Related Surface Properties Research Articles

Measurement of relative adhesion and surface properties of polyimide films using a surfce acoustic wave sensor

A surface acoustic wave (SAW) sensor is used to study the relative-humidity response of thin polyimide films on quartz, where interfacial and surface properties are varied. The results show differences in the comparative SAW humidity response for films applied with and without adhesion promoter and with and without a chromium interface layer deposited between the substrate and the polyimide film after temperature and humidity aging. Polyimide films were examined that were both sputter cleaned and non-sputter cleaned. The humidity response is particularly sensitive to the surface treatment of the polyimide film. A theoretical analysis has been done to obtain information on the physical mechanisms responsible for the SAW sensor humidity response. The analysis identifies three primary film properties that can influence this response. These properties are changes in density, elastic constants and stress of the film as a function of humidity. The more dominant of these factors appear to be density and elstic-constant changes.

Electron or Hole Liquids Flowing Through Antiferromagnetic Assemblies: Relevance to High Tc Materials

Abstract The effects of electron or hole liquids flowing through antiferromagnetic assemblies were discussed in early work by de Gennes. After a brief survey of his main conclusions, attention will be focused on the way such mobile carriers influence the magnetic properties of high Tc cuprates. The effective interaction J between localized Cu spins becomes a function of carrier concentration, p say, while the effective ionic magnetic moment becomes also dependent on p. Other recent work in which both itinerant and bound dopants have been studied are related to de Gennes findings. Finally, some comments are made on Fermi surface and transport properties in relation to certain theoretical models.

Physicochemical and structural implications for molecular recognition in immobilized metal affinity chromatography

A precise understanding of the mechanisms that govern selectivity in protein adsorption to metal-chelate complexes is required to provide a rational framework for predicting protein behavior in immobilized metal affinity chromatography (IMAC). This article highlights the contribution of solvent-linked parameters in ligand/ligate interactions in IMAC and, hence, brings new clues to selectivity engineering. This leads to the design of a rapid and convenient protocol for the purification of recombinant Actinoplanes missouriensis d-xylose isomerase (XI) and engineered variants produced in Escherichia coli on copper-loaded Chelating Sepharose Fast Flow, an agarose-based matrix derivatized with iminodiacetic acid (IDA) groups. The elucidation of the molecular mechanism by which XI recognizes and interacts with the immobilized metal-chelate complex, IDA-Cu(II), is further made possible by a combination of X-ray structure analysis, molecular modeling, genetic engineering, and mutant characterization. Substitution of lysine for a selected surface histidine residue at position 41 yields a mutant enzyme with near-wild-type properties. The same mutation, however, is shown to completely abolish XI adsorption onto IDA-Cu(II), and hence directly implicates histidine 41 as the predominant protein ligand to the copper-chelate complex. This study not only provides new insights into protocol design for purifying proteins by IMAC, but also describes structural and modeling approaches to analyzing protein surface properties in relation to molecular recognition events.

