Untersuchungen innerer Grenzfl?chen mit elektronenspektroskopischen Methoden

Summary The physical and chemical properties of interfaces such as grain boundaries and phase boundaries are very important for the mechanical properties of materials, for the grain boundary corrosion and grain boundary diffusion processes.The cohesive energy of interfaces can be significantly influenced by the microchemistry. Phosphorus, tin and antimony segregated to the grain boundaries, reduce the fracture toughness and the yield strength of technical steels. The concentrations of these elements causing these effects are in the range of a few ppm.The analytical problem is the characterisation of the microchemistry of grain boundaries and to correlate this information with the material properties. Fractions of atomic monolayers can be identified with a high lateral resolution. However, the interfaces have to be opened by fracturing the samples under UHV-conditions in the spectrometer.     

Effect of composition and drying method on glass transition temperature,water sorption characteristics and surface morphology of newly designed β-lactoglobulin/retinyl palmitate/disaccharides systems

Epoxy-based nanocomposites containing different concentrations (0–3%) of surface-modified graphene nanosheets (GNS) with 3-aminopropyltriethoxysilane were prepared and their thermal and mechanical properties including dynamic mechanical analysis, tensile strength, hardness, and abrasion tests were evaluated in order to have a database for thermo-mechanical properties of epoxy nanocomposites. The main aim of this study was to understand the optimum percentage of GNS which would perform the best reinforcing influence on mechanical and physical performance of an epoxy nanocomposite. The results explain how applying the analysis of variance (ANOVA) method as a useful tool in optimization of GNS concentration in preparation of high-performance epoxy-based nanocomposites.     

A step forward in metal nitride and carbide synthesis: from pure nanopowders to nanocomposites

Transition metal nitrides and carbides (MN/MC) are intriguing materials due to their combination of properties that place them between high-performance ceramics and pure metals. Recent progress in easier synthetic routes toward their production as bulk or nanostructured materials explains the current surge in sustained attention such progress has been receiving. After progressing toward easier syntheses of MN/MC nanosystems as pure phases, coupling MN/MC with a second phase for the production of hybrids and nanocomposites is considered a next important step in the development of these nanosystems. The coupled phase can simply be a different nitride or carbide; it also can be a polymer, a poly(ionic liquid) or a carbon phase, just to give a few examples. The combination of these phases with MN/MC nanoparticles could lead to multifunctional materials. The aim of the present review is to show how far the research concerning the production of MN/MC-based nanocomposites has progressed, especially in terms of controlled composition, morphology and properties. We discuss the most intensely investigated systems and related motivations, as well as partially unexplored yet appealing alternative materials.     

Effect of ZnO nanoparticles on the thermal and mechanical properties of epoxy-based nanocomposite

Effect of ZnO nanoparticles particles on the mechanical properties and the curing behavior of an epoxy nanocomposite were studied. Nanocomposites were prepared using different loadings of pre-dispersed ZnO nanoparticles having an average size of 40 nm. The surface topography and morphology of the nanocomposites were studied using atomic force microscope (AFM). The mechanical properties of nanocomposites were studied using analytical techniques including dynamic mechanical thermal analysis and micro-Vickers hardness. Effects of ZnO nanoparticles on the curing behavior of these nanocomposites were investigated utilizing isothermal and non-isothermal differential scanning calorimeter techniques. In addition, chemical compositions of coatings containing different ZnO nanoparticles contents were studied using a Fourier transform inferred. It was found that, ZnO nanoparticles can effectively influence the mechanical properties of epoxy coating. In addition, lower curing degrees, and therefore crosslinking density of epoxy coating including higher ZnO nanoparticles were obtained. This effect was completely different at low and high loadings of the particles.     

