Property surface

The surface of native polymeric (e.g., PDMS) chips is hydrophobic. This surface property has caused problems in filling aqueous solutions in the PDMS channels, and in support solution transport based on electroosmostic flow (EOF). 

The PDMS channels can also be primed with C02 gas which is readily dissolved in aqueous solution, and so no bubbles will be formed after solution filling [160], It was reported that gas bubbles in PDMS channels, if formed, can be removed by blocking the output port, and pressurizing the channel via the input port. This method is successful because of high gas permeability of PDMS [249], 

The PDMS channel can be rendered hydrophilic by oxidation (02 plasma treatment) [250,1025,1033]. However, the hydrophilic surface in air has a short useful lifetime ( 15 min) because the surface easily becomes hydrophobic again. 

Storing the treated PDMS under water maintained the channel hydrophilicity for 1 week [1025]. This loss of hydrophilic PDMS surface was possibly caused by the migration of uncross-linked PDMS oligomers to the surface [251]. 

PDMS channels can also be rendered hydrophilic by silanization with APTES (1% v/v) for 45 min [250]. It was found that by derivatizing the oxidized PDMS surface by APTES produced a hydrophilic surface for more than 10 days [171]. PDMS channels can also be rendered hydrophilic by acid treatments  

Surface properties are at the heart of all catalytic applications and are discussed in more specific terms elsewhere in the book, most notably in Chapters 2, 4, 6, and 15. Here, therefore, only the key aspects of the physics and chemistry of carbon surfaces will be highlighted. More extensive analysis is also offered in several recent reviews [24,94,129,154,155], 

Because of the almost ubiquitous presence of very narrow porosity in most catalytically relevant carbon materials, and no doubt because of their complex connectivity, the effective diffusivity in nanopores of particulate carbons is 

PHYSICOCHEMICAL PROPERTIES OE CARBON MATERIALS A BRIEF OVERVIEW 

Chemical Surface Properties While a few other porous solids can match most of the physical surface properties of carbon materials (except the very high surface areas, in excess of 2000 m /g), when it comes to surface chemistry the flexibility offered by carbons is rather unique. This is because of their unique proton-. 

The free surface energy for PE is 10 J (at 20 °C). The critical surface tension for LDPE ranges between 25.5 and 36 mN/m, while for HDPE it varies between 28 and 34.1 mN/m. 

Not only the strength properties, tensile strength and strain to rupture can be determined in the tensile strength test (ISO 1924, 1992), but also the tensile energy absorption, TEA, which is especially important for bag paper. The TEA value represents the nonelastic portion of the deformation energy and thus that portion of dissipated energy which should be high in the case of bag paper. 

Deformations in board and cardboard can also be produced by creasing. Testing the properties of creases requires defined production processes, e.g., DIN 55 437 Part 1. In Parts 2 and 3 of this standard, methods are described for the manual folding of the creases and for the visual evaluation of the folding or the technical evaluation of the creases with a folding-moment tester. 

Sometimes the topography of the paper surface is described using profile measurements laser scanning. The scanning profilometer uses point sensors in conjunction with high precision x- and y-stages to capture profiles and 3D data. The 

Another surface property of paper is the abrasion resistance. The mechanical abrasion resistance of surfaces is determined in the friction wheel process (DIN 53 109-93). In this process, the amount of abrasion which is obtained by abrading the conditioned or wet sample with an abrasion wheel of defined quality under defined conditions is measured. 

Plasma treatment is useful to activate the surface of a certain material. The treatment enhances the adhesion property. Basically, surface activation effects the introduction of chemical functionalities on the polymer surface in order to increase its surface energy. 

The wettability of ABS can be increased by the treatment with an atmospheric plasma torch (64).. This was established by contact angle measurements and other methods. The wettability was increased when the atmospheric plasma treatment was done in a slow manner. The decrease in contact angle with respect to water is explained due to a significant increase in the oxygen content, which is caused by the formation of carboxylic and hydroxyl groups on the polymer surface. 

After natural ageing, again an increase in the water contact angle, was observed. However, the values of the untreated polymer surface were never reached. 

