Layer Of Aqueous Solution Research Articles

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

Alkali-activated calcined clays are promising candidates for playing a prominent role in the future construction industry. These binders may achieve excellent mechanical performance, but one issue deserving attention is the proneness to plastic shrinkage and surface cracking. Tackling this issue requires the deployment of laboratory techniques that allow shrinkage-inducing mechanisms to be quantitatively assessed. Here, we demonstrate that time-lapse X-ray imaging can be used to quantify shrinkage immediately after mixing, when the binder is still in its fresh state, with excellent time and space resolution. The numeric quantification of strain is complemented by the real time visual inspection of the displacing sample interface and of the bleed aqueous solution layer that may form. Implementation of this method to a set of alkali-activated cement pastes, prepared by combining calcined clays having different mineralogical composition with sodium silicate activating solutions having different hbox {SiO}_2/hbox {Na}_2hbox {O} ratios, suggests that two main mechanisms control the early dimensional stability of alkali-activated calcined clays. These mechanisms are: (a) volumetric contraction occurring in response to capillary stress arising from water evaporation and (b) segregation by particle settling, favoured in the water-saturated regime.

Charge-Transfer-to-Solvent Reaction in a Hydrophobic Tetrabutylammonium Iodide Molecular Layer in Aqueous Solution.

We present ultrafast photoelectron spectroscopy of the charge-transfer-to-solvent reaction in a segregated TBAI (tetrabutylammonium iodide) molecular layer in aqueous solution. The reaction times and electron binding energies of transient species vary with TBAI concentration from a very low value of 1 × 10-3 mol L-1, which is in contrast to NaI solution exhibiting no concentration (0.01-1.0 mol L-1) dependence. The result from soft X-ray N(1s) spectroscopy indicates that the photoelectron intensity in TBAI aqueous solution is about 70 times enhanced as compared to that in NH4Cl aqueous solution for an identical salt concentration, and TBA+ drags I- to the surface region. At high TBAI concentrations, electrons released from I- are trapped and held in the TBAI molecular layer owing to electrostatic attraction by TBA+.

Blob Size Controls Diffusion of Free Polymer in a Chemically Identical Brush in Semidilute Solution.

The diffusion of rhodamine-labeled poly(ethylene glycol) (r-PEG) within surface-grafted poly(ethylene glycol) (s-PEG) layers in aqueous solution at 18 °C was measured by fluorescence correlation spectroscopy. The diffusion coefficient of r-PEG within s-PEG was controlled by the grafting density, σ, and scaled as σ–1.42±0.09. It is proposed that a characteristic blob size associated with the grafted (brush) layer defines the region through which the r-PEG diffusion occurs. The diffusion coefficients for r-PEG in semidilute solution were found to be similar to those in the brushes.

Preparation of Multiple Parallel Protein-polysaccharide Hybrid Gel Filaments Under Shear

Fabrication of anisotropic gel with characteristic structures has been reported using a flow system with three dimensional microfluidic devices. Such gel structures are mainly achieved by design and preparation of the microchannel for flowing pre-gel solution. In this research, we propose a method for preparing multiple parallel gel filaments by controlling viscoelastic properties of polymer assembly as the fluid of microfluidic devices. To promote the formation of heterogeneous assembly of different types of macromolecules, an aqueous two-phase separation (ATPS) technique was utilized. Two layers of aqueous solutions appear when the ATPS conditions including ionic strength, temperature, and solute concentration in certain combinations of two components are satisfied. In respective phase, some solute molecules form heterogeneous assemblies because the solutes in respective phase are highly concentrated. We previously reported that the alginate (Alg) could form the assembly with polyethylene glycol (PEG) in the induced phase of Alg/PEG/NaCl system. In aqueous media, the Alg assembly has the rigid structure because diaxial linkages in a successive region of guluronic acid are stabilized by hydrogen bonds. Destruction of hydrogen bonds of Alg molecules by interaction with PEG enables deformation of Alg assembly by shear. Gel filaments were prepared with a co-axial flow device as double glass tubes, where an inner tube (inner diameter 0.7 mm) was fixed at the insert position of the outer tube. Pre-gel solution and crosslinker solution respectively were flown to inner and outer tube using syringe pumps. The morphology of the gel filaments was observed by a scanning electron microscope. A single thick gel filament was obtained from aqueous sodium alginate solution, whereas multiple thin gel filaments were obtained when a mixed solution of Alg and PEG under the ATPS condition. Appearance of shear-thinning behavior for the Alg-rich phase suggests that the complexation of Alg with PEG was responsible for destruction of the rigid assembly due to breaking hydrogen bonds. In this poster, the method will be applied to the protein containing system to fabricate the protein-polysaccharide hybrid filaments.

