Surface-enhanced Raman scattering studies on aggregated silver nanoplates in aqueous solution

Four different sizes of citrate-protected silver nanoplates with the corresponding in-plane dipole resonance band at 530, 619, 778, and 858 nm, respectively, are synthesized for surface-enhanced Raman scattering (SERS) study. Their aggregation behaviors are monitored by use of UV-vis spectroscopy. During the aggregation process, a marked red shift of the in-plane dipole resonance of silver nanoplates is observed, whereas other resonance modes of them only have small alterations in the site or intensity. Aggregated silver nanoplates can serve as active SERS substrates with an enhancement factor of about 4.5 x 10(5) using 2-aminothiophenol as a probing molecule. The SERS performance of silver nanoplates is even superior to the commonly used Lee-Meisel silver colloid, making them very attractive for SERS applications.

Surface morphology evolution of a thin polymeric supramolecular film by tuning interactions

A polymeric supramolecule consisting of symmetric polystyrene-block-poly(4-vinylpytidine) (PS-b-P4VP), dodecylbenzenesulfonic acid (DBSA), and 3-pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology,of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)(1.0)(PDP)(1.0) matrix are observed for the as-cast film because the weight fraction, f(comb), of the P4VP(DBSA) (1.0)(PDP)(1.0) blocks is much higher than that of PS as a result of the non-covalent interactions of P4VP and DBSA and DBSA and PDR Upon annealing the PS-b-P4VP(1:1)(DBSA)(1.0)(PDP)(1.0) film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.

PEG-supported dipyridyl ligand for palladium-catalyzed Suzuki and Suzuki-type reactions in PEG and aqueous media

An air- and water-stable PEG-supported bidentate nitrogen ligand is prepared and its applications in the palladium-catalyzed Suzuki reaction of aryl halides with arylboronic acids in PEG and Suzuki-type reaction of aryl halides with sodium tetraphenylborate in aqueous media are reported. The homogeneous catalyst system is environmentally friendly and offers the advantages of high activity, reusability and easy separation.

Copper hexacyanoferrate multilayer films on glassy carbon electrode modified with 4-aminobenzoic acid in aqueous solution

4-Aminobenzoic acid (4-ABA) was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation during the electrooxidation process in 0.1 M KCl aqueous Solution. X-ray photoelectron spectroscopy (XPS) measurement proves the presence of 4-carboxylphenylamine on the GCE. Electron transfer processes of Fe(CN)(6)(3-) in solutions of various pHs at the modified electrode are studied by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changing the solution pH would result in the variation of the terminal group's charge state, based on which the surface pK(a) values were estimated. The copper hexacyanoferrate (CuHCF) multilayer films were formed on 4-ABA/GCE prepared in aqueous solution, and which exhibit good electrochemical behavior with high stability.

Spectroscopic investigation of the function of aqueous 2-hydroxyethylmethacrylate/glutaraldehyde solution as a dentin desensitizer

Fourier-transform (FT)-Raman and -infrared (IR) spectroscopy were employed to investigate the function of the aqueous 2-hydroxyethylmethacrylate/glutaraldehyde solution (Gluma) as a desensitizer. 2-Hydroxyethylmethacrylate (HEMA), glutaraldehyde (GA), and the mixture of HEMA/GA (i.e. Gluma) were used to interact with dentin, collagen, hydroxyapatite (HAP), and bovine serum albumin (BSA) individually. All the interactions were monitored by an FT-Raman spectrometer. FT-IR spectroscopy was also used in this study. The results show that HEMA could be absorbed by dentin and collagen; GA could cross-link collagen and BSA; and when BSA was added to Gluma, polymerization of HEMA occurred. The results suggest that Gluma acts as a desensitizer whereby, first, GA reacts with part of the serum albumin in dentinal fluid, which induces a precipitation of serum albumin, then, second, a reaction of GA with serum albumin induces polymerization of HEMA. The function of Gluma as a desensitizer to block dentinal tubules occurs via these two reactions.

