@article {2698, title = {Barrier Capacity of Hydrophilic Polymer Brushes To Prevent Hydrophobic Interactions: Effect of Graft Density and Hydrophilicity}, journal = {Macromolecules}, volume = {42}, number = {13}, year = {2009}, note = {ISI Document Delivery No.: 472NJTimes Cited: 7Cited Reference Count: 57Zou, Yuquan Rossi, Nicholas A. A. Kizhakkedathu, Jayachandran N. Brooks, Donald E.}, month = {Jul}, pages = {4817-4828}, type = {Article}, abstract = {The performance of biomaterials in contact with biological systems can be greatly affected by hydrophobic interactions at the interface between the biomaterial surface and surrounding biomolecules. Polymer brushes can function as a protective layer, preventing such interfacial hydrophobic interactions. In this paper, a systematic study of the barrier properties of a hydrophilic polymer brush is made by investigating the influence of graft density and its chemical nature (hydrophilicity/hydrophobicity) on hydrophobic interactions with the surface. To achieve this, it series of novel thermoresponsive poly-N-[(2,2-dimethyl-1,3-dioxolane)methyl]acrylamide (PDMDOMA) polymer brushes were grown from silicon wafers via surface-initiated atom transfer radical polymerization. Without changing graft density or degree of polymerization, the hydrophilicity of the PDMDOMA brushes was manipulated by partial or complete hydrolysis or the pendent dioxolane moieties. A lower critical solution temperature (LCST) was observed at 22-24 degrees C, below which the PDMDOMA brush was Found to be in a hydrated state (amphiphilic), while at temperatures above the LCST, the PDMDOMA brush formed a collapsed. more hydrophobic structure. A physical method was developed to analyze the ability of these brushes to act as a barrier against hydrophobic interactions based on AFM force-distance measurements. The adhesive forces between the Si3N4 tip and the silicon wafer surface upon (a) modification with ATRP initiator, (b) grafting of PDMDOMA brushes, and (c) partial and complete hydrolysis of PDMDOMA were investigated. Hydrophobic interactions decreased after each modification, while graft density and the degree of hydrolysis increased the barrier function of the surface layer. In particular, when graft density was above 0.22 chains/nm(2), the barrier capacity completely counteracted the hydrophobic interactions, as evidenced from the disappearance of the adhesive force in AFM measurements. Further Studies revealed that the barrier property its assessed by AFM correlated well with the wettability of the surfaces.}, keywords = {ATOMIC-FORCE MICROSCOPY, BLOOD-PLASMA, CELL-ADHESION, CHAIN-LENGTH, HUMAN, MOLECULAR-WEIGHT, protein adsorption, SERUM-ALBUMIN, SINGLE-MOLECULE, SURFACE, TRANSFER RADICAL POLYMERIZATION}, isbn = {0024-9297}, url = {://000268138500067}, author = {Zou, Y. Q. and Rossi, N. A. A. and Kizhakkedathu, J. N. and Brooks, D. E.} } @article {2674, title = {Competitive Adsorption of Toluene and n-Alkanes at Binary Solution/Silica Interfaces}, journal = {Journal of Physical Chemistry C}, volume = {113}, number = {47}, year = {2009}, note = {ISI Document Delivery No.: 520FMTimes Cited: 2Cited Reference Count: 48Yang, Zheng Li, Qifeng Hua, Rui Gray, Murray R. Chou, Keng C.}, month = {Nov}, pages = {20355-20359}, type = {Article}, abstract = {The competitive adsorption of toluene and n-alkanes at binary solution/silica interfaces was studied at room temperature using IR-visible sum frequency generation vibrational spectroscopy. The Surface coverage of toluene for toluene-pentane, toluene-heptane, and toluene-tetradecane mixtures was measured over the complete mole fraction range from 0 to 1. The competitive adsorption process was reversible, and the toluene coverage only depended oil the bulk mole fraction, not on the history of the system. The estimated molar adsorption free energy of toluene is 3.4 +/- 0.3, 1.8 +/- 0.3, and 0.84 +/- 0.3 kJ/mol higher than pentane, heptane, and tetradecane, respectively. Overall, toluene competes favorably on silica, and the molar adsorption free energy of alkanes increases as the chain length increases. It is consistent with the observed SFG spectra, indicating that the alkanes lie flat on the silica surface.}, keywords = {ACCELERATED SOLVENT-EXTRACTION, bitumen, CONFORMATION, FREQUENCY VIBRATIONAL SPECTROSCOPY, H STRETCHING MODES, LIQUID-CHROMATOGRAPHY, NORMAL-ALKYL CHAINS, ORIENTATION, SUM-FREQUENCY, SURFACE}, isbn = {1932-7447}, url = {://000271826100033}, author = {Yang, Z. and Li, Q. F. and Hua, R. and Gray, M. R. and Chou, K. C.} } @article {2673, title = {Structures of Water Molecules at the Interfaces of Aqueous Salt Solutions and Silica: Cation Effects}, journal = {Journal of Physical Chemistry C}, volume = {113}, number = {19}, year = {2009}, note = {ISI Document Delivery No.: 443FLTimes Cited: 6Cited Reference Count: 53Yang, Zheng Li, Qifeng Chou, Keng C.}, month = {May}, pages = {8201-8205}, type = {Article}, abstract = {Structures of water molecules at water/silica interfaces, in the presence of alkali chloride. were investigated using infrared-visible sum frequency vibrational spectroscopy. Significant perturbations of the interfacial water structure were observed on silica surfaces with the NaCl concentration as low as 1 x 10(-4) M. The cations, which interact with the Silica Surface via electrostatic interaction, play key roles in Perturbing the hydrogen-bond network of water molecules at the water/silica interface. This cation effect becomes saturated at concentrations around 10(-2) to 10(-1) M, where the sum frequency generation peaks at 3200 and 3400 cm(-1) decrease by 75\%. Different alkali cation species (Li+, Na+, and K+) produce different magnitudes of perturbation, with K+ > Li+ > Na+. This order can be explained by considering the effective ionic radii of the hydrated cations and the electrostatic interactions between the hydrated cations and silica Surfaces. The interfacial water structure associated with the 3200 cm(-1) band is more vulnerable to the cation perturbation, Suggesting that the more ordered water structure on silica is likely associated with the vincinal silanol groups, which create a higher local surface electrical field on silica.