Surface characterization of fluorinated polymers (PTFE,PVDF, PFA) for use in ultratrace analysis

Surface characterization of new unused PTFE, PFA and PVDF labware has been carried out by light microscopy, scanning electron microscopy, profilometry and atomic force microscopy. It has been found that in spite of higher micro-roughness, PFA exhibits the lowest nano-roughness and hence seems best suited as vessel material for relatively mild pressureless chemical operations for sample preparation of ultrapure substances, as container material for storage of ultrapure liquids, and for transport of such liquids, e.g., from the producer in the chemical to the end user in the microelectronics industry. This suitability refers only to the surface quality of the investigated materials. PTFE-surfaces, due to the sintering process of production, exhibit the most unfavourable surface quality of the investigated fluorinated polymers.     

Eco-friendly composite resins based on renewable biomass resources: Polyfurfuryl alcohol/lignin thermosets

The properties of an innovative polyfurfuryl alcohol (PFA)/lignin combined matrix have been investigated. Furfuryl alcohol (FA) and lignin are, respectively, monomeric and polymeric precursors issued from biomass feedstock. In the present work, a plasticized lignin (PL) has been blended during polymerization of FA into PFA. Two kinds of samples were prepared at different FA/lignin ratio. Structural investigations were made on resins by ¹³C NMR while the thermo-mechanical performances of the combined materials were studied using thermogravimetric (TGA) and dynamic mechanical analysis (DMA). TGA results have permitted us to determine the thermal stability and the composition of the cured material on the basis of the ash content. According with these results, it was found that the lignin ratio in the cured material is more important than in the initial threshold. The TGA reveals that the PFA/PL thermo-oxidative degradation occurs at higher temperature compared to the natural (PL) component system, together with a lower rate of decomposition. This underlines a good interpenetration of lignin within the furanic matrix. The morphologies of the combined PFA/lignin systems, controlled by scanning electron microscopy (SEM), reveal a monophasic structure. These observations are in good agreement with the presence of a unique relaxation peak as shown in the DMA results.     

Renewable resources as reinforcement of polymeric matrices: composites based on phenolic thermosets and chemically modified sisal fibers

Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.     

Polylactic acid incorporated polyfurfuryl alcohol bioplastics: thermal,mechanical and curing studies

Biodegradable polyfurfuryl alcohol (PFA)-based bioplastics, containing 0.5% to 3% (w/v) dissolvable polylactic acid (PLA) fabric, were successfully fabricated with p-toluene sulphonic acid as an acid catalyst by casting method in a silicon mould. By incorporating PLA, the 1st step thermal curing time of acid-catalysed furfuryl alcohol decreased from 96 h to 22 h. The fabricated bioplastics were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and tensile testing to evaluate their structure and properties. The results revealed that PFA-based bioplastics with 0.5% PLA showed higher tensile strength as well as higher elongation at break compared to neat PFA-based bioplastics. Also, the thermal stability of PFA bioplastic at 0.5% PLA increased compared to neat PFA. A “green” and solvent-free method for incorporating PLA in PFA resin to fabricate PLA incorporated PFA-based bioplastics has been delineated in this work.     

Adsorption/bioadsorption of phthalic acid, an organic micropollutant present in landfill leachates, on activated carbons

This study investigated the adsorption of phthalic acid (PA) in aqueous phase on two activated carbons with different chemical natures, analyzing the influence of: solution pH, ionic strength, water matrix (ultrapure water, ground water, surface water, and wastewater), the presence of microorganisms in the medium, and the type of regime (static and dynamic). The activated carbons used had a high adsorption capacity (242.9 mg/g and 274.5 mg/g), which is enhanced with their phenolic groups content. The solution pH had a major effect on PA adsorption on activated carbon; this process is favored at acidic pHs. PA adsorption was not affected by the presence of electrolytes (ionic strength) in solution, but was enhanced by the presence of microorganisms (bacteria) due to their adsorption on the carbon, which led up to an increase in the activated carbon surface hydrophobicity. PA removal varies as a function of the water type, increasing in the order: ground water相似文献   

Monodisperse, hypercrosslinked polymer microspheres as tailor-made sorbents for highly efficient solid-phase extractions of polar pollutants from water samples

In this detailed analytical study, we have evaluated in-house synthesised polymeric solid-phase extraction (SPE) sorbents in the form of monodisperse, hypercrosslinked polymer microspheres with diameters in the low micrometre range (approximately 4 microm). More specifically, their performance in the on-line SPE of a group of polar pollutants has been investigated thoroughly. The novel hypercrosslinked materials were compared with satisfactory results to commercial SPE sorbents with similar chemical and morphological properties, albeit that the commercial materials had higher particle sizes and broader particle size distributions. The on-line SPE method developed using these novel particles as packing material was applied successfully to ultrapure, mineral, tap and Ebre river water samples, with near total recoveries of all the analytes studied when 500 ml samples were percolated through the sorbents. Method validation with river water samples demonstrated good linearity, low detection limits as well as satisfactory precision in terms of repeatability and reproducibility, with values of relative standard deviation (%RSD) lower than 6.7 and 8.7%, respectively.     

