Search

Thermodynamic and surface properties of Ti-Al-Fe liquid ternary alloy have been assessed at temperatures 1873 K, 1973 K, 2073 K and 2173 K. The thermodynamic properties, such as activity have been studied using general solution model (GSM) and excess free energy of mixing has been studied using GSM, Kohler and Toop models. In surface properties, surface concentration has been computed using Butler's equation and surface tension of the liquid alloy has been studied using all the four above mentioned models feeding the database of liquid Ti-Al, Al-Fe and Ti-Fe sub-binary systems. The values of surface tension computed using GSM and Toop model are in well agreement with each other at all concentrations. Moreover, the computed values of excess free energy of mixing and surface tension decrease at elevated temperatures from all corners and at all considered cross-sections indicating the decrease in mixing tendency of the alloy. [ABSTRACT FROM AUTHOR]

Social scientists have developed dozens of different ways to quantify urban segregation with numerical statistics. Behind the scenes, some of these measurements are defined using multivariable functions that model the distribution of various groups in a geographical region. Using Bayes' theorem and kernel density estimation, we describe how to summarize population data in terms of smooth, two-dimensional surfaces. These surfaces give us ways of identifying neighborhood boundaries and visualizing segregation patterns. We also propose two new segregation measures using some familiar tools from third-semester calculus. Applications to United States census data are included. [ABSTRACT FROM AUTHOR]

The objective of this study is to systematically investigate the evolution of silver surface segregation of silver/titanium oxide nanocomposite coatings produced by reactive sputtering process. Different thickness barrier layers were deposited on the surface of Ag-TiOx two-dimensional (2D) and three-dimensional (3D) composite coatings at different deposition rates. In 2D mode, the SEM images and XPS patterns clearly show that the still strong silver segregation occurred even 50 nm thickness barrier coated with very low deposition rate (3 nm/min), while a sharp decrease of silver surface segregation can be achieved when high barrier deposition rate (20 nm/min) was applied. The high angle annular dark field (HAADF) STEM images reveal that the high silver mobility can be effectively suppressed under high barrier deposition rate. Similar phenomenon can be observed in 3D Ag-TiOx composite coatings. Moreover, the comparable study of the metallic titanium barrier layers show that a 30 nm barrier layer is enough to cover all the silver NPs, and silver atoms diffusion onto the surface was stopped under pure Ar atmosphere. The silver surface segregation evolution indicates that silver segregation could be the result of the combined effect of sputtering plasma and activated oxygen environment. [ABSTRACT FROM AUTHOR]

Many modern technologies rely on materials with controlled surface properties. A key property in many of these applications is surface energy; specifically a low surface energy is often desired so as to impart low adhesive behavior to the materials. The fluorine–carbon bond displays low polarizability, and so fluorocarbons show high resistance to interactions with both polar and non-polar molecules. Thus the commodity fluoropolymers within the PFTE family have been used widely in applications where low adhesion and solvent resistance are important. For several decades scientists have included perfluorinated or partly-fluorinated segments into specialty polymers in attempts to achieve low fouling behavior, and modification of virtually every class of macromolecule has been explored. Notably, over the past several decades, advances in polymerization techniques, specifically controlled radical polymerization, have made possible the creation of polymers with highly-specific and unique structures, for example, block and well-defined network copolymers. Accordingly, this review discusses traditional partly-fluorinated materials but primarily focuses on recent progress in the design of partly-fluorinated polymeric materials with low surface energy. The objective of the review is to provide a concise summary of the approaches taken to date, and to demonstrate, though example, areas with high potential for innovation in the future. [ABSTRACT FROM AUTHOR]

Experimental data in the literature are almost limited to determine the thermophysical properties of multicomponent complex alloys, especially due to the inability of laboratories to achieve the desired ideal conditions, due to the difficulty of protection from oxidation at high temperatures and other contamination at high temperatures, due to time and cost in laboratory studies. Due to these reasons, the theoretical data obtained in this subject is of great importance. In this study, a series of geometric and physical models, such as Chou's general solution model (GSM), Muggianu's Model, Kohler's Model, Toop's Model, Hillert's Model, Guggenheim's Model, Butler's Model, Egry's Model and ideal solution model for quasi-binary alloy system for Section A: Ni0.4(1 – x)CuxFe0.6(1 – x). and Section B: (NixCu0.2Fe0.8 – x) are used to calculate the surface tension-composition and surface tension-temperature curves of the Cu-Fe-Ni ternary liquid system are plotted. The data for this process is evaluated by means of an extended Redlich-Kister-Muggianu polynomial fit to the experimental values of the surface tensions of the binary liquid alloy systems. The obtained results for these models are also compared with the available data in the literature and relatively good agreements are observed. In addition, the surface segregation having important key factor in determining surface tension of the liquid alloy Ni-Fe-Cu has also been investigated in this work. [ABSTRACT FROM AUTHOR]