Effect of mechanical properties on the adhesive wear of metals

There have been consistent efforts to understand the wear behaviour of materials. Many of the investigations were carried out with the aim of correlating wear behaviour with the basic properties of the material in order to determine the property that most controls the wear process. Since wear is a complex phenomenon, not yet fully understood, and many types of wear exist, such correlations must be specific in giving the particular test conditions. Since two materials are involved in wear, and the effects are confined to regions very close to the interface, the correlations must in some way consider the relative surface properties. Many investigators [1-3] have been successful in relating wear resistance, especially to abrasive type of wear, to the hardness of the materials to show a nearly linear variation. Correlations with other properties have been limited in extent. Theories of wear were proposed a long time ago by Finkin [4], Merchant [5], Feng [6], Bowden and Tabor [7] and Kerridge [8], and have been modified to apply to many wear situations. Often results seem to indicate [9] that wear depends only on the conditions bearing load, sliding speed and relative hardness of the softer surface. Evidence has also been obtained [5, 7] to show that it is more the yield stress of the softer surface than any other property that controls wear. Burwell [2] proposed a model for calculating the wear rate of metals, in which the relative hardness was more important than any other property, although data obtained on the basis of this model were highly scattered. The model of Archard [9] was not applied to the case of pure metals. The most significant correlation seems to be that of Rabinowicz [10], in which wear was shown to be related to the surface energy. It is often believed that the friction at the wear interface is closely related to the wear behaviour. However , wear situations can exist in which the wear rate can vary abruptly with no significant change in the friction coefficient. However , a recent study has [11, 12] shown that the coefficient of friction measured in a pin-on-disc machine for a number of pure metals bears a predictable correlation with several mechanical properties of the metal. However , correlations do not seem to have been made for metals for their wear behaviour under purely adhesive conditions. It has been recognized [13] that nearly all materials tend to form a wear-resistant surface layer under adhesive conditions, to justify the comment that wear resistance is more a function of the properties of the surface layer than that of the bulk. It was therefore thought that correlating the properties of the metal with the adhesive wear behaviour would yield interesting results, and this was attempted. Part of the results obtained are summarized in this letter. Cylindrical wear pins 5 mm in diameter were obtained from rods of the desired metals (Table I). One flat end of the pin was ground with 600-grade emery and then slid on a rotating highly polished steel surface of a hardness 50 H R C machine for a total of 30 min. The bearing load used was 5 N and the relative sliding speed at the wear interface was 1.25 m s -1. Steady-state wear rates were calculated from the weight measurements and expressed as volume worn per unit sliding distance (cm 3 cm-1). The measured wear rates in all of the metals studied for the conditions of the experiment were-of the order of 10-9-10 .8 cm 3 cm -1 and are considered

Surface properties of some styrene/vinyl pyridine diblock co-polymers

Surface and interaction characteristics of styrene-4 vinyl pyridine (S-4VP) diblock copolymers have been investigated by the method of inverse gas chromatography. Both constituents of the diblock were found to be basic, the 4VP moiety being the stronger base. When adsorbed onto a standard chromatographic support (Chromosorb), a mildly acidic surface, the 4VP block is preferentially oriented to the substrate, leaving an air interphase which is enriched in polystyrene (PS). The surface enrichment by PS is furthered by the lower surface energy of the PS block. Thus, when adsorbed on acidic surfaces, the wettability and related surface properties of P(S-4VP) diblocks will resemble those of PS, in keeping with the observed compositional heterogeneities.

A saw Sensor Study of the Relative Adhesion and Surface Properties of Polyimide Films

ABSTRACTA surface acoustic wave (SAW) sensor is used to study the relative humidity response of polyimide films where interfacial and surface properties are varied. The relationship between these responses and the relative adhesion strength of these films is of particular interest since it could have application as a nondestructive, quantitative measure of adhesion strength. The results show clear differences in the SAW humidity response for cured and uncured films. There are also significant differences in the SAW humidity response for films applied with and without adhesion promoter. In addition the humidity response has proven to be particularly sensitive to the surface treatment of the polyimide film. These results suggest applications of the SAW sensor as a cure indicator, an in-situ sensor for the monitoring of film surface properties in process control applications and as an adhesion sensor.

The radiometric determination of total pigment and seston and its potential use in shelf seas

A total of 293 radiometric observations of subsurface reflectance and simultaneous measurements of pigment and seston provide the basis for improved algorithms relating surface properties to spectral reflectance R( λ). Without allowance for the effects of seston, total pigment concentration C (chlorophyll a + phaeopigment) for our entire data set fits an algorithm of the form C = aγ −b; γ = R(440 nm) R(550 nm) with constants a = −0·06 and b = 1·60. The effect of inorganic seston concentration, Σ i , over the range 0 < Σ i < 6 mg l −1, is to modify the exponent b such that it increases significantly according to b = 1·80 + 0·38 Σ i . This result confirms the trend apparent in discrete values of b for case 1 and case 2 waters, but also implies that there may be advantages in a (physically more realistic) continuous representation. Σ i is found to be related to the intensity of reflectance at 550 nm, but with a slope m which is controlled by the concentration of organic seston Σ o through the relation m = 0·094 − 1·046 Σ o . Owing to the highly variable nature of the organic component, Σ o cannot at present be reliably determined from the radiometric data. Hence, the general problem of determining C, Σ i and Σ o from radiometer data in remote sensing and in situ applications cannot generally be solved without additional estimates of Σ o .

