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Water Interface (water + interface)
Selected AbstractsDifferent Molecules Experience Different Polarities at the Air/Water Interface,ANGEWANDTE CHEMIE, Issue 35 2009Sobhan Sen Dr. Grenzerfahrung: Mit grenzflächenselektiver nichtlinearer Spektroskopie konnte für fünf Cumarinderivate ein signifikanter Unterschied in der solvatochromen Verschiebung an der Luft/Wasser-Grenzfläche nachgewiesen werden. Dies zeigt, dass strukturell verschiedene Moleküle selbst an derselben Grenzfläche eine deutlich unterschiedliche lokale effektive Polarität erfahren (siehe Bild; Pfeile kennzeichnen Übergangsdipolmomente). [source] Two-Dimensional Self-Assembly of Liquid-Crystalline Perylene Diimide Derivatives at the Air/Water InterfaceCHEMPHYSCHEM, Issue 12 2002Guodong Sui Dr. Sideways arrangement: The self-assembly of PPEEB liquid crystalline molecules at the air/water interface was investigated as a function of surface pressure. The self-assembly is caused by a compact edge-on molecular orientation, which gives rise to a range of different-sized aggregate microstructures. [source] Importance of Interfacial Adsorption in the Biphasic Hydroformylation of Higher Olefins Promoted by Cyclodextrins: A Molecular Dynamics Study at the Decene/Water InterfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Nicolas Sieffert Abstract We report herein a molecular dynamics study of the main species involved in the hydroformylation of higher olefins promoted by cyclodextrins in 1-decene/water biphasic systems at a temperature of 350,K. The two liquids form a well-defined sharp interface of approximately 7,Å width in the absence of solute; the decene molecules are generally oriented "parallel" to the interface where they display transient contacts with water. We first focused on rhodium complexes bearing water-soluble TPPTS3, ligands (where TPPTS3, represents tris(m -sulfonatophenyl)phosphine) involved in the early steps of the reaction. The most important finding concerned the surface activity of the "active" form of the catalyst [RhH(CO)(TPPTS)2]6,, the [RhH(CO)2(TPPTS)2]6, complex, and the key reaction intermediate [RhH(CO)(TPPTS)2(decene)]6, (with the olefin ,-coordinated to the metal center) which are adsorbed at the water side of the interface in spite of their ,6 charge. The free TPPTS3, ligands themselves are also surface-active, whereas the ,9 charged catalyst precursor [RhH(CO)(TPPTS)3]9, prefers to be solubilized in water. The role of cyclodextrins was then investigated by performing simulations on 2,6-dimethyl-,-cyclodextrin ("CD") and its inclusion complexes with the reactant (1-decene), a reaction product (undecanal), and the corresponding key reaction intermediate [RhH(CO)(TPPTS)2(decene)]6, as guests; they were all shown to be surface-active and prefer the interface over the bulk aqueous phase. These results suggest that the biphasic hydroformylation of higher olefins takes place "right" at the interface and that the CDs promote the "meeting" of the olefin and the catalyst in this peculiar region of the solution by forming inclusion complexes "preorganized" for the reaction. Our results thus point to the importance of adsorption at the liquid/liquid interface in this important phase-transfer-catalyzed reaction. [source] Confinement in Nanopores at the Oxide/Water Interface: Modification of Alumina Adsorption PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2008Manuel Baca Dr. Abstract There is limited knowledge on the influence of the pore size on surface phenomena (adsorption, dissolution, precipitation, etc.) at the oxide/water interface and a better understanding of the space confinement in nanoscale pores should have practical implications in different areas, such as transport of contaminants in the environment or heterogeneous catalyst preparation, to name a few. To investigate the modifications of the oxide adsorption properties at the oxide/water interface in a confined environment, the surface acidobasic and ion adsorption properties of six different aluminas (5 porous commercial aluminas with pore diameters ranging from 25 to 200,Å and 1 non-porous alumina) were determined by means of acid,base titration and Ni(II) adsorption. It is shown that the confinement has a moderate impact on the alumina adsorption capacity because all materials have similar surface charging behaviours and ion saturation coverages. However, a confined geometry has a much larger impact on the ion adsorption constants, which decrease drastically when the average pore diameter decreases below 200,Å. These results are discussed in terms of nanoscale pore space confinement. [source] Site-Selective Formation of Optically Active Inclusion Complexes of Alkoxo-Subphthalocyanines with ,-Cyclodextrin at the Toluene/Water InterfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2006Kenta Adachi Abstract Several subphthalocyanine derivatives that contain an alkoxo substituent as an axial ligand (RO-Subpc, R = 9-anthracenemethyl, benzyl, phenyl, 3,5-dimethylbenzyl, 3,5-dimethylphenyl, 4-methylbenzyl, and 4-methylphenyl) were synthesized. The formation of inclusion complexes of RO-Subpc with ,-CD in DMSO and at the toluene/water interface was investigated by