High pressure study on the phonon spectra and thermal properties in hafnium nitride and zirconium nitride

We report ab initio calculations of the thermal properties for transition metal nitrides, hafnium and zirconium nitride at ambient and high pressures. The assessment of thermodynamical properties like lattice specific heat, vibrational energy, internal energy and entropy for two nitrides has been carried out. The basic calculations of ingredient phonon density of states for the determination of thermal properties have been done using density functional perturbation theory including external perturbations like strains and electric fields in periodic systems. The ground state properties such as equilibrium lattice constants and bulk modulus obtained for two nitrides are in good agreement with the available experimental value. The calculated pressure variation of the phonon density of states shows trend similar to the experimental pressure dependent Raman spectra. The lattice specific heat, internal energy, entropy and Helmholtz energy increases with pressure.     

Hybrid cyanate ester resin-based nanocomposites: Increased indentation size effect due to anomalous composition of micron subsurface layer

Hardness of materials increases with decreasing indentation depth from macro-to nano-scales, which is known as the indentation size effect (ISE). This effect has been associated with indenter shape, frictional forces, dislocation models and other features. We show an anomalously high ISE for a 1-μm subsurface layer in the hybrid nanocomposites based on densely cross-linked Cyanate Ester Resins (CER) containing functionalized 3-D POSS or 2-D MMT nanoparticles (NP). This effect disappears after mechanical stripping of the surface layer. Energy dispersive X-ray (EDX) spectral analysis shows that this anomaly was caused by increased content of NP (Si and Al elements), by 2.5 times, in the 1-μm subsurface layer. The hardness of the 1-μm subsurface layer in these brittle nanocomposites is due to its peculiar composition, and must be taken into account when considering mechanical strength and frictional properties.     

Stability of new electrostatic discharge protection and electromagnetic wave shielding effectiveness from poly(vinyl chloride)/graphite/nickel nanoconducting composites

Poly(vinyl Chloride)/graphite nanosheet/nickel (PVC/GN) nancomposites are new alternative candidates for electrostatic charge dissipation and electromagnetic interference shielding applications due to their lightweight, ease processing and tunable conductivities. The structures of the nanocomposites were examined by means of scanning electron microscopy (SEM) and X-ray analysis. The mechanical properties such as hardness, modulus of elasticity and elongation at break as a function of GN content were examined. The applicability of the nanocomposites as electrostatic charge dissipation was tested in terms of displaying the variation of decay voltage with time. In addition, the dielectric properties such as real and imaginary permittivity of composites as functions of frequency were investigated. Finally, the electromagnetic properties were measured in the frequency range from 1 to 12 GHz and compared with theoretical modeling. The highest shielding effectiveness at microwave frequency of these nanocomposites was 47 dB which is realistic for defense applications like radar evasion.     

Tough interconnected polymerized medium and high internal phase emulsions reinforced by silica particles

Emulsion templating using high internal phase emulsions is an effective route to prepare low density and high porosity macroporous polymers known as polymerized high internal phase emulsions (polyHIPEs). Conventional polyHIPEs, synthesized from surfactant stabilized w/o emulsions have low permeabilities and poor mechanical properties. We present interconnected open macroporous low density nanocomposites produced by polymerizing the continuous phase of emulsion templates, which contained styrene, polyethyleneglycoldimethacrylate, and silylated silica particles. Polyethyleneglycoldimethacrylate and the silylated silica particles acted as crosslinker. The functionalized silica particles were incorporated into the polymer, which resulted in a significant improvement of the mechanical properties of the polyHIPEs without affecting the interconnected and permeable pore structures. The polyHIPEs contained up to 60 wt % silylated silica particles. Young's modulus of the reinforced macroporous polymers increased up to 600% compared with nonreinforced macroporous polymers. The mechanical performance was further increased by increasing the foam density of the macroporous nanocomposites from around 200 to 370 g/cm³ by raising the organic phase volume of the emulsion templates from 20 to 40 vol %. The macroporous polymers synthesized from less concentrated emulsions also possessed interconnected open porous although less permeable structures. The polyHIPE nanocomposites have a permeability of about 200 mD, whereas the polyMIPE nanocomposites still have permeabilities of around 50 mD. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1979–1989, 2010     