Surface properties and clay mineralogy of hydrated halloysitic soil clays. II: Evidence for the presence of halloysite/smectite (H/Sm) mixed-layer clays

AbstractSix clays from volcanic ash soils at different stages of weathering differ in their relative halloysite content with respect to kaolinite and several surface properties, namely CEC, and exchange selectivity for K+. These three parameters are related to each other in that they all decrease with increasing soil weathering stage. XRD data show that the hydrated 1:1 layer-silicates in these clays combine with smectite to form interstratified H/Sm clay minerals. In these mixed-layers, the content and layer charge of smectitic units decrease as the relative halloysite content in the clay decreases. These clays thus depict a weathering sequence that is parallel to the weathering sequence of the soils from which they originate. It is also shown that the smectites in the H/Sm minerals have the distinctive composition and ESR spectrum of Fe-rich 2:1 clay minerals belonging to the beidellite-nontronite series. The information obtained explains why these clays have high CEC and distinct affinities for K+. It is hoped that this study will help to clarify the controversy concerning the CEC and related surface properties attributed to hydrated halloysite.

A chemical and morphological study of phosphorylated chrysotile fibres, using FTIR, EPXMA and AAS

AbstractChanges in the surface composition of different chrysotile and chrysophosphate fibres upon leaching in oxalic acid and bidistilled water measured with Fourier transform infrared spectroscopy (FTIR) and electron probe x‐ray microanalysis (EPXMA) are presented. The results are supplemented with data obtained by atomic absorption spectroscopy (AAS) and colorimetry for the measurement of the leached magnesium, iron, phosphorus and chloride in solution. This assists in the elucidation of the potential consequences of fibre surface properties in relation to the carcinogenic potency and biological activity. This study demonstrates the potential of the FTIR and EPXMA techniques for the characterization of natural and physicochemically modified and depleted fibres.

Steptococcus pneumoniae and Staphylococcus aureus surface properties in relation to their adherence to human buccal epithelial cells

Adherence to host cells by pathogenic bacteria is achieved through both specific and non-specific mechanisms. The former involve bacterial adhesin and corresponding cell receptors (Gibbons and Van Houte, 1980), while the second include electric charges and hydrophobicity of bacterial cell walls. In a previous study (Beck et al., 1988), we showed that these two cell surface characteristics vary during growth of Staphylococcus aureus in a manner which should promote adherence to host cells. The aims of the current study were to assess: (1) whether the same growth-related variations in surface properties were present in another bacterial species, Streptococcus pneumoniae; (2) whether the adherence of the two types of bacteria to epithelial cells was in fact different at different growth times; and (3) whether such differences were consistent with the observed surface properties.

Surface and bulk properties of TiO2 in relation to sensor applications

Abstract Results are reported on measurements of surface conductivities and work functions of TiO2 single crystals and thin films, which are important in relation to the properties of TiO2 gas sensors and catalysts. We studied point defects and related surface and volume properties as well as gas/solid interactions with O2, H2 and CO. Elementary steps of solid/gas interaction mechanisms are deduced from results of the spectroscopic techniques XPS, AES, XAES, LEED, SEM, TDS, EELS and ELS.

Materials surface modification by plasma bombardment under simultaneous erosion and redeposition conditions

The first in-depth investigation of surface modification of materials by continuous, high-flux argon plasma bombardment under simultaneous erosion and redeposition conditions have been carried out for copper and 304 stainless steel using the PISCES facility. The plasma bombardment conditions are: incident ion flux range from 10 17 to 10 19 ions s −1 cm −2, total ion fluence between 10 19 and 10 22 ions cm −2, electron temperature range from 5 to 15 eV, and plasma density range from 10 11 to 10 13 cm −3. The incident ion energy is 100 eV. The sample temperature is between 300 and 650 K. Under redeposition-dominated conditions, the material erosion rate due to the plasma bombardment is significantly smaller (by a factor up to 10) than expected from the classical ion beam sputtering yield data. It is found that surface morphologies of redeposited materials strongly depend on the plasma bombardment condition. The effect of impurities on surface morphology is elucidated in detail. First-order models are implemented to interpret the reduced erosion rate and the surface morphology evolution. Also, fusion related surface properties of redeposited materials such as hydrogen reemission and plasma driven permeation have been characterized.

