Surface Chemistry (surface + chemistry)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Surface Chemistry

  • different surface chemistry


  • Selected Abstracts


    Influence of Surface Chemistry on Dehydrogenation in Carbon Cryogel Ammonia Borane Nanocomposites

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2009
    Saghar Sepehri
    Abstract This paper reports the synthesis and characterization of boron- and nitrogen-modified carbon cryogel (CC) ammonia borane (AB) nanocomposites (BNCC-AB) for hydrogen storage. Resorcinol,formaldehyde (RF) derived CCs were modified by homogeneous dispersion of AB in RF hydrogel prior to pyrolysis. Nanocomposites were fabricated by immersing CC in the AB solution. Nitrogen sorption analysis, X-ray photoelectron spectroscopy, and differential scanning calorimetry at multiple heating rates were used to study the structure and dehydrogenation properties of the nanocomposites. The results demonstrated lower dehydrogenation temperatures and reduced activation energies for AB when confined inside pores of B- and N-modified CCs relative to AB when confined in the unmodified CC with the same pore size.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


    Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Anne M. Ruminski
    Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source]


    The Influence of Surface Chemistry and Pore Size on the Adsorption of Proteins on Nanostructured Carbon Materials

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2010
    Munusami Vijayaraj
    Abstract Carbon films are synthesized by templating of anodic aluminum oxide films. These carbon materials exhibit nanochannels with controlled diameter and length. Selected chemical treatments are done to tailor the surface chemistry. The adsorption capacities of bovine serum albumin and cytochrome c are measured by temperature-programmed desorption with mass spectrometry (TPD-MS) analysis and with conventional biological assays. The first method allows quantification of the proteins that exhibit strong interactions with the surface, while the second one is used to obtain the total adsorption capacity. Moreover, the TPD-MS profiles, which are related to the structural modifications of the proteins during the adsorption, show that strong interactions take place with hydrophobic surfaces. When oxygenated functions are present, the adsorption capacity increases and the nature of the interactions is modified. The ratio of irreversible to reversible adsorption is significantly different for the two proteins, and is slightly related to the surface chemistry. The influence of nanochannel size is studied: below 50 nm, the coverage ratio shows that access to the porosity is limited by diffusion in the channel and by pore plugging, in agreement with the strong interactions of proteins with the carbon surface. [source]


    Graphite Oxides Obtained from Porous Graphite: The Role of Surface Chemistry and Texture in Ammonia Retention at Ambient Conditions

    ADVANCED FUNCTIONAL MATERIALS, Issue 10 2010
    Mykola Seredych
    Abstract Graphite oxides (GO) synthesized using Brodie and Hummers methods are tested for ammonia adsorption at ambient conditions with different contents of water in the system. Surface characterization before and after exposure to ammonia is performed using XRD, FTIR spectroscopy, potentiometric titration, thermal analysis, adsorption of nitrogen, and XPS. Oxidation of the same porous graphite using two methods results in materials with different textural and chemical features. On GO obtained using the Brodie method mainly epoxy and carboxylic groups are present whereas on the GO obtained using the Hummers method chemisorbed oxygen is also found. The contribution of the carboxylic groups in the latter material is greater. It also contains sulfur either in sulfones or as residual sulfuric acid. Ammonia is adsorbed either via reaction with surface groups or dissolution in water. The former is responsible for strong adsorption. The evidence of the catalytic effect of the carbon surface on activation of oxygen leading to surface oxidation is also observed. [source]


    Influence of Dielectric Surface Chemistry on the Microstructure and Carrier Mobility of an n-Type Organic Semiconductor

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
    Parul Dhagat
    Abstract This paper examines the microstructure evolution of 3,4,9,10-perylene-tetracarboxylic bis-benzimidazole (PTCBI) thin films resulting from conditions imposed during film deposition. Modification of the silicon dioxide interface with a hydrophobic monolayer (octadecyltrichlorosilane (OTS-18)) alters the PTCBI growth habit by changing the unit cell contact plane. PTCBI films deposited on oxide surface have an orientation of (011), while films atop OTS-treated oxide surface have a preferred orientation of (001). The quality of the self assembled monolayer does not appear to influence the PTCBI growth preference significantly yet it enhances the carrier mobility, suggesting that charge traps are adequately passivated due to uniform monolayer coverage. High-quality monolayers result in n-type carrier mobility values of 0.05,cm2V,1s,1 Increasing the substrate temperature during PTCBI film deposition correlates with an increase in mobility that is most significant for films deposited on OTS-treated surface. [source]


