Study on the origin of inverted phase in drying solution-cast block copolymer films

In a previous study, we reported observation of the novel inverted phase (the minority blocks comprising the continuum phase) in kinetically controlled phase separating solution-cast poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer films [Zhang et al. Macromolecules 2000, 33, 9561-7]. In this study, we adopt the same approach to investigate the formation of inverted phase in a series of solution-cast poly(styrene-b-butadiene) (SB) asymmetric diblock copolymers having nearly equal polystyrene (PS) weight fraction (about 30 wt %) but different molecular weights. The microstructure of the solution-cast block copolymer films resulting from different solvent evaporation rates, R, was inspected, from which the kinetically frozen-in phase structures at qualitatively different block copolymer concentrations and correspondingly different effective interaction parameter, chieff, can be deduced. Our result shows that there is a threshold molecular weight or range of molecular weight below which the unusual inverted phase is accessible by controlling the solvent evaporation rate. In comparing the present result with that of our previous study on the SBS triblock copolymer, we find that the formation of the inverted phase has little bearing on the chain architecture. We performed numerical calculations for the free energy of block copolymer cylinders and found that the normal phase is always preferred irrespective of the interaction parameter and molecular weight, which suggests the formation of the inverted phase to have a kinetic origin.

Preparation, characterization and quantized capacitance of 3-mercapto-1,2-propanediol monolayer protected gold nanoparticles

Monolayer protected gold nanoparticles (MPCs) are the focus of recent research for their stability and are deemed as the building blocks of bottom-up strategies. In this Letter, 3-mercapto-1,2-propanediol monolayer protected gold nanoparticles (MPD-MPCs) were synthesized and characterized by transmission electron microscopy, UV/Vis spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The value of quantized double-layer capacitance (1.13 aF) of MPD-MPCs in aqueous media was obtained by differential pulse voltammograms.

Self-assembled monolayers of novel surface-bound dendrons: Peripheral structure determines surface organization

The synthetic and functional versatility of dendrimers and their well-defined shapes make them attractive molecules for surface modification. We synthesized six structurally very similar surface-bound dendrons and used them as building blocks for the preparation of self-assembled monolayers (SAMs) on a gold surface. We studied the effects of the surface-bound dendron's main structure, peripheral substituents, and the coadsorption process on its self-assembling behavior. Using scanning tunneling microscopy (STM), we observed nanostripes for SAMs of the surface-bound dendron consisting of symmetrical benzene rings. When we changed the symmetrical dendron's structure slightly, by increasing or decreasing the numbers of benzene rings at one wedge, we found no ordered structures were formed by the asymmetrical dendrons. We also introduced two kinds of substituents, heptane chains and oligo(ethylene oxide) chains, to the symmetrical dendron's periphery. Heptane chains appear to enhance the interaction between symmetrical backbones, leading to the formation of stripes, while oligo(ethylene oxide) chains appear to weaken the interaction between symmetrical backbones, resulting in a homogeneous structure. Dendrons with both heptane and oligo(ethylene oxide) chains exhibit nanophase separation in a confined state, leading to the formation of a honeycomb structure.

Anion coordination and molecular assembly in C2-substituted thiamine-anion systems: effects of the anion and molecular conformation

The compounds (het)(PtCl6)2H(2)O 1, (het)(HgI4).H2O 2 (het = 2-(alpha-hydroxyethyl)thiamine) and (hpt)(Hg2Br6) 3 (hpt = 2-(alpha-hydroxypropyl)thiamine) have been prepared and structurally characterized by X-ray crystallography in order to study the influence of the anion and molecular conformation on the formation of supramolecular architectures that adsorb anionic species. Both het and hpt molecules adopt the usual S conformation for C2-substituted thiamine but differ from the F conformation for C2-free thiamine derivatives. Two types of characteristic ligand-anion complexation are observed, being of the forms C(6')-H...anion...thiazolium-ring (in 1 and 2) and N(4'1)-H...anion...thiazolium-ring (in 3). The reaction of het with PtCl62- or HgI42- gives a 1-D double-chain in 1, consisting of two hydrogen-bonded het chains, which are cross-linked by anions through hydrogen bonding and anion...aromatic-ring interactions, or a cationic 3-D framework in 2 formed by the stacking of hydrogen-bonded sheets with anion-and-water-filled channels. In the case of 3, hydrogen-bonded hpt dimers and HgBr62- anions form alternate cation-anion columns. A comparison with the cases of C2-free thiamine-anion complexes indicates that the change in molecular conformation results in novel supramolecular assemblies in 1 and 2 and an analogous architecture in 3, which also depends on the nature of the anions.