Nanoplasmonic mid-infrared biosensor for in vitro protein secondary structure detection

Plasmonic nanoantennas offer new applications in mid-infrared (mid-IR) absorption spectroscopy with ultrasensitive detection of structural signatures of biomolecules, such as proteins, due to their strong resonant near-fields. The amide I fingerprint of a protein contains conformational information that is greatly important for understanding its function in health and disease. Here, we introduce a non-invasive, label-free mid-IR nanoantenna-array sensor for secondary structure identification of nanometer-thin protein layers in aqueous solution by resolving the content of plasmonically enhanced amide I signatures. We successfully detect random coil to cross β-sheet conformational changes associated with α-synuclein protein aggregation, a detrimental process in many neurodegenerative disorders. Notably, our experimental results demonstrate high conformational sensitivity by differentiating subtle secondary-structural variations in a native β-sheet protein monolayer from those of cross β-sheets, which are characteristic of pathological aggregates. Our nanoplasmonic biosensor is a highly promising and versatile tool for in vitro structural analysis of thin protein layers.

Electrochemical Behavior of Li4Ti5O12 in Ionic Liquid/Water Bilayer Electrolyte

Introduction Lithium-ion batteries (LIBs) have been used in portable electronic devices, and recently expected to be used in large-scale energy facilities for electric vehicle or large energy storage systems. Flammable organic solvents were used in LIBs and it threaten the safety of LIBs. Therefore, nonflammable aqueous electrolytes have been investigated[1]. However, its narrow potential windows restrict the use of negative electrodes, which makes it difficult to obtain high voltage. In this study, we utilized stable liquid-liquid interface between water and hydrophobic ionic liquids in order to enhance the negative potential window. The electrochemical behavior of Li4Ti5O12(LTO) thin-film electrode, which cannot be used in aqueous solution, was investigated. Experimental LTO thin-film electrodes were prepared on a Pt substrate by a sol-gel method. LTO thin-film electrode was used as a working electrode. The bilayer electrolyte was formed on the working electrode: the upper layer was 1.0 mol dm −3 LiNO3 aqueous solution, and the lower layer was butyltrimethylammonium bis(trifluoromethylsulfonyl)amide (BTMATFSA) containing 1.0 mol kg −1 of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA). The counter electrode was platinum wire and the reference electrode was Ag/AgCl electrode (sat. KCl), and these electrodes were placed in the aqueous solution layer. Cyclic voltammetry was performed. Hereafter, all potentials are referred to as Ag/AgCl. Results Figure 1(a) shows the cyclic voltammograms of LTO thin-film electrode in bilayer electrolyte. At volume ratio of ionic liquid:aqueous solution = 3:4, clear redox peaks around ca. −1.33 V were observed. This reaction can be assigned to lithium-ion insertion/extraction into/from LTO. In contrast, Figure 1(b) shows that only large reduction current was observed and the redox peaks of LTO were not detected at volume ratio = 1:29. At this ratio, ionic liquid was miscible with aqueous solution. Thus, the reduction current below 0.9 V can be assigned to the hydrogen evolution reaction from water. These results reveal that bilayer electrolyte with clear interface prevent the hydrogen evolution reaction and enable lithium-ion to insert/extract into/from LTO. Reference [1] W. Li, J. R. Dahn, and D. S. Wainwright, Science, 264, 1115 (1994). Acknowledgment This work was partially supported by CREST, JST. Figure 1