Influence of interface structure on mass transport in phase boundaries between different ionic materials Experimental studies and formal considerations

Abstract  

Internal and external interfaces in solids exhibit completely different transport properties compared to the bulk. Transport parallel to grain or phase boundaries is usually strongly enhanced. Transport perpendicular to an interface is usually blocked, i.e., transport across an interface is often much slower. Due to the high density of interfaces in modern micro- and nanoscaled devices, a severe influence on the total transport properties can be expected. In contrast to diffusion in metal grain boundaries, transport phenomena in boundaries of ionic materials are still less understood. The specific transport properties along metal grain boundaries are explained by structural factors like packing densities or dislocation densities in the interface region. In most studies dealing with ionic materials, the interfacial transport properties are merely explained by the influence of space charge regions. In this study the influence of the interface structure on the interfacial transport properties of ionic materials is discussed in analogy to metallic materials. A qualitative model based on the density of misfit dislocations and on interfacial strain is introduced for (untilted and untwisted) phase boundaries. For experimental verification, the interfacial ionic conductivity of different multilayer systems consisting of stabilised ZrO₂ and an insulating oxide is investigated as a funtion of structural mismatch. As predicted by the model, the interfacial conductivity increases when the lattice mismatch is increased.     

The effects of nanofillers,stretching and recrystallization on microstructure,phase transformation and dielectric properties in PVDF nanocomposites

Poly(vinylidene fluoride) (PVDF) possesses many special physical properties, including high dielectric properties, which are highly dependent on its unique crystalline/phase structures. PVDF nanocomposites are expected to have more attractive performances for broader applications; however, the PVDF structures in the nanocomposites are affected by the nanofillers, and employing mechanical stretching or heating processes can cause recrystallization. In this study, we investigated the effects of carbon nanofibers (CNFs) on microstructure, phase transformation, and electric/dielectric in response to the mechanical stretching and followed by isothermal recrystallization. Results revealed that the phase behaviors and microstructure changes of the nanocomposites impact various properties including melting temperature, dielectric properties, etc. and therefore could impact their applications.     

Recent Progress in the Synthesis and Property Enhancement of Waterborne Polyurethane Nanocomposites: Promising and Versatile Macromolecules for Advanced Applications

Abstract

Waterborne polyurethanes (WPUs), owing to their environmental friendliness and non-flammability, are considered as a green class of materials for a wide spectrum of applications, like adhesives, coatings, drug delivery, and tissue engineering. However, to strengthen their thermal stability, water resistance, mechanical properties, and introduce new peculiarities to these polymers, the incorporation of different types of (nano) fillers within their molecular state, emerged novel opportunities and challenges in material sciences. This approach provides new vitality to these materials since the strong interactions between WPU matrices and fillers facilitate the formation of desired WPU composites (WPUCs). Therefore, WPUCs have greatly promoted the construction and designing of novel materials, like hyperbranched WPUs and their nanocomposites. Thus, the aim of the present article is to deeply overview the properties and application of WPUCs in the various realm. The review also provides a brief discussion on the design and synthesis of WPUs, WPUCs, hyperbranched WPUs, and their nanocomposites along with the implementation of naturally derived materials for the development of sustainable WPUCs.     

Structure and properties of nanostructured films based on refractory compounds

The results of studies of the structure and physicochemical properties of nanostructured films based on refractory carbides, borides, and nitrides are generalized. The possibility to obtain diamond-level hardness values is considered. The thermal stability of the hardness and the nanostructure of the films is discussed. The phase diagrams of refractory compounds in the nanocrystalline state are considered. The results of high-temperature oxidation of nanocrystal-line and amorphous films are described.     

Elastomer Nanocomposite; Properties

Polymer nanocomposites represent a class of materials that have assumed great importance in recent years and are the focus of extensive research. Unlike plastomer nanocomposites, the elastomer nanocomposites are in the stage of infancy in respect to their applications.

