Influence of water on the photooxidation of KHJ phenoxy resins, 1. Mechanisms

This study is devoted to the influence of water on the mechanisms of photooxidation of anticorrosion coatings based on epoxy resins used in extremely aggressive media like the marine environment. The two principal environmental parameters to be considered are sunlight (UV-light) and water. It is important to understand the role of these two environmental parameters on the ageing of epoxy anticorrosion coatings. On the basis of the effect of photooxidation on the molecular structure under “dry” conditions, water was introduced into the ageing process with either alternating cycles of irradiation/immersion in water or simultaneously by irradiation of the polymer in water. The presence of water had two effects on the photodegradation of PKHJ^® phenoxy resin; the first one was on the degradation of the main photoproduct (phenyl formates) formed during irradiation through a hydrolysis reaction leading to the release of formic acid. The second effect consisted of an increase in the photooxidation rate by the formation of photo-initiators.     

Changes in silicon elastomeric surface properties under stretching induced by three surface treatments

Poly(dimethylsiloxane) (PDMS) substrates are used in many applications where the substrates need to be elongated and various treatments are used to regulate their surface properties. In this article, we compare the effect of three of such treatments, namely, UV irradiation, water plasma, and plasma polymerization, both from a molecular and from a macroscopic point of view. We focus our attention in particular on the behavior of the treated surfaces under mechanical stretching. UV irradiation induces the substitution of methyl groups by hydroxyl and acid groups, water plasma leads to a silicate-like layer, and plasma polymerization causes the formation of an organic thin film with a major content of anhydride and acid groups. Stretching induces cracks on the surface both for silicate-like layers and for plasma polymer thin coatings. This is not the case for the UV irradiated PDMS substrates. We then analyzed the chemical composition of these cracks. In the case of water plasma, the cracks reveal native PDMS. In the case of plasma polymerization, the cracks reveal modified PDMS. The contact angles of plasma polymer and UV treated surfaces vary only very slightly under stretching, whereas large variations are observed for water plasma treatments. The small variation in the contact angle values observed on the plasma polymer thin film under stretching even when cracks appear on the surface are explained by the specific chemistry of the PDMS in the cracks. We find that it is very different from native PDMS and that its structure is somewhere between Si(O2) and Si(O3). This is, to our knowledge, the first study where different surface treatments of PDMS are compared for films under stretching.     

Preparation of nano-sized Pt metal particles by photo-assisted deposition (PAD) on transparent Ti-containing mesoporous silica thin film

We have investigated a novel technique for the preparation of nano-sized Pt metals on Ti-containing mesoporous silica (TMS) thin film by photo-assisted deposition (PAD). The transparent TMS thin film was prepared on a quartz plate through sol—gel/spin coating. XRD, UV-Vis and Ti K-edge XAFS measurements revealed the formation of isolated Ti oxide species with a tetrahedral-coordination geometry in the silica framework. Deposition of Pt metal precursor on TMS thin film under UV-light irradiation, followed by reduction with molecular hydrogen, afforded a transparent thin film (Pt/TMS). The formation of highly dispersed nano-sized Pt metals having narrow size distributions was determined by Pd L_III-edge XANES and TEM analysis. The TMS and Pt/TMS thin films have been demonstrated to exhibit a strong hydrophilic property, even before UV irradiation, compared to the common mesoporous silica and TiO₂ thin films. After UV-light irradiation, the contact angle of water droplet on the TMS and Pt/TMS thin films became extremely lower, indicating the appearance of the photo-induced super-hydrophilic property.     

Gold and silver nanorings formed at the air/water interface

Gold nanorings were prepared at the air/water interface through reduction of AuCl₄⁻ ions by UV-light irradiation or formaldehyde gas treatment at room temperature templated by thin films of phthalocyanine derivatives. Silver nanorings were produced at the air/water interface via reduction of Ag⁺ ions by UV-light irradiation templated by poly(9-vinylcarbazole) (PVK) thin films. These nanostructures were investigated by transmission electron microscopy (TEM), selective-area electron diffractometry (SAED), and high-resolution TEM (HRTEM). It was found that the gold nanorings are composed of close-packed nanoplates whose (1 1 0) crystal planes are parallel to the air/water interface; while silver rings are composed of nanoparticles. It is demonstrated that the ring-like aggregates formed by parallel linear supramolecules of the phthalocyanine derivatives and the ring-like structure of PVK supramolecules are responsible for the formation of the gold and silver nanorings, respectively.     

