Home About us Contact
|
Home About us Contact | ||
|
|
||
Surface Energy (surface + energy)
Kinds of Surface Energy Terms modified by Surface Energy Selected AbstractsAtomistic Simulation of the Surface Energy of Spinel MgAl2O4JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Chang Ming Fang Atomistic simulations with atomic potentials including anion polarizibility have been performed for the low-index surfaces of spinel MgAl2O4 with various terminations. The calculations show that for the most stable surface the surface energy is 2.27 J/m2 for the {100}, about 2.85 J/m2 for the {110}, and 3.07 J/m2 for the {111} orientation. The ratio between the experimental values to the calculated relaxed surface energies is about 1.5. Strong surface relaxation was found for the {110} and {111} orientation but only moderate surface relaxation for the {100} surface. [source] A Novel ABC Triblock Copolymer with Very Low Surface Energy: Poly(dimethylsiloxane)- block -Poly(methyl methacrylate)- block -Poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate)MACROMOLECULAR REACTION ENGINEERING, Issue 5 2008Zhenghong Luo Abstract Poly(dimethylsiloxane)- block -poly(methyl methacrylate)- block -poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate) was successfully synthesized via ATRP. The chemical composition and structure of the copolymer was characterized by NMR and FT-IR spectroscopy and molecular weight measurement. Gel permeation chromatography was used to study the molecular weight distribution of the triblock copolymer. The surface properties of the resulting copolymer were investigated. The effects of fluorine content and bulk structure on surface energy were investigated by static water contact angle measurements. Surface composition was studied by XPS. [source] Retardation of setting of plaster of Paris by organic acids: Understanding the mechanism through molecular modelingJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2004Jörg-Rüdiger Hill Abstract To develop an understanding of the action of specific formulations, the growth of gypsum crystals under the influence of retardation agents (tartaric and citric acid) has been studied using molecular modeling. Surface energies of gypsum and plaster crystal faces were calculated using established protocols. The crystal morphology predicted for gypsum crystals in the absence of retardation agents is in excellent agreement with experiment. The simulations show that only in an alkaline environment is the crystal morphology of gypsum changed by retardation agents. The simulations provide a detailed description of retardation, for example, the specific mechanisms by which tartaric and citric acid retard setting of gypsum and how they differ. At high pH meso, D(,), and L(+) tartaric acid inhibit both the growth of gypsum and the dissolution of plaster while at low pH tartaric acid and citric acid will principally inhibit the growth of gypsum. The simulations provide a molecular rationalization for a range of experimental observations and a basis for the selection of alternate retardation agents. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1438,1448, 2004 [source] Hydrophobic surface properties of fluoropolyetherimide blends for pervaporation membranesPOLYMER INTERNATIONAL, Issue 12 2003M Larhrafi Abstract The well-known polyetherimide (ULTEM 1000) is obtained by step-reaction of bisphenol. A diphthalic anhydride (BAPA) with m-phenylene diamine and newly related fluorinated poly etherimides synthesized from BAPA and 2,3-bis(2,2,3,3,4,4,5,5,5-nonafluoropentyl)butan-1,4 diamine (NFD) led to compatible blends over the entire range of composition. Miscible one-phase blends have been suggested by a good correlation of Tgversus NFD monomer unit weight fraction (w) (Fox and Couchman equations) and a regular morphology by scanning electron microscopy. Surface energy of blend films fell from 45.3 to 27.4 mJ m,2 for w , 0.1 corresponding to a NFD molar fraction y , 0.06. Cast-evaporated films from fluorinated copolyetherimides and blends with y < 0.15 were ductile and gave conveniently hydrophobic non-porous membranes that withstood the experimental conditions of pervaporation tests. Copyright © 2003 Society of Chemical Industry [source] Characterisation of Fuel Cell Membranes as a Function of Drying by Means of Contact Angle MeasurementsFUEL CELLS, Issue 3 2004H.