UV/Vis absorption spectroscopy, induced circular dichroism (ICD), and nuclear magnetic resonance (NMR) measurements. Interfacial tension measurements suggested that ,-CD adsorbed as a monolayer at the toluene/water interface and probably orientated towards the toluene phase with its primary face. The 1:1 composition of ,-CD,RO-Subpc inclusion complexes was confirmed in DMSO and at the toluene/water interface for BzO-Subpc, PhO-Subpc, MeBzO-Subpc, and MePhO-Subpc. A 2:1 inclusion complex of AnO-Subpc formed in DMSO. The observed ICD spectra of ,-CD,RO-Subpc inclusion complexes are discussed with respect to molecular modeling and the simulation based on Tinoco,Kirkwood theory. Interestingly, the ICD spectra of ,-CD,BzO-Subpc and ,-CD,MeBzO-Subpc inclusion complexes exhibited a negative sign in DMSO and a positive sign at the toluene/water interface. This reversal of the ICD sign strongly suggests a difference in the structure of the inclusion complexes: ,-CD at the interface formed the inclusion complex with its primary face, whereas the secondary face of ,-CD bound favorably to RO-Subpc in DMSO. [source] UV Polymerisation of Surfactants Adsorbed at the Nematic Liquid Crystal,Water Interface Produces an Optical ResponseCHEMPHYSCHEM, Issue 17 2009Paul D. I. Fletcher Prof. Abstract We have investigated the changes in crossed polariser optical textures produced by adsorption and UV polymerisation of a range of polymerisable surfactants at the interface between a nematic liquid crystal and water. Similar to non-polymerisable surfactants, the adsorption of polymerisable surfactants with sufficiently long hydrophobic tail groups produces a transition from planar to homeotropic anchoring. UV polymerisation of surfactants with a polymerisable group located in the hydrophobic tail region changes the anchoring from homeotropic back to planar. Polymerisation in the hydrophilic headgroup region does not produce an optical transition. We demonstrate that these systems can be used to "write with light" in the interfaces and that they form the basis of a UV sensor device in which the optical response is visible to the naked eye. [source] Transport Processes at ,-Quartz,Water Interfaces: Insights from First-Principles Molecular Dynamics SimulationsCHEMPHYSCHEM, Issue 7 2008Waheed A. Adeagbo Dr. Abstract Car,Parrinello molecular dynamics (CP,MD) simulations are performed at high temperature and pressure to investigate chemical interactions and transport processes at the ,-quartz,water interface. The model system initially consists of a periodically repeated quartz slab with O-terminated and Si-terminated (1000) surfaces sandwiching a film of liquid water. At a temperature of 1000 K and a pressure of 0.3 GPa, dissociation of H2O molecules into H+ and OH, is observed at the Si-terminated surface. The OH, fragments immediately bind chemically to the Si-terminated surface while Grotthus-type proton diffusion through the water film leads to protonation of the O-terminated surface. Eventually, both surfaces are fully hydroxylated and no further chemical reactions are observed. Due to the confinement between the two hydroxylated quartz surfaces, water diffusion is reduced by about one third in comparison to bulk water. Diffusion properties of dissolved SiO2 present as Si(OH)4 in the water film are also studied. We do not observe strong interactions between the hydroxylated quartz surfaces and the Si(OH)4 molecule as would have been indicated by a substantial lowering of the Si(OH)4 diffusion coefficient along the surface. No spontaneous dissolution of quartz is observed. To study the mechanism of dissolution, constrained CP,MD simulations are done. The associated free energy profile is calculated by thermodynamic integration along the reaction coordinate. Dissolution is a stepwise process in which two SiO bonds are successively broken. Each bond breaking between a silicon atom at the surface and an oxygen atom belonging to the quartz lattice is accompanied by the formation of a new SiO bond between the silicon atom and a water molecule. The latter loses a proton in the process which eventually leads to protonation of the oxygen atom in the cleaved quartz SiO bond. The final solute species is Si(OH)4. [source] Superhydrophobic Coatings: The Salvinia Paradox: Superhydrophobic Surfaces with Hydrophilic Pins for Air Retention Under Water (Adv. Mater.ADVANCED MATERIALS, Issue 21 201021/2010) The cover shows the sophisticated surface design of the floating water fern Salvinia. The unique surface architecture is composed of complex hydrophobic eggbeater-shaped hairs with hydrophilic terminal cells. The evenly distributed hydrophilic patches stabilize the air layer by pinning the air/water interface in place. The paradox combination of hydrophilic patches on superhydrophobic surfaces (the "Salvinia Effect") provides an innovative concept for smart biomimetic surfaces in maritime coatings and underwater applications, as reported by Wilhelm Barthlott, Thomas Schimmel, and co-workers on p. 2325. [source] Coupled ghost fluid/two-phase level set method for curvilinear body-fitted gridsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2007Juntao Huang Abstract A coupled ghost fluid/two-phase level set