}, keywords = {ADSORPTION, charge, DYNAMICS SIMULATIONS, ELECTROLYTE INTERFACE, hydration, INTERFACE, LIQUID WATER, SOLID/LIQUID, SUM-FREQUENCY SPECTROSCOPY, SURFACE, vibrational spectroscopy}, isbn = {1932-7447}, url = {://000265895500034}, author = {Yang, Z. and Li, Q. F. and Chou, K. C.} } @article {1626, title = {Nanotubules on plant surfaces: Chemical composition of epicuticular wax crystals on needles of Taxus baccata L}, journal = {Phytochemistry}, volume = {67}, number = {16}, year = {2006}, note = {ISI Document Delivery No.: 090QVTimes Cited: 13Cited Reference Count: 24Wen, Miao Buschhaus, Christopher Jetter, Reinhard}, month = {Aug}, pages = {1808-1817}, type = {Article}, abstract = {Needles of Taxus baccata L. were covered with tubular epicuticular wax crystals varying in diameters (100 and 250 nm) and lengths (300-500 and 500-1000 nm) on the abaxial and adaxial surfaces, respectively. Various sampling protocols were employed to study the chemical composition of the needle waxes on three different levels of spatial resolution. First, a dipping extraction of whole needles yielded the total cuticular wax mixture consisting of very long chain fatty acids (21\%), alkanediols (19\%), phenyl esters (15\%), and secondary alcohols (9\%) together with small amounts of aldehydes, primary alcohols, alkanes, alkyl esters, and tocopherols. Second, waxes from both sides of the needle were sampled separately by brushing with CHCl3-soaked fabric glass. Both sides showed very similar qualitative composition, but differed drastically in quantitative aspects, with nonacosan-10-ol (18\%) and alkanediols (33\%) dominating the abaxial and adaxial waxes, respectively. Third, the epi- and intracuticular wax layers were selectively sampled by a combination of mechanical wax removal and brushing extraction. This provided direct evidence that the tubular wax crystals contained high percentages of nonacosane-4,10-diol and nonacosane-5,10-diol on the abaxial surface, and nonacosan-10-ol on the adaxial surface of the needles. Together with these compounds, relatively large amounts of fatty acids and smaller percentages of aldehydes, primary alcohols, alkyl esters, and alkanes co-crystallized in the epicuticular layer. In comparison, the intracuticular wax consisted of higher portions of cyclic constituents and aliphatics with relatively high polarity. The formation of the tubular crystals is discussed as a spontaneous physicochemical process, involving the establishment of gradients between the epi- and intracuticular wax layers and local phase separation. (c) 2006 Elsevier Ltd. All rights reserved.}, keywords = {composition, CUTICULAR WAX, IN-VITRO RECONSTITUTION, LEAF CUTICULAR WAXES, LEAVES, SECONDARY ALCOHOLS, SURFACE, Taxaceae, Taxus baccata, yew needles}, isbn = {0031-9422}, url = {://000240966900015}, author = {Wen, M. and Buschhaus, C. and Jetter, R.} } @article {1469, title = {Surface characterization of polytetrafluoroethylene (PTFE) transfer films during rolling-sliding tribology tests using X-ray photoelectron spectroscopy}, journal = {Wear}, volume = {261}, number = {10}, year = {2006}, note = {ISI Document Delivery No.: 113XZTimes Cited: 4Cited Reference Count: 33Lu, X. Wong, K. C. Wong, P. C. Mitchell, K. A. R. Cotter, J. Eadie, D. T.}, month = {Nov}, pages = {1155-1162}, type = {Article}, abstract = {A disk-on-disk Amsler wear tester simulating the rolling-sliding motion and high pressure during wheel/rail contact, was used to study the wear performance of PTFE including its film transfer and material flow properties. The chemical composition of the transfer film formed on the wheel-disk surface at various test stages were analyzed by X-ray photoelectron spectroscopy (XPS). The friction curve of the PTFE films obtained on the Amsler can be divided into three regions, according to the friction level and disk surface morphology. Initially, there is a rapid increase of friction coefficient which is presumably accompanied by a fast material transfer from pre-coated rail-disk to the wheel-disk surfaces. In the second region, the friction remains stable throughout and the XPS results show the presence of PTFE on the wheel-disk surface which confirms a transfer of material between the two contact surfaces. In addition, the splitting of F 1s and C 1s photoelectron peaks of PTFE, as a result of a discrepancy in surface charging, suggests that the transfer film exists in two forms: thick patch and thin film. With an increase in rolling cycles, the thick patches become thinner, as well as its coverage reduces. By contrast, the thin film gains both in thickness and coverage. Using a simple model, the thin film is calculated to be only a few nanometers thick. At the beginning of the third region, only a thin film is left on the surface. Additional rolling leads to a rapid rise in friction and the transfer film thickness continues to decrease. The evidence supports the removal of PTFE out of the contact zone, and a high friction coefficient (mu = 0.6) is reached at the end of the test indicating an un-lubricated metal-metal contact. No major tribochemical reaction of PTFE is observed during this study. (c) 2006 Elsevier B.V. All rights reserved.