Beiträge zur ökologischen chemie—LXI : Photoreaktionen des aldrin/dieldrin-metaboliten dihydrochlordendicarbonsäure (4,5,6,7,8,8-hexachloro-4,7-methano-3a,4,7,7a-tetrahydroindan-1,3-dicarbonsäure)

Dicarboxylic acid (1) and its dimethylester (2) respectively were irradiated in solutions and in gaseous phase by UV-light of a high pressure mercury lamp with emission above 230 nm. Immersion wells of pyrex and quartz were used for the irradiation experiments. After an irradiation with UV-light having long wavelengths (λ > 300 nm), followed by a diazomethane treatment of the reaction mixture, compounds 5–11 could be isolated from solutions of the dicarboxylic acid (1) in acetone. Dimethylester (2) revealed comparable results. Compounds 3 and 4 were obtained by irradiating the dimethylester (2) in n-hexane and water/methanol respectively with wave-lengths below 300 nm. The dimethylester (2) gaseously distributed in air, yielded two isomeric products and a dechlorination product by irradiation with UV-light (λ < 300 nm). The bridged compound 5 is one of the isomeric photoproducts. This contribution mainly consists in the structural elucidation of products being formed under the influence of UV-light. The spectroscopical data of compounds 1–11 resulting in the proposed structures given in Fig 1 are discussed in the following text.     

基于聚醚胺(PEA)动态交联网络的多重响应性表面褶皱图案

刺激响应性表面图案赋予了材料动态可调的表面性能,是智能材料领域研究的热点,然而如何通过简单有效的方法构建这类动态表面图案也是该领域的难点.本文将动态硼酸酯键和光可逆二聚基团引入到聚醚胺(PEA)交联网络中,通过双层褶皱体系构建一系列具有光和湿度刺激响应性表面褶皱图案.在365 nm紫外光照和加热的条件下,蒽基团(AN)的光二聚与硼酸键的形成使得上表层聚醚胺模量变大,产生微米级表面褶皱图案;在254 nm紫外光照射或水蒸气作用下,聚醚胺网络解交联,表面褶皱图案消失;利用光化学时空分辨的特性,通过光掩膜板光照还可以制备多层次动态表面褶皱图案.这种多重刺激响应性表面褶皱图案为构建智能聚合物表面提供了新思路,在传感和防伪等领域具有潜在的应用前景.     

Cyclodextrins for remediation of soils contaminated with chlorinated organics

The effect of random methylated ??CD (RAMEB) on the efficiency of various remediation technologies was studied in lab-scale model-experiments applying soil and groundwater originating from a site contaminated with trichloroethylene (TCE). The solubility of TCE was enhanced to tenfold in 10% solution of RAMEB compared to that in water. This solubilizing effect was utilized for remediation of the TCE contaminated soil using enhanced groundwater extraction and in situ TCE oxidation by ISCO (= in situ chemical oxidation). The effect of CD on TCE extraction from soil was studied using two technologies: ground-water extraction followed by air stripping or UV irradiation. The RAMEB-enhanced ISCO was applied directly to the water-saturated soil without water extraction or separation. The efficiency of air stripping of TCE (removal by bubbling air through the contaminated ground-water obtained by extraction) was decreased in the presence of RAMEB due to the volatility decreasing effect of complexation. The efficiency of the entire technology (extraction and air stripping together) was, however, enhanced as three times more TCE was dissolved, and more than twice as much could be removed when 5% RAMEB solution was applied instead of water. Similar results were obtained by UV irradiation. Although the complexation has a protective effect against degradation caused by irradiation, the efficiency of the technology (extraction and subsequent UV irradiation) is enhanced to approximately threefold, because more than 10 times higher TCE concentration was found in the extract using 20% RAMEB concentration. ISCO is based on Fe-catalyzed oxidation using hydrogen peroxide. The catalytic effect of RAMEB was observed only when it was applied together with Fe(II) salts. Without Fe(II) the effect of complex formation dominated. When hydrogen peroxide and FeSO₄ were applied with RAMEB, over five times enhancement in TCE removal was obtained compared to the technology based on the addition of hydrogen peroxide and Fe(II) salts without RAMEB. This effect shows that the solubilizing effect on iron catalyst is at least as much or even more important than the solubilizing effect on TCE. The ternary complex formation with ferrous/ferric ion and TCE seems to be responsible for the enhanced efficacy.     

Stimuli-responsive properties of N-isopropylacrylamide-based ultrathin hydrogel films prepared by photo-cross-linking

To develop stimuli-responsive ultrathin polymer films on a solid substrate, a novel photo-cross-linkable polymer with both temperature- and pH-responsive properties was prepared. The photoreactive 4-aminobenzophenone (BP) was introduced onto the side groups of poly(N-isopropylaclylamide-co-2-carboxyisopropylaclylamide) [poly(NIPAAm-co-CIPAAm)]. This copolymer was designed for highly random sequences of comonomers. After the formation of spin-coated polymer films on a solid substrate, UV-light irradiation started the cross-linking reaction. The spin-coating processes and stability of the polymer films were quantitatively monitored by a quartz crystal microbalance (QCM), and the thickness was estimated using an atomic force microscope (AFM). These measurements confirmed the formation of a very plain polymer film, and the film thickness was precisely controlled by the concentration of the polymer solution used for spin coating. Moreover, the obtained films showed a high stability due to the cross-liking reaction and UV irradiation. Cyclic voltammetry using potassium ferricyanide revealed that the ions could permeate the photo-cross-linked ultrathin polymer films. The permeability of the ultrathin hydrogel films was dramatically changed by varying the pH and temperature of the aqueous media. These observations suggest that the preparation of isopropylacrylamide-based stimuli-responsive ultrathin hydrogel films is possible.     