    Effects of Surface Chemistry on the Nanomechanical Properties of Commercial Float Glass

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010
    Pavan V. Kolluru
    Nanoindentation was used to evaluate the mechanical properties of commercial float glass surfaces that were subjected to various surface cleaning treatments and other short-term corrosion conditions. The changes in the plane strain elastic modulus, where ,s and Es are the Poisson ratio and Young modulus of the specimen, respectively) and hardness after exposure to dilute hydrochloric acid (pH 0.9), reverse osmosis water (pH 7.1), and commercial cleaning solutions (pH 9.5) were found to be 0.5%,9% and 2%,35%, respectively. Similarly, weathering in a humid atmosphere and leaching in hot deionized water also had a distinct effect on the measured properties of the float glass surfaces. Moreover, both the surface cleaning treatments and the short-term corrosion exposures affected the tin side of the float glass differently than the air side. This work suggests that many of the discrepancies in the literature on the effect of tin concentration on the nanomechanical properties of float glass surfaces are likely due to variability in the surface cleaning and exposure history of the samples and calibration glasses that have been used. [source]


    Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: I, Surface Chemistry of the Powder

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2000
    Liwu Wang
    To develop novel dispersants for submicrometer-sized Si3N4 powder, the surface chemistry of a powder has been investigated using thermodesorption, carrier-gas heat extraction, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and zeta potential measurements. This study indicates that the powder surface is composed mainly of silanol groups and exhibits acidic behavior. Furthermore, the interaction affinity of various surface probe molecules with the powder surface has been studied using adsorption isotherms. The detailed description of the surface chemistry can be used as a guide for designing efficient dispersants, as will be presented in part II. [source]


    Surface Chemistry and Cell Biological Tools for the Analysis of Cell Adhesion and Migration

    CHEMBIOCHEM, Issue 6 2010
    Abigail Pulsipher
    Sticking with SAMs: Within the past few years, the surface-chemistry community has actively pursued the development and integration of strategies to control the interface between cells and a solid support. In doing so, tailored substrates that aim to mimic the extracellular matrix and induce cellular behavior have been generated. Recent advances in the design and utility of self-assembled monolayers (SAMs) as dynamic surfaces for the analysis of cell adhesion and migration will be discussed. [source]


    A Method for the Real-Time Observation of Endodermal Cell Behavior on Micropatterned Surfaces,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2009
    David C. Trimbach
    Surface chemistry and geometry have a strong influence on adhesion and proliferation of various cell types, including human embryonic stem cells (ES). Visceral endoderm like cells (END-2) is an important cell line which induces ES cells to differentiate into cardiomyocytes. In this study, we have investigated the effect of surface chemistry and geometry on the END-2 cell adhesion and proliferation on gold surface. [source]


    Interaction of Plasma Deposited HMDSO-Based Coatings with Fibrinogen and Human Blood Plasma: The Correlation between Bulk Plasma, Surface Characteristics and Biomolecule Interaction

    PLASMA PROCESSES AND POLYMERS, Issue 5 2010
    Ram P. Gandhiraman
    Abstract The success of a biomaterial depends on the nature of interaction and the progressive reaction between the biological components and the surface of the biomaterial. In order to control the interaction between the biomaterial and biological component, it is necessary to understand the factors that influence the protein adsorption and cell proliferation. Surface chemistry plays a crucial role in the success of any blood contacting biomaterial. Plasma enhanced chemical vapour deposition (PECVD) is an interesting commonly used technique for tailoring surface characteristics while retaining bulk material properties. Two different films, namely polymer-like and silica-like coatings, with varying surface characteristics have been deposited from hexamethyldisiloxane, by PECVD, on 316L stainless steel. A correlation between the bulk plasma, interfacial adhesion of the coating to 316L steel, surface characteristics and biomolecule interaction is presented in this work. The interfacial adhesion strength analysis demonstrated that silica-like coatings have higher adhesion strength to 316L stainless steel than polymer-like coatings, caused due to the formation of a strong FeOSi and CrOSi bonds. It was observed that the effect of nanoscale surface roughness (close to 6,nm) was less significant, and that the surface chemistry played a significant role in governing the fibrinogen adsorption. Highest fibrinogen adsorption on plain steel was due to the electrostatic interaction of the metal oxide layer with the protein. Hydrophobicity of the polymer-like film resulted in a higher fibrinogen binding than the silica-like films. [source]