Miscibility and crystallization of polytetrafluoro‐ethylene/poly(tetrafluoroethylene‐co‐perfluoropropylvinyl ether) blends

Miscibility and crystallization behavior have been studied for polytetrafluoroethylene(PTFE)/poly(tetrafluoroethylene‐co‐2 mol‐% perfluoropropylvinyl ether)(PFA copolymer) blends by the use of differential scanning calorimetry, electron microscopy, X‐ray diffractometry and dynamic mechanical spectroscopy. In the amorphous phase, the two components were miscible with each other over all blending ratios, and it was found that the PFA copolymer was compatible with the PTFE matrix, when the PFA content is ≤ 50 wt.‐%, while PTFE was mixed in the PFA matrix when the PFA content is >50 wt.‐%. All the blends were crystalline as well as PTFE and PFA. The crystallization behavior was closely connected to the polymer composition of the amorphous state described above. It was conjectured that the crystallization is controlled by the PTFE matrix when the PFA content is ≤ 50 wt.‐%, while by the PFA matrix when the PFA content is >50 wt.‐%.     

Surface structure of metal-organic framework grown on self-assembled monolayers revealed by high-resolution atomic force microscopy

The surface structure of an individual metal-organic framework (MOF) microcrystal grown on a functionalized surface has been successfully investigated for the first time in air and vacuum using high-resolution atomic force microscopy. Moreover, this detailed surface analysis has been utilized to optimize the MOF formation procedure to obtain a defect-free surface structure. Comparison of obtained data with recent microscopic studies performed on the same MOF crystal but grown by a conventional procedure clearly shows a much higher quality of crystals produced by surface oriented growth. Importantly, this method of preparing crystals suitable for microscopic analysis is also much faster (3 days compared to 2 years) and, in contrast to the conventional method, produces material suitable for in situ study. These results thus demonstrate for the first time the possibility of nanoscale investigation/modification of MOF surface structure.     

Nanoscale analyses of modified polypropylene microtubes internal surface: an approach covering topographical and force spectroscopic parameters

A nanoscale characterization of modified and unmodified polypropylene (PP) microtubes internal surface was performed to investigate their structural, chemical, and physical properties. Nanoroughness, stiffness, elasticity, attraction behavior, adhesion forces, and chemical environment were investigated to test some manufacturer statements regarding Axygen MAXYMum Recovery® products. They announced that this class of material presented special features, originated from a modification to the original PP resin and by using a diamond polished mould, providing lower retention and minor interference on laboratorial tests, such as low roughness and little interaction tendency. Then, in this study, modified and control internal surfaces of PP microtubes were compared by atomic force microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Nanoroughness and force spectroscopy parameters assessed by atomic force microscopy showed out as a sensible and high‐resolution technique, crucial to discriminate differences between the surfaces. This type of investigation can be considered as a promising approach that can be applied to other polymeric systems, considering nanoscale properties, physical/chemical modifications, and as an alternative route for quality control checking concerning polymeric surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

Aggregation states and surface wettability in films of poly(styrene-block-2-perfluorooctyl ethyl acrylate) diblock copolymers synthesized by atom transfer radical polymerization