}, keywords = {(XPS), COMPOSITES, CONTACT, friction, friction modifier, INTERFACE, LUBRICATION, MODIFIER, polytetrafluoroethylene (PTFE), SURFACE, third body, TOP, WEAR, WHEEL-RAIL ADHESION, wheel/rail contact, X-ray photoelectron spectroscopy}, isbn = {0043-1648}, url = {://000242632600012}, author = {Lu, X. and Wong, K. C. and Wong, P. C. and Mitchell, K. A. R. and Cotter, J. and Eadie, D. T.} } @article {1076, title = {Ground and first-excited global potential energy surfaces of the H2O+-He complex: Predictions of ion mobilities}, journal = {International Journal of Quantum Chemistry}, volume = {101}, number = {1}, year = {2005}, note = {ISI Document Delivery No.: 872KKTimes Cited: 2Cited Reference Count: 29}, month = {Jan}, pages = {1-7}, type = {Article}, abstract = {Ion mobilities of H2O+ drifting in helium are calculated and compared with experiment. These calculations employ global potential energy surfaces of the H2O+-He complex, which in the present case were calculated ab initio at the unrestricted MP2 level of theory using a basis set of aug-cc-pVTZ quality, and treating the ion as a rigid body. Details are presented of the general characteristics of both the ground and first-excited electronic states of the complex. Although only the ground-state surface was used for the mobility calculations, the ab initio determination of the ground state necessitated the inclusion of the first-excited state owing to the presence of a crossing between the two. This crossing is also described. Mobilities calculated from the global surfaces are in good agreement with experiment. (C) 2004 Wiley Periodicals, Inc.}, keywords = {AB-INITIO, COLLISIONAL ALIGNMENT, first-excited state, global energy, H2O+-He complex, HELIUM, INDUCED ROTATIONAL ALIGNMENT, ion mobility, MICROSOLVATION, MOLECULAR-DYNAMICS, MP2, SPECTRA, SUPERSONIC EXPANSIONS, SURFACE, VELOCITY, WATER CATION}, isbn = {0020-7608}, url = {://000225205900001}, author = {Chen, X. and Thachuk, M.} } @article {1260, title = {Nematic fluid structure in wall-field geometry}, journal = {Journal of Chemical Physics}, volume = {122}, number = {3}, year = {2005}, note = {ISI Document Delivery No.: 893VPTimes Cited: 6Cited Reference Count: 31}, month = {Jan}, pages = {9}, type = {Article}, abstract = {We describe an integral equation method for obtaining the distribution of a nematic fluid near a wall and interacting with a uniform orienting field. Complete density-orientational profiles are calculated for a model nematic with different wall-particle interactions and different orientations of the wall with respect to the field. For orienting walls we identify particular long-range correlations that are responsible for reorientation of the bulk nematic at zero external field. These correlations become stronger as the wall-particle interaction is increased in range; they become longer ranged as the orienting field is weakened. Special attention is focused on systems where the wall-particle interaction favors orientations perpendicular to the surface. The local director orientation can vary discontinuously with the distance from the surface when the orienting influences of the field and the wall are antagonistic. At high densities smectic-like structures appear. Adsorption phenomena are also discussed. For inert hard walls, the ordered fluid avoids the surface, and a surface layer where the particles tend to orient perpendicular to the bulk director appears. Experimentally, this might be seen as wetting of the wall by a less-ordered fluid. (C) 2005 American Institute of Physics.}, keywords = {ALIGNMENT, APPROXIMATION, LIQUID-CRYSTALS, MODEL, ORNSTEIN-ZERNIKE EQUATION, PHASE-TRANSITION, SOLID SUBSTRATE, SUBSTRATE INTERFACE, SURFACE}, isbn = {0021-9606}, url = {://000226748800030}, author = {Sokolovska, T. G. and Sokolovskii, R. O. and Patey, G. N.} } @article {793, title = {The effect of Ni2+ on zinc phosphating of 2024-T3 Al alloy}, journal = {Surface \& Coatings Technology}, volume = {187}, number = {2-3}, year = {2004}, note = {ISI Document Delivery No.: 860VHTimes Cited: 27Cited Reference Count: 32}, month = {Oct}, pages = {208-215}, type = {Article}, abstract = {Zinc phosphate (ZPO) conversion coatings formed on 2024-T3 aluminum alloy, and on high-purity aluminum, after dipping in coating baths containing different amounts of Ni2+, have been studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, scanning Auger microscopy (SAM) and electrochemical measurements. Significant variations are observed in coating morphology and in stability against corrosion for the 2024-Al alloy as the amount of Ni2+ in the coating solution increases through the 0-2000 ppm range. By contrast, for high-purity Al, the most marked changes in coating morphology occur only as the Ni2+ concentration reaches 2000 ppm. The presence of additional elements, and especially Cu, in the 2024-Al samples results in an increase in the number of cathodic sites and hence more coating is formed for corresponding conditions. Additionally, the existence of second-phase particles in the 2024-Al sample leads to variations in the coatings at the microstructural level across the surface. These differences include local variations in the amount of Ni2+ in the coatings, as well as the local coverage. (C) 2004 Elsevier B.V. All rights reserved.}, keywords = {aluminum alloy, ALUMINUM-ALLOY, Auger electron spectroscopy, chemical conversion, CHROMATE CONVERSION COATINGS, CORROSION PROTECTION, FILMS, Ni2+ additive, NICKEL, phosphating, photoelectron spectroscopy, STEEL, SURFACE, XPS}, isbn = {0257-8972}, url = {://000224371300011}, author = {Akhtar, A. S. and Susac, D. and Glaze, P. and Wong, K. C. and Wong, P. C. and Mitchell, K. A. R.