Nature and properties of ultrathin nanocrystalline gold films formed at the organic-aqueous interface

Ultrathin nanocrystalline films of gold formed at different temperatures at the organic-aqueous interface have been investigated by X-ray diffraction, electron microscopy, atomic force microscopy, and electronic spectroscopy. The films are smooth and continuous over relatively large length scales and are generally approximately 100 nm thick. The size of the nanocrystals is sensitive to the reaction temperature, which also determines whether the film is metallic or an activated conductor. The surface plasmon band of gold is highly red-shifted in the films. Alkanethiols perturb the structure of the films, with the magnitude of the effect depending on the chain length. Accordingly, the position of the plasmon band and the electrical resistance of the films are affected by interaction with alkanethiols; the plasmon band approaches that of isolated nanocrystals in the presence of long-chain thiols.     

Reaction of trimethylchlorosilane in spin-on Silicalite-1 zeolite film

We present a study on the hydrophobization of spin-on Silicalite-1 zeolite films through silylation with trimethylchlorosilane. Microporous and micro-mesoporous Silicalite-1 films were synthesized by spin coating of suspensions of Silicalite-1 nanozeolite crystallized for different times. Ellipsometric porosimetry with toluene and water adsorbates reveals that silylation decreases the porosity and makes the films hydrophobic. The decrease in porosity depends on the exposed surface area in the pores. Water contact angle measurements confirm the hydrophobicity. Fourier transform infrared spectroscopy reveals that the trimethylsilyl groups are chemisorbed selectively on isolated silanols and less on geminal and vicinal silanols due to steric limitations. Time-of-flight secondary-ion mass spectroscopy and in situ ellipsometry analysis of the reaction kinetics show that the silylation is a bulk process occurring in the absence of diffusion limitation. Electrical current leakage on films decreases upon silylation. Silylation with trimethylchlorosilane is shown to be an effective hydrophobization method for spin-on Silicalite-1 zeolite films.     

γ-ray and ultraviolet graft copolymerization of maleimide by vapor-phase method

Graft copolymerization of maleimide onto ethyl cellulose and polyethylene films by using its sublimation vapor was carried out under γ- or ultraviolet irradiation. When polyethylene film was used as a backbone polymer the grafting reaction proceeded without a perceptible sorption of monomer, while a considerable amount of monomer was captured into ethyl cellulose film and grafting of the sorbed monomer was observed. The monomer seemed to be monomolecularly dispersed in this film. The presence of air retarded the reaction. The grafted films were characterized by strong infrared absorption bands due to polymaleimide branching. The fractions assigned to the graft copolymer were isolated from the grafted films by selective elution. The grafted branches were supposed to be very short, judging from the polymaleimide contents of those fractions.     

Simulation of the random scission of C–C bonds in the initial stage of the thermal degradation of polyethylene

We performed molecular dynamics simulations to analyze the initial stage of the thermal degradation of polyethylene, which is dominated by the random scission reaction. The simulations were initiated from structures that were taken from previously equilibrated snapshots of the amorphous polymer and of a free-standing thin film. Isolated chains were also used for comparison. Our systems were coupled to a thermal heat bath, and the effect of different coupling constants was studied. Rate of random scission increases as the strength of the temperature coupling increases. Rates of reaction are almost similar in thin films and the bulk, whereas the rates are much faster in isolated chains. Expansion of the free-standing thin film accompanies degradation, producing fragments of various sizes. Chains of higher molecular weights than the initial chains can be produced due to recombination of fragments during the expansion of thin films. The polydispersity index of the resulting fragments is higher in thin films compared to the bulk. The bonds at the low density portion of the thin films have a higher probability of being broken.     

Formation and reaction of polyenesulfonic acid. III. Preparation and photoreaction of 1,3,5-hexatriene-1,6-disulfonic acid

As a model for the reaction between polyethylene films and gaseous SO₃, n-hexane was allowed to react with gaseous SO₃ to give 1,3,5-hexatriene-1,6-disulfonic acid (HTDS), which was isolated from the reaction products by column chromatography. Furthermore, it was found that an aqueous solution of HTDS-Na was sensitive to UV, which eliminated one of the sulfonic acid groups by a radical mechanism. sulfonic acids having less than three conjugated double bonds were not sensitive to UV.     