In an effort to detail the thermal variation of the bitumen microstructure, one sample of asphalt cement (CAP 30/45) was analyzed by atomic force microscopy before and after thermal treatment. Phase contrast and topography images showed that sample morphology is highly dependent on the thermal history of the sample. It can be observed that thermal treatment can lead either to asphaltene flocculation or to wax crystallization. In situ measurements indicated that, after thermal cycles, “bees” appear to be immersed in a lamellar structure that resembles a surface crystallization process. Conditions for the crystallization of the waxes as well as the stability of the “bee” are discussed. [ABSTRACT FROM PUBLISHER]

We recently demonstrated that addition of a surface active polymer (SAP) that segregates on the free (air) surface in liquid crystalline (LC) block copolymer films crucially alters the orientation of the mesogens and microphase separation domains. A block copolymer of poly(butyl methacrylate) (PBMA) combined with an azobenzene LC polymer has been blended as SAP in a polystyrene-based LC block copolymer films possessing similar structure. The present work reveals that the polymer design, the blend ratio, and molecular weight of the surface active polymer significantly affect the orientational alternation for the block copolymer film. The orientational alternation effect by the free surface segregation becomes significantly efficient when SAPs with higher molecular weight is employed. [ABSTRACT FROM AUTHOR]

The segregating nature of Cd–Pb liquid alloys has been reported using simple statistical theory of mixing. The energetics of mixing in liquid binary alloys has been analysed through the study of surface properties (surface tension and surface concentration), transport properties (viscosity and chemical diffusion) and various thermodynamic and structural functions. Positive deviation from Raoultian behaviour has been observed in the computed mixing parameters of the alloys. Our results are in good agreement with experimental data and support a weak demixing tendency in Cd–Pb liquid alloys. [ABSTRACT FROM PUBLISHER]

The Gibbs-approach based adsorption isotherm is applied to surface segregation in nanoparticles. A nanoparticle is treated to be as a composite with a core lattice and a surface shell and both core and shell possess their thermodynamic properties. The Gibbs-approach based adsorption isotherm has the ability to analyze simultaneously stresses, concentrations and their coupling behaviors in the surface shell and the core lattice. The thermodynamic analysis shows that the apparent solute concentration could be greatly enhanced in nanoparticles, due to a large surface volume fraction and a considerable increase in the lattice concentration that is, in turn, boosted by the concentration-induced stresses. [ABSTRACT FROM AUTHOR]

Graphene-based nano-objects such as nanotrenches, nanowires, nanobelts and nanoscale superstructures have been grown by surface segregation and precipitation on carbon-doped mono- and polycrystalline nickel substrates in ultrahigh vacuum. The dominant morphologies of the nano-objects were nanowire and nanosheet. Nucleation of graphene sheets occurred at surface defects such as step edges and resulted in the directional growth of nanowires. Surface analysis by scanning tunneling microscopy (STM) has clarified the structure and functionality of the novel nano-objects at atomic resolution. Nanobelts were detected consisting of bilayer graphene sheets with a nanoscale width and a length of several microns. Moiré patterns and one-dimensional reconstruction were observed on multilayer graphite terraces. As a useful functionality, application to repairable high-resolution STM probes is demonstrated. [ABSTRACT FROM AUTHOR]

A smectic polystyrene-poly(perfluorooctylethyl acrylate) block copolymer was synthesized by atom transfer radical polymerization and blended with a thermoplastic elastomer SEBS in different compositions. The mesophase structure and transition temperatures were investigated by DSC and WAXD. Thin films of the block copolymer and the blends exhibited large contact angles with both water and n-hexadecane, which resulted in low solid surface tensions. XPS findings at different photoemission angles confirmed the effective surface segregation of the mesogenic chains of the fluorinated polymer block. [ABSTRACT FROM AUTHOR]

The wetting behavior of water on methacrylate copolymer films was studied on anodically oxidized and micro-roughened aluminium surfaces and also on smooth model surfaces. The copolymerization of tert-butyl methacrylate with a methacrylate containing a fluoroorganic side chain led to a considerable decrease of the surface free energy, but not to a superhydrophobic behavior of polymer-coated, micro-roughened aluminium surfaces. However, copolymers containing both hydrophobic and hydrophilic sequences are able to form superhydrophobic films. X-ray photoelectron spectroscopy showed that an enrichment of the interface between the solid phase and the air by fluorine-containing polymer components was the reason for the strong decrease of the surface free energy. The hydrophilic segments of the copolymers improved the ability to wet the highly polar aluminium surface and to form films of higher density. [ABSTRACT FROM AUTHOR]