} } @article {865, title = {Evaluation of an atomic force microscopy pull-off method for measuring molecular weight and polydispersity of polymer brushes: Effect of grafting density}, journal = {Langmuir}, volume = {20}, number = {15}, year = {2004}, note = {ISI Document Delivery No.: 837VSTimes Cited: 16Cited Reference Count: 31}, month = {Jul}, pages = {6238-6245}, type = {Article}, abstract = {The accuracy of the molecular weights M-n and polydispersities of polymer brushes, determined by stretching the grafted chains using atomic force microscopy (AFM) and measuring the contour length distribution, was evaluated as a function of grafting density sigma. Poly(NN-dimethylacrvlamide) brushes were prepared by surface initiated atom transfer radical polymerization on latex particles with a ranging between 0.17 and 0.0059 chains/nm(2) and constant M-n. The polymer, which could be cleaved from the grafting surface by hydrolysis and characterized by gel permeation chromatography (GPC), had a M-n of 30 600 and polydispersity (PDI) of 1.35. The M-n determined by the AFM technique for the higher density brushes agreed quite well with the GPC results but was significantly underestimated for the lower sigma. At high grafting density in good solvent, the extended structure of the brush increases the probability of forming segment-tip contacts located at the chain end. When the distance between chains approached twice the radius of gyration of the polymer, the transition from brush to mushroom structure presumably enabled the formation of a larger number of segment-tip contacts having separations smaller than the contour length, which explains the discrepancy between the two methods at low sigma. The PDI was typically higher than that obtained by GPC, suggesting that sampling of chains with above average contour length occurs at sigma frequency that is greater than their spatial distribution.}, keywords = {CHAIN, DETACHMENT, DIBLOCK COPOLYMER MONOLAYERS, DYNAMICS, INTERFACE, LAYERS, NEUTRON REFLECTIVITY, SURFACE}, isbn = {0743-7463}, url = {://000222669800025}, author = {Goodman, D. and Kizhakkedathu, J. N. and Brooks, D. E.} } @article {748, title = {Adsorption of BTSE and gamma-APS organosilanes on different microstructural regions of 2024-T3 aluminum alloy}, journal = {Applied Surface Science}, volume = {207}, number = {1-4}, year = {2003}, note = {ISI Document Delivery No.: 655URTimes Cited: 30Cited Reference Count: 34}, month = {Feb}, pages = {40-50}, type = {Article}, abstract = {The adsorption of bis-1,2-(triethoxysilyl)ethane (BTSE) and gamma-aminopropyltriethoxysilane (gamma-APS) has been studied on 2024-T3 aluminum alloy samples using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The thickness and coverage of the BTSE film formed on a mechanically polished sample was found to be strongly affected by the distribution of second-phase particles on the alloy surface. Specifically, although the adsorption occurs on the alloy matrix away from the particles, and on the particles themselves, the regions immediately surrounding the particles had less BTSE. The amounts of this adsorption on an air-oxidized sample is increased on average, although the coating is non-uniform with regions (similar to100 mum) of higher and lower coverages. There appears to be a competition between the silane deposition and etching of the underlying oxide film for the initially oxidized sample. The adsorption of gamma-APS is different with films of relatively even thickness formed over large areas of the polished sample; hydrogen bonding through the amino groups probably helps the distribution in this case. (C) 2002 Elsevier Science B.V. All rights reserved.}, keywords = {aluminum alloy, DISSOLUTION, iron, metals, OXIDATION, PAINT ADHESION, PARTICLES, PITTING CORROSION, silane adsorption, SURFACE, surface microstructure}, isbn = {0169-4332}, url = {://000181571500007}, author = {Susac, D. and Sun, X. and Mitchell, K. A. R.} } @article {533, title = {Structure determination of Cu(410)-O using X-ray diffraction and DFT calculations}, journal = {Surface Science}, volume = {516}, number = {1-2}, year = {2002}, note = {ISI Document Delivery No.: 594AQTimes Cited: 12Cited Reference Count: 52}, month = {Sep}, pages = {16-32}, type = {Article}, abstract = {The Cu(4 1 0)-O surface, involving a 0.5 monolayer (ML) coverage of oxygen, is known to be extremely stable and a range of Cu(1 0 0) vicinal. surfaces facet to (4 1 0) in the presence of adsorbed oxygen. A new surface X-ray diffraction investigation of this surface has been conducted to determine its structure, and the detailed structural parameter values obtained are compared with the results of a density functional theory (DFT) calculation. The results show that the metal structure is unreconstructed, with the oxygen forming an overlayer with 0.25 ML O atoms at near-colinear step-edge sites and 0.25 NIL O atoms at mid-terrace hollow sites, approximately 0.6 Angstrom above the terraces. The large number of independent structural parameters potentially relevant to this vicinal surface presents a significant challenge for unique structural optimisation, but various missing row reconstruction models can be clearly excluded. Two detailed structural solutions are identified which give equally acceptable fits to the X-ray diffraction data after imposition of a Lennard-Jones penalty factor. These models differ especially in the O positions, but one is found to be more favoured by comparison with the results of the DFT calculations, and by considerations based on bond lengths and valence. Substantial relaxations from the bulk metal positions occur for the outermost Cu atoms; the ability of the vicinal surface to relax in this way may help to account for its stability compared with the missing row reconstruction induced by oxygen chemisorption on the Cu(1 0 0) surface. (C) 2002 Elsevier Science B.V. All rights reserved.