Showing papers in "Langmuir in 1997"
TL;DR: In this paper, it was shown that the Kelvin equation for the hemispherical meniscus, corrected for the statistical film thickness, is in quite good agreement with an experimental relation between the pore size and the capillary condensation pressure.
Abstract: MCM-41 siliceous molecular sieves were used to test the applicability of the Kelvin equation for nitrogen adsorption in cylindrical pores of the size from 2 to 65 nm It was shown that the Kelvin equation for the hemispherical meniscus, corrected for the statistical film thickness, is in quite good agreement with an experimental relation between the pore size and the capillary condensation pressure The agreement can be made quantitative in the pore size range from ca 2 to 65 nm, if a simple correction to the Kelvin equation is introduced The required statistical film thickness curve (t-curve) was calculated using nitrogen adsorption data for large pore MCM-41 samples and the obtained results were extrapolated using an adsorption isotherm for a macroporous silica gel Moreover, an accurate analytical representation of the t-curve was found Since both the corrected Kelvin equation for cylindrical pores and the t-curve have simple analytical forms, they can conveniently be used in a variety of methods
1,368 citations
TL;DR: In this paper, the synthesis of nanosized particles by using colloidal assemblies as a template is described, and it is found that these particles form crystals organized in a three-dimensional face-cent
Abstract: In this feature article, syntheses of nanosized particles by using colloidal assemblies as a template are described We asked ourselves the following question: What parameters play a role in the control of the size, shape, and polydispersity? We know that parameters such as the shape of colloidal assemblies, the hydration of the head polar group, the water molecules bounded to the interface, etc play a major role However, there are a number of exceptions preventing any generalization It is shown that the chemical mechanism in nanoparticles production in colloidal assemblies can differ from those usually observed in homogeneous solution This shows that the solution chemistry cannot always be transferred to colloidal systems It is possible to select the size and markedly reduce the polydispersity by a surface treatment of the nanoparticles This favors formation of mono- and multilayers made of nanoparticles, and it is found that these particles form crystals organized in a three-dimensional face-cent
776 citations
TL;DR: In this paper, the authors show that specific ion adsorption due to dispersion interactions can be dominant even at charged interfaces especially at high salt concentrations (∼0.1 ε).
Abstract: Present theories of colloid science do not account for specific ion effects as exemplified by the Hofmeister effect, surface tension of electrolyte solution interfaces, binding to micelles, effective charge in double layer interactions, and attractive interactions in low Hamaker constant systems. It is argued that specificity emerges naturally and can be rationalized if dispersion interactions acting on ions are included in the theory. These are in principle accessible from bulk solution properties. Specific ion adsorption due to dispersion interactions can be dominant even at charged interfaces especially at high salt concentrations (∼0.1Μ). The effects can be qualitatively different at air−water and oil−water surfaces. That part of extended Lifshitz theory for low Hamaker constant systems, in which the forces are mainly due to temperature and salt dependent interaction, is re-examined. It is shown to be at the same level of approximation as, and precisely equivalent to, the Onsager limiting law for the ...
541 citations
TL;DR: In this paper, an alternating layer-by-layer assembly of colloidal SiO2 particles with polycations has been investigated by quartz crystal microbalance (QCM), scanning electron microscopy, and atomic force microscopy (AFM).
Abstract: Alternate layer-by-layer assembly of colloidal SiO2 particles with polycations has been investigated by quartz crystal microbalance (QCM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). QCM measurement confirmed the high regularity and reproducibility of the assembling process that depends on particle concentration, particle size, and ionic strength. The individual adsorption step was completed within 15 s. The thickness of adsorbed layers increased with increasing SiO2 concentrations at the three particle sizes used (45, 25, and 78 nm in diameter), unlike the case for other polyion assemblies. It also increased with increasing ionic strength of aqueous SiO2 dispersions. According to SEM observation, the assembled film possessed surprisingly flat surfaces at optimized ionic strengths. AFM observation revealed that SiO2 particles were not closely packed. The neutralization ratio of SiO2 and PDDA was estimated by turbidity measurement. Comparison of turbidity and QCM data indicated t...