-P. Brack Abstract In another paper in this volume, it is demonstrated that the electrochemical interface in MEAs, and thus the polarization performance of the resulting fuel cells, can be improved by optimising the hot-pressing procedure in the MEA preparation. In particular, the extent of drying of the membrane during MEA preparation was shown to be critical. In the present investigation, the effect of the drying process, and thus water content, on the hydrophilicity, wetting, and surface energies of some fuel cell membranes is examined. Wetting and surface energies are well known to influence the bonding behaviour of materials. Conclusions about how membrane drying and changes in water content influence membrane bonding and the relative importance of these surface effects are drawn. [source] Origins and Applications of London Dispersion Forces and Hamaker Constants in CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000Roger H. French The London dispersion forces, along with the Debye and Keesom forces, constitute the long-range van der Waals forces. London's and Hamaker's work on the point-to-point dispersion interaction and Lifshitz's development of the continuum theory of dispersion are the foundations of our understanding of dispersion forces. Dispersion forces are present for all materials and are intrinsically related to the optical properties and the underlying interband electronic structures of materials. The force law scaling constant of the dispersion force, known as the Hamaker constant, can be determined from spectral or parametric optical properties of materials, combined with knowledge of the configuration of the materials. With recent access to new experimental and ab initio tools for determination of optical properties of materials, dispersion force research has new opportunities for detailed studies. Opportunities include development of improved index approximations and parametric representations of the optical properties for estimation of Hamaker constants. Expanded databases of London dispersion spectra of materials will permit accurate estimation of both nonretarded and retarded dispersion forces in complex configurations. Development of solutions for generalized multilayer configurations of materials are needed for the treatment of more-complex problems, such as graded interfaces. Dispersion forces can play a critical role in materials applications. Typically, they are a component with other forces in a force balance, and it is this balance that dictates the resulting behavior. The ubiquitous nature of the London dispersion forces makes them a factor in a wide spectrum of problems; they have been in evidence since the pioneering work of Young and Laplace on wetting, contact angles, and surface energies. Additional applications include the interparticle forces that can be measured by direct techniques, such as atomic force microscopy. London dispersion forces are important in both adhesion and in sintering, where the detailed shape at the crack tip and at the sintering neck can be controlled by the dispersion forces. Dispersion forces have an important role in the properties of numerous ceramics that contain intergranular films, and here the opportunity exists for the development of an integrated understanding of intergranular films that encompasses dispersion forces, segregation, multilayer adsorption, and structure. The intrinsic length scale at which there is a transition from the continuum perspective (dispersion forces) to the atomistic perspective (encompassing interatomic bonds) is critical in many materials problems, and the relationship of dispersion forces and intergranular films may represent an important opportunity to probe this topic. The London dispersion force is retarded at large separations, where the transit time of the electromagnetic interaction must be considered explicitly. Novel phenomena, such as equilibrium surficial films and bimodal wetting/dewetting, can result in materials systems when the characteristic wavelengths of the interatomic bonds and the physical interlayer thicknesses lead to a change in the sign of the dispersion force. Use of these novel phenomena in future materials applications provides interesting opportunities in materials design. [source] Atomistic Simulation of the Surface Energy of Spinel MgAl2O4JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Chang Ming Fang Atomistic simulations with atomic potentials including anion polarizibility have been performed for the low-index surfaces of spinel MgAl2O4 with various terminations. The calculations show that for the most stable surface the surface energy is 2.27 J/m2 for the {100}, about 2.85 J/m2 for the {110}, and 3.07 J/m2 for the {111} orientation. The ratio between the experimental values to the calculated relaxed surface energies is about 1.5. Strong surface relaxation was found for the {110} and {111} orientation but only moderate surface relaxation for the {100} surface. [source] Investigation of the mechanism of lubrication in starch,oil composite dry film lubricants,LUBRICATION SCIENCE, Issue 1 2007G. Biresaw Abstract The boundary coefficient of friction (COF) of starch,oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch-to-oil ratio. Based on the results, a mechanism of