method to simulate air/water turbulent flow for complex geometries using curvilinear body-fitted grids is presented. The proposed method is intended to treat ship hydrodynamics problems. The original level set method for moving interface flows was based on Heaviside functions to smooth all fluid properties across the interface. We call this the Heaviside function method (HFM). The HFM requires fine grids across the interface. The ghost fluid method (GFM) has been designed to explicitly enforce the interfacial jump conditions, but the implementation of the jump conditions in curvilinear grids is intricate. To overcome these difficulties a coupled GFM/HFM method was developed in which approximate jump conditions are derived for piezometric pressure and velocity and pressure gradients based on exact continuous velocity and stress and jump in momentum conditions with the jump in density maintained but continuity of the molecular and turbulent viscosities imposed. The implementation of the ghost points is such that no duplication of memory storage is necessary. The level set method is adopted to locate the air/water interface, and a fast marching method was implemented in curvilinear grids to reinitialize the level set function. Validations are performed for three tests: super- and sub-critical flow without wave breaking and an impulsive plunging wave breaking over 2D submerged bumps, and the flow around surface combatant model DTMB 5512. Comparisons are made against experimental data, HFM and single-phase level set computations. The proposed method performed very well and shows great potential to treat complicated turbulent flows related to ship flows. Copyright © 2007 John Wiley & Sons, Ltd. [source] Quantitative Determination of Surface Concentration of Human Apolipoprotein H with Capillary ElectrophoresisIUBMB LIFE, Issue 5 2000Shao-xiong Wang Abstract The phospholipid monolayer at an air/water interface is widely used to mimic the biological membrane. The dynamic process of the protein or peptide interacting with lipid molecules can be reflected in the change in surface pressure of the monolayer. But the conventional method used to measure the surface pressure change gives results that cannot easily be correlated with the contribution of a single protein molecule. Previously, measuring the surface concentration of the protein molecules at the air/water interface has required the protein to be labeled with radioactivity or fluorescence. Here, a new method using capillary electrophoresis is introduced to measure the surface concentration of the protein. The results show at least two advantages of the new method: The numerical results of protein concentration can be obtained in a more precise and rapid way; and there is no need to label the protein sample or to build a special monolayer setup. [source] Self-assembled films of hydrophobin protein HFBIII from Trichoderma reeseiJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Kaisa Kisko Hydrophobins are a group of small amphiphilic proteins which are known to self-assemble on interfaces. They contain eight conserved cysteine residues, which make four disulfide bridges. A new hydrophobin protein, HFBIII, from the fungus Trichoderma reesei contains one extra cysteine residue, giving the protein a naturally reactive site. The self-assembly of hydrophobin protein HFBIII was studied using grazing-incidence X-ray diffraction and reflectivity. HFBIII self-assembles into a hexagonally ordered monolayer at an air/water interface and also forms crystalline coatings on a silicon substrate. The lattice constants for the hexagonal coatings are a = b = 56.5,Å, , = 120°. The self-assembled structure in the HFBIII film is very similar to those formed by two other T. reesei hydrophobins, HFBI and HFBII. [source] Dynamic adsorption of octanols at air/water interfaceTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Chi M. Phan Abstract The dynamic adsorptions of 1-, 2- and 3-octanols at air/water interface were monitored using pendant drop method. It has been found that 1-octanol had strongest interfacial effects, yet slowest rate of adsorption. The experimental data were compared with diffusion-controlled and diffusion-kinetic-mixed models. Excepting 3-octanol at 1,mM, all systems required kinetic step. The effective kinetic constant was found varying with the concentration and the carbinol position. The results highlighted the influence of hydrophobic tails on the dynamic adsorption. Les adsorptions dynamiques de 1-, 2- et 3-octanols à l'interface air/eau ont été suivies à l'aide de la méthode de la goutte pendante. On a découvert que 1-octanol présente les effets interfaciaux les plus forts, mais le taux d'adsorption le plus lent. Les données expérimentales ont été comparées à l'aide de modèles par diffusion contrôlée et à mélange diffusion-cinétique. À l'exception de 3-octanol à 1,mM, tous les systèmes ont nécessité une étape cinétique. On a trouvé que la constante cinétique efficace varie avec la concentration et la position du carbinol. Les résultats ont mis en évidence l'influence des queues hydrophobes sur l'adsorption dynamique. [source] Through-Water Close Range Digital Photogrammetry in Flume and Field EnvironmentsTHE