Modified polyoxometalates: Hydrothermal syntheses and crystal structures of three novel reduced and capped Keggin derivatives decorated by transition metal complexes

Three novel polyoxometalate derivatives decorated by transition metal complexes have been hydrothermally synthesized. Compound 1 consists of [(PMo6Mo2V8O44)-Mo-VI-V-V-O-IV{CO (2,2'-bipy)(2)(H2O)}(4)](3+) polyoxocations and [(PMo4Mo4V8O44)-Mo-IV-V-V-O-IV{Co(2,2'-bipy)(2)(H2O)}(2)](3-) polyoxoanions, which are both built on mixed-metal tetracapped [PMo8V8O44] subunits covalently bonded to four or two {Co(2,2'-bpy)(2)(H2O)}(2+), clusters via terminal oxo groups of the capping V atoms. Compound 2 is built on [(PMo8V6O42)-V-VI-O-IV{Cu-I(phen)}(2)](5-) clusters constructed from mixed-metal bicapped [(PMo8V6O42)-V-VI-O-IV](7-) subunits covalently bonded to two {Cu(phen)}(+) fragments in the similar way to 1. The structure of 3 is composed of [(PMo9Mo3O40)-Mo-VI-O-V](6-) units capped by two divalent Ni atoms via four bridging oxo groups.

Synthesis and characterization of PCL/PEG/PCL triblock copolymers by using calcium catalyst

Triblock copolymer PCL-PEG-PCL was prepared by ring-opening polymerization of epsilon-caprolactone (CL) in the presence of poly(ethylene glycol) catalyzed by calcium ammoniate at 60 degreesC in xylene solution. The copolymer composition and triblock structure were confirmed by H-1 NMR and C-13 WR measurements. The differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed the micro-domain structure in the copolymer. The melting temperature T-c and crystallization temperature T-c of the PEG domain were influenced by the relative length of the PCL blocks. This was caused by the strong covalent interconnection between the two domains. Aqueous micelles were prepared from the triblock copolymer. The critical micelle concentration was determined to be 0.4-1.2 mg/l by fluorescence technique using pyrene as probe, depending on the length of PCL blocks, and lower than that of corresponding PCL-PEG diblock copolymers. The H-1 NMR spectrum of the micelles in D2O demonstrated only the -CH2CH2O- signal and thus confirmed. the PCL-core/PEG-shell structure of the micelles.

Layer-by-layer multilayer films self-assembled from a rare-earth-containing poly-oxometalate Na-9[Eu(W5O18)(2)] and poly (allylamine hydrochloride) and their photoluminescent properties

Ultrathin multilayer films of a rare-earth-containing polyoxometalate Na-9[Eu(W5O18)(2)] (EW) and Poly (allyamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. The fabrication process of the EW/PAH multilayer films was followed by UV-vis spectroscopy and ellipsometry, which show that the deposition process is linear and highly reproducible from layer to layer. An average EW/PAH bilayer thickness of ca. 2.1 nm was determine,by ellipsometry. In addition, the scanning electron microscopy (SEM) image of the EW/PAH film indicates that the film sufface is relatively uniform and smooth. The photoluminescent properties of these films were also investigated by fluoresence spectroscopy.

Hydrothermal synthesis, crystal structure and properties of [HPDA][H(2)PDA](2)[As-2(III)-AsMo8V4O40]center dot 3H(2)O (PDA = propane diamine)

[NH3CH2CH2CH2NH2][NH3CH2CH2CH2NH3](2)[(As2AsMo8V4O40)-As-III-Mo-V-O-IV].3H(2)O was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Crystal data: monoclinic, C2/c, a = 45.375(9) Angstrom, b = 11.774(2) Angstrom, c = 23.438(5) Angstrom, beta = 96.62(3)degrees. X-ray crystallographic study showed that the crystal structure was constructed by bicapped alpha-Keggin fragments [(As2AsMo8V4O40)-As-III-Mo-V-O-IV](5-) polyoxoanion. The title compound had a high catalytic activity for the oxidation of benzaldehyde to benzoic acid using H2O2 as oxidant in a liquid-solid biphase system.