Sputtering of Ni5Pd and NiPd5 alloys by 0.5-50 keV Ar ions has been studied by means of binary-collision simulation. Special attention was given to the angular distributions of sputtered atoms at the steady-state conditions and to the relevant concentrations of Ni and Pd surface atoms, SNi and SPd, respectively. The simulation results were compared with the experimental data published recently. The best-fit values of SNi and SPd favor segregation of Pd in Ni5Pd and segregation of Ni in NiPd5. For a Ni5Pd alloy, it is expected that the ratio SNi/SPd will increase with energy, at least up to 10-20 keV. [ABSTRACT FROM AUTHOR]

The angular distribution of atoms sputtered from NixPdy alloys (x, y=1, 5) under 3 and 10 keV Ar+ ion bombardment has been studied experimentally and using computer simulations. A collector technique combined with RBS to analyze the distribution of collected material was used. It was found that the Pd/Ni yield ratio increases with the polar ejection angle θ for all targets excluding NiPd5. This peculiarity of sputtering was explained by a reversion of atomic segregation at high initial concentrations of Pd atoms in the target. [ABSTRACT FROM AUTHOR]

We present two mean-field theories for the surface segregation from polymer mixtures at surfaces with variable interface diffuseness. We are motivated to study this issue since surface segregation can dramatically alter the behavior of polymers at surfaces, e.g., the wetting behavior of films, surface roughness, and phase separation in thin films. In particular, we are motivated by two results in the literature. First, experimentally it has been determined that surface segregation at the air surface is always significantly higher than at hard substrates. Second, Klein and his coworkers have prepared a series of cross-linked polymer films as substrates and found that the segregation from an overlayer polymer blend to these surfaces is directly correlated to the crosslink density. Our theories show that the surface segregation is strongly coupled to interface diffuseness, with the magnitude of the segregation increasing with increasing diffuseness. These results, which are in good agreement with experiments, arises since the blend prefers to place the component with the less favorable polymer-polymer energy at the surface. This effect is magnified at interfaces with increasing diffuseness. Coupled with findings that interface penetrability can give rise to new phenomena, such as phase transition induced surface roughening, we stress that surface diffuseness can play a critical role in polymer surface behavior. [ABSTRACT FROM AUTHOR]

We report on the preparation of amphiphilic diblock copolymers containing a hydrophilic segment, poly(acrylic acid)(PAA), and a polystyrene hydrophobic part. We analysed, by means of contact-angle measurements, how the hydrophilic segments usually bury themselves under the hydrophobic when exposed to air to reduce the surface free energy of the system. In contrast, in contact with water, the hydrophilic blocks have a tendency to segregate to the interface. We first describe the parameters that control the surface reconstruction when the environmental conditions are inversed from dry air to water vapour. Then, annealing time, temperature, composition and size of the diblock copolymers, and size of the matrix that influenced the surface migration process are the main parameters also considered. Finally, the density of the carboxylic functions placed at the surface was determined using the methylene blue method. [ABSTRACT FROM AUTHOR]

A correlative study of the bulk and surface properties of the ternary Ag-Sn-Zn liquid alloys has been undertaken by extending the descriptions of concerned binaries (Ag-Sn, Sn-Zn, and Ag-Zn), obtained from statistical mechanical theory in the frame-work of quassi-lattice approximations. An improved model, in which the selection of binary compositions involves the correlation of one particular component with other components of the ternary system, has been used to compute the free energy of mixing of Ag-Sn-Zn system. The concentration dependence of the surface tension and surface composition has been explained by obtaining expression for the activity coefficients and extending the surface description of binary systems. It is worth mentioning that same set of interaction energies as those used for the bulk and surface calculations of the concerned binaries has been used to investigate the concentration dependence of free energy of mixing, surface tension (σ) and surface composition of the ternary system. The theoretical investigation of binary systems suggest the presence of short range order in Ag-Sn and Ag-Zn systems leading to the formation of intermetallic compounds (Ag3Sn in Ag-Sn and AgZn in Ag-Zn) in the melt. Sn-Zn system is characterized by the existence of diatomic tin in the melt. The concentration dependence of the free energy of mixing of Ag-Sn-Zn system for three cross section (Ag : Sn = 1 : 1, 1 : 3 and 3 : 1) has been clearly explained by our theoretical model. There is slight decrease in σ for Ag : Sn = 1 : 1 up to xZn ≈ 0.4 whereas sharp decrease up to 50% Zn is observed in case of Ag : Sn = 3 : 1. The σ for Ag : Sn = 1 : 3 remains almost constant up to xZn ≈ 0.25. The surfaces of Ag-Sn-Zn system for all three cross section (Ag : Sn = 1 : 1, 1 : 3 and 3 : 1) are quite enriched with Sn-atoms. The degree of segregation is lowest in Ag : Sn = 3 : 1. [ABSTRACT FROM AUTHOR]