PHOTOGRAMMETRIC RECORD, Issue 99 2002Justin Butler Measurement of the structure of gravel-bed river surfaces is crucial for understanding both bed roughness and the sediment entrainment process. This paper describes the use of close range digital photogrammetry to measure and monitor change occurring in submerged river gravel-beds in both flume and field environments. High-resolution digital elevation models (DEMs) were obtained and two-media (through air and water) techniques were used to correct for the e.ects of refraction at the air/water interface. Although suitable refractive models have been developed, the use of proprietary software to generate DEMs automatically introduces the problem of how to re-establish collinearity. A simple refraction correction algorithm based upon analytical geometry was developed and is described. This algorithm was designed for use after initial DEM acquisition and allows any photogrammetric software package to be used for data acquisition. Application of this algorithm led to improvements in DEM accuracy by reducing the systematic, depth-dependent bias caused by refraction Research carried out in a flume environment allowed the algorithm to be tested by measuring a flooded and drained bed surface. Non-systematic differences between the "dry" and "wet" DEMs arose from reductions in stereomatching success in the two-media case. This effect was thought to be due to light attenuation and the introduction of residual parallax. Results suggest that close range digital photogrammetry can be used to extract high quality DEMs of submerged topography in both flume and field fluvial environments, which represents a particularly exciting development for fluvial geomorphologists [source] Two-Dimensional Self-Assembly of Liquid-Crystalline Perylene Diimide Derivatives at the Air/Water InterfaceCHEMPHYSCHEM, Issue 12 2002Guodong Sui Dr. Sideways arrangement: The self-assembly of PPEEB liquid crystalline molecules at the air/water interface was investigated as a function of surface pressure. The self-assembly is caused by a compact edge-on molecular orientation, which gives rise to a range of different-sized aggregate microstructures. [source] Studies on Properties of p -Nitrophenylazo Calix[4]arene DerivativesCHINESE JOURNAL OF CHEMISTRY, Issue 2 2003Jin Chuan-Ming Abstract The p -nitrophenylazo calix[4]arene derivatives 1a-1d with nonlinear optical (NLO) properties were prepared by the diazo-coupling reaction of calix[4]arene with p -nitrophenyl diazonium. The diazotization reaction of p -nitroaniline was carried out with isoamyl nitrite as a source of nitrous add in EtONa/EtOH under refluxing condition. X-Ray crystallographic analysis and 1H NMR spectra reveal that they exist as cone conformation in crystal state or in solution. HRS measurements at 1064 nm in THF indicate that p -nitro-phenylazo calix[4]arenes have higher hyperpolarizability ,z values than the corresponding reference compound 4-(4-nitrophenylazo)-2, 6-dimethyl-phenol, without red shift of the charge transfer band. The tetrakis p -nitrophenylazo calix[4]arene (2) with longer alkyl chains can form monolayer at the air/water interface. [source] Stabilization of human papillomavirus virus-like particles by non-ionic surfactantsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2005Li Shi Abstract Human papillomavirus (HPV) virus-like-particles (VLPs) produced by recombinant expression systems are promising vaccine candidates for prevention of cervical cancers as well as genital warts. At high protein concentrations, HPV VLPs, comprised of the viral capsid protein L1 and expressed and purified from yeast, are protected against detectable aggregation during preparation and storage by high concentrations of NaCl. At low protein concentrations, however, high salt concentration alone does not fully protect HPV VLPs from aggregation. Moreover, the analytical analysis of HPV VLPs proved to be a challenge due to surface adsorption of HPV VLPs to storage containers and cuvettes. The introduction of non-ionic surfactants into HPV VLP aqueous solutions provides significantly enhanced stabilization of HPV VLPs against aggregation upon exposure to low salt and protein concentration, as well as protection against surface adsorption and aggregation due to heat stress and physical agitation. The mechanism of non-ionic surfactant stabilization of HPV VLPs was extensively studied using polysorbate 80 (PS80) as a representative non-ionic surfactant. The results suggest that PS80 stabilizes HPV VLPs mainly by competing with the VLPs for various container surfaces and air/water interfaces. No appreciable binding of PS80 to intact HPV VLPs was observed although PS80 does bind to the denatured HPV L1 protein. Even in the presence of stabilizing level of PS80, however, an ionic strength dependence of HPV VLP stabilization against aggregation is observed indicating optimization of both salt and non-ionic surfactant levels is required for effective stabilization of HPV VLPs in solution. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1538,1551, 2005 [source] Facile One-Step Fabrication of Ordered Organic Nanowire FilmsADVANCED MATERIALS, Issue 41 2009Chengyi Zhang Squaraine nanowires self-organize into a well-ordered film through a simple solvent-evaporation process at the dichloromethane/water interface. The film can be transferred onto various substrates or stacked layer-by-layer into a multilayered structure. This one-step approach offers a low-cost method for producing scalable films of aligned organic nanowires suitable for large-scale applications. [source] Detection of single lipid bilayers with coherent anti-Stokes Raman scattering (CARS) microscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2003Eric O. Potma Abstract We investigated vibrational imaging of phospholipid bilayers with CARS microscopy. Single lipid membranes of supported bilayers, giant unilamellar vesicles and intact erythrocyte membrane are detected with the strong resonant signal of the C,H stretching vibration. In addition, it is shown that the CARS signal field of the lipids near the glass/water interface is amplified through mixing with the back-reflected non-resonant CARS field of the glass coverslip. Furthermore, interference effects between two separate bilayers are observed, allowing intermembrane distances to be determined beyond the diffraction-limited resolution of the microscope. Copyright © 2003 John Wiley & Sons, Ltd. [source] Seismic modelling study of a subglacial lakeGEOPHYSICAL PROSPECTING, Issue 6 2003José M. Carcione ABSTRACT We characterize the seismic response of Lake Vostok, an Antarctic subglacial lake located at nearly 4 km depth below the ice sheet. This study is relevant for the determination of the location and morphology of subglacial lakes. The characterization requires the design of a methodology based on rock physics and numerical modelling of wave propagation. The methodology involves rock-physics models of the shallow layer (firn), the ice sheet and the lake sediments, numerical simulation of synthetic seismograms, ray tracing, ,,p transforms, and AVA analysis, based on the theoretical reflection coefficients. The modelled reflection seismograms show a set of straight events (refractions through the firn and top-ice layer) and the two reflection events associated with the top and bottom of the lake. Theoretical AVA analysis of these reflections indicates that, at near offsets, the PP-wave anomaly is negative for the ice/water interface and constant for the water/sediment interface. This behaviour is shown by AVA analysis of the synthetic data set. This study shows that subglacial lakes can be identified by using seismic methods. Moreover, the methodology provides a tool for designing suitable seismic surveys. [source] Water-Insoluble, Whey Protein- based Microspheres Prepared by an All-aqueous ProcessJOURNAL OF FOOD SCIENCE, Issue 1 2004M. ROSENBERG ABSTRACT: Calcium-alginate coated microspheres consisting of whey proteins and a model sensitive core, paprika oleoresin, were prepared using an all-aqueous process. Core-in-wall emulsions containing 20% or 25% whey protein isolate and 15% to 50% (wt/wt) core were investigated. Retention of proteins and core during the process ranged from 84.9% to 95.6% and from 91.4% to 95.7%, respectively. Results indicated that microspheres were water-insoluble and the encapsulated sensitive core was effectively protected against oxidative deterioration. This protection could be attributed to the protein-based layer adsorbed at the oil/water interface. The matrix of the microspheres exhibited microstructural features of an interactive composite-type material. Results suggested the potential suitability of the microspheres as delivery systems for controlled core release in food applications. [source] Mechanism of emulsion polymerization of styrene using a reactive surfactantJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2001X. Wang Abstract The emulsion polymerization of styrene using the reactive surfactant sodium dodecyl allyl sulfosuccinate (TREM LF-40) was studied. The polymerization kinetics were found to be unusual in that Rp was not directly proportional to Np (Rp , Np0.67). Several reasons are stated to explain the unusual kinetics, including chain transfer to TREM LF-40, copolymerization of styrene with TREM LF-40, and the influence of the homopolymer of TREM LF-40 [poly(TREM)] and/or the copolymer [poly(TREM- co -styrene)] on the entry and exit rates of free radicals. The possibility of both chain transfer and copolymerization exists primarily at the oil/water interface, whereas both can also occur in the aqueous and monomer phases. Bulk polymerizations of styrene in the presence of TREM LF-40 and poly(TREM) were conducted, and the results show that the reaction rate decreased for the styrene/TREM LF-40 system. Latex characterization by serum replacement and titration measurements provided evidence for the chemical bonding of TREM LF-40 to the polymer particles. The fraction of chemically bound reactive surfactant decreased with increasing surfactant concentration and increased with increasing initiator concentration. Relatively high contact angles of water on films cast from the latexes showed that TREM LF-40 did not migrate significantly to the surface of the film, which was consistent with the latex-surface characterization results. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3093,3105, 2001 [source] Analytic Determination of Hydrocarbon Transmissivity from Baildown TestsGROUND WATER, Issue 1 2000David Huntley Hydrocarbon baildown tests involve the rapid removal of floating hydrocarbon from an observation or production well, followed by monitoring the rate of recovery of both the oil/air and oil/water interfaces. This test has been used erroneously for several years to calculate the "true thickness" of hydrocarbon in the adjacent formation. More recent analysis of hydrocarbon distribution by Farr et al. (1990), Lenhard and Parker (1990), Huntley et al. (1994), and others have shown that, under vertical equilibrium conditions, there is no thickness exaggeration of hydrocarbon in a monitoring well, though there is a significant volume exaggeration. This body of work can be used to demonstrate that the calculation of a "true hydrocarbon thickness" using a baildown test has no basis in theory. The same body of work, however, also demonstrates that hydrocarbon saturations are typically much less than one, and are often below 0.5. Because the relative permeability decreases as hydrocarbon saturation decreases, the effective conductivity and mobility of the hydrocarbon is much less than that of water, even ignoring the effects of increased viscosity and decreased density. It is important to evaluate this decreased mobility of hydrocarbon due to partial pore saturation, as it has substantial impacts on both risk and remediation. This paper presents two analytic approaches to the analysis of hydrocarbon baildown test results to determine hydrocarbon transmissivity. The first approach is based on a modification of the Bouwer and Rice (1976) analysis of slug withdrawal test data. The second approach is based on a modification of Jacob and Lohman's (1952) constant drawdown,variable discharge aquifer test approach. The first approach can be applied only when the effective water transmissivity across the screened interval to water is much greater than the effective hydrocarbon transmissivity. When this condition is met, the two approaches give effectively identical results. [source] Confinement in Nanopores at the Oxide/Water Interface: Modification of Alumina Adsorption PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2008Manuel Baca Dr. Abstract There is limited knowledge on the influence of the pore size on surface phenomena (adsorption, dissolution, precipitation, etc.) at the oxide/water interface and a better understanding of the space confinement in nanoscale pores should have practical implications in different areas, such as transport of contaminants in the environment or heterogeneous catalyst preparation, to name a few. To investigate the modifications of the oxide adsorption properties at the oxide/water interface in a confined environment, the surface acidobasic and ion adsorption properties of six different aluminas (5 porous commercial aluminas with pore diameters ranging from 25 to 200,Å and 1 non-porous alumina) were determined by means of acid,base titration and Ni(II) adsorption. It is shown that the confinement has a moderate impact on the alumina adsorption capacity because all materials have similar surface charging behaviours and ion saturation coverages. However, a confined geometry has a much larger impact on the ion adsorption constants, which decrease drastically when the average pore diameter decreases below 200,Å. These results are discussed in terms of nanoscale pore space confinement. [source] Role of grafting in the emulsion polymerization of vinyl acetate with poly(vinyl alcohol) as an emulsifier.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001Abstract The role of grafting in particle nucleation during the emulsion polymerization of vinyl acetate with partially hydrolyzed poly(vinyl alcohol) (PVA) as an emulsifier and potassium persulfate as an initiator was investigated. The polymerizations were carried out in batch with a low solids (10%) recipe. An automated reaction calorimeter (Mettler RC1) was used for the direct monitoring of the kinetics of emulsion polymerizations with three medium molecular weight PVAs differing in their degrees of blockiness (Poval 217EE > 217E > 217). Smith,Ewart case 1 kinetics (average number of free radicals per particle < 0.5) were followed in all cases, and no constant rate in interval II was observed. Contrary to what was expected, a nonlinear relationship was observed between the rate of polymerization (Rp) and the number of particles (Np). At Rp max,Np (217E) > Np (217EE) > Np (217), and the final Np was independent of the degree of blockiness of PVA. The particle size distributions were broad (particle diameter = 20,100 nm) and bimodal. On the basis of these data, we concluded that particle nucleation was continuous and was accompanied by extensive limited aggregation during the particle growth stages. The evolution of the amounts of grafted PVA and poly(vinyl acetate) (PVAc) were determined in polymerizations employing the two PVAs differing the most in blockiness (Poval 217EE and 217). The grafted PVAc followed similar profiles, increasing with conversion, particularly near the end of the two reactions. The amounts of grafted PVAc were about the same in the final latexes (37,39%). In