In general, in polymer composites, the matrix and the filler are bonded to each other by weak intermolecular forces and covalent bonding are rarely involved. If the filler could be dispersed in the polymer matrix at the nanometre level and is able to interact with the matrix by chemical bonding, nanocomposites with significant properties improvement are obtained. These improvements can include mechanical properties (module, strength, etc.), thermal resistance, decrease in gas permeability (barrier), flammability, etc.

This paper is a review of the property improvements of different elastomers using nanofillers like silicates, carbon black, metallic powders, cellulose crystals, mixture of nanofillers, etc, with the intention of obtaining elastomer nanocomposites.     

Graphene‐polymer nanocomposites for biomedical applications

Despite the significant efforts in the synthesis of new polymers, the mechanical properties of polymer matrices can be considered modest in most cases, which limits their application in demanding areas. The isolation of graphene and evaluation of its outstanding properties, such as high thermal conductivity, superior mechanical properties, and high electronic transport, have attracted academic and industrial interest, and opened good perspectives for the integration of graphene as a filler in polymer matrices to form advanced multifunctional composites. Graphene‐based nanomaterials have prompted the development of flexible nanocomposites for emerging applications that require superior mechanical, thermal, electrical, optical, and chemical performance. These multifunctional nanocomposites may be tailored to synergistically combine the characteristics of both components if proper structural and interfacial organization is achieved. The investigations carried out in this aim have combined graphene with different polymers, leading to a variety of graphene‐based nanocomposites. The extensive research on graphene and its functionalization, as well as polymer graphene composites, aiming at applications in the biomedical field, are reviewed in this paper. An overview of the polymer matrices adequate for the biomedical area and the production techniques of graphene composites is presented. Finally, the applications of such nanocomposites in the biomedical field, particularly in drug delivery, wound healing, and biosensing, are discussed.     

Recent advances in heterogeneous catalysts for the synthesis of imidazole derivatives

Among the bioactive heterocyclic frameworks, nitrogen containing multisubstituted imidazoles are versatile building blocks of many naturally occurring products. Imidazoles possess wide range of biological properties including anticancer, anti-inflammatory, antimicrobial, and antihypertensive activities with potential applications in other sectors. Multicomponent reactions in combination with heterogeneous catalysts and nanocomposites have contributed significantly to organic synthesis in general and imidazoles, in particular with high functional group tolerance. Owing to their tunable properties, lower operational cost, thermal stability, recyclability, and easily separation from products, heterogeneous catalysts and nanocomposites are integral part of numerous pharmaceutical, agrochemical, and industrial processes. There has been increased focus on the development of green and sustainable catalytic procedures for the building of novel and biologically potent imidazole conjugates. This article emphasizes the recent advances in recyclable catalysts and protocols, and their merits for the synthesis of diverse multisubstituted imidazole conjugates by one-pot reaction approach and the catalyst and reactant interactions.     

Tailor-made polymers through selective modification

Despite being generally regarded as “mass materials” without a high degree of sophistication in public, plastics are revolutionizing our life with new innovations on a day-to-day basis. While stunning developments like self-healing polymers or high-performance nanocomposites are still in a basic phase of their development, recent years have seen “commodity” materials like polyolefins evolving into performance polymers with a variety of technically demanding applications. This has become possible through a selective modification of the material properties on all structural and productional levels: Catalyst and chain structure, copolymerisation and phase morphology, conventional and reactive compounding, processing and crystallinity. A state-of-art review and an outlook on future developments for polyolefins in general, but polypropylene in particular, is given.     

Analysis of Variance (ANOVA) for Optimizing the Nano-SiO2 Content of High Performance Epoxy Nanocomposites

Epoxy based nanocomposite samples containing SiO₂ nanoparticles (0.0–3.0 %w) were prepared for physical and mechanical evaluation. Some thermomechanical and physical properties of samples were investigated using dynamic mechanical analysis (DMA), tensile strength, hardness and abrasion tests. The main aim of experimentation was to realize the optimum amount of nano-SiO₂ which would demonstrate the best improving effect on mechanical and physical properties of nanocomposite samples and finding how significant a factor is for improving in physical and mechanical properties. Analysis of variance (ANOVA) was applied for optimization of SiO₂ content in epoxy based nanocomposites.     