The peculiarities of the phase state and phase separation in filled polymer blends are considered on the basis of experimental data. It was established that the phase behavior of the filled blends is determined by the formation at the interface with solid of the surface layers of both components. The composition of these layers differs from that in bulk due to surface segregation and adsorption in the filled melt. In the surface layers the thermodynamic parameters of the interaction between two polymers are changed. The factors leading to the change in the position and shape of the phase diagrams of filled blends are discussed. It is shown that dynamics of the phase separation in filled blends is determined by the loss of the molecular mobility of the chains of both components in the surface layers. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics (MD) simulations are used to investigate the effect of the nanocluster size on surface segregation phenomena of Pt alloys containing 10, 30, 50, 70 and 90% Pd. Atomic distribution is examined in graphite-supported nanoclusters with approximate diameters of 2 and 4 nm, using a simulated annealing procedure with temperatures varying from 1200 down to 353 K. Following this annealing route, it is found that at concentrations of Pd below a certain threshold, Pt segregates to the surface, whereas Pd segregates to the surface when the overall concentration of Pd is above that threshold. Moreover, the threshold concentration depends on the size, being approximately 50% for the 2 nm nanocluster and in the order of 60% for the 4 nm nanocluster. It is also found that the percent of the surface enriched either in Pt or Pd at a given overall concentration, as well as the nature of the exposed crystallographic faces, depend significantly on the cluster size. Our studies suggest that surface segregation behavior in Pt–Pd supported nanoclusters is influenced by: differences in surface energies, interaction of the clusters with the substrate, and probably most importantly by the fabrication protocol. The implications of these issues on catalytic processes are discussed. [ABSTRACT FROM AUTHOR]

Migration and surface segregation of linear aliphatic carboxylic acids in styrene-butadiene rubber matrix have been studied together with an effect of the top layer formed on friction of styrene-butadiene rubber (SBR) vulcanisates. The relationship between migration rate of carboxylic acids and bloom thickness as well as its topography and morphology is discussed. The influence of bloom geometry and micromechanical properties of the elastomer on its tribological properties is presented. [ABSTRACT FROM AUTHOR]

The surface science of polymer materials is a dynamic field, largely because of application in such areas as composite materials, wetting, coatings, adhesion, friction, and biocompatibility. In this review, we have focused on the study of surface segregation in poly(dimethylsiloxane) (PDMS) containing block copolymers using X-ray photoelectron spectroscopy (XPS). accomplished in our laboratory for this recent decade. We will give insight on XPS which is an effective quantitative tool to probe an air-polymer interface of a few tens of nanometers thick for Investigating surface segregation in common multiphase polymer systems as well as in PDMS containing block copolymers. [ABSTRACT FROM AUTHOR]

An overview of features of the structures of the liquid-vapor interfaces of metals and alloys is presented. The organizing theme of the overview is the role played by the inhomogeneous electron density distribution in the liquid-vapor interface, and how that distribution leads to atomic distributions that differ from those in the liquid-vapor interfaces of dielectric substances. The influence of the structure of the liquid-vapor interface on its electrical and optical properties is also briefly discussed. [ABSTRACT FROM AUTHOR]

A thermodynamic approach to adhesion of polymer blends to solid is proposed. The different cases of compatible and incompatible blends are considered. The difference has been achieved between adhesion of polymer blends obtained by mixing two polymers in the region of two-phase melt and polymer alloys that initially by mixing are in the region of one-phase state and then, by changing temperature, transition into two-phase region. The mechanism of adhesion joint formation is different for polymer blends and polymer alloys, possibly related to phase transformation by cooling the melt in presence of a solid. The effects depend on the nature of the critical solution temperature. The conditions of the complete wetting the surface by one mixture component (or phase) and incomplete wetting by both components are established. General conclusions have been drawn as to the distinction between adhesion of polymer blends and alloys and adhesion of individual polymers to the surface. For polymer blends and alloys with complete wetting of the surface by one component, the interphase is formed by two layers: a first layer in direct contact with the solid surface (wetting layer) and a second layer between wetting layer and blend matrix. If adhesion between wetting layer and a matrix is lower than adhesion between wetting layer and solid, the failure of adhesion joints will take place in the zone of the contact between two blend components. After the phase inversion, there occurs a transition of the failure zone to the interface with solid. The transition from adhesion failure between the blend components to adhesion between the blend matrix and solid is a specific feature of adhesion of two-phase blends or alloys. [ABSTRACT FROM AUTHOR]