Modification of perfluorinated polymers by high-energy irradiation

This review surveys about the possibilities for the modification of perfluorinated polymers using high-energy irradiation: degradation, functionalization, branching, and cross-linking. The reaction mechanisms for the different reaction conditions are discussed. Electron irradiation of polytetrafluoroethylene (PTFE) with a very high dose leads to a complete degradation of the macromolecules to low-molecular products. In the presence of oxygen perfluorocarboxylic acids and in an inert atmosphere, mixtures of perfluorinated olefins and paraffins can be obtained. Virgin PTFE is disintegrated by high-energy irradiation in air with a lower dose into a micropowder modified with COOH groups. This powder can be homogeneously incorporated in other polymers. So, the special properties of PTFE can be made effective in these polymers. Micropowders functionalized with COOH groups and polyamides (PA) form by reactive extrusion PTFE-PA blockcopolymers which can be used as slide bearing materials. The copolymers poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) and poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) irradiated in air show a significantly higher degree of COOH functionalization compared with PTFE. Irradiation of molten PTFE in an inert atmosphere leads to formation of different kinds of double bonds, CF₃ side groups, long-chain branches as well as cross-links. Irradiation of PFA in vacuum results in the generation of COF and COOH groups; in molten state also branches and cross-links are formed.The focus of the present paper is on the work that has been carried out at the Institute of Polymer Research Dresden.     

Modification of fluoropolymers by means of electron beam irradiation

High molecular weight polytetrafluoroethylene (PTFE) is transformed to free-flowing micropowder by treatment with electron beams. In case of irradiation in presence of air carboxylic acid fluoride groups are incorporated which rapidly hydrolyze to carboxylic groups in the surface-near regions due to atmospheric humidity. These polar groups reduce the hydrophobic and oleophobic properties so much that homogeneous compounding with other materials becomes possible. In addition to PTFE, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) and perfluoropropylvinylether (PFA) were modified. In case of identical irradiation conditions, the concentration of carboxylic groups is much higher in FEP and PFA than in PTFE, which is due to the lower crystallinity of the copolymers.

Electron beam irradiation of PTFE was performed in vacuum at elevated temperature above the melting point. The changes in the chemical structure were studied. The concentration of CF₃ branches was found to be much higher as compared to room temperature irradiation.

In a practical test PTFE micropowders functionalized by electron irradiation were compounded with epoxy resins, with polyoximethylene and with polyamides. Such compounds are characterized by very good frictional and wearing behaviour in dry-running tests.     

Modification of isotactic polypropylene film by radiation-induced graft copolymerization

In the present communication we report on the radiation induced grafting of methyl methacrylate (MMA) onto irradiated isotactic polypropylene film (IPP) by Peroxidation method to prepared grafted membrane (IPP-g-MMA). The radioactive isotope ⁶⁰Co was used as the source of gamma radiation. A plausible mechanism of grafting has been proposed. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters such as radiation dose, inhibitor concentration, monomer concentration, reaction time and reaction temperature respectively. Maximum percentage of grafting (85%) was obtained at [radiation dose] = 25 kGy, [inhibitor concentration] = 0.04 wt%, [MMA] = 6 wt%, [Reaction Temperature] = 60 °C in a [Reaction time] of 120 min. The evidence of grafted membrane was characterized by Fourier transform infrared spectroscopy, Atomic force microscopy method, Scanning electron microscopy which indicates that MMA has been grafted onto IPP. Hydrolysis of the grafted membranes in 1 N NaOH transformed ester groups of the grafted membranes to carboxylic acid and hydroxyl groups to form hydrolyzed grafted membranes. Hydrolyzed grafted membranes were investigated for their swelling behavior. Swelling properties of the hydrolyzed grafted membranes were performed in different solvents such as water, N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO). Maximum percentage swelling value of IPP-g-MMA was observed in pure DMSO, followed by DMF and water.     