Dispersion copolymerization of acrylamide with quaternary ammonium cationic monomer in aqueous salts solution

Dispersion copolymerization of acrylamide (AM) with 2-methylacryloylxyethyl trimethyl ammonium chloride (DMC) has been carried out in aqueous salts solution containing ammonium sulfate and sodium chloride with poly(acryloylxyethyl trimethyl ammonium chloride) (PDAC) as the stabilizer and 2,2'-azobis[2-(2-inidazolin-2-yl)propane]-dihydro chloride (VA-044) as the initiator. A new particle formation mechanism of the dispersion polymerization for the present system has been proposed. The effects of inorganic salts and stabilizer concentration on dispersion polymerization have been investigated. The results show that varying the salt concentration could affect the morphology and molecular weight of the resultant copolymer particles significantly. With increasing the stabilizer concentration, the particle size decreased at first and then increased, meanwhile the effect on the copolymer molecular weight was the contrary. These results had been rationalized based on the proposed mechanism.

New double-ceramic-layer thermal barrier coatings based on zirconia-rare earth composite oxides

A series of La2O3-ZrO2-CeO2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr >= 0.7/0.3, and below this ratio only mixtures of La2Zr2O7 (pyrochlore) and La2O3-CeO2 (fluorite) exist. Averagely speaking, the increase of CeO2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La-2(Zr0.7Ce0.3)(2)O-7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering. Based on the large thermal expansion coefficient of La2Ce3.25O9.5, the low thermal conductivities and low sintering abilities of La2Zr2O7 and La-2(Zr0.7Ce0.3)(2)O-7, double-ceramic-layer thermal barrier coatings were prepared. The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings.

Thermal stability of double-ceramic-layer thermal barrier coatings with various coating thickness

Double-ceramic-layer (DCL) coatings with various thickness ratios composed of YSZ (6-8 wt.% Y2O3 + ZrO2) and lanthanum zirconate (LZ, La2Zr2O7) were produced by the atmospheric plasma spraying. Chemical stability of LZ in contact with YSZ in DCL coatings was investigated by calcining powder blends at different temperatures. No obvious reaction was observed when the calcination temperature was lower than 1250 degrees C, implying that LZ and YSZ had good chemical applicability for producing DCL coating. The thermal cycling test indicate that the cycling lives of the DCL coatings are strongly dependent on the thickness ratio of LZ and YSZ, and the coatings with YSZ thickness between 150 and 200 mu m have even longer lives than the single-layer YSZ coating. When the YSZ layer is thinner than 100 mu m, the DCL coatings failed in the LZ layer close to the interface of YSZ layer and LZ layer. For the coatings with the YSZ thickness above 150 mu m, the failure mainly occurs at the interface of the YSZ layer and the bond coat.

Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate: Synthesis and characterization

Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate using poly(2-acrylamido-2-methylpropanesulfonic acid sodium) as the stabilizer and ammonium persulfate (APS) as the initiator was investigated. The influence of initiator concentration, stabilizer concentration, ammonium sulfate concentration, chain-transfer agent concentration, and polymerization temperature on the copolymerization was discussed. The results showed that varying the ammonium sulfate concentration could affect the particle size and the intrinsic viscosity of the copolymer significantly. With increasing the stabilizer concentration, the particle size of the copolymer decreased first, and then increased, meanwhile the intrinsic viscosity of the copolymer decreased. The increase of initiator concentration, chain-transfer agent concentration, and polymerization temperature resulted in the increase in the particle size. Polydisperse spherical particles were formed in the system, and the kinetics for the dispersion copolymerization were discussed.

3-Mercaptopropionic Acid Capped Gold Nanoclusters: Quantized Capacitance in Aqueous Media

3-Mercaptopropionic add monolayer protected gold nanoclusters (MPA-MPCs) were synthesized and characterized by transmission electron microscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The exact value of quantized double-layer capacitance of MPCS in aqueous media was obtained by differential pulse voltammograms.