starch,oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (,Gads) of the polar oils onto the starch surface. The analysis gave ,Gads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non-polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane,starch than that for the polar oil,starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements. Published in 2006 by John Wiley & Sons, Ltd. [source] Implementation of the GaN lateral polarity junction in a MESFET utilizing polar doping selectivityPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Ramón Collazo Abstract The difference in surface energies between the Ga-polar orientation and the N-polar orientation of GaN translates into a completely different behavior for the incorporation of intentional and unintentional impurities. Oxygen is found to be an impurity with higher concentration in the N-polar films than in Ga-polar films and is the cause of n-type conductivity observed in N-polar films. Utilizing this doping selectivity we fabricated a depletion-mode metal-semiconductor field effect transistor (MESFET) with n-type N-polar domains as source and drain and a Ga-polar channel on polarity-patterned wafers. The difference in the electronic properties of the different domains, i.e., as-grown N-polar domains are n-type conductive and Ga-polar domains are insulating, allows for laterally selective doped areas that can be realized for improving contact resistance to the n-type conduction channel. Basically, the N-polar domains acted as the ohmic contacts to the channel localized in a Ga-polar domain. A MESFET with a Schottky gate was fabricated as an example of implementation of this novel structure showing a lowering in the specific contact resistivity. [source] Structural stability of clean GaAs nanowires grown along the [111] directionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Rita Magri Abstract Using a first-principles approach we have calculated the formation energies of small diameter GaAs nanowires (NWs) with both zinc-blende and wurtzite structure grown along the [111] direction. The section of the wires is hexagonal and the side facets are oriented either {11-20} and {10-10} in the case of the wurtzite structure, and {110} and {112} for the zinc-blende structure. The formation energy of the nanowires as a function of their radius is then interpreted in terms of a model in which the energy contributions from the bulks, the flat surfaces and the ridges are taken explicitly into account. We find that the nanowire stability is mainly explained by the competition between the bulk energy, favoring the zincblende structure and the surface energies favoring the wurtzite structure. We find also that the directly calculated formation energies of some small diameter wurtzite NWs can be reproduced by our model taking into account only the bulk and flat surface contributions. That is, the ridges do not contribute substantially to the nanowire formation energy. Inspection of the ridge structure and band structure reveals that this good agreement occurs when the NWs are semiconducting and the ridges do not add more dangling bonds to the surface with respect to those provided by the sidewalls. Within our model we find the critical diameter for the wurtzite-zinc-blende transition at 6.3 nm. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermodynamic characterization of hybrid polymer blend systemsPOLYMER ENGINEERING & SCIENCE, Issue 6 2009Amos Ophir A thermodynamic model was used to predict the morphology of hybrid multicomponent polymer blend systems. Two systems were studied, both including two noncompatible polymers, a third compatibilizer polymer and layered, organo-treated clays. The polar and nonpolar contributions of the surface energies of the components of the systems were calculated using measurements of the contact angles. The morphology of the multicomponent systems and the relative position of the organo-clays within them, were predicted by calculating the interaction energies between the different components of the system and evaluating these values according to the Vaia and Giannelis thermodynamic model for polymer melt intercalation in organically modified layered silicates. The experimental results show good correlation with the prediction that the organo-clays will have higher affinity to the compatibilizer polymer component situated at the interface between the two noncompatible blend components. In addition, the presence of the organo-clays in this interface was found to have a significant additional compatibilizing effect between the two polymer phases. The results presented in this work support the idea that hybrid formation via polymer melt intercalation depends mostly on energetic factors that can be determined from surface energies of polymers and organo-modified layered silicates, also in the case of multiphase polymer system. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Effect of phosphonate additive on crystallization of gypsum in phosphoric and sulfuric acid mediumCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2002H. El-Shall Abstract Understanding the mechanisms of growth and inhibition during crystallization of calcium sulfate is of primary importance for many industrial applications. For instance, inhibition of the crystallization process may be required to prevent scale formation in pipes, boilers, heat exchangers, reactors, reverse osmosis membrane surfaces, cooling water systems, secondary oil recovery utilizing water flooding techniques and desalination evaporators, etc. On the other hand, control growth and morphology of gypsum crystals is desired in achieving higher filtration rate and higher productivity of phosphoric acid from phosphate rocks. In this regard, this basic study is carried out to understand effect of Aminotris (methylenephosphonic acid (ATMP) on calcium sulfate dihydrate (gypsum) crystallization. The time elapsed between the achievement of supersaturation and the appearance of a solid phase (termed as induction time) is measured under different supersaturation ratios ranging from 1.018 to 1.979. The data are used to calculate the surface energy, critical nucleus size, and crystal growth rates of gypsum under different conditions. The results show that, the induction time decreases exponentially with increasing the supersaturation ratio. In addition, the surface energy decreases with ATMP compared to the baseline (without ATMP). Interestingly, with addition of the ATMP, the crystals mean and median diameters are found to decrease. The inhibition efficiency ranges from 16% to 59% depending on supersaturation ratio. [source] Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room TemperatureADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Fredrik Östlund Abstract Robust nanostructures for future devices will depend increasingly on their reliability. While great strides have been achieved for precisely evaluating electronic, magnetic, photonic, elasticity and strength properties, the same levels for fracture resistance have been lacking. Additionally, one of the self-limiting features of materials by computational design is the knowledge that the atomistic potential is an appropriate one. A key property in establishing both of these goals is an experimentally-determined effective surface energy or the work per unit fracture area. The difficulty with this property, which depends on extended defects such as dislocations, is measuring it accurately at the sub-micrometer scale. In this Full Paper the discovery of an interesting size effect in compression tests on silicon pillars with sub-micrometer diameters is presented: in uniaxial compression tests, pillars having a diameter exceeding a critical value develop cracks, whereas smaller pillars show ductility comparable to that of metals. The critical diameter is between 310 and 400,nm. To explain this transition a model based on dislocation shielding is proposed. For the first time, a quantitative method for evaluating the fracture toughness of such nanostructures is developed. This leads to the ability to propose plausible mechanisms for dislocation-mediated fracture behavior in such small volumes. [source] The mechanism of fluid infiltration in peridotites at Almklovdalen, western NorwayGEOFLUIDS (ELECTRONIC), Issue 3 2002O. Kostenko Abstract A major Alpine-type peridotite located at Almklovdalen in the Western Gneiss Region of Norway was infiltrated by aqueous fluids at several stages during late Caledonian uplift and retrogressive metamorphism. Following peak metamorphic conditions in the garnet,peridotite stability field, the peridotite experienced pervasive fluid infiltration and retrogression in the chlorite,peridotite stability field. Subsequently, the peridotite was infiltrated locally by nonreactive fluids along fracture networks forming pipe-like structures, typically on the order of 10 m wide. Fluid migration away from the fractures into the initially impermeable peridotite matrix was facilitated by pervasive dilation of grain boundaries and the formation of intragranular hydrofractures. Microstructural observations of serpentine occupying the originally fluid-filled inclusion space indicate that the pervasively infiltrating fluid was characterized by a high dihedral angle (, > 60°) and ,curled up' into discontinuous channels and fluid inclusion arrays following the infiltration event. Re-equilibration of the fluid phase topology took place by growth and dissolution processes driven by the excess surface energy represented by the ,forcefully' introduced external fluid. Pervasive fluid introduction into the peridotite reduced local effective stresses, increased the effective grain boundary