Well-defined poly(styrene-block-2-perfluorooctyl ethyl acrylate) [P(St-b-PFA)] copolymers with various chemical compositions were synthesized by atom transfer radical polymerization. Films of P(St-b-PFA) were structurally characterized, from bulk to surface, on the basis of transmittance electron microscopic observation and small-angle X-ray scattering, X-ray photoelectron spectroscopic, and contact angle measurements. For a comparison, poly(styrene-random-2-perfluorooctyl ethyl acrylate) [P(St-ran-PFA)] copolymers were also synthesized by conventional free radical polymerization. While P(St-b-PFA) with the 2-perfluorooctyl ethyl acrylate (PFA) content higher than 18.7 mol % formed a typical phase-separated cylinder structure, P(St-b-PFA) with a lower PFA content and P(St-ran-PFA) were in a miscible state. Since the perfluoroalkyl groups possess extremely low surface energy, they were preferentially segregated at the film surface, resulting in the formation of the PFA surface layer. This was the case for all P(St-b-PFA) films examined, although the aggregation state at the surface was strongly dependent on the PFA content. In the case of the P(St-b-PFA) with the PFA content higher than 18.7 mol %, both advancing and receding contact angles for water were 120 degrees and even larger with almost no hysteresis. In addition, extremely excellent oil-repellent surface properties such as advancing and receding contact angles for dodecane of 76 degrees and 75 degrees were also observed. However, these intriguing liquid-repellent properties were not observed for the films of miscible P(St-b-PFA) and P(St-ran-PFA). Therefore, it can be concluded that the internal structure beneath the surface as well as the surface itself should be deeply considered to design excellent and stable liquid-repellent materials.     

Surface-directed and ethanol-induced DNA condensation on mica

The adsorption of lambda-phage DNA onto mica was investigated with atomic force microscopy. We found that the morphologies depended on the solvent conditions in the sample preparation procedure. Flat-lying networks of hybridized single-stranded DNA were obtained if ultrapure water was used. If buffered conditions are maintained during the whole of the preparation procedure, single double-stranded DNA molecules are adsorbed. The adsorbed double-stranded DNA molecules subsequently can be condensed in situ on the surface by a brief rinse with anhydrous ethanol in the presence of divalent magnesium cations. The majority of these surface-directed and ethanol-induced condensed structures are toroids, but a small fraction of rods also has been observed. Analysis of the height and lateral dimensions shows that the toroids are single-molecular and disk-like with a height of one to two DNA diameters. The thin toroid morphology appears to be a general phenomenon of surface-directed condensation, irrespective of the nature of the condensing ligands and the specific surface interaction.     

Langmuir-Blodgett films of octadecanethiol--properties and potential applications

Octadecanethiol (ODT) is known to form self-assembled monolayer on noble metal surfaces which has potential technological applications. Langmuir-Blodgett (LB) technique is another useful method of obtaining highly ordered assembly of molecules. It is of interest to find whether ODT molecules can also form a stable Langmuir monolayer which facilitates the preparation of LB films. In literature, it has been reported that ODT molecules form an unstable Langmuir monolayer. We have studied the stability of the monolayer of the ODT molecules at air-water interface using surface manometry and microscopy techniques. We find the monolayer to be stable on ultrapure water of resistivity greater than 18MOmega cm. However, the behavior changes in the presence of even small amount of additives like NaOH or CdCl2 in the subphase. Our AFM studies on the LB films of ODT deposited from ion-free ultrapure water showed streak-like bilayer domains. The LB films of ODT deposited from CdCl2 containing aqueous subphase yield dendritic domains of the complexed unit grown over ODT monolayer. These nanostructures on surfaces may have potential applications in molecular electronics.     

Pre-Irradiation Grafting of Styrene into Modified Fluoropolymers

Summary: The grafting of styrene into commercially available fluoropolymer films by the pre-irradiation method has been investigated. Poly(tetrafluoroethylene) (PTFE), poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), poly(tetrafluoroethylene-co-perfluoropropylvinyl ether) (PFA) and poly(tetrafluorethylene-co-ethylene) (ETFE) were chosen as the base polymer material. The influence of the base material, the pre-irradiation dose, and the storage time between the irradiation and the grafting step on the yield of grafting was examined. The base materials were pre-treated by irradiation in the molten state under oxygen-free conditions in order to create branches and cross-links. The effect of pre-treatment on the yield of grafting was studied.     

Estimation of metal impurities in high-purity nitric acids used for metal analysis by inductively coupled plasma-mass spectrometry.

A simple method to estimate the amounts of ultra-trace metal impurities in nitric acid reagents has been developed. The determination of sixty-four metals in nitric acid was accomplished by direct measurements of 0.1 M nitric acids accurately diluted with ultrapure water by ICP-MS. Though accurate metal concentration could not be obtained for all of the elements, we could effectively evaluate the nitric acid quality by comparing the ion counts of the samples, ultrapure water and standard metal solutions for a calibration prepared with Ultrapur nitric acid.     