Electroconductive Green Metal-polyaniline Nanocomposites: Synthesis and Application in Sensors

Polyaniline (PANI) is one of the most extensively used conducting polymer due to its fascinating properties including conducting, thermal, optical, magnetic and electrochemical properties, simple synthesis procedure and low cost of monomer. It has attracted major attention in a variety of applications including electrochemical sensors, catalysts, supercapacitors and biosensors. However, its limitations such as insolubility in common solvents, low process-ability and poor mechanical properties have led to the development of new approaches to improve it properties. Metal nanoparticles (MNPs) such as silver, gold, copper and palladium have been combined with PANI to improve on its properties which has led to a new class of materials known as metal/PANI nanocomposites. These hybrid nanocomposites incorporate advantages of both MNPs and polymers which effectively improves the properties of the individual materials. Various synthesis techniques including in situ polymerization, ɤ-radiolysis, electrodeposition, complexation, vacuum deposition and interfacial polymerization have been used in the formation of metal/PANI nanocomposites. These nanocomposites have been used in various sensor and biosensor applications due to their excellent conductivity, ease of synthesis, excellent redox potentials, chemical and thermal stability. This review highlights the various metal/PANI nanocomposites, their various synthesis techniques and their application in sensors and biosensors. The importance of these nanocomposites in sensing and signaling various toxic heavy metals such as mercury, lead and silver and toxic gases such as hydrogen sulphide, ammonia and chloroform has been discussed. In addition the review covers the applications of metal/PANI nanocomposites in biosensor systems for the detection of glucose, DNA, protein, cholesterol, drugs and hydrogen peroxide.     

Microemulsions: Options To Expand the Synthesis of Inorganic Nanoparticles

Microemulsions (MEs) are ideal for obtaining high‐quality inorganic nanoparticles. As thermodynamically stable systems with a nanometer‐sized droplet phase that serves as a nanoreactor, MEs have obvious advantages for the synthesis of nanoparticles. MEs also have disadvantages, such as their complexity as multicomponent systems, the low amount of obtainable nanoparticles, their limited thermal stability, the fact that hydrolyzable or oxidizable compounds are often excluded from synthesis, the partly elaborate separation of nanoparticles, as well as the removal of surface‐adhered surfactants subsequent to synthesis. This Review presents some strategies to further expand the options of ME‐based synthesis of inorganic nanoparticles. This comprises the crystallization of nanoparticles in “high‐temperature MEs”, the synthesis of hollow nanospheres, the use of hydrogen peroxide or liquid ammonia as the polar droplet phase, and the synthesis of base metals and nitrides in MEs.     

Effect of radiation dose on the properties of natural rubber nanocomposite

Effect of radiation dose and carbon nanotubes (CNT) on the mechanical properties of standard Malaysian rubber (SMR) was investigated in this study. SMR nanocomposites containing 1–7 phr CNT were prepared using the solvent casting method and the nanocomposites were radiated at doses of 50–200 kGy. The change in mechanical properties, especially, tensile strength (Ts), elongation at break (Eb), hardness and tensile modulus at 100% elongation (M₁₀₀) were studied as a function of radiation dose. The structure and morphology of reinforced natural rubber was investigated by FESEM, TEM and AFM in order to gain further evidence on the radiation-induced crosslinking. It was found that the Ts, M₁₀₀ and the hardness of the SMR/CNT nanocomposites significantly increased with radiation dose; the elongation at break exhibited an increase up to 100 kGy, and a downward trend thereafter. Results on gel fraction further confirmed the crosslinking of SMR/CNT nanocomposites upon radiation.