contrast, the grafting of PVA was nearly complete by the time monomer droplets had disappeared in each reaction (25% conversion). However, the extent of grafting differed significantly, with the blockier PVA having about one-third the grafting of the more random PVA (,10% vs ,30%). In these low solids recipes, grafting appeared to be primarily a solution event, occurring predominantly in the aqueous phase and not at the particle/water interface, as was previously speculated. The PVAc grafts grew until the molecules became water-insoluble and precipitated, forming polymer particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3633,3654, 2001 [source] Molecular Dynamics Simulations of the Orientation and Reorientational Dynamics of Water and Polypyrrole Rings as a Function of the Oxidation State of the PolymerMACROMOLECULAR THEORY AND SIMULATIONS, Issue 1 2005Jose J. López Cascales Abstract Summary: Polypyrrole is one of the most widely-studied conducting polymers due to its steady electrochemical response and good chemical stability in different solvents, including organic and inorganic ones. In this work, we provide for the first time valuable information in atomic detail concerning the steady and dynamic properties of pyrrole rings as a function of the oxidation state of the polymer. The study was carried out by Classical molecular dynamics simulation, where the system was modelled by 256 polypyrrole chains of 10 pyrrole rings each. Water was explicitly introduced in our simulations. Besides the uncharged or reduced state, two steady oxidation states of the polymer have been simulated by introducing a net charge (+1) on 85 and 256 of the polypyrrole chains. To balance the charges emerging in these oxidised states, 85 and 256 chloride ions (Cl,1) respectively, were introduced into the system. From an analysis of the simulated trajectories, the orientation and relaxation times of water and pyrrole rings were evaluated for the different oxidation states of the polymer across the polypyrrole/water interface. The calculated densities for different oxidation states describe the swelling or shrinking process during electrochemical oxidation or reduction respectively. The rotational relaxation times calculated for the polypyrrole rings decrease with increasing oxidation of the polymer, which is in a good agreement with experimental electrochemical data. Almost no variation in pyrrole ring orientation was measured for the different oxidation states of the polymer, even compared with polypyrrole bulk. As regards the water structure in the vicinity of the polypyrrole/water interface, both the orientation and orientation relaxation time were strongly affected by the presence of charges in the polymer. Thus, the water dipole was strongly orientated in the vicinity of the water/polypyrrole interface and its orientational relaxation time increased by one order of magnitude compared with bulk water, even when only one-third of the total polymer chains were oxidised. The results attained in this work were validated with experimental results, when they were available. Polypyrrole ring orientation and water orientation at the polypyrrole/water interface. (a) 256 rPPy and (b)171 rPPy,+,85 oPPy. [source] Hydrophobically Directed Aldol Reactions: Polystyrene-Supported L -Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presence of Water,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2007Michelangelo Gruttadauria Abstract A simple synthetic methodology for the preparation of a polystyrene-supported L -proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been explained in terms of the formation of a hydrophobic core in the inner surface of the resin, whereas the hydrophilic proline moiety lies at the resin/water interface. Such a microenvironment both promotes the aldol reaction and increases the stereoselectivity. Recycling investigations have shown that this material can be reused, without loss in levels of conversion and stereoselectivity, for at least five cycles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Site-Selective Formation of Optically Active Inclusion Complexes of Alkoxo-Subphthalocyanines with ,-Cyclodextrin at the Toluene/Water InterfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2006Kenta Adachi Abstract Several subphthalocyanine derivatives that contain an alkoxo substituent as an axial ligand (RO-Subpc, R = 9-anthracenemethyl, benzyl, phenyl, 3,5-dimethylbenzyl, 3,5-dimethylphenyl, 4-methylbenzyl, and 4-methylphenyl) were synthesized. The formation of inclusion complexes of RO-Subpc with ,-CD in DMSO and at the toluene/water interface was investigated by UV/Vis absorption spectroscopy, induced circular dichroism (ICD), and nuclear magnetic resonance (NMR) measurements. Interfacial tension measurements suggested that ,-CD adsorbed as a monolayer at the toluene/water interface and probably orientated towards the toluene phase with its primary face. The 1:1 composition of ,-CD,RO-Subpc inclusion complexes was confirmed in DMSO and at the toluene/water interface for BzO-Subpc, PhO-Subpc, MeBzO-Subpc, and MePhO-Subpc. A 2:1 inclusion complex of AnO-Subpc formed in DMSO. The observed ICD spectra of ,-CD,RO-Subpc inclusion complexes are discussed