Epoxy‐amine reticulates observed by infrared spectrometry. II. Modifications of structure and of hydration abilities after irradiation in a dry atmosphere

This article is part of a series of articles devoted to the study of the responsibilities of both humidity and irradiation in the aging process of amine‐cured epoxy resins. The basic technique used in this study is infrared spectrometry. In a previous article we have observed, with this technique, hydration of two kinds of epoxy resins, which are widely used in the nuclear industry. In this article the same technique is used to observe the same resins, which have been previously submitted to ionizing radiations. It allows us to determine the effects these radiations have on these resins at molecular level and how they consequently modify their hydration mechanisms. It could thus be established that irradiation by electrons almost does not induce modifications on resins cured with aromatic diamines, which results in their hydration capacity being only slightly changed. Irradiation by γ rays induces stronger modifications, which reflect themselves in a greater capacity of absorption of water and different ways of fixing H₂O molecules. Epoxy resins cured with alkyl diamines are more sensitive to irradiation and, after it, absorb a greater amount of H₂O molecules. After irradiation, steric conditions, which hinder H₂O molecules to bind on other H₂O molecules, apparently become less severe. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 329–340, 2000     

Modification of new polymer materials based on aminostyrene by irradiation

The ultra-violet (UV) irradiation induced modification of the mechanical and optical properties of several polymer composites containing 4-aminostyrene and glycidyl methacrylate and their dependences on radiation dose, structure and ageing have been investigated. The nano- and microindentation techniques were used for determination of the mechanical parameters of as-grown and irradiated materials. The light-induced structural changes result in an increase of the hardness and elastic modulus of the polymer layers up to five and three times, respectively. It is also shown that the influence of polymer structure is significant. The conditions for improvement, degradation and stabilization of physical properties by UV irradiation were established. Load and depth sensing indentation has proved to be a powerful tool for an accurate estimation of mechanical properties of cross-linking polymer compositions. Variable-energy positron annihilation spectroscopy (slow-positron beam technique) was developed to measure defect depth profiles in the near-surface region. The increase of S-parameter with the increase of nano-hardness and elastic modulus has been determined for these materials.     

Epoxy–amine reticulates observed by infrared spectrometry. III. Modifications of the structure and hydration abilities after irradiation in a humid atmosphere

This article is the third part of a series devoted to the study of the responsibilities of both humidity and irradiation in the aging process of amine‐cured epoxy resins. The basic technique used in this study was infrared spectrometry. In previous articles, we described the hydration of two kinds of epoxy resins widely used in the nuclear industry. In the first article, we reported results concerning the hydration of unirradiated resins; in the second article, these resins were first submitted to ionizing radiation in a dry atmosphere. In this article, we describe the effects of irradiation in a humid atmosphere and compare these effects to what was observed after irradiation in a dry atmosphere, as described in the previous articles. These effects were subtle: the humidity of the ambient atmosphere apparently protected the resins from oxidative degradation because, after irradiation in a humid atmosphere, a smaller number of carboxylic groups were formed. However, the water uptake increased after irradiation in a humid atmosphere. Thus, the humidity of the ambient atmosphere at the same time favored the rupture of chains, which released steric hindrances and allowed a greater number of H₂O molecules to reach hydrophilic sites in the resin. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1129–1136, 2001     

Two-dimensional infrared spectral signature and hydration of the oxalate dianion

Ultrafast vibrational spectra of the aqueous oxalate ion in the region of its carboxylate asymmetric stretch modes show novel relaxation processes. Two-dimensional infrared vibrational echo spectra and the vibrational dynamics obtained from them along with measurements of the anisotropy decay provide a picture in which the localization of the oxalate vibrational excitation onto the carboxylate groups occurs in ~450 fs. Molecular dynamics simulations are used to characterize the vibrational dynamics in terms of dihedral angle motion between the two carboxylate planes and solvation dynamics. The localization of the oxalate vibrational excitation onto the carboxylates is induced by the fluctuations in the carboxylate vibrational frequencies which are shown by theory and experiment to have a similar correlation time as the anisotropy decay.     

Dosimetry by a cellulose triacetate film dosimeter in proton-beam irradiation

The basic characteristics of cellulose triacetate (CTA) film dosimeter have been investigated with 5, 8, and 15 MeV proton beams. The optical density change per unit absorbed dose for 8 and 15 MeV protons is the same as that given for electron beams, but a little smaller for 5 MeV protons. The CTA dosimeter was found to be useful to obtain dose distributions with high spatial resolution in samples exposed to proton beams.     