467 citations
TL;DR: In this article, the effect of a 4-carboxyphenyl or 4-nitrophenyl thin film at the surface of a glassy carbon electrode on their electrochemical responses in the presence of various electroactive probes has been investigated.
Abstract: The effect of a 4-carboxyphenyl or a 4-nitrophenyl thin film at the surface of a glassy carbon electrode on their electrochemical responses in the presence of various electroactive probes has been investigated. The grafting of a substituted phenyl group to a glassy carbon electrode was achieved by electrochemical reduction of the corresponding substituted phenyldiazonium derivative in acetonitrile. The blocking properties of the film depend primarily on electrostatic and electrolyte/solvent effects. Permselectivity for the 4-carboxyphenyl film can be achieved by controlling the dissociation of the carboxy group. The substituted phenyl layer is much more compact and less permeable in contact with a nonaqueous solvent than with an aqueous solvent presumably because the layer is poorly solvated. Electrochemical impedance measurements indicate that the kinetics of electron transfer are slowed down when the time used to modify the glassy carbon electrode is increased. Cyclic voltammetry and X-ray photoelectron...
464 citations
TL;DR: In this article, a self-assembled structure of cationic poly(allylamine) modified by ferrocene (PAA-Fc) and anionic GOx was deposited electrostatically layer-by-layer on negatively charged alkanethiol-modified Au surfaces.
Abstract: We report the redox mediation of glucose oxidase (GOx) in a self-assembled structure of cationic poly(allylamine) modified by ferrocene (PAA-Fc) and anionic GOx deposited electrostatically layer-by-layer on negatively charged alkanethiol-modified Au surfaces. Successive PAA-Fc and GOx layers were deposited by alternate immersion of the thiol-modified Au in the respective polyelectrolyte and enzyme solutions. The uptake of thiol, redox polymer, and GOx on the surface was monitored by quartz crystal microbalance. Cyclic voltammetry shows nearly ideal surface waves of ferrocene in the polymer with charge independent of sweep rate; the redox surface concentration was obtained from integration of the ferrocene/ferricinium voltammetric peaks. The redox charge increases in step with the number of PAA-Fc layers deposited. Enzyme catalysis for the oxidation of β-d-glucose was achieved with a multilayer PAA-Fc/GOx assembly, with each GOx layer contributing equally to the catalytic response. Only a small fraction of...
414 citations
TL;DR: In this paper, alternating polyelectrolyte/protein layers were constructed in order to increase the binding layer capacity (i.e. sensitivity) of the thin film with respect to IgG detection.
Abstract: Alternating polyelectrolyte films constructed by the sequential adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) have been used as substrates for the immobilization of immunoglobulin G (IgG) and anti-IgG. Anti-IgG has also been immobilized in multilayer films by the alternate deposition of PSS and anti-IgG. The assembly process of the multilayer films was monitored using a quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). Film growth was achieved up to at least nine (5 anti-IgG and 4 PSS) layers. The utility of these films for immunosensing has been investigated via their subsequent interaction with IgG. The alternating polyelectrolyte/protein layers were constructed in order to increase the binding layer capacity (i.e. sensitivity) of the thin film with respect to IgG detection. The sensitivity, determined using IgG mass uptake data from quartz crystal microgravimetry, was found to be linearly dependent on the number of anti-IgG layers (and hence th...
398 citations
379 citations
TL;DR: This work investigates the binding of the protein catalase to gold surfaces modified by self-assembled monolayers (SAMs) of 3-mercaptopropanoic acid, 3-MPA, 11-MUA, and a mixture of the two acid thiols.