    Confinement effects on the morphology of photopatterned porous polymer monoliths for capillary and microchip electrophoresis of proteins

    ELECTROPHORESIS, Issue 14 2008
    Mei He
    Abstract We find that the morphology of porous polymer monoliths photopatterned within capillaries and microchannels is substantially influenced by the dimensions of confinement. Porous polymer monoliths were prepared by UV-initiated free-radical polymerization using either the hydrophilic or hydrophobic monomers 2-hydroxyethyl methacrylate or butyl methacrylate, cross-linker ethylene dimethacrylate and different porogenic solvents to produce bulk pore diameters between 3.2 and 0.4,m. The extent of deformation from the bulk porous structure under confinement strongly depends on the ratio of characteristic length of the confined space to the monolith pore size. The effects are similar in cylindrical capillaries and D-shaped microfluidic channels. Bulk-like porosity is observed for a confinement dimension to pore size ratio >10, and significant deviation is observed for a ratio <5. At the extreme limit of deformation a smooth polymer layer ,300 nm thick is formed on the surface of the capillary or microchannel. Surface tension or wetting also plays a role, with greater wetting enhancing deformation of the bulk structure. The films created by extreme deformation provide a rapid and effective strategy to create robust wall coatings, with the ability to photograft various surface chemistries onto the coating. This approach is demonstrated through cationic films used for electroosmotic flow control and neutral hydrophilic coatings for electrophoresis of proteins. [source]


    Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Anne M. Ruminski
    Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source]


    Patterned Hydrogels for Controlled Platelet Adhesion from Whole Blood and Plasma

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2010
    Tobias Ekblad
    Abstract This work describes the preparation and properties of hydrogel surface chemistries enabling controlled and well-defined cell adhesion. The hydrogels may be prepared directly on plastic substrates, such as polystyrene slides or dishes, using a quick and experimentally simple photopolymerization process, compatible with photolithographic and microfluidic patterning methods. The intended application for these materials is as substrates for diagnostic cell adhesion assays, particularly for the analysis of human platelet function. The non-specific adsorption of fibrinogen, a platelet adhesion promoting protein, is shown to be completely inhibited by the hydrogel, provided that the film thickness is sufficient (>5,nm). This allows the hydrogel to be used as a matrix for presenting selected bioactive ligands without risking interference from non-specifically adsorbed platelet adhesion factors, even in undiluted whole blood and blood plasma. This concept is demonstrated by preparing patterns of proteins on hydrogel surfaces, resulting in highly controlled platelet adhesion. Further insights into the protein immobilization and platelet adhesion processes are provided by studies using imaging surface plasmon resonance. The hydrogel surfaces used in this work appear to provide an ideal platform for cell adhesion studies of platelets, and potentially also for other cell types. [source]


    PEI,PEG,Chitosan-Copolymer-Coated Iron Oxide Nanoparticles for Safe Gene Delivery: Synthesis, Complexation, and Transfection

    ADVANCED FUNCTIONAL MATERIALS, Issue 14 2009
    Forrest M. Kievit
    Abstract Gene therapy offers the potential of mediating disease through modification of specific cellular functions of target cells. However, effective transport of nucleic acids to target cells with minimal side effects remains a challenge despite the use of unique viral and non-viral delivery approaches. Here, a non-viral nanoparticle gene carrier that demonstrates effective gene delivery and transfection both in vitro and in vivo is presented. The nanoparticle system (NP,CP,PEI) is made of a superparamagnetic iron oxide nanoparticle (NP), which enables magnetic resonance imaging, coated with a novel copolymer (CP,PEI) comprised of short chain polyethylenimine (PEI) and poly(ethylene glycol) (PEG) grafted to the natural polysaccharide, chitosan (CP), which allows efficient loading and protection of the nucleic acids. The function of each component material in this nanoparticle system is illustrated by comparative studies of three nanoparticle systems of different surface chemistries, through material property characterization, DNA loading and transfection analyses, and toxicity assessment. Significantly, NP,CP,PEI demonstrates an innocuous toxic profile and a high level of expression of the delivered plasmid DNA in a C6 xenograft mouse model, making it a potential candidate for safe in vivo delivery of DNA for gene therapy. [source]