Dependence of structure of dehydrated PVA on the crystallinity of the original PVA

Poly(vinyl alcohol) (PVA) films having different crystallinities were prepared by elongating PVA films to different degrees and heating the films with and without elongation treatment at several temperatures between 60 and 200°C. Then, they were dehydrated by heating from 80°C to 230 or 330°C in hydrogen chloride gas. Infrared spectral measurements were made on the dehydrated PVA films obtained. Absorbances of the absorption bands due to several groups seen in the infrared spectra depended only on the density of original PVA films, regardless of its degree of elongation. From these dependences, it was found that the dehydration reaction progressed more easily in the crystalline region than in the amorphous region, that the aromatic rings with four or five adjacent hydrogen atoms were formed mainly in the amorphous region and those with two adjacent hydrogen atoms in the crystalline region, and that the aromatic rings with two isolated hydrogen atoms were formed in both the amorphous and crystalline regions. Relative concentrations of the groups of which the dehydrated PVA were composed were estimated. Comparison of the numbers of carbon atoms among the composing groups indicated that the main groups were the methylene group and the aromatic ring.     

Uptake and UV-photooxidation of gas-phase PAHs on the surface of atmospheric water films. 1. Naphthalene

The adsorption and photochemical reaction of naphthalene vapor at the air-water interface of water films (22 microm and 450 microm) were studied in a horizontal flow reactor. Experiments were conducted in the regime where gas-phase mass transfer resistance did not limit the uptake. The equilibrium uptake was dependent on water film thickness only below 1 microm. Bulk water-air and air-to-interface partition constants were estimated from the experiments. The equilibrium partition constant between the water film and air decreased with increasing temperature. Photochemical reaction products were isolated in the water film after exposure to UV light. Four main oxygenated products were identified (1,3-indandione, 1(3H)-isobenzofuranone (phthalide), 2H-1-benzopyran-2-one (coumarin), and 1-naphthol). The initial rates of product formation were 46 to 154% larger for the thin film (22 microm) compared to both a thick film (450 microm) and bulk aqueous phase photooxidation. The atmospheric implications of reactions in water films are discussed.     

Studies on the preparation of hydrolyzed starch-g-PAN (HSPAN)/PVA blend films--Effect of the reaction with epichlorohydrin

Absorbent hydrolyzed starch-g-PAN (HSPAN)/polyvinylalcohol (PVA) blend films crosslinked with epichlorohydrin (ECH) were prepared to overcome the phase separation and improve the mechanical properties of blend films. The absorbency of HSPAN/PVA blend films decreased with PVA contents due to the reduction of HSPAN contents which is known to play a major role in absorbing ability of the film. And also the absorbency decreased with the ECH contents due to the crosslinking reaction. As far as the solubility is concerned, it increased with PVA contents which is water soluble. But because of the crosslinking reaction between HSPAN and PVA by ECH, the solubility decreased with ECH contents. In the mechanical properties, the strength as well as the strain at break of the HSPAN/PVA blend films were improved very much if compared with HSPAN film, and those mechanical properties were improved even more by the reaction with ECH. The DSC thermograms of HSPAN films showed two major endothermic peaks at 32 and 128 °C, while those of PVA film showed two major endothermic peaks at 49 and 190 °C. In the non-crosslinked blend films, each four endothermic peak was apparent. But as the ECH content increased, both peaks at 128 and 190 °C disappeared and a new peak appeared at the intermediate temperature. In other words, the compatibility of blend films was increased by the reaction with ECH. Also, from the results of TGA, it was confirmed that the thermal degradation of blend films was decelerated by the crosslinking reaction.     

