Interfacial phenomena between brittle and polymeric films

An ovrerview of a new theory for describing interfacial phenomena in layered composites is presented. Relations are given for determining the adhesion of thin brittle films on flexible substrates, for determining residual strains resulting from drying solvent cast films, and for calculating thermoelastic strains in unsymmetric laminates. An experimental technique to measure the adhesion is discussed and values are obtained using experimental data. Residual strains are also calculated using the derived relations and solvent d in data.     

Electrocatalytic oxidation of organic compounds on noble metals in aqueous solution

The oxidatioin of organic compounds on noble metal electrodes in aqueous solution is a complex reaction due to the occurrence of several adsorbed intermediates and reaction products or by-products. This leads to a lot of electrocatalytic problems, such as the elucidation of the nature of reaction products and the structure of adsorbed species, the role of the electrode material, the effect of the structure of the organic compound, and the role of the composition of the electrolytic solution. These topics are illustrated with the help of various organic compounds (formic acid, methanol, ethanol, ethylene-glycol, C—2 compounds derived from ethylene—glycol, butanol isomers) using principally two experimental approaches: cyclic voltammetry at the macroscopic level and infrared spectroscopy (either FTIRS or EMIRS) at the microscopic level.     

Interfacial phenomena - Bioadhesion and Biocompatibility

The physical-chemical interaction between components of biological fluids and solid materials is considered with regard to performance of synthetic membranes. The possibilities to reduce irreversible bioadhesion (fouling) of membranes, and to achieve biocompatibility, are discussed on the basis of the theory of colloidal adhesion, recent knowledge on so-called hydration forces and experiences from biomaterials.     

Interfacial and diffusion phenomena in emulsion polymerisation

Evidence is presented which shows that both free-radical and monomer species can be subject to mass transfer resistances in an emulsion polymerisation. The possible causes of these resistances are analysed. In most cases, simple diffusional resistances will not affect the course of an emulsion polymerisation appreciably. However, interfacial resistance to mass transfer which occurs at the water-particle boundary can have noticeable effects on the polymerisation. The practical consequences of these phenomena are discussed. These can be of particular importance in emulsion copolymerisation.     

Alloys cathodically modified with noble metals

The truly remarkable corrosion resistance of alloys containing small amounts of noble metals relies on the principle that the high exchange-current density for the reduction of hydrogen can shift the corrosion potential of the alloy to a value in the passive region, causing it to passivate spontaneously. Research indicates that additions of 0.1 to 0.4% PGMs to chromium in sulphuric acid cause the alloy to self-passivate easily and also increased the corrosion resistance by several orders of magnitude. The effectiveness of the PGMs in promoting corrosion resistance was found to decrease in the order Pt>Pd>Ir>Ru>Os. An enrichment of PGMs at the surface of the alloys occurred during the period of active dissolution. The effect of cathodic additions in ferritic stainless steels became more enhanced with an increase in the chromium content of an alloy. Furthermore, if molybdenum and a PGM occur together in an alloy, a synergistic beneficial effect is exerted on the corrosion resistance. The effect of the cathodic modification of austenitic stainless steels is not as dramatic as for ferritic stainless steels. Little is known about the effect of PGMs on the corrosion behaviour of duplex stainless steels. Work on titanium-palladium alloys led to the development of a commercial titanium-palladium alloy containing 0.2% palladium, which is especially suited to reducing conditions. By contrast with the chromium and stainless-stell alloys, the addition of PGMs to titanium was found not to be detrimental to its corrosion resistance in highly oxidizing media. The surface alloying of materials with PGMs by various methods could prove to be a more cost-effective method than bulk alloying.     