    Hydrophilic interaction LC of peptides: Columns comparison and clustering

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2010
    Sylvia Van Dorpe
    Abstract A wide variety of hydrophilic interaction chromatography (HILIC) stationary phase surface chemistries are currently available. Although their selectivity can be considerably different, column comparison or clustering using peptides is limited. In this study, ten pharmaceutically relevant model peptides are analyzed on seven different HILIC columns (bare silica, amide, poly-hydroxyethyl aspartamide, diol and zwitterionic) for the evaluation of their performance and classification. The responses examined include single and multiple responses: plate number, asymmetry factor, LOD, geometric mean resolution, resolution product, time corrected resolution product, peak capacity and chromatographic response function. Column classification was performed using hierarchical clustering and principal component analysis. Moreover, the overall performance quality of the HILIC columns was compared using a linear desirability function. Hierarchical clustering and principal component analysis showed consistent clusters. The zwitterionic phase was clustered apart from the other HILIC columns and both poly-aspartamide columns were clustered together. In addition, the two bare silica phases represent two different clusters, and thus different selectivities. Overall, the responses showed the best performance for one of the bare silica columns (Alltima-Alltech), followed by the zwitterionic phase (ZIC)-HILIC. Thus, these columns, belonging to different clusters, were found to be the best performing systems in pharmaceutical peptide analysis for the selected peptide set. [source]


    Quantum Dot-based Energy Transfer: Perspectives and Potential for Applications in Photodynamic Therapy

    PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2006
    Anna C. S. Samia
    ABSTRACT Quantum dots have emerged as an important class of material that offers great promise to a diverse range of applications ranging from energy conversion to biomedicine. Here, we review the potential of using quantum dots and quantum dot conjugates as sensitizers for photodynamic therapy (PDT). The photophysics of singlet oxygen generation in relation to quantum dot-based energy transfer is discussed and the possibility of using quantum dots as photosensitizer in PDT is assessed, including their current limitations to applications in biological systems. The biggest advantage of quantum dots over molecular photosensitizers that comes into perspective is their tunable optical properties and surface chemistries. Recent developments in the preparation and photophysical characterization of quantum dot energy transfer processes are also presented in this review, to provide insights on the future direction of quantum dot-based photosensitization studies from the viewpoint of our ongoing research. [source]


    Influence of filler type and content on properties of styrene-butadiene rubber (SBR) compound reinforced with carbon black or silica

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2004
    Sung-Seen Choi
    Abstract Rubber compounds are filled with reinforcing fillers to improve their physical properties. Carbon black and silica have different surface chemistries to each other. Differences in properties of carbon black- and silica-reinforced styrene-butadiene rubber (SBR) compounds were studied. Variation of properties of carbon black- or silica-filled compounds with the filler content was also investigated. The silica-filled compounds without any coupling agent and dispering agent were prepared to investigate the influence of polar materials-adsorption on the silica surface. Viscosity and crosslink density increased with increase of the filler content. Hardness, modulus, tensile strength, and wear property were improved more and more by increasing the filler content. Viscosity of the silica-filled compound was higher than that of the carbon black-filled one. Cure rate of the silica-filled compound became slower as the filler content increased, while that of the carbon black-filled one became faster. Difference in properties between the carbon black- and silica-filled compounds were explained by the poor silica dispersion and the adsorption of cure accelerator on the silica surface. Copyright 2004 John Wiley & Sons, Ltd. [source]


    The Influence of Doping Levels and Surface Termination on the Electrochemistry of Polycrystalline Diamond