The nature of the charges developed on abrasive surface when introduced into solutions depends upon the solution pH, ionic strength, and the surface 

In general, silica surface has a higher number of hydroxyl groups (4 per nm ) [99] than alumina, ceria, titania, and diamond. As a matter of fact, the number of functional groups on diamond particles is very small without surface treatment. Therefore, silica has an advantage in accommodating polishing 

It is well known that the surface properties, such as roughness, porosity, wettability, chemical composition, and morphology, are critical to the in vivo performance of a biomaterial. Thus, surface characteristics of CPs have been studied using various methods. 

SEM provides nanoscale details, including shape, structure, roughness, and porosity of CP surfaces and can also be used to measure the thickness of CP films. Additionally, with EDX functionahty SEM can be used to identify the elemental composition of a CP surface. Similarly, XPS (x,y spatial resolution 1 pm) and AES (resolution 5 nm) can provide quantitative data on the chemical composition of a material surface. Accordingly, XPS and AES have been widely used to identify the doping level/species of CP films, while MALDI-TOF-MS have been used for qualitative identification of biomolecules incorporated in CP matrices. 

Other techniques, such as atomic force microscopy (AFM), and dynamic contact angle measurement (DCA) have been performed to measure the surface roughness and hydro-philicity of the sample, respectively. 

Secure adhesion of the CP film on a substrate is another important mechanical property for long-term function of a bioimplant device. Pull-off tests (ASTM standard procedure D-4541-95) and other ASTM adhesion and hardness assays may provide valuable information on the adherence of CP films to metal substrates [1,137]. 

Electrochemical stability is an essential requirement for CPs designed for any long-term bioelectric applications. Cychc voltammetry (CV) is used to measure the electrochemical characteristics of a CP sample, including the reduction/oxidation potentials and reversibility. By performing CV over multiple cycles the long-term electrochemical stability of a sample can be assessed. This technique has been shown to be particularly important in the 

Some of the most relevant characteristics for a material intended to be used as a CL are those related to the surface 

Despite the fact that inorganic membranes are, in general, more stable mechanically than organic membranes, available mechanical properties data for commercial inorganic membranes are sketchy and these are not yet standardized for comparing various membranes. It appears that the methods used for obtaining various mechanical strength data are based on those for solid (nonporous) bodies and most of them arc listed as ASTM procedures. 

Tabulated in Table 3.3 are the various mechanical properties taken from product brochures of commercial inorganic membranes. The table is not intended for comparing different membranes as the reported data may not be obtained under similar test conditions. However, it is expected to give at least 

AI2O3 (Alcoa) AI2O3 (NGK) ZtOj (SPEC) Glass (Asahi) Ag (Osmonics) 

The structural elements of commercial inorganic membranes exist in three major geometries disk, tube or tube bundle, and multichannel or honeycomb monolith. The disks are primarily used in laboratories where small-scale separation or purification needs arise and the membrane filtration is often performed in the flow-through mode. The majority of industrial applications require large filtration areas (20 to over 200m ) and, therefore, the tube/tube bundle and the multichannel monolithic forms, particularly the latter, predominate. They are almost exclusively operated in the cross-flow mode. 

Surface area of a powder increases geometrically with decreasing particle size, so that the volume fraction of the outermost layer of ions on the surface increase significantly, which has a significant effect on properties of the powder. With the development of nanotechnology, it is readily to synthesize powders with nanosized particles (1-100 nm). Therefore, characterization of surface properties becomes more and more important. Specifically for ceramics or transparent ceramics, the consolidation of fine ceramic powders with liquid suspensions to produce more uniform green bodies has been shown to play an important role in the fabrication ceramics, especially when special or complex structures are required. Because the quality of microstructure of the consolidated body is determined by the dispersion behavior of the powder and the interaction between the particles in the suspension, which is closely related to the surface properties of the particles, controlling the physical and chemical properties of particles is a critical to ceramics fabrication. 

Furthermore, the surface properties of the powders have direct effect on the densification and microstructural evolution of green bodies during the firing process. This is because the surfaces of the particles will form interfaces and grain boundaries, which are actually the sources and sinks for the diffusion of various species within the materials. Therefore, the structure and composition of the interfaces and grain boundaries will determine the behaviors of densification and 

Electron, ion, and photon emissions from the outermost layers of the particle surface can be used to reveal the qualitative or quantitative information on chemical composition of the surface of ceramic powders. The most widely used techniques include (i) Auger electron spectroscopy (AES), (ii) X-ray photoelectron spectroscopy (XPS), which is also known as electron spectroscopy for chemical analysis (ESCA), and (iii) Secondary ion mass spectrometry (SIMS). 