Simultaneous ellipsometric and chronoamperometric study of barrier aluminium oxide growth and dissolution in acetate buffer

In situ ellipsometric and chronoamperometic measurements were applied simultaneously to monitor barrier oxide growth and dissolution on aluminium. The steady-state thickness prior to each potential step was determined by electrochemical impedance spectroscopy (EIS) for calibration of the transient data. The growth of the barrier oxide, following a positive potential step, was consistent with the Cabrera-Mott inverse square logarithmic growth law. About 20 % of the measured current resulted in barrier oxide growth. The oxide dissolution rate, following a negative potential step, was controlled by diffusion of aluminium ions into the test solution. The obtained dissolution rate was thus much smaller than the corresponding oxide growth rates. Oxide solubilities calculated from Fick’s second law, by using literature data for the diffusion coefficient of Al3+, were about two orders of magnitude larger than that obtainable from thermodynamic considerations. The methodology developed provides the kinetic and solubility data needed for improving the existing know-how about the growth and dissolution kinetics of the barrier oxide layer in aqueous solution.

Synthesis of tripodal catecholates and their immobilization on zinc oxide nanoparticles.

A common approach to generate tailored materials and nanoparticles (NPs) is the formation of molecular monolayers by chemisorption of bifunctional anchor molecules. This approach depends critically on the choice of a suitable anchor group. Recently, bifunctional catecholates, inspired by mussel-adhesive proteins (MAPs) and bacterial siderophores, have received considerable interest as anchor groups for biomedically relevant metal surfaces and nanoparticles. We report here the synthesis of new tripodal catecholates as multivalent anchor molecules for immobilization on metal surfaces and nanoparticles. The tripodal catecholates have been conjugated to various effector molecules such as PEG, a sulfobetaine and an adamantyl group. The potential of these conjugates has been demonstrated with the immobilization of tripodal catecholates on ZnO NPs. The results confirmed a high loading of tripodal PEG-catecholates on the particles and the formation of stable PEG layers in aqueous solution.

In Situ Surface-enhanced Raman Analysis of Water Libration on Silver Electrode in Various Alkali Hydroxide Aqueous Solutions

In electrochemistry, it is often necessary to conduct both experimental and theoretical investigations, including analysis of the standard electrode potential, the electric double layer, the diffusion layer, the diffusion coefficient of the ion, and thermodynamic parameters. The accumulation of this vast array of electrochemical data forms the basis of contemporary research on electrochemical devices such as batteries, capacitors and fuel cells. The electric double layer in aqueous solutions composes solvated ions and water molecules, additionally and occasionally composes specifically adsorbed atom and contact adsorbed atoms. Considering the electric double layer in aqueous solution, one of the fundamental issue is the dynamical motion of water molecules at the double layer region. In order to investigate this issue, focusing the vibration of water molecules at the double layer region is necessary. The vibration of water molecules includes several vibrating modes; translation, libtation, bending vibration, stretching vibration and so on. Specially, the libration of water molecules may decide the water structure at the double layer.

Synthesizing and stabilizing copper nanoparticles by coating with a silica layer in aqueous solution

Synthesizing and stabilizing copper nanoparticles by coating with a silica layer in aqueous solution

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution. Part II

AbstractGold electrodes modified with S‐containing compounds and gold were used for determination of norepinephrine (NEP) in aqueous solution. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 µM to 600 µM with the detection limit ≤0.090 µM for the electrodes modified at 2D template and in the range of 0.1 µM to 700 µM with the detection limit ≤0.075 µM for the electrodes modified at 3D template. The results have shown that modified electrodes could clearly resolve the oxidation peaks of norepinephrine, ascorbic (AA) and uric acid (UA) with peak‐to‐peak separation enabling determination of NEP, AA and UA in the presence of each other.