    ELECTROANALYSIS, Issue 6 2004
    Matthew
    Abstract The influence of surface chemistry and boron doping density on the redox chemistry of Fe(CN) at CVD polycrystalline diamond electrodes is considered. It is demonstrated that for this couple both the doping density and the surface chemistry are important in determining the rate of charge transfer at the electrode/electrolyte interface. For hydrogen terminated CVD diamond metallic electrochemical behavior is always observed, even at boron doping densities as low as 71018,cm,3. In contrast, the electrochemical behavior of oxygen terminated CVD diamond varies with doping density, a metallic response being observed at high doping density and semiconductor behavior at low doping density. It is shown that the results attained may be explained by a surface state mediated charge transfer mechanism, thus demonstrating the importance of controlling surface chemistry in electroanalytical applications of diamond. [source]


    Dynamic coating of SU-8 microfluidic chips with phospholipid disks

    ELECTROPHORESIS, Issue 15 2010
    Tiina Sikanen
    Abstract In this work, PEG-stabilized phosphatidylcholine lipid aggregates (disks), mimicking mammalian cell membranes, were introduced as a new biofouling resistant coating for SU-8 polymer microchannels. A rapid and simple method was developed for immobilization of PEGylated phosphatidylcholine disks in microchannels. Microfluidic chips made from SU-8, PDMS, or glass were dynamically coated with the PEGylated disks followed by characterization of their surface chemistry before and after coating. On the basis of the observed changes in EOF and nonspecific protein adsorption, the affinity of the PEGylated disks was shown to be particularly strong toward SU-8. The PEG-lipid coating enabled permanent change in EOF in SU-8 microchannels with an initial value of 4.510,8,m2,V,1,s,1, decreasing to 2.110,8,m2,V,1,s,1 (immediately after modification), and, eventually, to 1.510,8,m2,V,1,s,1 (7 days after modification) for 9,mM sodium borate (pH 10.5) as BGE. As determined by the Wilhelmy plate measurements and microchip-CE analysis of BSA, the PEG-lipid coating also enabled efficient biofouling shield against protein adsorption, similar to that of low amounts of SDS (3.5,mM) or Tween-20 (80,,M) as buffer additives. These results suggest that dynamically attached PEG-lipid aggregates provide stable, biomimicking surface modification that efficiently reduces biofouling on SU-8. [source]


    Antheraea assama Silk Fibroin-Based Functional Scaffold with Enhanced Blood Compatibility for Tissue Engineering Applications,

    ADVANCED ENGINEERING MATERIALS, Issue 5 2010
    Naresh Kasoju
    Abstract The architecture and surface chemistry of a scaffold determine its utility in tissue engineering (TE). Conventional techniques have limitations in fabricating a scaffold with control over both architecture and surface chemistry. To ameliorate this, in this report, we demonstrate the fabrication of an Antheraea assama silk fibroin (AASF)-based functional scaffold. AASF is a non-mulberry variety having superior qualities to mulberry SF and is largely unexplored in the context of TE. First, a 3D scaffold with biomimetic architecture is fabricated. The scaffold is subsequently made blood compatible by modifying the surface chemistry through a simple sulfation reaction. EDX and FTIR analysis demonstrate the successful sulfation of the scaffold. SEM observations reveal that sulfation has no any effect on the scaffold architecture. TGA reveals that it has increased thermal stability. The sulfation reaction significantly improves the overall hydrophilicity of the scaffold, as is evident from the increase in water holding capacity; this possibly enhances the blood compatibility. The enhancement in blood compatibility of the sulfated scaffold is determined from in vitro haemolysis, protein adsorption and platelet adhesion studies. The sulfated scaffold is non-toxic and supports cell adhesion and growth, as revealed by indirect and direct contact-based in vitro cytotoxicity assays. This study reveals that the AASF-based functional scaffold, which has biomimetic architecture and blood-compatible surface chemistry, could be suitable for TE applications. [source]


    A Method for the Real-Time Observation of Endodermal Cell Behavior on Micropatterned Surfaces,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2009
    David C. Trimbach
    Surface chemistry and geometry have a strong influence on adhesion and proliferation of various cell types, including human embryonic stem cells (ES). Visceral endoderm like cells (END-2) is an important cell line which induces ES cells to differentiate into cardiomyocytes. In this study, we have investigated the effect of surface chemistry and geometry on the END-2 cell adhesion and proliferation on gold surface. [source]