The principle of X-ray photoelectron spectroscopy (XPS) is a well-known photoelectric effect, in which the sample is irradiated by a source of low-energy X-rays that leads to the emission of electrons from the lower energy atomic orbitals, as shown schematically in Fig. 4.9b. The kinetic energy of the emitted photo-electrons, Ek, is given by  

For quantitative analysis, a principal peak is selected for each element, whose intensity is measured as the peak area excluding the background. The fractional atomic concentration of an element. A, is given by  

The preceding sections have focused on the properties of the bulk oxide. However, computer simulation techniques are also well established tools in the study of the structural and defect chemistry of oxide surfaces, which are often difficult to characterize by experiment alone. 

Using atomistic (static lattice) methods, Sayle et al. first modeled the (110), (310) and (111) surfaces of Ce02. The (110) and (310) surfaces are known as type I surfaces i.e. they are charge neutral with stoichiometric proportions of anions and cations in each plane (parallel to the surface). The potential for each plane is exactly zero due to the cancellation of the effects of the positive and negative charges and therefore there is no dipole moment perpendicular to the surface. The (111) surface of ceria is a type II surface, i.e. the surface terminates with a single anion plane and consists of a neutral three-plane repeat unit. 

Surface energies were calculated by the following expression  

Vyas et investigated an extensive set of ceria surfaces using four different interatomic potential models they find that while there are differences in the absolute surface energies the relative energies do not vary, producing an octahedral-type crystal morphology. 

In addition to atomistic (static lattice) methods, MD techniques have been used by Baudin et to study 20 — 30 A thick Ce02 slabs with 2-D periodicity of the three low index surfaces (111), (Oil) and (001). The simulations were performed within a 

The structure of films has been studied by several methods, such as X-ray diffraction, IR spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, although the simplest and least expensive technique is that of optical diffraction measurements. 

Commonly, roughness can be tailored by using additives. These are mainly based on combinations of inert, inorganic particles of different sizes and the weight ratio of large to small particle sizes. These particles should be well dispersed in the base film to prevent abrasion, which is influenced by the particle shape and the kind of embedding in the polymer matrix. The affinity of these particles to the solid polymer seems to be based on adhesion of the melt to the solids and to cohesive forces in the solid state. This phenomenon, however, has not yet been explored in sufficient detail. 

Scratch resistance depends on the hardness of the added particles. The problem of a lack of this property can be addressed by adding chemically identical particles of different crystal modification and Mohs hardness. The preferred additives are silica, alumina, layered silicates such as kaolin, titania, barium sulfate and calcium carbonate. The latter is only suitable for the DMT process owing to side reaction caused by acidity during the terephthalic acid (TPA) route. 

The outer shape of the grains is conserved during reduction and the porosity of the reduced sample thus has a simple relation to the amount of iron oxide in the unreduced sample. 

For an industrial catalyst the pore volume [113,114] increases during the entire reduction. The pore volume distribution of the reduced catalyst has a maximum at a pore radius of 100-120 A and at a 260-430 A [99,115]. The smaller pores are formed by the reduction of magnetite [99] the larger pores are formed by the reduction of wustite [99]. 

For an industrial catalyst the BET area increases during the entire reduction [114], increases at first and passes through a maximum at 90% reduction [113] or 95% reduction [117, 119]. 

After reduction, chemisorbed hydrogen has been detected by Laser Raman spectroscopy [120]. 

The CO chemisorption area increases slowly at 30-90% reduction and then increases rapidly at 96-100% reduction [113, 117-119, 121]. 

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Flotation. Flotation is a gravity separation process which exploits differences in the surface properties of particles. Gas bubbles are generated in a liquid and become attached to solid particles or immiscible liquid droplets, causing the particles or droplets to rise to the surface. This is used to separate mixtures of solid-solid particles and liquid-liquid mixtures of finely divided immiscible droplets. It is an important technique in mineral processing, where it is used to separate different types of ore. 