}, keywords = {ADSORPTION, and, and topography, chemisorption, copper, CU(100), DETERMINATION, DIFFRACTION, ENERGY ION-SCATTERING, INITIO MOLECULAR-DYNAMICS, MISSING-ROW, MORPHOLOGY, OXYGEN, OXYGEN-INDUCED RECONSTRUCTION, RECONSTRUCTION, reflection, relaxation and reconstruction, roughness, SCANNING-TUNNELING-MICROSCOPY, SURFACE, surface structure, SURFACE-STRUCTURE, SURFACES, VICINAL COPPER SURFACES, vicinal single crystal, WAVE BASIS-SET, X-ray scattering}, isbn = {0039-6028}, url = {://000178027000003}, author = {Vlieg, E. and Driver, S. M. and Goedtkindt, P. and Knight, P. J. and Liu, W. and Ludecke, J. and Mitchell, K. A. R. and Murashov, V. and Robinson, I. K. and de Vries, S. A. and Woodruff, D. P.} } @article {405, title = {Synthesis and characterization of polymer brushes of poly(N,N-dimethylacrylamide) from polystyrene-latex by aqueous atom transfer radical polymerization}, journal = {Macromolecules}, volume = {35}, number = {11}, year = {2002}, note = {ISI Document Delivery No.: 554GUTimes Cited: 64Cited Reference Count: 51}, month = {May}, pages = {4247-4257}, type = {Article}, abstract = {Negatively charged polystyrene latex was synthesized, and a copolymer shell of 2-(methyl-2{\textquoteright}-chloropropionato)ethyl acrylate (HEA-Cl) and styrene was added, from which poly(N,N-dimethylacrylamide) (PDMA) was polymerized by atom transfer radical polymerization in aqueous suspension at room temperature. Increasing monomer concentration in the presence of CuCl or CuBr and one of three ligands (N,N,N{\textquoteright},N{\textquoteright},N"-pentamethyldiethylenetriamine (PMDETA), 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), and tris [2-(dimethylamino)ethyl] amine (Me6TREN)) produced grafts whose molecular weight increased to over 600 000 and polydispersities in the range of 1.3-1.8, determined from chains recovered following cleavage by base. Hydrodynamic brush thicknesses were 70-800 nm, and average chain separations, calculated from M-n and the mass of polymer recovered per particle, varied from 4.0 to 1.1 nm. Very high grafting densities were achieved with good molecular weight control, the highest densities yet reported for high molecular weight polymer chains grown from a surface. Control of the polymerization was improved by addition of Cu(II) to enhance deactivation of free radicals, by including a low concentration of exogenous hydrophobic initiator at high monomer concentration and by reducing latex concentration. Increasing the concentration of exogenous initiator reduced graft thickness but eliminated control over the polydispersity. The unusual conditions required for optimization of the reaction and the observation of decreasing chain separation as M-n increased were explained by invoking a model of the particle surface that took into account the finite depth and high copolymer concentration of the region in which chains were initiated and particularly the fixed charges due to the sulfate initiator of shell copolymerization.}, keywords = {(METH)ACRYLAMIDES, ADSORPTION, AMBIENT-TEMPERATURE, BLOCK-COPOLYMERS, CARBOCATIONIC, FACILE, POLYELECTROLYTE BRUSHES, POLYMERIZATION, SELF-ASSEMBLED MONOLAYERS, SURFACE, SYNTHESIS, TETHERED CHAINS}, isbn = {0024-9297}, url = {://000175728100006}, author = {Jayachandran, K. N. and Takacs-Cox, A. and Brooks, D. E.} } @article {4704, title = {{Formation of Pd2X2(mu-S)(mu-dpm)(2) by reaction of PdX2(dpm) with H2S in the presence of alumina (X = halogen}, journal = {Journal of Molecular Catalysis a-Chemical}, volume = {139}, number = {2-3}, year = {1999}, note = {ISI Document Delivery No.: 162RZTimes Cited: 5Cited Reference Count: 21}, month = {Mar}, pages = {159-169}, type = {Article}, abstract = {Alumina promotes the reaction of PdX2(dpm) (3) (X = Cl, Br, I) with H2S to form Pd2X2(mu-S)(dpm)(2) (2)(1) and HX, with chemisorption of the HX (quantified by titration) providing the driving force; although no intermediate species are detected, the reaction likely proceeds via mercapto species formed via {\textquoteright}alumina activated H2S{\textquoteright}. XPS studies show interactions of species 2 and 3 with alumina, these interactions being weak as demonstrated by recovery of the species on dissolution using an appropriate solvent. For the iodide system, adsorbed HI on alumina undergoes partial photodecomposition to give I-2 and H atoms. (C) 1999 Elsevier Science B.V. All rights reserved.}, keywords = {ALUMINA, ASPECTS, bis(diphenylphosphino)methane, CONVERSION, CRYSTAL, DERIVATIVES, DINUCLEAR PALLADIUM(I) COMPLEXES, H2S, HYDROGEN-SULFIDE, Mechanistic, models, Pd2X2(mu-S)(mu-dpm)(2), PdX2(dpm), SURFACE}, isbn = {1381-1169}, url = {://000078361700006}, author = {Wong, T. Y. H. and James, Brian R. and Wong, P. C. and Mitchell, K. A. R.} } @article {4655, title = {Tensor LEED analysis for the Cu(111)-(root x root 7)R19.1 degrees-S surface structure}, journal = {Surface Science}, volume = {441}, number = {2-3}, year = {1999}, note = {ISI Document Delivery No.: 253RWTimes Cited: 11Cited Reference Count: 36}, month = {Nov}, pages = {425-435}, type = {Article}, abstract = {A tensor LEED analysis is reported for the (root 7 x root 7)R19.1 degrees structure formed by S at the Cu(lll)surface. A new structural model is found which corresponds to a modified version of the copper sulphide overlayer model first proposed by Domange and Oudar. In that model, the topmost layer has 3/7 monolayer each of Cu and S atoms, but the modification involves one S atom per unit mesh moving down to displace a Cu atom from the second metal layer. Relaxations among the topmost Cu atoms result in one S atom being effectively three-fold coordinate while the other two are sixfold coordinate and 12-fold coordinate: the averaged S-Cu bond lengths are indicated to equal 2.19, 2.47 and 2.62 Angstrom respectively. Some discussion is included of factors that may influence this choice of surface structure. (C) 1999 Elsevier Science B.V. All rights reserved.