diffusion rates and caused extensive recrystallization and some grain coarsening of the infiltrated volumes. Grain boundary migration associated with this recrystallization swept off abundant intragranular fluid inclusions in the original chlorite peridotite, leading to a significant colour change of the rock. This colour change defines a relatively sharp front typically located 1,20 cm away from the fractures where the nonreactive fluids originally entered the peridotite. Our observations demonstrate how crustal rocks may be pervasively infiltrated by fluids with high dihedral angles (, > 60°) and emphasize the coupling between hydrofracturing and textural equilibration of the grain boundary networks and the fluid phase topology. [source] The Role of OTS Density on Pentacene and C60 Nucleation, Thin Film Growth, and Transistor PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Ajay Virkar Abstract In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two-dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3,cm2,V,1,s,1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport. [source] Thickness-Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films,ADVANCED FUNCTIONAL MATERIALS, Issue 17 2007H.-L. Cheng Abstract Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (,tilt) of the pentacene molecule from the c- axis toward the a- axis. We propose a growth model that rationalizes the ,tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C,C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries. [source] Siloxane Copolymers for Nanoimprint Lithography,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2007P. Choi Abstract Presented here is the novel use of thermoplastic siloxane copolymers as nanoimprint lithography (NIL) resists for 60,nm features. Two of the most critical steps of NIL are mold release and pattern transfer through dry etching. These require that the NIL resist have low surface energy and excellent dry-etching resistance. Homopolymers traditionally used in NIL, such as polystyrene (PS) or poly(methyl methacrylate) (PMMA), generally cannot satisfy all these requirements as they exhibit polymer fracture and delamination during mold release and have poor etch resistance. A number of siloxane copolymers have been investigated for use as NIL resists, including poly(dimethylsiloxane)- block -polystyrene (PDMS- b -PS), poly(dimethylsiloxane)- graft -poly(methyl acrylate)- co -poly(isobornyl acrylate) (PDMS- g -PMA- co -PIA), and PDMS- g -PMMA. The presence of PDMS imparts the materials with many properties that are favorable for NIL, including low surface energy for easy mold release and high silicon content for chemical-etch resistance,in particular, extremely low etch rates (comparable to PDMS) in oxygen plasma, to which organic polymers are quite susceptible. These properties give improved NIL results. [source] Modification of the Surface Properties of Indium Tin Oxide with Benzylphosphonic Acids: A Joint Experimental and Theoretical StudyADVANCED MATERIALS, Issue 44 2009Peter J. Hotchkiss Benzylphosphonic acids with various fluorine substitutions are designed and synthesized. They are used to modify ITO such that the work function can be tuned over a range of 1.2 eV while keeping the surface energy relatively constant. The experimentally measured work function changes are also compared to and agree well with those estimated from DFT calculations. [source] Semiconductor-Dielectric Blends: A Facile All Solution Route to Flexible All-Organic TransistorsADVANCED MATERIALS, Issue 42 2009Wi Hyoung Lee A one-step process for the production of all-organic, all-solution-processed field-effect transistors (FETs) can be achieved using triethylsilylethynyl anthradithiophene (TES-ADT). TES-ADT has a lower surface energy than poly(methyl methacrylate) (PMMA), which results in a segregation and crystal formation of TES-ADT at the air,film interface after spin-casting and subsequent solvent annealing. The resulting FETs comprise vertically phase-separated semiconducting and dielectric layers and exhibit high performances. [source] Antiadhesion Surface Treatments of Molds for High-Resolution Unconventional Lithography,ADVANCED MATERIALS, Issue 23 2006J. Lee A new strategy to achieve antiadhesion surface coatings is introduced. The approach, which uses molds coated in a thin film of poly(dimethylsiloxane) (PDMS, see figure) to achieve the antiadhesive surfaces, is applicable to virtually any type of mold material due to the use of silane chemistry and the low surface energy of PDMS. This allows simple and rapid replication of high complexity, high-aspect-ratio nanostructures with excellent replication fidelity. [source] Thickness-Driven Orthorhombic to Triclinic Phase Transformation in Pentacene Thin Films,ADVANCED MATERIALS, Issue 7 2005F. Drummy Pentacene films are