Subfractionation of cell populations by partitioning in dextran-poly (ethylene glycol) aqueous phases

Partitioning of cells in dextran-poly(ethylene glycol) aqueous two-phase systems depends on the interaction between the surface properties of the cells and the physical properties of the phases. The latter can be manipulated to a considerable extent by selection of polymer concentrations and ionic composition and concentration. If salts (e.g., phopshate) are used that have an unequal affinity for the two phases, an electrostatic potential difference between the phases results and, at appropriately high polymer concentrations, the partition coefficient of cells is determined predominantly by membrane charge-associated properties. By “balancing” the magnitude of the electrostatic potential difference against that of the interfacial tension (primarily a function of polymer, but also phosphate, concentrations) one can obtain phase systems that give usable partition coefficients for most cell populations (1). In work under way in our laboratory on the effects of different chemical and enzymatic modifications on the relative surface properties of rat red blood cells of different ages, we have now found that certain phase compositions did not resolve such treated cell subpopulations while other phase compositions did. Thus not all charged phase systems in which cell populations as a whole have usable partition coefficients are equally capable of detecting or subfractionating cell subpopulations. It is therefore essential, before drawing conclusions on the nonseparability of cell subpopulations, to test cell separability in charged phase systems of different compositions if the system initially chosen does not afford a subfractionation.

Hydrogen absorption by Th 7Fe 3 and the related magnetic, structural and surface properties

The Pauli paramagnetic Th 7Fe 3 was reported to form the ferromagnetic hydride Th 7Fe 3H 30 with the Curie temperature T c ≈ 350 K. We show that Th 7Fe 3 if hydrogenated violently disproportionates into Th 4H 15 and into a Fe-rich ferromagnetic Th-Fe-compound. When hydrogenated slowly, a ternary hydride Th 7Fe 3H ≈24 of unknown structure is formed. The ternary hydride is not ferromagnetic down to 80 K. XPS analysis reveals that the 2 p3/2 electron states of Fe are chemically shifted from 707.0 eV binding energy in elemental Fe to 706.6 eV in Th 7Fe 3 indicating an electronic charge transfer to the Fe. Oxygen exposure causes surface segregation with the formation of Th oxide and Fe precipitations which accounts for the readiness of hydrogen absorption by Th 7Fe 3.

Measurement of the electrokinetic properties of vaccinia and reovirus by laser-illuminated whole-particle microelectrophoresis

The electrokinetics of vaccinia virus and reovirus type 3 were studied in dilute electrolyte solutions by whole-particle microelectrophoresis with dark-field laser illumination. The electrophoretic mobilities were dependent upon pH and electrolyte composition. The isoelectric point of vaccinia virus in dilute NaCl was 4.8 ± 0.1; that of reovirus was 3.8 ± 0.1. The mobility of reovirus was −2.65 ± 0.30 μm · s −1 · V −1 · cm −1. Treatments known to cause irreversible changes in the structure of vaccinia, such as heating to 90°C or exposure to pH 10, altered the virus's mobility under the reference conditions. The practical range of whole-particle microelectrophoresis thus extends to microorganisms as small as reovirus, allowing their electrokinetic and related surface properties to be studied.

Fiber Surface Properties in Relation to Linear Assemblies During Processing

Samples of smooth and rough staple polyester fibers, serving as models, taken from linear assemblies at various stages of processing on the three important yarn systems were evaluated for surface and geometric properties. It was found that asperity count decreases substantially with successive stages of processing, indicating that processing tends to reduce surface roughness at the microscopic level. Results showed that process ing does not affect the frictional characteristics of either the smooth or rough model-fiber samples. While average staple lengths are appreciably reduced by processing on the three systems, no significant differences in this effect, as between smooth and rough fibers, were observed. In general, while it was found that both samples lost crimp during processing, there was greater crimp retention in the smooth than in the rough fibers.