}, keywords = {ADSORPTION, chemisorption, copper, ENERGY-ELECTRON-DIFFRACTION, LAYERS, low energy electron diffraction, LOW INDEX SINGLE CRYSTAL, METAL-SURFACES, MOLECULE, RAY STANDING-WAVE, RECONSTRUCTION, RU(0001), SUBSTRATE, SULFUR, sulphur, SURFACE, surface reconstruction}, isbn = {0039-6028}, url = {://000083570400024}, author = {Saidy, M. and Mitchell, K. A. R.} } @article {4151, title = {LEED crystallographic analysis for the structure formed by 2 ML of O at the Zr(0001) surface}, journal = {Surface Science}, volume = {380}, number = {2-3}, year = {1997}, note = {ISI Document Delivery No.: XF843Times Cited: 17Cited Reference Count: 29}, month = {May}, pages = {540-547}, type = {Article}, abstract = {A tensor LEED analysis is reported for the Zr(0001)-(1 x 1)-O surface which involves oxygen at a total coverage of 2 monolayers. The structure is indicated to have two layers of O: one forms an overlayer in which the O atoms bond to hollow sites of three-fold coordination on the regular metal surface. while the other laver has the O atoms in tetrahedral hole sires between the first and second metal layers. The stacking sequence, designated as (C)B(A)AB, corresponds to the first three layers of anion-terminated cubic ZrO2, although some lateral compression is needed for superposition on the regular hcp Zr structure. The absorption of O in the tetrahedral holes results in a significant expansion in the first-to-second Zr-Zr interlayer spacing to about 3.44 Angstrom from the bulk vaue of 2.57 Angstrom. The O-Zr bond lengths are estimated to equal 2.07 Angstrom for the overlayer O atoms, and 2.21 Angstrom for the O atoms in tetrahedral hole sites, Comparisons are made with the structures of the corresponding 0.5 and 1 ML surfaces formed by the O/Zr(0001) system. (C) 1997 Elsevier Science B.V.}, keywords = {ENERGY-ELECTRON-DIFFRACTION, GROWTH, LEED crystallography, low index single crystal surface, OXIDE THIN-FILMS, OXYGEN, SINGLE-CRYSTAL SURFACES, STRUCTURE, SURFACE, ZIRCONIUM}, isbn = {0039-6028}, url = {://A1997XF84300044}, author = {Wang, Y. M. and Li, Y. S. and Mitchell, K. A. R.} } @article {4128, title = {Modeling and structure of mercury-water interfaces}, journal = {Journal of Chemical Physics}, volume = {107}, number = {6}, year = {1997}, note = {ISI Document Delivery No.: XP280Times Cited: 37Cited Reference Count: 78}, month = {Aug}, pages = {2122-2141}, type = {Article}, abstract = {The modeling and nature of the physisorption of water at the metal (Hg)-water interface is explored in this paper. We have evaluated potential models that fit into three general classes that are employed in the literature. These classes are distinguished by the manner in which the isotropic interactions between the metal and the water are modeled: namely, as non-attractive, weakly attractive, and strongly attractive. In the present studies the metal is described by a jellium model. In our model, in addition to the isotropic water potential there is an interaction between the jellium and the water molecules which depends on the orientation of the water molecule with respect to the metal surface. We find that hard potentials without isotropic attractive terms dewet. The density of water near hydrocarbon-like potentials remains close to the bulk value but the interaction isn{\textquoteright}t strong enough to structure the water near the interface, nor are the adsorption energies sufficiently high. The strongly attractive potentials seem to be the most appropriate. For such models we have checked the sensitivity of the results to the parameters in our model including surface corrugation. We find that the structural results are insensitive to the parameters employed suggesting that they not only provide a good classical description of the Hg-water interface but may be readily adaptable to describe the physisorption of water on metals in general. Although we find the layering of water molecules and the pattern of hydrogen bonding near these surfaces, which have been described as ice-like in previous studies, the actual arrangement of the water molecules near these surfaces is distinctly different from the structure of ice. (C) 1997 American Institute of Physics.}, keywords = {CHARGED ELECTRODES, COMPUTER-SIMULATION, DOUBLE-LAYER, ELECTROLYTE, HALIDE-IONS, INTERFACE, LIQUID WATER, METAL INTERFACE, MOLECULAR-DYNAMICS SIMULATION, SURFACE, TIP4P WATER}, isbn = {0021-9606}, url = {://A1997XP28000045}, author = {Shelley, J. C. and Patey, G. N. and Berard, D. R. and Torrie, G. M.} } @article {3809, title = {Boundary condition effects in simulations of water confined between planar walls}, journal = {Molecular Physics}, volume = {88}, number = {2}, year = {1996}, note = {ISI Document Delivery No.: UN985Times Cited: 86Cited Reference Count: 32}, month = {Jun}, pages = {385-398}, type = {Article}, abstract = {In computer simulations of water between hydrophobic walls the results exhibit a strong dependence upon the boundary conditions applied. With the minimum image (MI) convention the water molecules tend to be orientationally ordered throughout the simulation cell (Valleau, J. P., and Gardner, A. A., 1987, J. chem. Phys., 86, 4162) whereas, if a spherical cut-off (SC) is applied, strong orientational order is found only in the immediate vicinity of the surface (Lee, C. Y., McCammon, J. A., and Rossky, P. J., 1984, J. chem. Phys., 80, 4448). These conflicting observations have remained