化工过程的界面现象

<正> 化工的传质、传热、动量传递与反应等过程往往是通过各类相界面进行,研究与之有关的界面现象有助于从本质上来认识化工过程的客观规律。现在界面现象已是化学工程的基础理论研究的一个重要方面。     

Ignition-extinction of ethane-air mixtures over noble metals

Surface ignition-extinction, homogeneous ignition and autothermal behavior of ethane-air mixtures are examined over Pt, Pd, Rh, Ir and Ni foils for the full range of fuel-air ratios. The observed trends are explained in terms of metal-oxygen bond strengths and reaction pathways catalyzed by these metals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interfacial phenomena in cellulose/polyethylene composites

A systematic study of the mechanical properties of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) filled with cellulose was conducted. When benzoyl peroxide (BPO) was used and when the components were mixed at 160°, the yield strength of the LLDPE/cellulose composite increased by 70% whereas that of HDPE increased by only 15%. If BPO is replaced by dicumyl peroxide (DCP) the yield strength attains a plateau value at a lower concetration. Yield strength for the cellulose/LLDPE system, where the cellulose had been pretreated with silane, showed a relatively small improvement as compared to the effect of the peroxides addition. The presence of gel in the compound is also discussed.     

Comprehensive approach to intrinsic charge carrier mobility in conjugated organic molecules, macromolecules, and supramolecular architectures

Si-based inorganic electronics have long dominated the semiconductor industry. However, in recent years conjugated polymers have attracted increasing attention because such systems are flexible and offer the potential for low-cost, large-area production via roll-to-roll processing. The state-of-the-art organic conjugated molecular crystals can exhibit charge carrier mobilities (μ) that nearly match or even exceed that of amorphous silicon (1-10 cm(2) V(-1) s(-1)). The mean free path of the charge carriers estimated from these mobilities corresponds to the typical intersite (intermolecular) hopping distances in conjugated organic materials, which strongly suggests that the conduction model for the electronic band structure only applies to μ > 1 cm(2) V(-1) s(-1) for the translational motion of the charge carriers. However, to analyze the transport mechanism in organic electronics, researchers conventionally use a disorder formalism, where μ is usually less than 1 cm(2) V(-1) s(-1) and dominated by impurities, disorders, or defects that disturb the long-range translational motion. In this Account, we discuss the relationship between the alternating-current and direct-current mobilities of charge carriers, using time-resolved microwave conductivity (TRMC) and other techniques including field-effect transistor, time-of-flight, and space-charge limited current. TRMC measures the nanometer-scale mobility of charge carriers under an oscillating microwave electric field with no contact between the semiconductors and the metals. This separation allows us to evaluate the intrinsic charge carrier mobility with minimal trapping effects. We review a wide variety of organic electronics in terms of their charge carrier mobilities, and we describe recent studies of macromolecules, molecular crystals, and supramolecular architecture. For example, a rigid poly(phenylene-co-ethynylene) included in permethylated cyclodextrin shows a high intramolecular hole mobility of 0.5 cm(2) V(-1) s(-1), based on a combination of flash-photolysis TRMC and transient absorption spectroscopy (TAS) measurements. Single-crystal rubrene showed an ambipolarity with anisotropic charge carrier transport along each crystal axis on the nanometer scale. Finally, we describe the charge carrier mobility of a self-assembled nanotube consisting of a large π-plane of hexabenzocoronene (HBC) partially appended with an electron acceptor. The local (intratubular) charge carrier mobility reached 3 cm(2) V(-1) s(-1) for the nanotubes that possessed well-ordered π-stacking, but it dropped to 0.7 cm(2) V(-1) s(-1) in regions that contained greater amounts of the electron acceptor because those molecules reduced the structural integrity of π-stacked HBC arrays. Interestingly, the long-range (intertubular) charge carrier mobility was on the order of 10(-4) cm(2) V(-1) s(-1) and monotonically decreased when the acceptor content was increased. These results suggest the importance of investigating charge carrier mobilities by frequency-dependent charge carrier motion for the development of more efficient organic electronic devices.     