Fabrication of the selective-growth ZnO nanorods with a hole-array pattern on a p-type GaN:Mg layer through a chemical bath deposition process

ZnO nanorod arrays were effectively selective-grown on a p-type GaN:Mg layer through chemical bath deposition (CBD) at a low temperature hydrothermal synthesis (85 °C) with a ZnO seed layer. The 5 μm-diameter hole-array patterns of the ZnO seed layer were grown on a p-type GaN:Mg layer in aqueous solution with a mercury lamp illumination. The diameter and the height of ZnO nanorods were measured as the values of 500 nm and 3 μm, respectively. The growth orientation, surface morphology, and aspect ratio of the ZnO nanorods can be controlled and formed on the hole-array patterned ZnO seed layer. The peak wavelength of the photoluminescence spectrum was measured at 384 nm.

Hybrid Materials from Electropolymerized Thin Polymer Layer - Based Electrodes for the Elaboration of a New Generation of Electrochemical Sensors of NO in Solution

The measurement of nitric oxide NO is important for direct examination of its regulatory roles in biological systems and the major important criteria in making NO electrochemical sensors are the design of electrode arrays having various arrangements. Electrodeposited nickel phthalocyanine films on electrodes brought a substantial contribution to the development of efficient sensors, but such surface modification suffers from the highly corrosive media used for the nickel complex and instability. We explore here the possibility of developing soft methods to chemically modify the electrode surface. We report on preliminary results obtained with Pt ultramicroelectrodes modified with electropolymerized phenol, eugenol, o-phenylene diamine and aniline thin layers in aqueous solution at pH 7.4. The sensitivity towards NO and the selectivity of the obtained electrodes against biologically relevant interfering analytes (nitrite, ascorbate, dopamine and hydrogen peroxide) are analyzed by chronoamperometry.

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution

AbstractGold nanoparticles (Au‐NPs), cystamine (CA) and 3,3′‐dithiodipropionic acid (DTDPA) modified gold bare electrodes were applied in voltammetric sensors for simultaneous detection of norepinephrine (NEP), ascorbic (AA) and uric (UA) acids. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 μM to 600 μM M with the detection limit ≤0.091 μM for the electrodes modified at 2D template and in the range of 0.1 μM to 700 μM M with the detection limit ≤0.087 μM for the electrodes modified at 3D template The results have shown that using modified electrodes it is possible to perform electrochemical analysis of norepinephrine without interference of ascorbic and uric acids, whose presence is the major limitation in norepinephrine determination at a bare gold electrode. The modified SAMs electrodes show good selectivity, sensitivity, reproducibility and high stability.

Nonequilibrium processes in reactions of hot tritium atoms with cooled solid targets. Attenuation of the flow of tritium atoms in adsorption layers of alkyltrimethylammonium bromides

The permeability for atomic tritium of adsorption layers of aqueous solutio ns of alkyltrimethylammonium bromides RN(CH3)3Br differing in the length of the hydrocarbon radical R (C12H25, C14H29, C16H33) was studied. The change in the radioactivity of alanine present in the examined solutions was used as the measure of the attenuation of the flow of reactive tritium atoms. The formation of an adsorption monolayer of surfactant molecules on the liquid-gas phase boundary caused the radioactivity of alanine to decrease by a factor of 6.5 (R = C12H25) to 8 (R = C16H33) relative to the experiment with a straight alanine solution. A correlation between the structure of the adsorbed layers of alkyltrimethylammonium bromides and their permeability to atomic tritium is discussed.

Direct polymerization of surface‐tethered polyelectrolyte layers in aqueous solution via surface‐confined atom transfer radical polymerization

AbstractThe direct polymerization of deprotonated acidic monomers in aqueous solutions was achieved via surface‐confined atom transfer radical polymerization (SC‐ATRP) to produce surface‐tethered polyelectrolyte brushes. Layers of poly(itaconic acid), poly(methacrylic acid), and sodium poly(styrene sulfonate) were grown by SC‐ATRP from self‐assembled initiator monolayers of [BrC(CH3)2COO(CH2)11S]2 on gold substrates. The polymer layers were characterized with variable‐angle ellipsometry and external‐reflection Fourier transform infrared spectroscopy. Without intervention, atom transfer radical polymerization catalysts were deactivated by complexation with the deprotonated acidic monomers, disproportionation, and dissociation during the polymerization of these monomers in water; the result was the cessation of polymer growth. The addition of an alkali salt to the reaction media suppressed catalyst deactivation, allowing polymer layers to increase in thickness linearly for longer periods of time with respect to salt‐free conditions. This result suggested an improved degree of polymerization control. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 566–575, 2007