unresolved, and clearly raise troubling questions concerning the validity of simulation results for water between surfaces of all types. In the present paper we explore this problem by carrying out a detailed analysis of the results obtained with various types of boundary condition. These include Ewald calculations carried out with a central simulation cell adapted to describe the slab geometry of interest. It is shown that the order observed in MI calculations is an artefact of that particular truncation. The reason for this is isolated and discussed. Similar problems are found if a cylindrical cut-off is employed. The Ewald and SC methods gave qualitatively similar results for systems similar to those considered in previous simulations. However, for some geometries problems can also arise with the SC method. We conclude that in general the slab-adapted Ewald method is the safest choice.}, keywords = {ADSORPTION, CHARGED ELECTRODES, COMPUTER-SIMULATION, IONS, LIQUID WATER, METAL WALLS, models, MOLECULAR-DYNAMICS SIMULATION, MONTE-CARLO SIMULATIONS, SURFACE}, isbn = {0026-8976}, url = {://A1996UN98500006}, author = {Shelley, J. C. and Patey, G. N.} } @article {3564, title = {XPS STUDIES OF THE STABILITY OF A MIXED ZIRCONIUM-OXIDE AND SULFIDE THIN-FILM}, journal = {Surface Review and Letters}, volume = {2}, number = {2}, year = {1995}, note = {ISI Document Delivery No.: RD591Times Cited: 1Cited Reference Count: 12}, month = {Apr}, pages = {165-169}, type = {Article}, abstract = {A 25 Angstrom film formed by depositing zirconium (similar to 2 Angstrom min(-1)) onto gold foil in the presence of H2S (similar to 5 X 10(-8) mbar) and H2O (similar to 1 X 10(-9) mbar) has been studied by XPS. This film has an outer region composed of a mixed zirconium oxide/sulphide, while below there is metallic zirconium plus Zr/Au alloy in contact with gold. This film appears stable on heating to 400 degrees C under UHV insofar as the sulphide part does not change, although the oxide part increases apparently as a result of some reaction of metallic zirconium with ambient water. By contrast, when this preheated film at room temperature was treated with a hydrogen plasma, the sulphide component was completely removed and the whole film was converted to the ZrO2-like form with enhanced formation of OH groups. The hydrogen plasma treatment is therefore capable of desulphurising the mixed zirconium oxide/sulphide film.}, keywords = {OXYGEN, SURFACE}, isbn = {0218-625X}, url = {://A1995RD59100005}, author = {Wong, P. C. and Li, Y. S. and Zhou, M. Y. and Mitchell, K. A. R.} } @article {2931, title = {MOLECULAR-SOLVENT MODEL FOR AN ELECTRICAL DOUBLE-LAYER - EFFECTS OF IONIC POLARIZABILITY}, journal = {Journal of Chemical Physics}, volume = {99}, number = {5}, year = {1993}, note = {ISI Document Delivery No.: LU722Times Cited: 21Cited Reference Count: 29}, month = {Sep}, pages = {3990-3997}, type = {Article}, abstract = {The effect of ionic polarizability on properties of the electrical double layer is considered by extending a theory of Kusalik and Patey [J. Chem. Phys. 92, 1345 (1990)] to the case of an ion at a distance r from a charged macroion. The reference hypernetted-chain theory is solved for a fully molecular model of the double layer and the results are compared with previous results for an identical model without polarizability and with experimental data for double layers in alkali halide solutions. Polarizability is found to have a large effect on the differential capacitance at high surface charges and to make a substantial contribution to the experimentally observed asymmetry in this quantity. This effect is shown to have its origin, not in any structural change in the double layer, but in the contribution to the potential from the induced polarization of the ions themselves.}, keywords = {AQUEOUS-ELECTROLYTE SOLUTIONS, SURFACE}, isbn = {0021-9606}, url = {://A1993LU72200091}, author = {Wei, D. Q. and Torrie, G. M. and Patey, G. N.} } @article {7242, title = {AN ALTERNATIVE PREPARATION OF ORGANOFUNCTIONALIZED SILICA-GELS AND THEIR CHARACTERIZATION BY 2-DIMENSIONAL HIGH-RESOLUTION SOLID-STATE HETERONUCLEAR NMR CORRELATION SPECTROSCOPY}, journal = {Journal of the American Chemical Society}, volume = {114}, number = {9}, year = {1992}, note = {ISI Document Delivery No.: HQ814Times Cited: 70Cited Reference Count: 11}, month = {Apr}, pages = {3252-3255}, type = {Article}, abstract = {High-resolution solid-state Si-29 CP/MAS NMR spectroscopy has been used to characterize methyl functionalized silica gels prepared by the copolymerization of tetraethoxysilane and methyltriethoxysilane. One-dimensional Si-29 CP/MAS NMR indicates that the two components are present in the correct proportions in the gel, but it is not sensitive to the degree of mixing. A two-dimensional H-1/Si-29 correlation experiment clearly demonstrates that the two components are not phase-separated, but are mixed in the final gel.}, keywords = {CROSS-POLARIZATION, NUCLEAR MAGNETIC-RESONANCE, SURFACE}, isbn = {0002-7863}, url = {://A1992HQ81400014}, author = {Fyfe, C. A. and Zhang, Y. and Aroca, P.