Interfacial phenomena controlling particle morphology of composite latexes

A thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Seeded batch emulsion polymerization was carried out at 70°C using as seed monodisperse polystyrene latex particles having different surface polarity. The surface polarity was estimated by contact angle measurement at the latex “film”/water interface for octane as the probe liquid. Methyl methacrylate and ethyl methacrylate were polymerized in a second stage seeded emulsion polymerization using polystyrene particles as seed in the presence of a nonionic stabilizer, nonyphenol polyethylene oxide (Igepal Co-990). Two types of initiators, potassium persulfate (K₂S₂O₈) and azobisiobutyronitrile (AIBN), were used to change the interfacial tension between the second stage polymer (in monomer) and water interface. The values of the interfacial tension of polymer solutions in the second stage monomer vs. the aqueous phase, measured by drop-weight–volume method under conditions similar to those prevailing during the polymerization, correlated well with the determined particle surface polarity and the observed TEM particle morphology. The results showed that, rather than the polymer bulk hydrophilicity, the surface particle polarity is the controlling parameter in deciding which phase is inside or outside in the composite particle. The variation of the polymer phase interfacial tension with polymer concentration was also estimated. Based on experimentally measured interfacial tensions, composite particle configurations were predicted. The predicted morphologies showed good agreement with the observed particle morphologies of the composite latexes.     

Millisecond catalytic reforming of monoaromatics over noble metals

The millisecond autothermal reforming of benzene, toluene, ethylbenzene, cumene, and styrene were independently studied over five noble metal‐based catalysts: Pt, Rh, Rh/γ‐Al₂O₃, Rh–Ce, and Rh–Ce/γ‐Al₂O₃, as a function of carbon‐to‐oxygen feed ratio. The Rh–Ce/γ‐Al₂O₃ catalyst exhibited the highest feedstock conversion as well as selectivities to both synthesis gas and hydrocarbon products (lowest selectivities to H₂O and CO₂). Experimental results demonstrate a high stability of aromatic rings within the reactor system. Benzene and toluene seem to react primarily heterogeneously, producing only syngas and combustion products. Ethylbenzene and cumene behaved similarly, with higher conversions than benzene and toluene, and high product selectivity to styrene, likely due to homogeneous reactions involving their alkyl groups. Styrene exhibited low conversions over Rh–Ce/γ‐Al₂O₃, emphasizing the stability of styrene in the reactor system. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Interfacial electronic structures between fullerene and multilayer graphene for n-type organic semiconducting devices

The interfacial electronic structure of fullerene (C₆₀) deposited on a multilayer graphene (MLG) film was measured using in situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy. The energy level alignment at the interface of C₆₀/MLG was estimated by the shifts in the highest occupied molecular orbital (HOMO) and the vacuum level during step-by-step deposition of C₆₀ on the MLG. The shift of the HOMO level indicates that there is a small band bending at the interface of C₆₀/MLG. The vacuum level was shifted 0.06 eV toward the low binding energy with additional C₆₀ on the MLG. The measurements reveal that the height of the electron injection barrier is 0.59 eV, while the hole injection barrier height is 2.01 eV. We present a complete interfacial energy level diagram for C₆₀/MLG.     

Synthesis and reactivities of cubane-type sulfido clusters containing noble metals

Cubane-type sulfido clusters containing noble metals are newcomers compared with the corresponding clusters of the first transition series metals and molybdenum, which have been extensively studied in relation to metalloenzymes and industrial hydrodesulfurization catalysts. This Account reviews the recent progress in studies on the synthesis and reactivities of these noble metal cubane-type clusters. One of the goals in this new area lies in development of the unique catalysis of the noble metals embedded in the robust and redox-active cubane-type cores. Rational synthetic approaches indispensable to the preparation of such effective cluster catalysts are discussed to a significant extent.     

Hydrodesulfurization over noble metals supported on ZSM-5 zeolites

Pt/HZSM-5 showed high and stable catalytic activity for the hydrodesulfurization of thiophene at 400°C and its catalytic activity was higher than that of commercial CoMo/Al₂O₃ catalyst. Pt/HZSM-5 zeolite was not poisoned by hydrogen sulfide in the hydrodesulfurization of thiophene and hydrocracking of hydrocarbons. The catalytic activity of Pt/HZSM-5 decreased with increase of SiO₂/Al₂O₃ ratio in HZSM-5. The Brønsted acid site of HZSM-5 and spillover hydrogen formed on Pt particle in Pt/HZSM-5 catalyst play an important role for the hydrodesulfurization of thiophene.     