Abstract: The attachment of biomolecules, in particular proteins, onto solid supports is fundamental in the development of advanced biosensors, bioreactors, affinity chromatographic separation materials, and many diagnostic techniques. In addition, the effective investigation of biomolecular structure and function with scanning probe microscopy often requires a strong attachment of the biomolecule to a substrate. Here, we investigate the binding of the protein catalase to gold surfaces modified by self-assembled monolayers (SAMs). The chemical and physical adsorption of the protein molecules onto SAMs of 3-mercaptopropanoic acid (3-MPA), 11-mercaptoundecanoic acid (11-MUA), and a mixture of the two acid thiols (mixed) was investigated by utilizing tapping mode atomic force microscopy, scanning tunneling microscopy, surface plasmon resonance (SPR), static secondary ion mass spectrometry, and X-ray photoelectron spectroscopy. The surface concentration of catalase adsorbed on the SAMs decreased in the following order:...
378 citations
TL;DR: In this article, a few nanometers in size and composed of close-packed and well-ordered molecules have been fabricated by simultaneous nanoshaving using an atomic force microscopy (AFM) tip and alkanethiols' self-assembly on gold.
Abstract: Nanostructures down to a few nanometers in size and composed of close-packed and well-ordered molecules have been fabricated by simultaneous nanoshaving using an atomic force microscopy (AFM) tip and alkanethiols' self-assembly on gold. Compared with other microfabrication methods, this procedure allows more precise control in terms of the size and geometry of the fabricated features. An edge resolution better than 2 nm can be routinely obtained. In addition, the fabricated nanostructures can be quickly changed, modified, and characterized in situ. These advantages should make this method very useful in the development of prototypical nanoelectronic devices and, perhaps more importantly, in the study of spatially confined chemical reactions.
367 citations
TL;DR: In this paper, a theory for a new type of colloid behavior whereby particles deposited on a surface by electrophoresis are manipulated to form two-dimensional crystals is described.
Abstract: We describe a theory for a new type of colloid behavior whereby particles deposited on a surface by electrophoresis are manipulated to form two-dimensional crystals. Since the particles are equally charged, the clustering is opposite that expected from electrostatic considerations. Such behavior is consistent with migration due to electrohydrodynamic flows associated with polarization layers and ion currents. Provided colloid stability is maintained, the assembly processes take place with both dc and ac fields and may be modulated by adjusting the field strength or frequency. No migration is present at frequencies above 1 MHz. Two-dimensional fluid and crystalline states can be formed on the electrode surface. Experiments with patterned electrodes demonstrate the presence of the electrohydrodynamic flow. A mathematical model of the electrohydrodynamics provides insight into the assembly process.
TL;DR: In this article, the formation and structure of aqueous dispersions of lipid-based liquid crystalline phases, namely reversed types of hexagonal and bicontinious cubic phases, were investigated.
Abstract: The present study concerns the formation and structure of aqueous dispersions of lipid-based lyotropic liquid crystalline phases, namely reversed types of hexagonal and bicontinious cubic phases. As stabilizer a nonionic triblock polymer proves to be efficient for dispersions of both phases. We demonstrate that these dispersions contain submicron particles with a preserved inner periodicity. The morphology and inner structure of the dispersed particles are characterized by means of SAXS (small-angle X-ray scattering) and cryo-TEM (cryo-transmission electron microscopy). The particle shape is shown to reflect the crystallinity of the lipid structure. Thus the morphology of particles from cubic phases differs from that of the ones obtained from the hexagonal phase. Furthermore, an interesting difference is found in the partitioning of the polymer in the two types of dispersions. The polymer is localized within the core as well as at the surface of the dispersed particles of the cubic phase, whereas the core...
TL;DR: In this article, small charged gold disks were generated by electroplating gold into photoresist molds and derivatizing these disks with charged self-assembled monolayers.
Abstract: We use electrostatic interactions to direct the patterning of gold disks having ∼10-μm diameters on functionalized surfaces. Planar and curved substrates with patterned surface charge were generated either by microcontact printing or by photolithography. Small charged gold disks were generated by electroplating gold into photoresist molds and derivatizing these disks with charged self-assembled monolayers. When agitated as a suspension in contact with the patterned surfaces, the charged gold disks deposited specifically but as disordered aggregates on regions presenting the opposite charge. Positively-charged disks deposited on phosphonate-, carboxylate-, and SiOH-terminated surfaces but not on trimethylammonium- and dimethylammonium-terminated surfaces, and vice versa for negatively-charged disks. Methyl- and CF3-terminated surfaces resisted deposition of disks of either charge. Selective and dense assembly was achieved in methanol, ethanol, 2-propanol, and dioxane; in water, deposition was nonspecific. ...