Raman Spectroelectrochemistry of Ordered C60 Fullerene Layers

Electrochemical nanostructuring of ordered C60 fullerene layers in aqueous solution was studied by in situ Raman spectroelectrochemistry. A completely changed molecular film structure was found for nanostructured films. C60 polymers/oligomers and hydrogenated C60 were identified as the main fullerene structures after nanostructuring. No significant contributions of AxC60 fullerides (A=alkaline metal; x=1, 3, 6) were found.

Individually addressable gel-integrated voltammetric microelectrode array for high-resolution measurement of concentration profiles at interfaces.

The application of a novel voltammetric probe, based on an individually addressable gel-integrated microelectrode array (IA-GIME), for real-time, high-spatial resolution concentration profile measurements at interfaces is described. Reliability and validity of steep metal concentration gradients obtained with this novel system have been demonstrated by performing systematic tests at well-controlled liquid-liquid and liquid-solid interfaces. The liquid-liquid interface was formed by two layers of aqueous solutions with different components; only one layer contained trace metal ions (Pb(II) and Cd(II)); the individually addressable microelectrode array was placed at the interface of the liquid-liquid system; the concentration profiles were recorded as function of time; and the effective diffusion coefficients were calculated. The liquid-"solid" interface was formed from an aqueous solution layer overlying a bed of silica particles saturated with an aqueous solution. The sensor array has been used to monitor the diffusion processes of Tl(I) or Pb(II) from the liquid phase to the "solid" phase. The influences of porosity, geometry of the porous media, and complexation between metal ion and silica, on the diffusion processes, have been studied. All these results show that correct diffusion profiles of metal ions at interfaces can be obtained with 200-microm resolution with the IA-GIME. They also demonstrate that, for measurements in "solid" phase, the aforementioned factors must be considered carefully for correct calibration of any electrodes and the gel-integrated microelectrodes are unique tools to enable calibration of the sensors with synthetic solutions.

Relaxation Processes in Surface Excess Layers of Aqueous Solutions of Poly(ethylene oxide)

The dynamic surface behavior of the surface excess film adsorbed at the air-liquid interface of dilute solutions of poly(ethylene oxide) has been investigated using surface quasielastic light scattering over a q range of 200 to 1300 cm -1 . Molecular weights of 15 000, 106 000 and 828 000 in 0.1%w/w solution in water were investigated. Capillary wave frequencies were close to simple predictions based on the density and surface tension of the solutions, whereas the dampings were higher than predicted, due to the extra surface viscosities of the adsorbed polymer. Light scattering data were further analyzed to yield the four surface viscoelastic parameters which are currently used to model the surface behavior-surface tension, γ 0 , transverse shear viscosity, γ', dilational modulus, e 0 , and dilational viscosity, e'-as a function of the capillary wave frequency. Variations in the dilational modulus and viscosity indicated the presence of a relaxation process in the surface film: this was fitted to a model describing the surface relaxation in terms of diffusion between the bulk solution and a subsurface layer. Including an adsorption barrier in the model enabled the quantitative description of the observed variation in both the dilational modulus and the dilational viscosity, and also provided a rationale for the negative dilational viscosities observed.

Synthesis of Nanosized Gold−Silica Core−Shell Particles

Gold colloids have been homogeneously coated with silica using the silane coupling agent (3-aminopropyl)trimethoxysilane as a primer to render the gold surface vitreophilic. After the formation of a thin silica layer in aqueous solution, the particles can be transferred into ethanol for further growth using the Stober method. The thickness of the silica layer can be completely controlled, and (after surface modification) the particles can be transferred into practically any solvent. Varying the silica shell thickness and the refractive index of the solvent allows control over the optical properties of the dispersions. The optical spectra of the coated particles are in good agreement with calculations using Mie's theory for core−shell particles.