Pre-irradiation induced grafting of styrene into crosslinked and non-crosslinked polytetrafluoroethylene films for polymer electrolyte fuel cell applications. I: Influence of styrene grafting conditions

Crosslinked and non-crosslinked polytetrafluoroethylene (PTFE) films [RX-PTFE and V-PTFE films, respectively], were irradiated in air at room temperature using γ-rays from a ⁶⁰Co source. The irradiated films were grafted with styrene in liquid phase. The grafting of styrene into PTFE films was proved by FT-IR spectroscopy. The influence of the reaction temperature and pre-irradiation doses on the resulted degree of grafting was discussed. The grafting speed and the degree of grafting were determined by the reaction temperature and pre-irradiation doses. The apparent activation energies were calculated as 39.7 kJ/mol for RX-PTFE films and 59.5 kJ/mol for V-PTFE films. The dependence index on absorbed doses at pre-irradiation for RX-PTFE films is 0.66, and for V-PTFE films it is 1.57. The geometric size changes of the grafted films were measured and discussed. Interestingly, the thickness of the grafted films was strongly influenced by the reaction temperature. The tensile strength and the elongation at break of the non-grafted and grafted RX-PTFE and V-PTFE films were measured. The grafted films then are sulfonated by chlorosulfonic acid for polymer electrolyte fuel cell (PEFC) applications and the highest IEC value gained is over 3. The analysis of the sulfonated films are now in progress.     

Direct precursor conversion reaction for densely packed Ag2S nanocrystal thin films

Successful realization of highly crystalline and densely packed Ag2S nanocrystal (NC) films has been achieved by directly converting precursor molecules, Ag(SCOPh), on preheated substrates. When an aliquot of Ag(SCOPh) solution dissolved in trioctylphosphine (TOP) is applied on preheated solid substrates at 160 degrees C, such as SiO2/Si, H-terminated Si, and quartz. Ag2S NC thin films have been formed with instant phase and color changes of the precursor solutions from pale yellow homogeneous solution to black solid films. The average diameter of individual Ag2S NCs forming thin films is ca. 25 nm, as confirmed by examining both isolated Ag2S NCs from thin films and as-made thin film samples by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Powder X-ray diffraction (XRD) pattern shows that the synthesized Ag2S NCs have well-defined monoclinic acanthite phase. Direct precursor conversion process has resulted in densely packed Ag2S NCs with reduced interparticle distances owing to efficient removal of TOP during the reaction. Compared to the devices fabricated by the drop-coating process, Ag2S thin film devices fabricated by direct precursor conversion process have shown a ca. 300-fold increased conductance. Such Ag2S NC devices have also displayed reliable photoresponses upon white light illumination with high photosensitivity (S approximately equal to 1).     

The reaction of carbonyl groups in polyethylene films—I: The reaction with 2,4-dinitrophenylhydrazine

A method is detailed for the study of the reaction of 2,4-dinitrophenylhydrazine with polyethylene films containing carbonyl groups. The difference between films u.v.-irradiated in air and those made with a ketone-containing copolymer is studied. There is also a study of the effects of thickness of film. Progress of reaction was monitored by u.v.-spectroscopy. The u.v. absorbance increased with time of immersion in the 2,4-dinitrophenylhydrazine solution, and with increasing thickness of film. An explanation is advanced for the difference between the two types of film: it is related to differences between the distribution of carbonyl groups through the films. Most of the carbonyl groups in the photo-oxidised films made from polyethylene were on the surface. There is evidence that 2,4-dinitrophenylhydrazine can penetrate and react throughout the films.     

Electron transfer kinetics in photosynthetic reaction centers embedded in polyvinyl alcohol films

The coupling between electron transfer and protein dynamics has been studied at room temperature in isolated reaction centers (RCs) from the photosynthetic bacterium Rhodobacter sphaeroides by incorporating the protein in polyvinyl alcohol (PVA) films of different water/RC ratios. The kinetic analysis of charge recombination shows that dehydration of RC-containing PVA films causes reversible, inhomogeneous inhibition of electron transfer from the reduced primary quinone acceptor (Q(A)(-)) to the secondary quinone Q(B). A more extensive dehydration of solid PVA matrices accelerates electron transfer from Q(A)(-) to the primary photooxidized electron donor P(+). These effects indicate that incorporation of RCs into dehydrated PVA films hinders the conformational dynamics gating Q(A)(-) to Q(B) electron transfer at room temperature and slows down protein relaxation which stabilizes the primary charge-separated state P(+)Q(A)(-). A comparison with analogous effects observed in trehalose-coated RCs suggests that protein motions are less severely reduced in PVA films than in trehalose matrices at comparable water/RC ratios.     