TL;DR: In this article, the authors used an ultrahigh-vacuum scanning tunneling microscope to find evidence for a novel mechanism by which Au vacancy islands formed during assembly of alkanethiol monolayers on Au(111).
Abstract: Using an ultrahigh-vacuum scanning tunneling microscope we have discovered evidence for a novel mechanism by which Au vacancy islands form during assembly of alkanethiol monolayers on Au(111). Our results suggest a model whereby excess Au atoms are forced out of the surface layer by relaxation of the compressed herringbone reconstruction. This creates adatoms on, and vacancies in, the surface layer. On large terraces the vacancies nucleate into islands while the adatoms migrate and adsorb at ascending step edges. At saturation coverage of alkanethiols the surface exhibits ≈6% of a monolayer of vacancy islands. These results show that complex interactions between the assembling thiols and the herringbone reconstruction influence the mesoscopic aspects of the final monolayer surface.
TL;DR: Aqueous solution properties of a poly(ethylene oxide)-block-poly(propylene oxide)-poly(block poly (ethylene oxoxide) (PEO−PPO−PEO) amphiphilic copolymer (Pluronic L64: EO13PO30EO13) were studied in the presence of various alkali halide salts (LiCl, KCl, NaCl and NaBr, and NaI), sodium thiocyanate (NaSCN), and urea ((NH2)2CO) as mentioned in this paper
Abstract: Aqueous solution properties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO−PPO−PEO) amphiphilic copolymer (Pluronic L64: EO13PO30EO13) were studied in the presence of various alkali halide salts (LiCl, KCl, NaCl, NaBr, and NaI), sodium thiocyanate (NaSCN), and urea ((NH2)2CO). Differential scanning calorimetry (DSC) was employed for the determination of both the unimer-to-micelle transition (critical micellization temperature, CMT) and the phase separation (cloud point, CP). DSC is particularly useful in the case of Pluronic L64 where the detection of the CMT by optical techniques is hindered by the presence of a hydrophobic impurity. The presence of LiCl, KCl, NaCl, and NaBr decreased both CMT and CP (in the order Cl- > Br- and Na+ > K+ > Li+), whereas addition of NaSCN and urea resulted in a CMT and CP increase (in the order NaSCN > urea). NaI appeared to be an intermediate case as it decreased the CMT but increased the CP. Variation of the anion type (rather than...
TL;DR: In this article, composite molecular films are fabricated by self-assembly of dendritic macromolecules of two adjacent generations using the electrostatic layer-by-layer deposition.
Abstract: Composite molecular films of (AB)x type are fabricated by self-assembly of dendritic macromolecules of two adjacent generations using the electrostatic layer-by-layer deposition. Polyamidoamine dendrimers with surface amine groups for generations 4, 6, and 10 (G4, G6, G10) and carboxylic groups for generations G3.5, G5.5, and G9.5 have been used as building units. The molecular films are explored by scanning probe microscopy and X-ray reflectivity. All even generations are observed to form homogeneous, stable monolayers on a silicon surface. The thickness of a single monolayer varies with generation (molecular weight) from 1.8 nm (G4) to 2.8 nm (G6) and 5.6 nm (G10). Average thickness of a molecular layer in multilayer films is much smaller than the diameter of ideal spherical dendritic macromolecules. The model of molecular ordering of dendrimer films assumes compressed dendritic macromolecules of oblate shape with the axial ratio in the range from 1:3 to 1:6. The high interaction strength between “stick...
TL;DR: In this paper, the relative contrast of chemically different regions depends sensitively on the driving amplitude A0 and set point amplitude ratio rsp = Asp/A0, where Asp is the set-point amplitude.