A cunning strategy in design of polymeric nanomaterials with novel microstructures

A relative approach, based on the dynamic density functional theory, for simulating the solvent evaporation rate dependence of self-assembly process of block copolymers in solution is proposed. The di- and triblock copolymers are first chosen as the candidates for exploration of novel microstructures. The results reveal that asymmetrical block copolymers with unequal block length, which generally exhibit disordered microdomain patterns in melts, have the ability to assemble into periodic ordered microdomain patterns by properly controlling solvent evaporation rate, e.g., diblock copolymers may assemble into lamellar microstructures with lamellar thickness proportional to individual block length. This simulation suggests a strategy of design and manufacture of polymeric nanomaterials with novel microstructures.

Gold nanoparticles as fine tuners of electrochemical properties of the electrode/solution interface

Recently, a novel approach for preparing SERS and SPR substrates was developed, which indicates a potential application in tailoring the interfacial structure of an electrode surface. In this study, (3-mercaptopropyl)trimethoxysilane (MPTMS) was selected as a polymeric adhesive layer, and a low concentration of colloid Au solution was used to achieve a more accurate control over interface morphology at nanoscale dimensions due to slow self-assembling kinetics of gold nanoparticle's. Subsequent seeding growth of these MPTMS-supported submonolayers of gold nanoparticles in Au3+/NH2OH aqueous solution enlarges particle size and eventually results in the generation of conductive gold films (similar to previous (3-aminopropyl)trimethoxysilane-supported gold films). Such tunable interface structure was evaluated by atomic force microscopy (AFM). Also, ac impedance spectroscopy (ACIS) and cyclic voltammograms were performed to evaluate electrochemical properties of the as-prepared interfaces by using Fe(CN)(6) (3-/4-) couples as a probe. Furthermore, relevant theories of microarray electrodes were introduced into this study to explain the highly tunable electrochemical properties of the as-prepared interfaces. As a result, it is concluded that the electrochemical properties toward Fe(CN)(6) (3-/4-) couples are highly dependent on the active nanoelectrode (nanoparticles) area fraction and nanoparticles are fine-tuners of interfacial properties because the number density. (numbers/unit area) and size of nanoparticles are highly tunable by self-assembling and seeding growth time scale control. This is in agreement with the theoretical expectations for a microarray electrode if a single nanoparticle tethered to a blocking SAM is taken as a nanoelectrode and 2-D nanoparticle assemblies are taken as nanoelectrode arrays.

Investigation of electrochemical charging behaviors of "naked" gold nanoparticles ensembles in aqueous media

Gold nanopartides were Immobilized onto the electrode surface by simple self-assembly technique. Interestingly, the ensembles of these nanopartides exhibit quantized charging behaviors in aqueous solution. Possible mechanism for such behaviors was proposed.

Novel tris(2,2-bipyridine)ruthenium(II) cathodic electrochemiluminescence in aqueous solution at a glassy carbon electrode

A novel approach of generating cathodic electrochemiluminescence lof Ru(bpy)(3)(2+) at -0.4 V triggered by reactive oxygen species is reported for detecting alkylamines and some organic acids.

Interactions of thiamine monophosphate (TMP) with one- and two-dimensional polymeric halogenomercurate anions. Crystal structures of (TMP)(Hg2Br5)center dot 0.5H(2)O and (TMP)(2)(Hg3I8)

An investigation into the interactions between thiamine monophosphate (TMP) and anions has resulted in the preparation and X-ray characterization of the compounds (TMP)(Hg2Br5).0.5H(2)O (1) and (TMP)(2)(Hg3I8) (2). In each compound the TMP molecule exists as a monovalent cation in the usual F conformation. The halogenomercurate anions occur in two-dimensional (2-D) network in 1 or one-dimensional (1-D) chain in 2. In both 1 and 2, the structures consist of alternating cationic sheets of the hydrogen-bonded TMP molecules and anionic sheets of the polymeric halogenomercurate anions. The TMP molecule binds to the polymeric anions through the characteristic 'anion bridge I', C(2)-H..X...pyrimidinium (X = Br in 1 and 1 in 2), and electrostatic interactions between electropositive S(1) and halogen atoms. The 'anion bridge II' of the type N(4'1)-H...X...thiazolium (X = phosphate group) plays a role in stabilizing the molecular conformation. The biological implication of the host-guest-like complexation between TMP and polymeric anions is discussed.