    Fatigue as a process of cyclic brittle microfracture

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2005
    R. SUNDER
    ABSTRACT While fatigue crack growth in vacuum may occur by slip alone, environmental fatigue including crack growth in air is strongly influenced by crack-tip surface chemistry that adversely affects ductility. Cumulative diffusion, combined with adsorption and chemisorption in the loading half-cycle may promote instantaneous crack extension by brittle microfracture (BMF). Unlike slip, the BMF component will be sensitive to parameters that affect near-tip stresses, such as load history and constraint. BMF dominates near-threshold environmental fatigue. Being a surface phenomenon, it loses its significance with increasing growth rate, as slip-driven crack extension gains momentum and growth becomes less sensitive to environment. The BMF model provides for the first time, a scientific rationale for the residual stress effect as well as the related connection between stress,strain hysteresis and load-sequence sensitivity of metal fatigue including notch response. Experimental evidence obtained on a variety of materials under different loading conditions in air and vacuum appears to support the proposed model and its implications. [source]


    Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Anne M. Ruminski
    Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source]


    The Influence of Surface Chemistry and Pore Size on the Adsorption of Proteins on Nanostructured Carbon Materials

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2010
    Munusami Vijayaraj
    Abstract Carbon films are synthesized by templating of anodic aluminum oxide films. These carbon materials exhibit nanochannels with controlled diameter and length. Selected chemical treatments are done to tailor the surface chemistry. The adsorption capacities of bovine serum albumin and cytochrome c are measured by temperature-programmed desorption with mass spectrometry (TPD-MS) analysis and with conventional biological assays. The first method allows quantification of the proteins that exhibit strong interactions with the surface, while the second one is used to obtain the total adsorption capacity. Moreover, the TPD-MS profiles, which are related to the structural modifications of the proteins during the adsorption, show that strong interactions take place with hydrophobic surfaces. When oxygenated functions are present, the adsorption capacity increases and the nature of the interactions is modified. The ratio of irreversible to reversible adsorption is significantly different for the two proteins, and is slightly related to the surface chemistry. The influence of nanochannel size is studied: below 50 nm, the coverage ratio shows that access to the porosity is limited by diffusion in the channel and by pore plugging, in agreement with the strong interactions of proteins with the carbon surface. [source]


    Interaction of Zoospores of the Green Alga Ulva with Bioinspired Micro- and Nanostructured Surfaces Prepared by Polyelectrolyte Layer-by-Layer Self-Assembly

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
    Xinyu Cao
    Abstract The interaction of spores of Ulva with bioinspired structured surfaces in the nanometer,micrometer size range is investigated using a series of coatings with systematically varying morphology and chemistry, which allows separation of the contributions of morphology and surface chemistry to settlement (attachment) and adhesion strength. Structured surfaces are prepared by layer-by-layer spray-coating deposition of polyelectrolytes. By changing the pH during application of oppositely charged poly(acrylic acid) and polyethylenimine polyelectrolytes, the surface structures are systematically varied, which allows the influence of morphology on the biological response to be determined. In order to discriminate morphological from chemical effects, surfaces are chemically modified with poly(ethylene glycol) and tridecafluoroctyltriethoxysilane. This chemical modification changes the water contact angles while the influence of the morphology is retained. The lowest level of settlement is observed for structures of the order 2,m. All surfaces are characterized with respect to their wettability, chemical composition, and morphological properties by contact angle measurement, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. [source]


    Quantification of Grafting Densities Achieved via Modular "Grafting-to" Approaches onto Divinylbenzene Microspheres

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
    Leena Nebhani
    Abstract The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels,Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this "grafting-to" method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, Mn,=,4200,g,mol,1; polydispersity index, PDI,=,1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2,,1020 chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn,=,6000,g,mol,1, PDI,=,1.25; Mn,=,26,000,g,mol,1, PDI,=,1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T,=,60,C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7,chains,nm,2 for Mn,=,6000,g,mol,1 and 4,chains,nm,2 for Mn,=,26,000,g,mol,1, or 2.82,,1019 and 1.38,,1019,chains g,1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry. [source]