Abstract: Blends of two polymers, poly(ethene-co-styrene) (PES) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), were examined with tapping mode atomic force microscopy (AFM) using various values of the driving amplitude A0 and set-point amplitude ratio rsp = Asp/A0, where Asp is the set-point amplitude. In height and phase images of PPO/PES blend samples, the relative contrast of chemically different regions depends sensitively on the rsp and A0 values. As the tip−sample force is increased from small to large, both phase and height images of PPO/PES blend samples can undergo a contrast reversal twice. This makes it difficult to assign the features of height and phase images to different chemical components without performing additional experiments. Phase and height images were interpreted by analyzing several factors that affect the dependence of phase shift and amplitude damping on rsp and A0.
TL;DR: In this paper, copper(II) acetate in water and 2-ethoxyethanol using hydrazine under reflux was used to synthesize nanoparticles with a distinct absorption peak in the region 572−582 nm.
Abstract: In this paper, copper nanoparticles were prepared by the reduction of copper(II) acetate in water and 2-ethoxyethanol using hydrazine under reflux. The synthesized nanoparticles exhibit a distinct absorption peak in the region 572−582 nm. The average size variation from 6.6 to 22.7 nm in ethoxyethanol and from 15.5 to 30.2 nm in water was achieved by the addition of various amounts of a protective polymer (poly(N-vinylpyrrolidone)). The nonlinear optical properties of the copper colloids were first measured using the Z-scan technique. The χ(3)/α0 values obtained were found to be of the magnitude of 10-11−10-12 esu cm, which are in good agreement with the reported values obtained for copper nanoparticles embedded in glass.
TL;DR: In this article, the surface chemical composition, the crystalline structure, and the oxidation state of Co and Ni in the bulk as well as on the surface were characterized by X-ray diffraction (XRD), infrared spectroscopy (IRS).
Abstract: Films of general composition CoxNi1-xOy with x = 0, 11.1, 22.2, 33.3, 44.4, 55.6, 66.7, 77.8, 88.9, and 100 mol %, prepared by thermal decomposition of 2-propanol solutions of Ni and Co nitrates on Ni supports, have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IRS), and X-ray photoelectron spectroscopy (XPS). These techniques have provided the surface chemical composition, the crystalline structure, and the oxidation state of Co and Ni in the bulk as well as on the surface. The results have revealed, in addition to previous work where NiO and NixCo2-xO4 solid solutions were found to be the predominant crystalline phases, that Ni and Co hydroxides interact in the surface layer of nanosized crystallites of the oxide phase. The interaction in the hydroxylated surface has a redox character and results in two oxidation states (+2 and +3) for both Ni and Co ions. This work has shown that Co hydroxide fragments are localized in the periphery of Ni hydroxide domains. The redox interaction...
TL;DR: In this paper, the effect of specific chemical functionalities on the growth of bovine aortic endothelial cells (BAEC) was investigated using a set of well-characterized, chemically functionalized surfaces prepared by self-assembly of alkanethiolate monolayers on gold surfaces using the molecules X(CH2)15SH with X = −CH3, −CH2OH, −CO2CH3 and −CO 2H.
Abstract: The effect of specific chemical functionalities on the growth of bovine aortic endothelial cells (BAEC) was investigated using a set of well-characterized, chemically functionalized surfaces prepared by self-assembly of alkanethiolate monolayers on gold surfaces using the molecules X(CH2)15SH with X = −CH3, −CH2OH, −CO2CH3, and −CO2H. Cells seeded on a substrate in serum-containing culture medium interact with the adsorbed protein layer rather than the substrate. Therefore, the role of two serum proteins, albumin (Alb) (a nonadhesive or blocking protein) and fibronectin (Fn) (an adhesive protein), in cell growth was evaluated by measuring the amount of each protein bound and the tightness of binding (determined by resistance to SDS solubilization) on the self-assembled monolayers (SAMs). BAEC growth varied significantly with surface functionality. Cell growth increased in the following order: −CH2OH < −CO2CH3 < −CH3 ≪ −CO2H, illustrating the effect of specific surface groups. Cell growth on all monolayer...