thermally evaporated onto amorphous carbon-coated mica substrates held at room temperature. The crystal structure and morphology of the films are analyzed using electron microscopy and diffraction, and a new orthorhombic structure is characterized for films below a critical thickness (see Figure). Evidence that the orthorhombic structure is thermodynamically stable at low film thickness due to its low (001) surface energy is obtained. [source] Control of Molecular Transport Through Stimuli-Responsive Ordered Mesoporous Materials,ADVANCED MATERIALS, Issue 15 2003Q. Fu External and reversible control of the size and surface energy of the pores in mesoporous architectures has been achieved. The method involves modification of mesoporous silica by atom transfer radical polymerization of N -isopropyl acrylamide (the precursor to a stimuli- responsive polymer). The resulting polymer-grafted particles allow the adsorption and transport of molecular species to be dynamically controlled as illustrated in the Figure for the release of rhodamine 6G from the particles at 50,°C. [source] Study of conformational and optical rotation for the alaninamideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2007Shulei Zhao Abstract Six stationary points of alaninamide have been located on the potential surface energy (PES) at the B3LYP/6-311++G(2d,2p) level of theory both in the gas phase and in aqueous solution. In the aqueous solution, to take the water solvent effect into account, the polarizable continuum model (PCM) method has been used. Accurate geometric structures and their relative stabilities have been investigated. The results show that the intramolecular hydrogen bond plays a very important role in stabilizing the global minimum of the alaninamide. Moreover, the consistent result in relative energy using high-level computations, including the MP2 and MP3 methods with the same basis set [6-311++G(2d,2p)], indicates that the B3LYP/6-311++G(d,p) level may be applied to the analogue system. More importantly, the optical rotation of the optimized conformers (both in the gas phase and in aqueous solution) of alaninamide have been calculated using the density functional theory (DFT) and Hartree,Fock (HF) method at various basis sets (6-31+G*, 6-311++G(d,p), 6-311++G(2d,2p) and aug-cc-pvdz). The results show that the selection of the computation method and the basis set in calculation has great influence on the results of the optical rotations. The reliability of the HF method is less than that of DFT, and selecting the basis set of 6-311++G(2d,2p) and aug-cc-pvDZ produces relative reliable results. Analysis of the computational results of the structure parameters and the optical rotations yields the conclusion that just the helixes in molecules caused the chiral molecules to be optical active. The Boltzmann equilibrium distributions for the six conformers (both in the gas phase and in the aqueous solution) are also carried out. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Investigation of the postcure reaction and surface energy of epoxy resins using time-of-flight secondary ion mass spectrometry and contact-angle measurementsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009Firas Awaja Abstract Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate correlations between the molecular changes and postcuring reaction on the surface of a diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F based epoxy resin cured with two different amine-based hardeners. The aim of this work was to present a proof of concept that ToF-SIMS has the ability to provide information regarding the reaction steps, path, and mechanism for organic reactions in general and for epoxy resin curing and postcuring reactions in particular. Contact-angle measurements were taken for the cured and postcured epoxy resins to correlate changes in the surface energy with the molecular structure of the surface. Principal components analysis (PCA) of the ToF-SIMS positive spectra explained the variance in the molecular information, which was related to the resin curing and postcuring reactions with different hardeners and to the surface energy values. The first principal component captured information related to the chemical phenomena of the curing reaction path, branching, and network density based on changes in the relative ion density of the aliphatic hydrocarbon and the C7H7O+ positive ions. The second principal component captured information related to the difference in the surface energy, which was correlated to the difference in the relative intensity of the CxHyNz+ ions of the samples. PCA of the negative spectra provided insight into the extent of consumption of the hardener molecules in the curing and postcuring reactions of both systems based on the relative ion intensity of the nitrogen-containing negative