistry of such films. We focus on both experimental methods and data analysis strategies and include the following topics: high-resolution spectra curve fitting, aging, chemical derivatization, and depth profiling by angle- and energy-resolved XPS.
Melamine resins were used as 50-µm-thick fire retardant coatings for polypropylene (PP). Preceding deposition, low-pressure plasma polymer films of allyl alcohol were coated onto PP to improve the adhesion between PP and melamine resin coatings. The efficiency of such fire retardant coatings was confirmed by flame tests. The plasma-deposited polymer and the dip-coated melamine resin films were characterized by Fourier transform infrared-attenuated total reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The adhesion of coatings was measured using a 90° peel test with a doubled-faced adhesive tape. To detect the locus of failure, the peeled layer surfaces were inspected using optical microscopy and XPS. Thermal properties of PP thick melamine resin-coated films were analyzed by thermogravimetric analysis.
Melamine and melamine resins are widely used as fire-retardants for polymer building materials. Cured melamine systems are used in heat-sensitive items, such as furniture and window frames and sills. In this work, differently cured methylated poly(melamine-co-formaldehyde) (cmPMF) resins were used as fire-retardant coverage for poly(styrene) (PS) and poly(ethylene) (PE) building materials. Such polymer layers should have several tenths of micrometers thickness to produce sufficient fire retardancy. These thick layers were produced by dip-coating. To promote sufficient adhesion of such thick coating to the polyolefin substrates, also in the case of high temperatures occurring at fire exposure, the polymer substrates were firstly coated with a few hundred nanometer thick adhesion-promoting plasma polymer layer. Such thin plasma polymer layers were deposited by low-pressure plasma polymerization of allyl alcohol (ppAAl). It was assumed that the hydroxyl groups of ppAAl interact with the melamine resin; therefore, ppAAl was well suited as adhesion promoter for thick melamine resin coatings. Chemical structure and composition of polymer films were investigated using infrared-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). Peel strengths of coatings were measured. After peeling, the peeled polymer surfaces were also investigated using optical microscopy and XPS the layers for identification of the locus of peel front propagation. Thermal properties were analyzed using TGA (thermo-gravimetric analyses). Finally, the fire-retardant properties of such thick coated polymers were evaluated by exposure to flames.
Thin poly(acrylic acid) PAA films were deposited by pulsed plasma polymerization on different organic and inorganic substrates. The structureproperty relationships of the deposited acrylic acid polymers were studied in dependence on the monomer pressure by various techniques and probes. The surface and bulk properties of the plasma deposited films were investigated by X-ray photoelectron spectroscopy, attenuated total reflection infrared, and broad band dielectric spectroscopy. The experimental infrared frequencies of PAA films are compared with those predicted from quantum mechanical calculation. The concentration of the COOH groups in the film (stored in ambient air) decreased by about 15 % compared to the as-prepared sample. The plasma deposited PAA probably form a highly branched product. However, the dielectric measurements show that in addition to the hydrogen bonds, self condensation process was able to hinder the localized fluctuation as well. These processes lead to form a cross-linked network polymer film. Nevertheless, a low energy is sufficient to break these processes during heating at atmospheric pressure. Therefore, homogenized samples with free branches (functional group) were obtained after a first heating with structures close to conventional polymerized acrylic acid. Thus, a thermally stable product was obtained.
Melamine and melamine resins are widely used as fire retardants for polymer materials used in pharmaceutical, plastic, textile, rubber, and construction industry. Melamine-based flame retardants act by blowing off intumescent layers, char formation, and emission of quenching ammonia gas and diluent molecular nitrogen. Special advantages are: low cost, low smoke density and toxicity, low corrosive activity, safe handling, and environmental friendliness. Methylated poly(melamine-co-formaldehyde) (mPMF) was used as thick (≥40 µm) fire-retardant coating for plasma pretreated polymers. A combined low-pressure plasma pretreatment consisting of oxygen plasma exposure followed by deposition of thin poly(allylamine) (ppAAm) and poly(allyl alcohol) (ppAAl) plasma polymers as adhesion promoters have improved the adhesion of thick mPMF coatings strongly. Chemical structure and composition of deposited polymer films were characterized by infrared-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). After peeling, the peeled layer surfaces were also investigated for identification of the locus of failure and their topography using optical microscopy and XPS. Often the adhesion promotion was so efficient that the peeling of coating was not possible. Thermal properties of plasma polymers and dip-coating films were analyzed by thermogravimetric analysis. Significant improvement of fire-retardant properties of coated polymers was confirmed by flame tests.
Copolymers of acrylic acid and styrene (AA/S) were prepared by pulsed plasma deposition technique. Their structure–property relationships were studied in dependence on the comonomer ratio. Both, the regularity of the structure and the composition of the thin copolymer films were investigated by bulk-sensitive (dielectric spectroscopy, FTIR, and differential scanning calorimetry) as well as surface-sensitive methods such as X-ray photoelectron spectroscopy (XPS). For an unambiguous identification of the functionality of the deposited films the COOH groups were estimated by derivatization with trifluoroethanol and subsequent XPS measurement as well as by the quantitative analysis of the FTIR data. As a result, the concentration of COOH groups on the surface and in the bulk is increasing with the fraction of AA in precursor mixture in a non-monotonous way but similar to the dependence obtained by conventional free radical polymerization.
Mixtures of hexamethyldisiloxane (HMDSO) and oxygen have been used for deposition of SiO2-like layers by plasma polymerization under low-pressure conditions onto polyethylene and polystyrene used as basecoat. Water glass was cast onto these 0.5 µm plasma thick siloxane-like layers with a thickness of 5 to 40 µm. The adhesion of these bilayer systems and their flame resistance were tested.
The effect of different plasma parameters such as monomer/gas ratio, pressure and power input into the discharge on the deposition rate and the composition of the formed layers was studied. Characterization and chemical composition of the formed films were performed using infrared, X-ray photoelectron and solid state nuclear magnetic resonance spectroscopy.
Peel strengths of composites were measured and the locus of peel front propagation was detected. Thermal properties of composites were analyzed by thermo-gravimetric analysis. Finally, the fire-retardant properties of thick coated polymers were determined by exposure to flames and the behavior of coatings on the polymers during flaming was observed visually.
Polystyrene (PS) spin coated thin films were modified by O2 and Ar plasma as
well as by UV irradiation treatments. The modified PS samples were compared with
plasma polymerized and commercial polystyrene. The effects of plasma (O2 and Ar) and
UV irradiation treatments on the surface and the bulk properties of the polymer layers were
discussed. The surface properties were evaluated by X-ray Photoelectron Spectroscopy and
Contact angle measurements and the bulk properties were investigated by FTIR and
dielectric relaxation spectroscopy. As a result only one second treatment time was sufficient
to modify the surface. However, this study was also dedicated to understand the effect
of plasma and plasma irradiation on the deposited layers of plasma polymers. The
dielectric measurements showed that the plasma deposited films were not thermally stable
and underwent an undesired post-plasma chemical oxidation.