    Molecular Mimetic Self-Assembly of Colloidal Particles

    ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
    Zhengwei Mao
    Abstract This article presents an overview of the current progress in molecular mimetic self-assembly of colloidal particles. Firstly, the recent study of colloidal particles at interfaces is highlighted, underlining the mesoscopic mimicry of the surface activity of amphiphilic molecules using colloidal particles. Secondly, various strategies developed thus far to impart colloidal particles with anisotropy in terms of chemical composition, surface chemistry and particle morphology, which are regarded as mesoscopic atoms and molecules, are reviewed. Thirdly, an overview of the current theoretical and experimental results of using the rules of molecular synthesis and self-assembly to direct self-assembly of colloidal particles is presented. Finally, the experimental challenges associated with molecular mimetic self-assembly of colloidal particles are outlined, giving a rather conservative conclusion of the status quo of this new research field with a very optimistic outlook. [source]


    Designer Biomaterials for Nanomedicine

    ADVANCED FUNCTIONAL MATERIALS, Issue 24 2009
    Nishit Doshi
    Abstract Nanotechnology has had tremendous impact on medical science and has resulted in phenomenal progress in the field of drug delivery and diagnostics. A wide spectrum of novel nanomaterials including polymeric particles, liposomes, quantum dots, and iron oxide particles have been developed for applications in therapeutic delivery and diagnostics. This has resulted in control over the rate and period of delivery and targeting of drugs to specific organs in the human body. This feature article focuses on the delivery of drugs using polymeric particles. The size, choice of polymer, surface chemistry, shape, and mechanical properties of the particles are parameters that critically affect particle function. Numerous biomaterials and fabrication techniques have been developed in the last decade that focus on novel design parameters, such as shape and mechanical properties and the interplay of these parameters with the size and surface chemistry of particles. Recent advances with particular focus on the importance of particle shape are highlighted, and the challenges that are yet to be fulfilled are underscored. [source]


    Tailoring Macromolecular Expression at Polymersome Surfaces

    ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
    Adam Blanazs
    Abstract A series of amphiphilic ABC triblock copolymers are synthesized by atom transfer radical polymerization, wherein the ,A' and ,C' blocks are hydrophilic and the pH-sensitive ,B' block can be switched from hydrophilic in acidic solution to hydrophobic at pH 7. Careful addition of base to the molecularly dissolved copolymer in acidic solution readily induces the self-assembly of such triblock copolymers at around neutral pH to form pH-sensitive polymersomes (a.k.a. vesicles) with asymmetric membranes. By systematic variation of the relative volume fractions of the ,A' and ,C' blocks, the chemical nature of the polymer chains expressed at the interior or exterior corona of the polymersomes can be selected. Treatment of primary human dermal fibroblast cells with these asymmetric polymersomes demonstrates the biological consequences of such spatial segregation, with both polymersome cytotoxicity and endocytosis rates being dictated by the nature of the polymersome surface chemistry. The pH-sensitive nature of the polymersomes readily facilitates their dissociation after endocytosis due to the relatively low endosomal pH, which results in the rapid release of an encapsulated dye. Selective binding of anionic substrates such as DNA within the inner cationic polymersome volume, coupled with a biocompatible exterior, leads to potential gene delivery applications for these pH-sensitive asymmetric nanovectors. [source]


    Porous Polymer Coatings: a Versatile Approach to Superhydrophobic Surfaces

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
    Pavel A. Levkin
    Abstract Here, a facile and inexpensive approach to superhydrophobic polymer coatings is presented. The method involves the in situ polymerization of common monomers in the presence of a porogenic solvent to afford superhydrophobic surfaces with the desired combination of micro- and nanoscale roughness. The method is applicable to a variety of substrates and is not limited to small areas or flat surfaces. The polymerized material can be ground into a superhydrophobic powder, which, once applied to a surface, renders it superhydrophobic. The morphology of the porous polymer structure can be efficiently controlled by composition of the polymerization mixture, while surface chemistry can be adjusted by photografting. Morphology control is used to reduce the globule size of the porous architecture from micro down to nanoscale thereby affording a transparent material. The influence of both surface chemistry as well as the length scale of surface roughness on the superhydrophobicity is discussed. [source]