ions and showed molecular correlations with the sample surface energy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Fabrication and characterization of solution cast MWNTs/PEI nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009Lu Shao Abstract Under mild conditions with the aid of ultrasonic, multi-walled carbon nanotubes (MWNTs) have been functionalized by mixed acid treatment which was proved by FTIR and XPS. According to SEM, acid treatment on MWNTs decreased the thickness of the membrane. However, no devastating damage and fracture happened on MWNTs after acid treatment under mild conditions. Precipitation observation illustrated that the enhanced solubility of MWNTs in water, ethanol, and dimethylformaide (DMF). Further, MWNTs/polyetherimide (PEI) nanocomposite films have been prepared by the simple solution casting method. The dispersion of MWNTs in polyetherimide (PEI) matrix was observed by Atomic Force Microscopy (AFM) which illustrated the improved dispersion for acid treated MWNTs in PEI. The adding of MWNTs in PEI decreased the dispersive component of surface energy and increased the polar component of surface energy, which resulted in the decrement of film surface energy. Differential scanning calorimetry showed that the glass transition temperature of PEI increased by about 4°C after the introduction of MWNTs. This improvement was related to the better affinity between MWNTs and PEI matrix, which also resulted in the improvement of mechanical strength in MWNTs/PEI nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Direct fluorination of Twaron fiber and investigation of mechanical thermal and morphological properties of high density polyethylene and Twaron fiber compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008J. Maity Abstract Composites consisting of high density polyethylene (HDPE) reinforced with randomly oriented chopped Twaron fibers (both fluorinated and nonfluorinated) show a significant increase in mechanical and thermal properties. To increase the better fiber matrix adhesion, the Twaron fiber is surface fluorinated using elemental fluorine. The surface of the Twaron fiber becomes very rough and the diameter of Twaron fiber increases from , 12 to 14 ,m after fluorination. The composites were prepared using solution method to overcome the damage of the fiber. The tensile strength and the Young's modulus increases with increasing fiber content. The tensile strength and modulus of modified fiber (fluorinated Twaron fiber) composites is much higher than nonmodified fiber composites indicating that there is better mechanical interlocking between the modified fiber and the matrix. Thermal properties obtained from DSC and DTA-TG analysis of the fluorinated fiber composites are also improved. Contact angle measurements, as well as the surface energy measurements, indicate that the composites are more wettable and is maximum for fluorinated fiber composites i.e., surface energy for fluorinated fiber composites is highest. Crystallinity is also higher for fluorinated fiber composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Synthesis and crystallization behavior of acetal copolymer/silica nanocomposite by in situ cationic ring-opening copolymerization of trioxane and 1,3-dioxolaneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Lanhui Sun Abstract The acetal copolymer/silica nanocomposite was prepared by in situ bulk cationic copolymerization of trioxane and 1,3-dioxolane in the presence of nanosilica. The crystallization behavior of acetal copolymer/silica nanocomposite was studied by AFM, DSC, XRD, and CPOM, and the macromolecular structure of acetal copolymer/silica nanocomposite was characterized by FTIR and 1H-NMR. The 1H-NMR results showed that the macromolecular chain of acetal copolymer had more than two consecutive 1,3-dioxolane units in an oxymethylene main chain, while that of acetal copolymer/silica nanocomposite had only one 1,3-dioxolane unit in an oxymethylene main chain. There existed interaction between the macromolecular chains and nanoparticles (such as hydrogen bonds and coordination). On one hand, nanoparticles acted as nucleation center, which accelerated the crystallization rate but reduced the crystallinity. The spherulite sizes also decreased with addition of nanoparticles attributed to the nucleation effect. On the other hand, the presence of nanoparticles interrupted the spherical symmetry of the crystallite. In conclusion, the high surface energy and small scale of nanoparticles have a prominent impact on the polymerization mechanism and crystallization behavior of nanocomposite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Evaluation of the crystallization kinetics and melting of polypropylene and metallocene-prepared polyethylene blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Mohammad