with respect to molecular modeling and the simulation based on Tinoco,Kirkwood theory. Interestingly, the ICD spectra of ,-CD,BzO-Subpc and ,-CD,MeBzO-Subpc inclusion complexes exhibited a negative sign in DMSO and a positive sign at the toluene/water interface. This reversal of the ICD sign strongly suggests a difference in the structure of the inclusion complexes: ,-CD at the interface formed the inclusion complex with its primary face, whereas the secondary face of ,-CD bound favorably to RO-Subpc in DMSO. [source] Bioavailability of solid and non-aqueous phase liquid (NAPL)-dissolved phenanthrene to the biosurfactant-producing bacterium Pseudomonas aeruginosa 19SJENVIRONMENTAL MICROBIOLOGY, Issue 9 2001Marta García-Junco The biodegradation of phenanthrene by the biosurfactant-producing strain Pseudomonas aeruginosa 19SJ was investigated in experiments with the compound present either as crystals or dissolved in non-aqueous phase liquids (NAPLs). Growth on solid phenanthrene exhibited an initial phase not limited by dissolution rate and a subsequent, carbon-limited phase caused by exhaustion of the carbon source. Rhamnolipid biosurfactants were produced from solid phenanthrene and appeared in solution and particulate material (cells and phenanthrene crystals). During the carbon-limited phase, the concentration of rhamnolipids detected in culture exceeded the critical micelle concentration (CMC) determined with purified rhamnolipids. The biosurfactants caused a significant increase in dissolution rate and pseudosolubility of phenanthrene, but only at concentrations above the CMC. Externally added rhamnolipids at a concentration higher than the CMC increased the biodegradation rate of solid phenanthrene. Mineralization curves of low concentrations of phenanthrene initially dissolved in two NAPLs [2,2,4,4,6,8,8-heptamethylnonane and di(2-ethylhexyl)phthalate] were S-shaped, although no growth was observed in the population of suspended bacteria. Biosurfactants were not detected in solution under these conditions. The observed mineralization was attributed not only to suspended bacteria, but also to bacterial populations growing at the NAPL,water interface, mineralizing the compound at higher rates than predicted by abiotic partitioning. We suggest that rhamnolipid production and attachment increased the bioavailability of phenanthrene, so promoting biodegradation activity. [source] Influence of soil pH on the sorption of ionizable chemicals: Modeling advancesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Antonio Franco Abstract The soil,water distribution coefficient of ionizable chemicals (Kd) depends on the soil acidity, mainly because the pH governs speciation. Using pH-specific Kd values normalized to organic carbon (KOC) from the literature, a method was developed to estimate the KOC of monovalent organic acids and bases. The regression considers pH-dependent speciation and species-specific partition coefficients, calculated from the dissociation constant (pKa) and the octanol,water partition coefficient of the neutral molecule (log Pn). Probably because of the lower pH near the organic colloid,water interface, the optimal pH to model dissociation was lower than the bulk soil pH. The knowledge of the soil pH allows calculation of the fractions of neutral and ionic molecules in the system, thus improving the existing regression for acids. The same approach was not successful with bases, for which the impact of pH on the total sorption is contrasting. In fact, the shortcomings of the model assumptions affect the predictive power for acids and for bases differently. We evaluated accuracy and limitations of the regressions for their use in the environmental fate assessment of ionizable chemicals. [source] Potential for 4- n -nonylphenol biodegradation in stream sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008Paul M. Bradley Abstract The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring- 14C]4- n -nonylphenol (4- n -NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfalls and incubated under oxic conditions showed rapid and complete mineralization of [U-ring- 14C]4-n-NP to 14CO2 in all three systems. In contrast, no mineralization of [U-ring- 14C]4- n -NP was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring- 14C]4- n -NP mineralization in sediments from upstream and downstream of the respective WWTP outfalls was inversely correlated with the biochemical oxygen demand (BOD) of the streambed sediments. These results suggest that the net supply of dissolved oxygen to streambed sediments is a key determinant of the rate and extent of 4-NP biodegradation in stream systems. In the stream systems considered by the present study, dissolved oxygen concentrations in the overlying water column (8,10 mg/L) and in the bed sediment pore water (1,3 mg/L at a depth of 10 cm below the sediment,water interface) were consistent with active in situ 4-NP biodegradation. These results suggest WWTP procedures that maximize the delivery of dissolved oxygen while minimizing the release of BOD to stream receptors favor efficient biodegradation of 4-NP contaminants in wastewater-impacted stream environments. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||