Light-driven phase transition in a cubic-phase-forming binary system composed of 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic acid and an azobenzene derivative

Binary mixtures were prepared from an azobenzene derivative and a liquid-crystal (LC) compound that exhibits smectic?C (SmC) and bicontinuous cubic (Cub(bi)) LC phases. Reversible switching between the two phases in response to UV-light irradiation was observed. This light-driven SmC-to-Cub(bi) transition is the first example showing the increased dimensionality of molecular ordering with isomerization of azobenzenes (see figure).     

Photooxidative behaviour of polyethylene/polyamide-6 blends

The photochemical behaviour of several polyethylene/polyamide-6 blends was studied under conditions of artificial accelerated weathering. Particular attention was paid to five different compositions ranging from pure polyethylene to pure polyamide with blends of PE/PA-6 of various compositions: 75/25, 50/50 and 25/75 wt/wt%. Analysis by infrared spectroscopy of the chemical modifications caused by photooxidation showed that exposing the polyethylene/polyamide-6 blends to UV-light irradiation led to the formation of oxidation photoproducts in both polymer phases. In agreement with both the mechanical and spectroscopic analyses, the photooxidation rate of the blends was observed to be much higher than that of the homopolymers. The results given in this paper suggest that photooxidation of the PE/PA blends starts in the polyamide phase and that the subsequent photooxidation of the polyethylene phase may be initiated by the radicals coming from the oxidation of PA.     

Antibonding plasmon modes in colloidal gold nanorod clusters

The optical response of nanoplasmonic colloids in disperse phase is strictly related to their shape. However, upon self-assembly, new optical features, for example, bonding or antibonding modes, emerge as a result of the mutual orientations of nanoparticles. The geometry of the final assemblies often determines which mode is dominating in the overall optical response. These new plasmon modes, however, are mostly observed in silico, as self-assembly in the liquid phase leads to cluster formation with a broad range of particle units. Here we show that low-symmetry clustering of gold nanorods (AuNRs) in solution can also reveal antibonding modes. We found that UV-light irradiation of colloidal dispersions of AuNRs in N-methyl-2-pyrrolidone (NMP), stabilized by poly(vinylpyrrolidone) (PVP) results in the creation of AuNRs clusters with ladderlike morphology, where antibonding modes can be identified. We propose that UV irradiation induces formation of radicals in solvent molecules, which then promote cross-linking of PVP chains on the surface of adjacent particles. This picture opens up a number of relevant questions in nanoscience and is expected to find application in light induced self-assembly of particles with various compositions and morphologies.     

HNdNb2O7/(Pt,TiO2)的制备和光催化性能的研究

利用层间插入反应,合成HNdNb2O7/(Pt,TiO2 )层状光催化纳米复合材料.采用X射线衍射、紫外-可见光漫反射、比表面积测定分析等分析手段对所制备的材料进行了表征.通过光照分解水,考察了所制备的材料的光催化性能,结果表明所制备的HNdNb2O7 /(Pt ,TiO2 )纳米复合材料具有较高的光催化分解水效率并且其光催化活性稳定.     

Photoresponsive crown ethers. 10. Metal complexation by light-switched crown ethers immobilized in polymer matrices

The crosslinked polystyrene beads which immobilized two terminal azophenoxide groups of an azobenzene-crown(24-crown-8)-azobenzene unit were synthesized. The polymer beads adsorbed Cs⁺ in the dark while they rapidly released Cs⁺ into the solution under UV-light irradiation, and the photoresponsive complexation occurred reversibly. On the other hand, the crosslinked polystyrene beads which immobilized one terminal azophenoxide group of an azobenzene-crown (24-crown-8) unit scarcely (or only to a smaller extent) exhibited such a photoresponsive behavior. Similarly, the polymer beads which immobilized two terminal azophenoxide groups of an azobenzene-crown (18-crown-6) azobenzene unit reversibly adsorbed and desorbed K⁺ in response to UV-light irradiation. The novel photoresponsive behavior is ascribed to a conformational distortion of the crown rings which induced by the photoisomerization of the azobenzene moiety, although the photoinduced polarity change of the polymer beads is not completely ruled out. The results suggest that the polymer support is useful as a “fixed point” to enforce the conformational changes of immobilized functional molecules.     