When used to separate solid-solid mixtures, the material is ground to a particle size small enough to liberate particles of the chemical species to be recovered. The mixture of solid particles is then dispersed in the flotation medium, which is usually water. Gas bubbles become attached to the solid particles, thereby allowing them to float to the surface of the liquid. The solid partices are collected from the surface by an overflow weir or mechanical scraper. The separation of the solid particles depends on the different species having different surface properties such that one species is preferentially attached to the bubbles. A number of chemicals are added to the flotation medium to meet the various requirements of the flotation process ... 

A solid, by definition, is a portion of matter that is rigid and resists stress. Although the surface of a solid must, in principle, be characterized by surface free energy, it is evident that the usual methods of capillarity are not very useful since they depend on measurements of equilibrium surface properties given by Laplace s equation (Eq. II-7). Since a solid deforms in an elastic manner, its shape will be determined more by its past history than by surface tension forces. 

An important application of foams arises in foam displacement, another means to aid enhanced oil recovery. The effectiveness of various foams in displacing oil from porous media has been studied by Shah and co-workers [237, 238]. The displacement efficiency depends on numerous physicochemical variables such as surfactant chain length and temperature with the surface properties of the foaming solution being an important determinant of performance. 

Surface heterogeneity may merely be a reflection of different types of chemisorption and chemisorption sites, as in the examples of Figs. XVIII-9 and XVIII-10. The presence of various crystal planes, as in powders, leads to heterogeneous adsorption behavior the effect may vary with particle size, as in the case of O2 on Pd [107]. Heterogeneity may be deliberate many catalysts consist of combinations of active surfaces, such as bimetallic alloys. In this last case, the surface properties may be intermediate between those of the pure metals (but one component may be in surface excess as with any solution) or they may be distinctly different. In this last case, one speaks of various effects ensemble, dilution, ligand, and kinetic (see Ref. 108 for details). 

Studies of surfaces and surface properties can be traced to the early 1800s [1]. Processes that involved surfaces and surface chemistry, such as heterogeneous catalysis and Daguerre photography, were first discovered at that time. Since then, there has been a continual interest in catalysis, corrosion and other chemical reactions that involve surfaces. The modem era of surface science began in the late 1950s, when instmmentation that could be used to investigate surface processes on the molecular level started to become available. 

Surfaces are investigated with surface-sensitive teclmiques in order to elucidate fiindamental infonnation. The approach most often used is to employ a variety of techniques to investigate a particular materials system. As each teclmique provides only a limited amount of infonnation, results from many teclmiques must be correlated in order to obtain a comprehensive understanding of surface properties. In section A 1.7.5. methods for the experimental analysis of surfaces in vacuum are outlined. Note that the interactions of various kinds of particles with surfaces are a critical component of these teclmiques. In addition, one of the more mteresting aspects of surface science is to use the tools available, such as electron, ion or laser beams, or even the tip of a scaiming probe instrument, to modify a surface at the atomic scale. The physics of the interactions of particles with surfaces and the kinds of modifications that can be made to surfaces are an integral part of this section. 

Shrimpton N D, Cole M W, Steele W A and Chan M H W 1992 Rare gases on graphite Surface Properties of Layered Structures ed G Benedek, (Dordrecht Kluwer) pp 219-69... 

Surface properties enter tlirough the Yoimg-Laplace equation of state for the surface pressure ... 

Shen Y R 1989 Surface-properties probed by second-harmonic and sum-frequency generation Nature 337 519-25... 

King D A and Woodruff D P (eds) 1988 Surface properties of electronic materials The Chemical Physics of Solid Surfaces and Heterogeneous Cafa/ys/svol 5 (Amsterdam Elsevier)... 

The representation of molecular surfaces, including the display of molecular surface properties, can be regarded as the next level of this hierarchy, but will be addressed in Sections 2,10 and 2,11 in this volume. 

The calculation of autocorrelation vectors of surface properties [25] is similar (Eq. (21), with the distance d XiXj) between two points and Xj on the molecular surface within the interval between d[ and d a certain property p, e.g., the electrostatic potential (ESP) at a point on the molecular surface and the number of distance intervals 1). 

The representation of molecules by molecular surface properties was introduced in Section 2.10. Different properties such as the electrostatic potential, hydrogen bonding potential, or hydrophobicity potential can be mapped to this surface and seiwe for shape analysis [44] or the calculation of surface autocorrelation vectors (refer to Section 8.4.2). 

Methods of analyzing the diversity of the selected subset ensure that an appropriate chemical space is covered. Descriptors such as fingerprints, and 2D, and 3D descriptors, as well as molecular surface properties, which can be... 