Modification of photocatalytic TiO2 thin films by electron beam irradiation

Noble metal-modified TiO₂ films were prepared by electron beam deposition of Pt, Pd, Au and Ag on the surface of TiO₂ films with diameters ranging from <1 nm to 500 nm. The morphology of the films was characterized by X-ray diffractometry (XRD), field emission scanning electron microscope (FMSEM) and transmission electron microscope (TEM). The photocatalytic capability of the films were tested and compared by degradation of methyl orange (MO) in aqueous solutions under both UV and visible light illumination.     

Surface hydration of aqueous calcium minerals as studied by Fourier transform Raman and infrared spectroscopy

Rapid hydration reactions of several calcium minerals are studied using Fourier transform (FT) Raman and infrared (IR) spectroscopy. Oleate adsorption over aqueous synthetic fluorite, calcite and gypsum (pH 9) is investigated and adsorption mechanisms are discussed.     

Carbon black nanoparticles film electrode prepared by using substrate-induced deposition approach

A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB) nanoparticles deposited onto a gelatin-covered indium tin oxide/glass support using the surface-induced deposition (SID) approach, is presented. Some parameters of the novel SID method were optimized and the surface image and functionalization of the investigated carbon black film electrode (CBFE) was inspected by employing scanning electron microscopy and infrared spectroscopy. A cyclic voltammetry (CV) study was conducted in which the electron-transfer kinetics and CBFE interfacial characteristics were evaluated employing several selected reference redox systems, such as [Ru(NH₃)₆]^3+/2+, [Fe(CN)₆]^3−/4− and Fe^3+/2+ in aqueous, and ferrocene/ferrocenium in acetonitrile media. CV recordings were also performed in order to compare the electrochemical behavior of the CBFE with that of some well-known and established bare carbon-based electrodes. In order to confirm the validity of the CB film preparation method, the electroanalytical performance of the proposed CBFE was examined by carrying out linear sweep voltammetry of ascorbic acid (AA), anodic stripping square-wave voltammetry of Cu(II) in acidic medium, and amperometric measurements of hydrogen peroxide under flow injection conditions. The sensing characteristics of the novel carbon film electrode, demonstrated in this preliminary study, comprise: (i) a wide working potential window ranging from +1.0 to −1.3 V (depending on the solution pH), (ii) a wide applicable pH range (at least from 2 to 12), (iii) low voltammetric background (<5 μA cm⁻²), (iv) a satisfactory linear voltammetric and amperometric response (r² > 0.99) to various analytes, (v) good reproducibility (for example, r.s.d. of 2% in amperometric detection of H₂O₂ and r.s.d. of 8.5% for electrode-to-electrode CV runs), and (vi) stable and fast current response (at least 100 CV runs with negligible change in CV response). The main advantages of the proposed CBFE originate from the unique CB film formation procedure that enables fast, simple, inexpensive and non-toxic CBFE preparation, which can find application in advanced electrochemical devices and is suitable for mass production.     

Modification of epoxidised natural rubber film surface by polymerisation of methyl methacrylate

Epoxidised natural rubber (ENR) latex, having 25% of epoxide content, was prepared by in situ epoxidation reaction using performic acid. The ENR latex film surface was modified by immersing into methyl methacrylate (MMA) emulsion and then alkaline aqueous solution of ferrous ion/fructose for redox-initiated polymerisation. Increasing polymerisation time caused an increase in percent conversion of MMA swelled in ENR sheet. The presence of poly(methyl methacrylate) on the ENR surface was examined by attenuated total reflection-Fourier transform infrared spectroscopy. The nano-scale indentation experiment performed on the cross-section of the modified ENR sheet indicated that MMA polymerisation occurred mainly near the rubber’s surface. The surface morphology observed under scanning electron microscopy and atomic force microscopy revealed a pronounced roughness which, consequently, decreased the friction coefficient of ENR surface.     

Modification of nitrile-terminated biphenylthiol self-assembled monolayers by electron irradiation and related applications

Here we describe the behavior of self-assembled monolayers (SAMs) of 4'-cyanobiphenyl-4-thiol (CBPT) on Au(111) upon electron irradiation. Under such a treatment, the aromatic framework of CBPT SAMs is laterally cross-linked while the nitrile groups, located at the SAM-ambience interface, are reduced to active amine moieties which can be used as docking sites for the coupling of other species. This makes CBPT monolayers as a promising system for conventional and chemical lithography as well as for nanofabrication. Along these lines, we demonstrate the preparation of complex polymer brushes, patterning of the underlying substrate, and fabrication of molecule-thin, free-standing membranes on the basis of CBPT SAMs. The balance between the application-favorable processes and defragmentation in these films is studied in detail, and comparison to the well-established (for the relevant applications) system of 4'-nitrobiphenyl-4-thiols is performed. Taking CBPT SAMs as a model system, the effect of the energy of the primary electrons on the extent of the chemical transformation and cross-linking in substituted aromatic SAMs is investigated.     