A novel reactor for photochemical post-column derivatisation in HPLC

Summary It is well known that UV-absorbing substances can be transformed into fluorescent substances by irradiation with UV-light. This principle is used for HPLC by means of a post-column reactor. The factors influencing the performance of the reactor, such as contribution to peak broadening and optimization of the photochemical reaction, are discussed leading to a new and versatile design.Dedicated to Professor Dr. István Halász for his 60th birthday.     

UV-light and visible-light photochromism of inorganic–organic multilayer films based on polyoxometalate and poly(acrylamide)

Novel UV-light and visible-light photochromic inorganic–organic multilayers composed of polyoxometalates (phosphomolybdic acid (PMoA)) and poly(acrylamide) (PAM) were prepared by the layer-by-layer (LbL) self-assembly method. The grown process, composition, surface topography, and photochromic properties and mechanism of the multilayer films were investigated by ultraviolet–visible (UV–vis) spectra, Fourier transform infrared spectra (FT-IR), atomic force microscopy (AFM), electron resonance spectra (ESR), and X-ray photoelectron spectra (XPS). Irradiation with UV-light or visible-light, the transparent films changed from colorless to blue and showed reversible photochromism. PMoA/PAM LbL films had higher photochromic efficiency under UV-light irradiation than visible-light irradiation. The bleaching process occurred when the films were in contact with O₂ in the dark or heated in air. The photochromic process of PMoA/PAM LbL film was in accordance with radical mechanism.     

Spectroscopic Characterization of Carbazole-TCAQ Charge-Transfer Salt

Spectroscopic characterizations of carbazole-TCAQ salt were investigated by means of UV-visible and fluorescence spectra. The results show that carbazole and TCAQ can form a kind of charge-transfer salt whose characteristic adsorption is π→π^* of 248 nm when the mixture of the two compounds is irradiated by UV-light, and the charge-transfer salt becomes more stable with the increase of irradiation time.     

Photoinduced polymer-stabilised chiral nematic liquid crystal films reflecting both right- and left-circularly polarised light

A phototunable polymer-stabilised liquid crystal film reflecting both right- and left-circularly polarised light has been successfully fabricated by a washout/refill method. The film was obtained by prefabricating the polymer network with a left-handed helical structure and then refilling a light-driven chiral nematic liquid crystal with a right-handed helical structure into the network. Interestingly, the reflection wavelength and the reflectivity properties can be precisely tuned by UV-light irradiation. A hyper-reflective notch, the reflectivity of which approaches 100%, was achieved in a layer when the pitch lengths of the two opposite helical structures are almost the same. Moreover, their original state can be properly returned by visible-light irradiation.     

Coumarinyl(thienyl)thiazoles: novel photochromes with modulated fluorescence

Novel photochromic 5-(3'-coumarinyl)-4-(3'-thienyl)thiazoles have been synthesized. These compounds display intensive fluorescence emission in the open form A, which is modulated by light. Fluorescence intensity decreases significantly upon irradiation of A with UV-light (lambda<400 nm) due to formation of the cyclic form B. Irradiation of B with visible light (lambda>470 nm) promotes its opening and the recovering of fluorescence. Novel dihetarylethenes undergo photochromic modulation of fluorescence both in solution and in polymeric matrices.     

Effect of β-nucleation on crystallization of photodegraded polypropylene

The work deals with crystallization of photodegraded polypropylene containing various amounts of β-nucleating agent based on N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide. Compression-moulded samples were irradiated by UV-light, melted and subsequently non-isothermally crystallized. The results showed that the crystallization temperature decreased with increasing irradiation time. The irradiation caused the splitting of crystallization exotherms into two peaks indicating two crystallization mechanisms. The presence of β-nucleating agent in the material suppressed the peak splitting; the higher was the amount of nucleating agent in the sample, the later was the splitting observed.     

STM investigation of the photoisomerization of an azobis-(benzo-15-crown-5) molecule and its self-assembly on Au(111)

Scanning tunneling microscopy (STM) has been employed to investigate the photoisomerization of azobis-(benzo-15-crown-5) on Au(111). A self-assembled monolayer of azobis-(benzo-15-crown-5) with a (3 x 7) symmetry was observed on Au(111). After ex-situ UV-light irradiation, a new adlayer structure with a different molecular arrangement could be seen on Au(111), although the domain size of the ordered packing is small. On the basis of a high-resolution STM image and photochemical reaction result, schematic models have been proposed for the original and ex-situ irradiated adlayers. After in-situ UV-light irradiation, the ordered arrays disappeared and many bright clusters emerged at domain boundaries. The results presented here provide direct evidence at the molecular level for a photochemical reaction.