Razavi-Nouri Abstract The kinetics of the isothermal crystallization of a polypropylene (PP) random copolymer containing 5 mol % ethylene, a metallocene linear low-density polyethylene (m -LLDPE) with 3.3 mol % hexene-1 as a comonomer, and three blends were studied with differential scanning calorimetry at temperatures sufficiently high to prevent any crystallization of m-LLDPE. The analysis was carried out with the Avrami equation. The overall crystallization rate and the equilibrium melting temperature of the PP copolymer decreased with increasing amounts of m-LLDPE in the blends. The former was attributed to the effect of m-LLDPE in reducing the number of primary nuclei, and the latter was attributed to a lowering of the fold surface energy due to the limited partial miscibility of the blend components. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 634,640, 2007 [source] Endothelial cell growth on silicon modified hydrogenated amorphous carbon thin filmsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008A. A. Ogwu Abstract The biological response of human microvascular endothelial cells (HMEC-1) seeded on Si-DLC films and on control surfaces was evaluated in terms of initial cell enhancement, growth, and cytotoxicity. The microstructure of the films was characterised by Raman spectroscopy and X-ray photoelectron spectroscopy. The effect of changes in microstructure, surface energy, surface electronic state, and electronic conduction, on the biological response of the films to endothelial cells was investigated. Endothelial cell adhesion and growth was found to be affected by changes in the microstructure of the films induced by silicon doping and thermal annealing. We observed a significant statistical difference in endothelial cell count between the as-deposited DLC and Si-DLC films using the one sample t -test at a p -value of 0.05. We also found a statistically significant difference between the adhesion of HMEC films on DLC and Si-DLC films at various annealing temperatures using the one-way ANOVA F statistic test at p < 0.05 and the post-hoc Tukey test. One sample t -test at p < 0.05 of MTT-assay results showed the endothelial cells to be viable when seeded on DLC/Si-DLC films. We suspect that the increased adhesion of endothelial cells induced by increasing the amount of silicon in the Si-DLC films is associated with the development of a suitable surface energy due to silicon addition, which neither favored cell denaturing nor preferential water spreading before cellular attachment on the film surface. The presence of an external positively charged dipole on the Si-DLC films confirmed by our Kelvin probe measurements is also expected to enhance the adhesion of endothelial cells that are well known to carry a negative charge. The Si-DLC films investigated hold potential promise as coatings for haemocompatible artificial implants. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Fabrication and surface modification of macroporous poly(L -lactic acid) and poly(L -lactic- co -glycolic acid) (70/30) cell scaffolds for human skin fibroblast cell cultureJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 3 2002Jian Yang Abstract The fabrication and surface modification of a porous cell scaffold are very important in tissue engineering. Of most concern are high-density cell seeding, nutrient and oxygen supply, and cell affinity. In the present study, poly(L -lactic acid) and poly(L -lactic- co -glycolic acid) (70/30) cell scaffolds with different pore structures were fabricated. An improved method based on Archimedes' Principle for measuring the porosity of scaffolds, using a density bottle, was developed. Anhydrous ammonia plasma treatment was used to modify surface properties to improve the cell affinity of the scaffolds. The results show that hydrophilicity and surface energy were improved. The polar N-containing groups and positive charged groups also were incorporated into the sample surface. A low-temperature treatment was used to maintain the plasma-modified surface properties effectively. It would do help to the further application of plasma treatment technique. Cell culture results showed that pores smaller than 160 ,m are suitable for human skin fibroblast cell growth. Cell seeding efficiency was maintained at above 99%, which is better than the efficiency achieved with the common method of prewetting by ethanol. The plasma-treatment method also helped to resolve the problem of cell loss during cell seeding, and the negative effects of the ethanol trace on cell culture were avoided. The results suggest that anhydrous ammonia plasma treatment enhances the cell affinity of porous scaffolds. Mass transport issues also have been considered. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 62: 438,446, 2002 [source] | ||||||||||||||||||||||||||||||||||