Rapid micropatterning of mesoporous silica film by site-selective low-energy electron beam irradiation

Rapid microfabrication of mesoporous silica film at low temperature was achieved with low-energy electron beam (LEEB) irradiation. A mesostructured film (thickness approximately 200 nm), which was prepared through hydrolysis and condensation of tetramethoxysilane in the presence of hexadecyltrimethylammonium chloride, was irradiated with LEEB at 25 kV and 300 microA under pressures of 10 and 1000 Pa. The surfactant molecules can be eliminated completely at temperatures less than 40 degrees C after only 10 min (10 Pa) and 5 min (1000 Pa) of irradiation, resulting in conversion to a highly ordered mesoporous silica film without cracking. The LEEB-irradiated film also showed reasonable chemical resistance toward dilute hydrofluoric acid solution due to sufficient consolidation by cross-linking of silicate networks during the irradiation. The unirradiated regions were etched away preferentially to the irradiated areas; therefore, rapid micropatterning of the mesoporous silica film was possible by area-selective LEEB irradiation followed by chemical etching.     

Patterning of cells on a PVC film surface functionalized by ion irradiation

Micropatterns of cells on a poly(vinyl chloride) (PVC) film surface were created by using ion irradiation. A PVC film was irradiated with H⁺ ions through a pattern mask in order to create patterns of the hydrophilic/hydrophobic regions on the PVC surface. The effect of ion irradiation on the surface properties of the PVC film was characterized by using Fourier transform‐infrared spectroscopy (FT‐IR), water contact angle measurement, and X‐ray photoelectron spectroscopy (XPS). The results revealed that the chemical environment of the PVC film surface was effectively changed by ion irradiation due to dehydrochlorination and oxidation. The in vitro cell culture on the patterned PVC film surface showed selective adhesion and proliferation of the cells on the ion‐irradiated regions. Well‐defined 50 µm patterns of the cells were obtained on the PVC film surface irradiated to 1 × 10¹⁵ ions/cm². Copyright © 2009 John Wiley & Sons, Ltd.     

Formation of a novel porphyrin-gold nanoparticle network film induced by IR light irradiation

IR light irradiation of a mixed toluene solution of ammonium salt-stabilized gold nanoparticles with 3.8 +/- 0.8 nm core diameter and a porphyrin thioacetate derivative affords a thin photoactive film of the cluster-porphyrin network.     

On the ultrafast infrared spectroscopy of anion hydration shell hydrogen bond dynamics

Molecular Dynamics simulations are used to examine the title issue for the I-/HOD/D2O solution system in connection with recent ultrafast infrared spectroscopic experiments. It is argued that the long "modulation time" associated with the spectral diffusion of the OH frequency, extracted in these experiments, should be interpreted as reflecting the escape time of an HOD from the first hydration shell of the I- ion, i.e., the residence time of an HOD in this solvation shell. Shorter time features related to the oscillation of the OH ...I- hydrogen bond and the breaking and making of this bond are also discussed.     

DNA-gold nanorod conjugates for remote control of localized gene expression by near infrared irradiation

Gold nanorods were attached to the gene of enhanced green fluorescence protein (EGFP) for the remote control of gene expression in living cells. The UV-vis spectroscopy, electrophoresis, and transmission electron microscopy (TEM) were used to study the optical and structural properties of the EGFP DNA and gold nanorod (EGFP-GNR) conjugates before and after femto-second near-infrared (NIR) laser irradiation. Upon NIR irradiation, the gold nanorods of EGFP-GNR conjugates underwent shape transformation that resulted in the release of EGFP DNA. When EGFP-GNR conjugates were delivered to cultured HeLa cells, induced GFP expression was specifically observed in cells that were locally exposed to NIR irradiation. Our results demonstrate the feasibility of using gold nanorods and NIR irradiation as means of remote control of gene expression in specific cells. This approach has potential applications in biological and medical studies.