Model experiments for the interfacial reaction between polymers during reactive polymer blending

Bilayer film Fourier transform infrared (FTIR) model experiments are designed to provide a well-defined interface for study which can be probed by infrared spectroscopy during the interdiffusion and reaction of two reactive polymers. This provides a model experiment to determine the kinetics and extent of reaction between functionalized polymers during reactive polymer blending. This type of experiment provides data on the reaction at a stagnant interface which is necessary for the analysis of the interface while it is simultaneously undergoing deformation. It is also useful as a screening or preliminary experiment on reactive blending systems in that the extent of reaction may be followed for different systems at different temperatures. Experiments reported here trace the reaction of a styrene–maleic anhydride copolymer with two different amine terminated polymers. Results are obtained for the interdiffusion and reaction of a styrene-maleic anhydride copolymer with two amine terminated polymers: a butadiene-acrylonitrile copolymer and Nylon 11. The kinetics from these experiments include contributions due to both interdiffusion and chemical reaction. The chemical reaction kinetics may be isolated from the diffusion kinetics by performing experiments on well-mixed systems which are prepared by casting films of the polymer mixtures from a mutual solvent. © 1994 John Wiley & Sons, Inc.     

Superclean Growth of Graphene Using a Cold-Wall Chemical Vapor Deposition Approach

Chemical vapor deposition (CVD) has become a promising approach for the industrial production of graphene films with appealing controllability and uniformity. However, in the conventional hot-wall CVD system, CVD-derived graphene films suffer from surface contamination originating from the gas-phase reaction during the high-temperature growth. Shown here is that the cold-wall CVD system is capable of suppressing the gas-phase reaction, and achieves the superclean growth of graphene films in a controllable manner. The as-received superclean graphene film, exhibiting improved optical and electrical properties, was proven to be an ideal candidate material used as transparent electrodes and substrate for epitaxial growth. This study provides a new promising choice for industrial production of high-quality graphene films, and the finding about the engineering of the gas-phase reaction, which is usually overlooked, will be instructive for future research on CVD growth of graphene.     

Cyanide-bridged NiCr and alternate NiFe-NiCr magnetic ultrathin films on functionalized Si(100) surface

Sequential growth in solution (SGS) was performed for the magnetic cyanide-bridged network obtained from the reaction of Ni(H(2)O)(2+) and Cr(CN)(6)(3-) (referred to as NiCr) on a Si(100) wafer already functionalized by a Ni(II) complex. The growth process led to isolated dots and a low coverage of the surface. We used the NiFe network as a template to improve the growth of the magnetic network. We elaborated alternate NiFe (paramagnetic)-NiCr (ferromagnetic) ultrathin films around 6 nm thick. The magnetic behaviour confirmed the alternate structure with the ferromagnetic zones isolated between the paramagnetic ones since the evolution of the blocking temperature is consistent with the evolution of the layers' thickness expected from the SGS process.     

Synthesis and characterisation of tungsten(VI) oxo-salicylate complexes for use in the chemical vapour deposition of self-cleaning films

Tungsten(VI) oxo-salicylate complexes were prepared in moderate yield (47 to 63%) by the reactions of WOCl4 and two equivalents of either 3-methylsalicylic acid (MesaliH2) or 3,5-di-isopropylsalicylic acid (di-i-PrsaliH2). Performing the reaction in refluxing toluene afforded the two analogous ditungsten complexes 1, [{WO(Mesali)(MesaliH)}2(mu-O)], and 2, [{WO(di-i-Prsali)(di-i-PrsaliH)}2(mu-O)], however in refluxing hexane the mononuclear tungsten complex , [WO(di-i-Prsali)(di-i-PrsaliH)Cl], was isolated. The single crystal X-ray study of revealed a pseudo-octahedral geometry around the tungsten centres. Aerosol assisted chemical vapour deposition of or afforded brown tungsten trioxide thin films. These films were converted to yellow fully oxidised WO3 on annealing in air at 550 degrees C for 30 minutes. The yellow WO3 films demonstrate preferred orientation on the substrate and show interesting functional properties-photo induced hydrophilicity and photocatalytic activity.     