Fiber Surface Properties in Relation to Linear Assemblies During Processing 1

Two polyester fiber samples, differing only in surface roughness, which served as models, were processed on the cotton and woolen staple yarn systems. As was found in earlier experiments on the worsted system, static and dynamic cohesion tests on slivers and rovings indicated that geometrically smoother fibers (those having fewer asperities on the surface) lead to greater cohesion in fiber assemblies. Similarly, in slivers composed of blends of the polyester models with cotton and with wool fibers, the cohesion was found to increase steadily with an increasing proportion of smooth fibers. A similar effect of surface roughness on cohesion was found in slivers composed of uncrimped fibers. The degree of twist normally used in staple yarns was found to restrict sufficiently the relative movement of fibers to mask the direct effects of fiber surface roughness in the tensile loading of yarns. However, the influence of roughness on the behavior of assemblies during drafting, in the early stages of processing, was reflected in the even ness and average tensile properties of the yarns. Smooth fibers in continuous-filament form were found to lead to higher frictional forces in yarn-to-yarn and yarn-to-metal tests.

Fiber Surface Properties in Relation to Linear Assemblies During Processing1

This paper reports the results of processitig on the worsted system. Two model fiber samples, which differed only in surface roughness, were specially prepared and cut into lengths suitable for processing on the worsted yarn system (also for the cotton and woolen yarn systems). Static and dynamic cohesion tests on sliver and roving samples indicated that geometrically smoother fibers (those having fewer asperities on the surface) lead to greater cohesion in fiber assemblies. Similarly, in blends of smooth and rough fibers in slivers, the cohesion was found to increase consistently with increas ing percentage of smooth fibers. As indicated by performance during opening processes, geometrically smooth fibers were found to be more difficult to separate from one another. The rougher fiber samples appeared to open much more easily and more thoroughly than the smooth sam ples in the same number of operations. In subsequent processes, the greater cohesion of the smooth samples was found to lead to reduced actual drafts under certain processing conditions. It was found that the degree of twist normally used in staple yarns itself sufficiently restricts the relative movement of fibers to mask the direct effects of fiber surface properties under tensile load. However, results indicated that twist masks the direct effects of fiber surface properties in the yarns (at near optimum twist), but the yarns reflect in evenness, average tensile properties, and actual draft—features introduced in earlier processing.

Surface properties in relation to atelectasis and hyaline membrane disease.

Recent observations suggest that a low surface tension may be an important attribute of the lining of the air passages of the lung.1-4The purpose of this paper is to present evidence that the material responsible for such a low surface tension is absent in the lungs of infants under 1,100-1,200 gm. and in those dying with hyaline membrane disease. The role of this deficiency in the pathogenesis of the disease is considered. Surface tension operates so as to minimize the area of the surface. In the lungs, where the internal surface (the alveolar lining) is curved concave to the airway, the tendency of the surface to become smaller promotes collapse. Although the forces not only of surface tension but also of the elastic tissue tend to collapse the lungs, their behavior differs in one important respect. When the lung contains only a small volume of air, the elastic

EFFECT OF FURNACE GASES ON PHYSICAL PROPERTIES OF WET‐PROCESS CAST‐IRON ENAMELS*

AbstractLead‐bearing and leadless cast‐iron enamels, applied directly on the iron, and leadless enamels, applied over a ground coat, were fired in normal, low oxygen‐high nitrogen, high carbon dioxide, and high water‐vapor atmospheres, and the effect upon the surface and physical properties in relation to impact and thermal resistance was determined. The enamels in some cases were applied over graphited castings, fired in the several atmospheres, and tested. The behavior of different types of enamel fired in various atmospheres differs, the leadless enamel applied over ground coat showing the least effect. High water‐vapor content appears generally to be more deleterious than the other atmospheric conditions.