Formation of nanosized bimetallic particles based on noble metals

Methods for the preparation of nanosized alloys from noble metals by decomposition of monomolecular precursors are described, and the results of these studies are reported. Other aspects of the synthesis procedure and properties of bimetallic nanostructures are also considered. Thermolysis of noble metal compounds led to the formation of an ultradisperse powder of their alloys. This method affords catalysts with a uniform distribution of active particles. Nanosized particles of a number of alloys in hydrogen and inert media were prepared. The optimum parameters of the reduction of complex compounds (gas medium, thermolysis temperature, heating rate, and annealing time) were determined to obtain ultradisperse powders with the required particle size, phase composition, and structure. For Co-Pt and Pt-Pd systems, bimetallic catalysts deposited on γ-Al₂O₃ and Sibunit can be obtained; these catalysts show higher activity in selective oxidation of CO compared with monometallic catalysts.     

Interfacial phenomena of aqueous systems in dense carbon dioxide

The interfacial tensions of initially pure liquids (water, ethanol and corn germ oil) and water–ethanol mixtures against dense carbon dioxide as well as against dense carbon dioxide mixtures with water and ethanol at 313 K and at pressures up to 27 MPa are measured. The wettabilities of ethanol and water on PTFE, glass and steel surrounded by pressurized carbon dioxide are also included in this paper. The interfacial tension results reported are the static values as well as the values which are measured during mass transfer.Generally, it is known that the interfacial tension depends on the composition of the coexisting phases. However, up to now, it is not clear whether only the composition of the interface does have an influence on the interfacial tension or if the composition of the bulk phase also affects this property. The detail discussion on this issue can be found in this paper. In this regard, the estimated pressure difference over the meniscus of a water drop with a diameter of 5 mm is reported.During mass transfer some interesting but scarcely reported drop phenomena such as drop kicking, upwards motion of the continuous phase around the drop, rising bubbles and intense mixing in the drop phase are observed. They are closely related to the interfacial turbulence, free convection, diffusion and stranding of the carbon dioxide molecules.The contact angle of ethanol and water drop over a pressure range of 27 MPa on PTFE, stainless steel and glass surfaces in the presence of dense carbon dioxide are included.     

Alternative view of anodic surface oxidation of noble metals

The idea of underpotential oxidation of water, taking place on the surface of noble metals in the range of potentials preceding molecular oxygen evolution, is more than 40-years old. Chemisorbed oxygen atom—O_chem is considered to be the main intermediate in the underpotential oxidation of H₂O, leading eventually to chemical oxidation of noble metals and formation of anhydrous surface oxides of MeO type. This concept is still used for the evaluation of the real surface area of the noble metal electrodes and also for the interpretation of new experimental results.The existence of reversible metal-oxide electrodes demonstrated experimentally for Pt, Pd, Rh, Ir and Au electrodes, oxidized anodically in the range of potentials preceding O₂ evolution, shows that noble metals do have electrochemistry of their own. Nanometric layers of amorphous, slightly soluble hydroxides, hydrous oxides or oxides can form electrochemically on the electrode surface during the anodic process and be reduced during the cathodic one. Such alternative concept admits the reversibility of anodic and cathodic processes and changes essentially the understanding and interpretation of the phenomena of anodic oxidation of noble metals.     

Investigation of charge-transfer complexes formation between photoluminescent graphene oxide and organic molecules

Charge-transfer complexes have formed between photoluminescent graphene oxide and organic electron-donating molecules. With the increase of electron-donating power of molecules, the colour of solutions containing complexes became darker; UV absorption was red-shifted to longer wavelength and a new charge-transfer complex emission was also enhanced.