} } @article {7162, title = {CHARACTERIZATION OF SPUTTER DEPOSITED TUNGSTEN FILMS FOR X-RAY MULTILAYERS}, journal = {Journal of Vacuum Science \& Technology a-Vacuum Surfaces and Films}, volume = {10}, number = {2}, year = {1992}, note = {ISI Document Delivery No.: HK010Times Cited: 27Cited Reference Count: 24}, month = {Mar-Apr}, pages = {273-280}, type = {Article}, abstract = {The microstructural and optical properties of tungsten thin films prepared by dc magnetron sputtering were investigated as a function of the argon pressure. The films were characterized by x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), x-ray diffraction (XRD), grazing x-ray reflectometry (GXR), and spectroscopic ellipsometry (SE). From the analysis of the XPS data, the films were found to consist of a base tungsten layer, a graded oxide transition layer, and a surface oxide layer. Also, the thickness of the oxide layers were determined. XRD indicated that the films were either amorphous or composed of crystallites with grain size < 100 angstrom. STM and GXR have revealed that the films grown at low pressures were the smoothest. Finally, SE measurements allowed the determination of the dielectric function of a compact tungsten layer. Further SE analysis of the films indicated that with increasing argon pressure, the films developed into a more voided columnar structure.}, keywords = {SILICON, SURFACE}, isbn = {0734-2101}, url = {://A1992HK01000002}, author = {Aouadi, M. S. and Parsons, R. R. and Wong, P. C. and Mitchell, K. A. R.} } @article {7259, title = {TEMPORAL EMISSION AND ABSORPTION CHARACTERISTICS OF SILVER, LEAD AND MANGANESE IN FURNACE ATOMIZATION PLASMA EXCITATION SPECTROMETRY}, journal = {Journal of Analytical Atomic Spectrometry}, volume = {7}, number = {7}, year = {1992}, note = {ISI Document Delivery No.: JY532Times Cited: 15Cited Reference Count: 37}, month = {Oct}, pages = {1039-1046}, type = {Article}, abstract = {The temporal behaviour of the signal measured for Ag, Pb and Mn in furnace atomization plasma excitation spectrometry was studied using atomic emission and atomic absorption spectrometry. Analyte was deposited both on the wall and on the r.f. electrode with and without the r.f. power applied. Analyte condensation on the r.f. electrode is observed when no plasma is formed. When the plasma is formed inside the furnace it heats the electrode such that, for Ag and Pb, condensation is not observed except for large amounts of analyte. For Ag and Mn, the appearance temperatures and peak temperatures are not significantly affected by the plasma relative to the response obtained using a graphite furnace. For Pb, appearance and peak temperatures are shifted significantly earlier. For Pb, atom formation may be effected by the presence of CO in the gas phase generated from oxidation of the graphite furnace wall and electrode. The role of carbon in atom formation was studied by depositing the sample on both tungsten and graphite electrodes.}, keywords = {ASCORBIC-ACID, ATOMIC-ABSORPTION, DOUBLE PEAKS, ELECTROTHERMAL ATOMIZATION, FAPES, FURNACE ATOMIZATION PLASMA EXCITATION SPECTROMETRY, GRAPHITE FURNACE, GRAPHITE-FURNACE, LEAD AND MANGANESE SIGNALS, MECHANISMS, silver, SURFACE, TEMPERATURE, vaporization}, isbn = {0267-9477}, url = {://A1992JY53200002}, author = {Hettipathirana, T. D. and Blades, M. W.} } @article {7209, title = {THERMOLYSIS OF RU3(CO)10[FE(ETA-C5H4PPRI2)2] - STRUCTURE OF RU3(CO)8(MU-H)2[ETA-PC5H4)FE(ETA-C5H4PPRI2)] AND RU3(CO)8(MU-H)(MU-OH)[MU-FE(ETA-C5H4PPRI2)2]}, journal = {Organometallics}, volume = {11}, number = {2}, year = {1992}, note = {ISI Document Delivery No.: HE298Times Cited: 21Cited Reference Count: 30}, month = {Feb}, pages = {853-858}, type = {Article}, abstract = {{Heating Ru3(CO)10(Fc{\textquoteright}(PPr(i)2)2) (Fc{\textquoteright} = Fe(eta-C5H4)2) in refluxing cyclohexane affords three products in moderate yields. The complex Ru3(CO)8(mu-H)2[(eta-PC5H4)Fe(eta-C5H4PPr(i)2)] (7) was characterized by X-ray diffraction. It crystallizes in the triclinic system, space group P1BAR, with a = 11.782 (4) angstrom}, keywords = {BENZYNE COMPLEXES, CLUSTER CHEMISTRY, COORDINATION, MOLECULAR-STRUCTURE, OSMIUM, RAY CRYSTAL-STRUCTURE, SURFACE, X-RAY}, isbn = {0276-7333}, url = {://A1992HE29800052}, author = {Cullen, W. R. and Rettig, S. J. and Zheng, T. C.} } @article {7122, title = {MOLECULAR-SOLVENT MODELS OF ELECTRICAL DOUBLE-LAYERS}, journal = {Electrochimica Acta}, volume = {36}, number = {11-12}, year = {1991}, note = {ISI Document Delivery No.: GJ354Times Cited: 1Cited Reference Count: 17INTERDISCIPLINARY CONF ON ELECTRIFIED INTERFACESSEP 16-21, 1990ASILOMAR, CAAMER PHYS SOC, INT SOC ELECTROCHEM, IBM, US DOE, NATL SCI FDN, USN, OFF NAVAL RES}, pages = {1669-1675}, type = {Proceedings Paper}, abstract = {This paper summarizes some recent work directed towards the construction of a wholly molecular theory of the solution side of an electrical double layer using modern liquid state theory. The influence of surface charge on the solvent restructuring near the surface and the consequences of this for the ionic distributions in the double layer are discussed and related to the role of the continuum solvent description embodied in Gouy-Chapman theory.}, keywords = {APPROXIMATION, AQUEOUS-ELECTROLYTE SOLUTIONS, DOUBLE LAYER THEORY, INFINITE DILUTION, MOLECULAR MODELS, STATISTICAL MECHANICS, SURFACE, WATER}, isbn = {0013-4686}, url = {://A1991GJ35400004}, author = {Torrie, G. M. and Patey, G. N.} } @article {7139, title = {RATE CONSTANTS FOR THE ETCHING OF INTRINSIC AND DOPED POLYCRYSTALLINE SILICON BY BROMINE ATOMS}, journal = {Journal of Applied Physics}, volume = {69}, number = {4}, year = {1991}, note = {ISI Document Delivery No.: EZ664Times Cited: 21Cited Reference Count: 15}, month = {Feb}, pages = {2635-2638}, type = {Article}, abstract = {{The rate constants for the reaction of bromine atoms with intrinsic and heavily doped n+-type polycrystalline silicon, as well as their temperature dependencies, are reported for the first time. The rate constant for intrinsic silicon is given as k = (4 +/- 2) x 10(7) nm min-1 Torr-1e-(62 +/- 2kJ/mol)/RT and for n+-type silicon with a phosphorus number density of 5 x 10(18) cm-3}, keywords = {CHLORINE, FLUORINE, SI, SURFACE}, isbn = {0021-8979}, url = {://A1991EZ66400126}, author = {Walker, Z. H. and Ogryzlo, E. A.} }