TL;DR: In this article, a layer-by-layer adaption method for multilayer assemblies of polymeric materials was proposed. But this method was applied to poly[2-(9-carbazolyl)ethyl methacrylate.
Abstract: This paper is concerned with a novel layer-by-layer adsorption method for preparing multilayer assemblies of polymeric materials. We employed two kinds polymers, poly[2-(9-carbazolyl)ethyl methacry...
TL;DR: In this article, the authors used the alkytrimethylammonium bromide surfactant series, CnTAB, n = 10, 12, 14, 16, to perform a systematic study of the forces and stability of foam films produced from soluble cationic surfactants.
Abstract: The alkytrimethylammonium bromide surfactant series, CnTAB, n = 10, 12, 14, 16, is used to perform a systematic study of the forces and stability of foam films produced from soluble cationic surfactants. Both surface tension and disjoining pressure isotherms are measured for each surfactant. This information is then combined with neutron reflectivity and dynamic surface tension results found in the literature to provide an understanding of how the surfactant chain length can effect the forces and stability in thin-liquid films. For stable films, we find good quantitative agreement between the interaction forces measured in foam films and those reported from surface force studies on similar systems. We also find that the surfactant's hydrocarbon chain length and packing can strongly influence film stability. For highly purified surfactants an abrupt increase in film stability is seen when extending the chain length from C12TAB to C14TAB. When an uncharged cosurfactant is present, this stability transition ...
TL;DR: In this paper, a method for the application of colloid monolayers to almost any surface where these difficulties are circumvented is presented, at first the monlayers are fabricated on glass substrates and afterwards floated off on a water surface.
Abstract: Hexagonally closed packed monolayers of colloids have found more and more applications, e.g. as lithographic masks. The monolayers are usually produced with the help of a self-organizing process where a suspension of colloids is applied to the desired substrate and left to dry. This method requires a good wettability and smoothness of the substrate, which severely limits the number of possible substrates. We present a new method for the application of colloid monolayers to almost any surface where these difficulties are circumvented. At first the monolayers are fabricated on glass substrates and afterwards floated off on a water surface. From there, they are transferred to the desired substrate. Examples where transferred monolayers were used as lithographic masks are shown on glass, indium tin oxide, and tungsten diselenide. The transfer of a colloid monolayer to a copper grid for transmission electron microscopy demonstrates the applicability of the technique to curved surfaces as well.
TL;DR: In this article, it is suggested that, at low copper ion concentrations, copper ions bound onto the surface of CdS nanoparticles exist as isolated Cu+ ions, which leads to formation of a new, red-shifted, luminescence band.
Abstract: Nonstoichiometric cadmium sulfide nanoparticles ([Cd2+]/[S2-] = 3) in 2-propanol were surface-modified with Cu2+ ions. Addition of copper(II) perchlorate to CdS nanoparticles leads to binding of copper ions onto the surface of the semiconductor, accompanied by rapid reduction of Cu2+ to Cu+, as confirmed by EPR and absorption spectra. Copper(II) perchlorate also quenches the recombination luminescence of CdS nanoparticles effectively. The quenching data obey a static interaction model, which confirms the binding of copper ions onto CdS. The latter was confirmed also by ultrafiltration and ICP spectroscopy. Copper ions bound onto the surface of CdS lead to formation of a new, red-shifted, luminescence band. The maximum of the new band is at 14 700 cm-1 compared to that of the original band at 17 900 cm-1. It is suggested that, at low copper ion concentrations, copper ions bound onto the surface of CdS nanoparticles exist as isolated Cu+ ions. They create a new energy level in the bandgap at about 1.2 eV be...
TL;DR: In this article, the authors performed a microscopy characterization of solid crystals made of monodisperse SiO2 nanometric spheres and found that for a wide range of particle diameters, the cubic phase is the only one present.
