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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.
Substrate-induced self-assembly of donor-acceptor type compounds with terminal thiocarbonyl groups
(2013)
Two types of conjugated thiocarbonyl-terminated compounds have been synthesized and their ability to be adsorbed on surfaces of the different nature, namely, glass, polytetrafluoroethylene (PTFE), and gold has been studied. Different morphology of the films prepared by thermal vacuum evaporation and drop-casting from solutions has been observed depending on the surface used. It has been found that gold surface has a unique property to influence self-assembly of both monolayer and larger aggregates or crystals of the compounds, in contrast to glass and PTFE substrates. It was found that thiocarbonyl group is able to be chemisorbed to the gold surface. However, it was concluded that in spite of the fact that the thiocarbonyl groups are important for the chemical interaction with the gold surface, physical adsorption on the substrate surface, compoundcompound and compound–solvent (when using solution) interactions are of great significance to drive self-assembly of the final film.
For simulation and acceleration of artificial polymer ageing, polyolefin foils were exposed to low-pressure Ar plasma. Plasma particle bombardment and irradiation induce C–C and C–H bond scissions by σ→σ* excitations on the surface and in near-surface layers. Consequently, radicals are generated. They react by recombination, cross-linking, metastable trapping of the radical site or formation of olefinic double bonds. The long-living and metastable trapped C-radicals as well as double bonds in polyolefins were immediately exposed to bromine vapour without breaking the vacuum after switching-off the plasma. These reactive sites rapidly react with the molecular bromine under formation of C–Br bonds. For 5 min of argon plasma exposure, the elemental concentration of bromine was 13% for polyethylene and 22% Br/C for polypropylene as analysed by X-ray photoelectron spectroscopy. Nevertheless, not all C radical sites have reacted with bromine. Later on, when the polyolefins brought in contact with ambient air, an additional post-plasma reaction of the remaining trapped radicals with oxygen was observed. The oxygen concentrations were lower after bromine gassing, thus repressing partially the post-plasma oxidation in the analysed layer (ca. 6 nm) by radical quenching. Such bromination took place either at the surface or in near-surface layers because the Attenuated Total Reflectance (ATR)-FTIR spectra (sampling depth ca. 2500 nm) did not show significant changes for argon plasma-treated PE foils with and without bromine vapour exposure. Further addition of bromine may also occur on C=C double bonds.
Plasma-chemical bromination applied to graphitic materials, in particular to highly ordered pyrolytic graphite is reviewed. The resulting bromination efficiency of the plasma-chemical treatment was subject of systematic process optimization. The plasma of elemental bromine vapour produced bromine concentrations on graphene surfaces of more than 30 % Br/C using either inductively or capacitively coupled low-pressure radio-frequency plasmas. Plasma brominated graphite surfaces have been studied by Near Edge X-ray Absorption Fine Structure, X-ray Photoelectron Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. The introduction of bromine into graphene-like graphite layers and its binding situation were investigated. To study the physical effect of the plasma bromination process, Kr plasma was also used because of its chemical inertness but similar atomic mass. Covering the samples with a Faraday cage or with a LiF window should help to differentiate between physical, chemical and radiation effects of the plasma. Bromination was assigned to radical or electrophilic addition of bromine onto fully substituted aromatic double bonds (sp² C) with exothermal reaction enthalpy. Low bromination shows a strong decay of aromatic double bonds, higher bromination percentage let disappear all aromatic rings. The formed C–Br bonds were well suited for efficient grafting of organic molecules by post-plasma wet-chemical nucleophilic substitution. This grafting onto the graphene surface was demonstrated using aminosilane and different diamines. The bromination of double bonds changes the hybridization of carbon atoms from plane sp² to tetrahedral sp³ hybridization. Thus, the plane topography of graphene is destroyed and the conductivity is lost.
Activators regenerated by electron transfer–atom radical transfer polymerization (ATRP) as a controlled living polymerization are distinguished by their acceptance of small amounts of transition-metal complexes and oxygen and by their tolerance of reducing agents at a high concentration. The precondition of all ATRP applications is the use of homolytic or heterolytic cleavable halides as a dormant species; this allows the propagation of monomer chains. Hence, alkyl bromides are slightly cleavable and are the preferred initiators for ATRP. The bromination of polymer slides used as macroinitiators was carried out under gentle bromoform plasma conditions. This led to an oxidation-resistant stable bromine layer. More than 20 bromines per 100 carbons on the polymer scaffold were permanently bound to the substrate after plasma treatment. The resulting amounts of secondary and tertiary bromines on the polymer scaffold exhibited a suitable macroinitiator concentration for the surface-initiated polymerization of methyl methacrylate and glycidyl methacrylate.
The study of protein corona formation on nanoparticles (NPs) represents an actual main issue in colloidal, biomedical and toxicological sciences. However, little is known about the influence of polymer shells on the formation and time evolution of protein corona onto functionalized NPs. Therefore, silicapoly(ethylene glycol) core–shell nanohybrids (SNPs@PEG) with different polymer molecular weights (MW) were synthesized and exhaustively characterized. Bovine serum albumin (BSA) at different concentrations (0.1–6 wt%) was used as model protein to study protein corona formation and time evolution. For pristine SNPs and SNPs@PEG (MW = 350 g/mol), zeta potential at different incubation times show a dynamical evolution of the nanoparticle–protein corona. Oppositely, for SNPs@PEG with MW ≥2000 g/mol a significant suppression of corona formation and time evolution was observed.
Furthermore, AFM investigations suggest a different orientation (side-chain or perpendicular) and Penetration depth of BSA toward PEGylated surfaces depending on the polymer length which may explain differences in protein corona evolution.
A facile and versatile synthetic route for controlling the size and surface potential of organic–inorganic hybrid silica nanoparticles (NPs) is introduced in this paper. For polymer-grafted NPs, the density of polymer chains on the surface is strongly affected by the concentration of precursor. Nevertheless, for condensed NPs, the precursor concentration determines the particle size but not the density of polymer chains on the surface or the adsorption of bovine serum albumin (BSA). Results presented here may have Major implications in biomedical and colloidal chemistry since interfacial and colloidal properties are known to drive several processes associated with nanoparticles in biological media.
Production of new types of effective and green softeners for polyvinylchloride (PVC) is one of the important concerns in chemical industry. The paper reports results of investigations on obtaining symmetric esters of a series of fatty acids and triethylene glycol (TEG) and their use as effective PVC plasticizing agents. The esterification process was conducted in the presence of nano-grade titanium dioxide Degussa P-25 and specified by environmentally sound technology. Good compatibility and low volatility of the bio-based type esters in PVC formulations were shown and higher physico-mechanical features of the PVC composites were established. The esters may be recommended as effective and environmentally friendly PVC softeners to replace commonly used phthalates.
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.