Rippled domain formation in phase-separated mixed Langmuir-Blodgett films

The morphology and composition of phase-separated Langmuir and Langmuir-Blodgett films of stearic acid (C17H35COOH) (SA) mixed with perfluorotetradecanoic acid (C13F27COOH) (PA) have been investigated using a combination of atomic force microscopy (AFM) measurements and surface pressure-area isotherms. At elevated surface pressures, the mixed film phase-separated to form a distinct series of lines (ripples), as opposed to the hexagons that have previously been observed with mixed films with longer alkyl chain fatty acids. At low surface pressures, phase separation is still observed, though a range of different domain structures was formed. The chemical composition of the phase-separated domains has been investigated by AFM-based compositional mapping, which has allowed unambiguous identification of the chemical composition of the domains. A simple mechanistic model describing how domain formation takes place in this system is presented.     

Neutron activation analysis of ultrapure water in a 500 ml silicon single crystal irradiation flask

Trace element analysis of ultrapure liquids requires the avoidance of contamination not only during preparation but also during irradiation of the sample. Double subboiling distilled water activated within flasks made out of synthetic quartz shows a significant correlation between irradiation time, quality of the flasks and the determined trace element concentration. The resulting falsification of the analysis and limitation of sensitivity seems to be caused by diffusion-like processes during irradiation. Even though single crystal FZ-silicon is rather brittle, it has been possible to fabricate a 500 ml irradiation flask out of this extremely pure material. The flask as well as its application in the analysis of double subboiling distilled water are discussed in the article.     

A Facile Method for Preparation of Superhydrophobic Surfaces with Poly(furfuryl Alcohol)/PTFE Composites

A stable superhydrophobic surface have been fabricated with poly(furfuryl alcohol) (PFA)/polytetrafluoroethylene (PTFE) composite coatings on steel substrates by using a facile method. The observation of field emission scanning electron microscopy revealed that the hierarchical microstructures formed on the surfaces are controlled by varying the curing temperature. This method can be easily operated on substrates of steel, therefore is readily developed to other engineering metal substrates such as aluminum, copper, etc.     

Characterization of surface modifications of stainless steel samples after electron and ion bombardment by SEM, AES, and XPS

The interaction of inert or reactive gas plasmas with the surface of stainless steel has been investigated with the aim, to modify the surface and hence to reduce the outgassing rate of the material, an important factor for the production of an ultrahigh vacuum. The plasma treatments investigated may be an alternative to the common used in situ baking. The samples have been exposed to electrons, argon and oxygen ions either in a DC glow discharge or in a microwave discharge. The DC glow discharge in Ar/O₂, the most effective plasma treatment reduces the outgassing rate by a factor of 10. After this treatment the surfaces of the samples have been investigated with respect to the topography and the chemical composition (depth profile) by Secondary Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS), respectively. The surface modifications resulting from the different treatments of the samples have been correlated to the outgassing rate.     

Study of the effect of formamide and N,N-dimethylformamide on the synthesis of CdS nanoparticles in a SiO2 matrix by sol-gel method

The influence of formamide (F) and N,N-dimethylformamide (DMF) in drying and firing of CdS nanocrystals in SiO₂ glasses by a sol-gel method has been studied. It has been established that pore size distribution and surface area are different with the use of DMF and that influences the quality of the final product. The presence of CdS semiconductor nanoparticles has been demonstrated by transmission electronic microscopy (TEM), and the quantum confinement effect due to the size of nanoparticles is denoted by a blue shift in the visible absorption spectra. From the results obtained in this paper, it is clear that DMF has an influence on final material microstructure.     

Understanding and Manipulating Inorganic Materials with Scanning Probe Microscopes

Scanning probe microscopies, such as scanning tunneling microscopy and atomic force microscopy, are uniquely powerful tools for probing the microscopic properties of surfaces. If these microscopies are used to study low-dimensional materials, from two-dimensional solids such as graphite to zero-dimensional nanostructures, it is possible to elucidate atomic-scale structural and electronic properties characteristic of the bulk of a material and not simply the surface. By combining such measurements with chemical synthesis or direct manipulation it is further possible to elucidate relationships between composition, structure, and physical properties, thus promoting an understanding of the chemical basis of material properties. This article illustrates that the combination of scanning probe microscopies and chemical synthesis has advanced our understanding of charge density waves, high-temperature superconductivity, and nanofabrication in low-dimensional materials. This new approach to studying materials has directly contributed to our knowledge of how metal dopants interact with charge density waves and elucidated the local crystal chemistry of complex copper oxides, microscopic details of the superconducting states in materials with a high superconducting transition I_c, and new approaches to the fabrication of multi-component nanostructures. Coupling scanning probe microscopy measurement and manipulation with chemical synthesis should provide an approach to understanding material properties and creating complex nanostructures in general.