Abstract: It is well-known that stacking of hard spheres results in close-packed structures. However, until recently, it was not clear which of the various possible phases (cubic, hexagonal, mixed, or random) was the stable one. We have performed a microscopy characterization of solid crystals made of monodisperse SiO2 nanometric spheres. It was found that, for a wide range of particle diameters, the cubic phase is the only one present. This largely serves to confirm recent theoretical calculations by L. V. Woodcock which conclude that the cubic phase is the most stable one. This opens new prospects in the application of colloidal crystals to photonic band gap engineering.
TL;DR: The structure of self-assembled monolayers of thiophenols (I), benzyl mercaptans (II), biphenylthiols (III), and 4-biphenylmethanethiols(IV) on the surface of Au(111) were compared using cyclic vol...
Abstract: The structure of self-assembled monolayers of thiophenols (I), benzyl mercaptans (II), biphenylthiols (III), and 4-biphenylmethanethiols (IV) on the surface of Au(111) are compared using cyclic vol...
TL;DR: In this article, self-assembled monolayers (SAMs) adsorbed on Au(111) were studied with an atomic force microscope (AFM) to confirm the influence of the lateral interaction between adsorbe...
Abstract: n-Alkanethiol (CnH2n+1SH) self-assembled monolayers (SAMs) adsorbed on Au(111) were studied with an atomic force microscope (AFM) to confirm the influence of the lateral interaction between adsorbe...
TL;DR: In this paper, it was determined that the material within the redox active layer was distributed over a distance of at least 2.5 layer pairs away from the nominal location of the active layer, and the evidence for extensive interpenetration between layers was confirmed using variable-angle XPS.
Abstract: Polyelectrolyte multilayers containing electrochemically active viologen units have been constructed using the layer-by-layer deposition technique with poly(styrenesulfonate) and poly(butanylviologen) as polyanion and polycation, respectively. All redox active material is electrochemically addressable in multilayers made from these polymers. Cyclic voltammetry, ellipsometry, and UV−vis spectroscopy indicate a systematic dependence of the amount of material contained in these ultrathin films on the number of deposition cycles, although initial layers are significantly thinner. When the distance between a redox active layer and the electrode was varied by interposing non-electrochemically active layer pairs, it was determined that the material within the redox active layer was distributed over a distance of at least 2.5 layer pairs away from the nominal location of the redox active layer. This evidence for extensive interpenetration between layers was confirmed using variable-angle XPS, which revealed a 1:1...
TL;DR: In this paper, the mean relative size of metallic crystallites (drel(VS)) and their dispersion (FE) in supported metal catalysts have been developed, which apply well to various thermodynamically probable crystallite shapes including fcc cubooctahedra of varying geometry.
Abstract: Universal mathematical relations between the mean relative size of metallic crystallites (drel(VS)) and their dispersion (FE) in supported metal catalysts have been developed. The relations are: drel(VS) = 5.01/FE for FE 0.2 the commonly used definition of dVS should be modified. The developed relations apply well to various thermodynamically probable crystallite shapes including fcc cubooctahedra of varying geometry, icosahedra, surface-reconstructed cubooctahedra, bcc rhombic dodecahedra, and hcp truncated bipyramids. The new relations are more precise than the commonly used equation dVS = a/FE, where a is a constant specific to a given metal.
TL;DR: In this article, the polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) have been successfully grown up to 24 layers on gold surfaces.
Abstract: Thin organic films fabricated by the successive deposition of the polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) have been successfully grown up to 24 layers on gold surfaces. These films are formed via electrostatic attraction between adjacent layers of opposite charge. Their construction has been examined using a quartz crystal microbalance (QCM), reflection spectroscopy (RS), surface plasmon resonance (SPR), and X-ray photoelectron spectroscopy (XPS). The thickness of the multilayer assemblies increases with the number of adsorbed layers, although a linear increase is observed only after the deposition of four polyelectrolyte layers ((PAH/PSS)2). The (PAH/PSS)2 film facilitates regular, stepwise deposition of subsequent PAH and PSS layers. The thickness of (PAH/PSS)2 on gold was determined independently by QCM, SPR, and XPS to be 7.9 ± 0.6 nm. The PAH/PSS layer pair thickness after regular film growth was calculated to be 10.0 ± 0.8 nm. The formation of these thi...