Facile fabrication of polymer-dispersed liquid crystal films via nucleophile-initiated thiol-ene click reaction

Nucleophile-initiated thiol-ene click reaction was employed to prepare polymer-dispersed liquid crystal (PDLC) films initiated by 4-dimethylaminopyridine (DMAP). The PDLC films were prepared in different temperature. It is found that the reaction temperature has a big influence on the electro-optical properties of PDLC films and 60°C is the optimal temperature to fabricate PDLC film which has high ON state transmittance (T_on) and low OFF state transmittance (T_off). UV-Visible spectrophotometer, scanning electron microscopy and polarised optical microscope were employed to explore the obtained PDLC films. Nucleophile-initiated thiol-ene click reaction, without UV-light, probably provides a new pathway to prepare PDLC films.     

固相配位化学反应研究LXVII．金属铜表面M－S（M＝Mo，W）簇合物膜的组成

采用ＦＴＩＲ、ＸＰＳ和ＡＥＳ研究了金属铜表面Ｍ－Ｓ（Ｍ＝Ｍｏ，Ｗ）簇合物膜。结果表明，Ｍｏ（Ｗ）与铜表面的Ｃｕ＿２Ｏ反应，形成了Ｍｏ（Ｗ）－Ｓ－Ｃｕ键；簇合物膜由Ｍｏ（Ｗ）、Ｓ、Ｃｕ、Ｏ元素组成，分别呈＋６、－２、＋１、－２价，膜为多分子层结构并保持ＭｏＳ＿４，或ＷＳ＿２单元，膜表面只有Ｃｕ、Ｏ而不存在Ｍｏ（Ｗ）、Ｓ．膜层厚度与反应时间有关，时间越长，膜越厚。膜为多组分的复杂体系，其颜色是各组分统计分布的结果。     

Kinetics of Photocatalytic Degradation of Formic Acid over Silica Composite Films Based on Polyoxometalates

The composite films, XW11O39^n-/SiO2,(X refers to Si,Ge or P,respectively) were prepared by tetraethoxysilane (TEOS) hydrolysis sol-gel method via spin-coating technique. Formation of the composite films is due to strong chemical reaction of organic silanol group with the surface oxygen atoms of XW11O39^n-, resulted in the saturation of the surface of the lacunary polyoxometalates (POMs). Therefore,the coordination structural model of the films was proposed. As for the films, retention of the primary Keggin structure was confirmed by UV-vis, FT-IR spectra and MAS NMR. The surface morphology of the films was characterized by SEM, indicating that the film surface is relatively uniform, and the layer thickness is in the range of 250-350nm. Aqueous formic acid (FA) (0-20mmol/L) was degraded into CO2 and H2O by irradiating the films in the near-UV area. The results show that all the films have photocatalytic activities and the degradation reaction follows Langmuir-Hinshelwood first order kinetics.     

钛酸钡薄膜生长初期粒子形态及其反应机理的模拟研究

在激光分子束外延生长钛酸钡(BaTiO₃,BTO)薄膜过程中,初期多粒子碰撞反应过程是薄膜形成的关键过程。本文采用密度泛函理论中的广义梯度近似(DFT/GGA),在PW91/DNP水平上研究了Ba、Ti、O、O₂、BaO、TiO₂以及BTO分子在真空中的优先反应形成与演化过程,计算研究了它们碰撞反应及其中间体的形成机理,获得了相应中间体的几何结构、过渡态及反应活化能,并运用前线轨道理论分析了BTO分子形成机理。对比BTO、SrTiO相似文献