SP (Graphical Representation and Analysis of Surface Properties) A Nicholls, Columbia University, New York, USA. 

The surface properties of metals are such that the surface tends to relax inwards bu systems described by two-body interactions tend to relax outwards. 

In discussions of the surface properties of solids having a large specific surface, it is convenient to distinguish between the external and the internal surface. The walls of pores such as those denoted by heavy lines in Fig. 1.8 and 1.11 clearly comprise an internal surface and equally obviously the surface indicated by lightly drawn lines is external in nature. In many cases, however, the distinction is not so clear, for the surfaces of the primary particles themselves suffer from imperfections in the forms of cracks and fissures those that penetrate deeply into the interior will contribute to the internal surface, whereas the superficial cracks and indentations will make up part of the external surface. The line of demarcation between the two kinds of surface necessarily has to be drawn in an arbitrary way, but the external surface may perhaps be taken to include all the prominences and all of those cracks which are wider than they are deep.,The internal surface will... 

Furthermore, it must be remembered that highly disperse materials are, from their very nature, difficult to prepare with exactly reproducible surface properties, in respect of either the extent of the surface or the nature of the surface itself. Consequently, highly precise values of the absolute area of individual samples, even if attainable by some method as yet undeveloped, would be of little more value in practice than the BET specific surface, calculated from carefully measured isotherms. 

Sonochemistry is also proving to have important applications with polymeric materials. Substantial work has been accomplished in the sonochemical initiation of polymerisation and in the modification of polymers after synthesis (3,5). The use of sonolysis to create radicals which function as radical initiators has been well explored. Similarly the use of sonochemicaHy prepared radicals and other reactive species to modify the surface properties of polymers is being developed, particularly by G. Price. Other effects of ultrasound on long chain polymers tend to be mechanical cleavage, which produces relatively uniform size distributions of shorter chain lengths. 

In milk fat, cholesterol is associated with Hpoproteins in the milk fat globule. It is also a component of animal membranes and controls rigidity and permeabihty of the membranes. Cholesterol has interesting surface properties and can occur in Hquid crystalline forms. Plants contain sterols such as P-sitosterol [83-46-5] (4b) or stigmasterol [83-48-7] (4c). Their functions in plant metaboHsm are not yet well understood. Analysis of sterols has proven useful for detection of adulteration of edible fats (9). 

Surface Protection. The surface properties of fluorosihcones have been studied over a number of years. The CF group has the lowest known intermolecular force of polymer substituents. A study (6) of liquid and solid forms of fluorosihcones has included a comparison to fluorocarbon polymers. The low surface tensions for poly(3,3,3-trifluoropropyl)methylsiloxane and poly(3,3,4,4,5,5,6,6,6-nonafluorohexyl)methylsiloxane both resemble some of the lowest tensions for fluorocarbon polymers, eg, polytetrafluoroethylene. 

Volatilization. The susceptibility of a herbicide to loss through volatilization has received much attention, due in part to the realization that herbicides in the vapor phase may be transported large distances from the point of application. Volatilization losses can be as high as 80—90% of the total applied herbicide within several days of application. The processes that control the amount of herbicide volatilized are the evaporation of the herbicide from the solution or soHd phase into the air, and dispersal and dilution of the resulting vapor into the atmosphere (250). These processes are influenced by many factors including herbicide application rate, wind velocity, temperature, soil moisture content, and the compound s sorption to soil organic and mineral surfaces. Properties of the herbicide that influence volatility include vapor pressure, water solubility, and chemical stmcture (251). 

Aesthetic properties are of greatest concern in decorative laminates. These include gloss, appearance, cleanabiUty, wear resistance, stain resistance, and other surface properties. Physical properties are of most importance for industrial laminates. These include strength, electrical and thermal properties, expansion coefficient, and punchabiUty. The definitions of the laminate grades in these standards foUow. 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

Turbidity. Turbidity in water is removed by ozonation (0.5—2 ppm) through a combination of chemical oxidation and charge neutralization. GoUoidal particles that cause turbidity are maintained in suspension by negatively charged particles which are neutralized by ozone. Ozone further alters the surface properties of coUoidal materials by oxidizing the organic materials that occur on the surface of the coUoidal spherical particles. 

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