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Weifeng Bu

Publications and source records attributed to Weifeng Bu.

10 recordsLinked to original sources
PubMed2006

Self-organized microporous structures based on surfactant-encapsulated polyoxometalate complexes.

Self-organized microporous structures based on a series of surfactant-encapsulated polyoxometalate complexes (SECs) have been prepared by using ordered condensed droplets as a template. Among these structures, ordered honeycomb structures were obtained and characterized in detail by taking (DODA)(12)H[Eu(SiW(11)O(39))2] (SEC-1) as an example. Optical microscope, atomic force microscopic, and scanning electron microscopic measurements confirmed the formation of three-dimensional microporous structure, in which the top surface shows a highly ordered honeycomb structure. As compared to common solvent-casting films, the corresponding honeycomb films are more hydrophobic and possess more ordered lamellar structures. Both the wettability and the size of SECs exert significant influence on the formation of microporous structures. The proper hydrophobicity of SECs was proposed to be an essential factor for the formation of honeycomb films, and large-sized SECs are favorable for the fabrication of highly ordered honeycomb structures. The conditions for the formation of different surface morphologies have been discussed in terms of the contact angle of SECs at the interface between water and chloroform, and a contact angle slightly greater than 90 degrees is found to be a prerequisite for the formation of honeycomb structures. The results reported in this paper not only help to further comprehend the mechanism of the formation of honeycomb structures, but also provide some guidance for the design of ordered microporous films based on organic/inorganic hybrid materials, exemplified by the organic/nanoparticle complexes.

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PubMed2005

Self-assembled multibilayers of europium alkanoates: structure, photophysics, and mesomorphic behavior.

A series of europium alkanoates (C(n-1)H(2n-1)CO(2))(3)Eu, (n = 14, 16, 18, 20) have been synthesized and characterized in detail. X-ray diffraction and Fourier transform infrared spectroscopic measurements confirm the multibilayer structure of these homologues. In such bilayers, the europium ionic layers are well separated by the highly ordered alkyl chains which are in an all-trans conformation and perpendicular to both sides of the europium ionic layers. There is a mixed-coordination type of chelating bidentate and bridging bidentate between the carboxylate groups and the europium ions. All samples exhibit characteristic emission of europium, though the luminescent intensity has been partly quenched by the carboxylate groups. Differential scanning calorimetry (DSC) shows multiple melting points for these homologues, and temperature-dependent X-ray diffraction measurements also confirm the existence of the mesophase on heating. This mesophase is not truly liquid crystalline, but is similar to the smectic A phase of organic rodlike molecules. Meanwhile, it seems that with increasing atomic number of lanthanide ions, longer alkyl chains will be required to form such a mesophase for the corresponding lanthanide alkanoates.

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PubMed2005

Polyoxometalate-based vesicle and its honeycomb architectures on solid surfaces.

The introduction of cationic surfactant DODA as counterions of [Eu(H2O)2SiW11O39]5- can form a mesoscopic supramolecular assembly of (DODA)4H[Eu(H2O)2SiW11O39], which aggregates into vesicles in chloroform. This POM-based vesicle can be further transferred into three-dimensional microporous architectures under moist air. The present methodology shows that, by combining inorganic chemistry and colloidal surface chemistry, a sequential self-assembling approach based on a series of linkable preorganized building blocks allows access to the fabrication of technological applicably POM-based microsized patterns, alternated with the soft lithographic method.

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PubMed2005

Length-controlled rodlike self-assemblies in binary mixed langmuir-blodgett monolayers on mica.

In this paper, atomic force microscopy (AFM) has been used to investigate the morphology of monolayers of the amphiphilic rod-coil diblock molecule (EO7OPV) containing oligo(phenylene vinylene) dimer (OPV) and poly(ethylene oxide) (PEO) as well as the morphology of mixed monolayers of EO7OPV and palmitic acid (PA) deposited onto mica by the Langmuir-Blodgett technique. At surface pressures higher than 3 mN/m, EO7OPV forms regular-shaped aggregates with a monomolecular layer structure, where the hydrophilic PEO blocks are adsorbed onto the mica substrate and the hydrophobic OPV blocks form an ordered crystalline OPV layer on the top of the PEO layer through the strong pi-pi stacking interaction. In the mixed LB monolayers of EO7OPV and PA, the phase separation occurs. At a certain mixed ratio, EO7OPV molecules form rodlike domains with regular shape and uniform size at surface pressures higher than 3 mN/m. With the increase of the molar fraction of PA, the rodlike domains consisting of EO7OPV are elongated. The length of the rodlike domains can be tuned easily in a large range by altering the molar ratio of EO7OPV and PA. In addition, the rodlike domains are oriented to specific directions, corresponding to the directions of the potassium ion array on the mica surface having 6-fold symmetry. We demonstrate the possible formation mechanism and the elongation origin of rodlike domains in mixed LB monolayers and propose the two-step formation process of oriented rodlike domains deposited onto the mica substrate.

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PubMed2004

Surfactant-encapsulated polyoxometalloeuropate: polarized Eu3+ emission in the highly ordered self-organizing film.

An organic/inorganic composite, (DODA)(9)EuW(10)O(36).9H(2)O, can form a highly ordered self-organizing film with a layered structure and almost fully interdigitated alkyl chains at solid supports. EuW10O36(9-) is deduced to be oriented in its self-organizing film, resulting in its polarized emission, which offers an accessible approach to fabricating the functional thin films containing polyoxometalates.

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PubMed2004

Polyoxometalates matrixed into surfactants: synthesis, characterizations, and conformations of surfactants.

We synthesized two surfactant-encapsulated polyoxometalate (POM) clusters (SECs), (DODA)(15)[H(3)Mo(57)V(6)(NO)(6)O(189)(H(2)O)(12)(VO)(6)].13H(2)O (SEC-2, DODA: dimethyldioctadecyl ammonium) and (DODA)(12)[Eu(H(2)O)P(5)W(30)O(110)].28H(2)O (SEC-3). SECs were characterized in detail by elemental analysis, UV-Vis absorption spectroscopy, FTIR, 1H NMR, thermogravimetric analysis, Langmuir isotherms, and powdered X-ray diffractions. SEC-2 can form a stable monolayer at the air-water interface. SEC-2 and SEC-3 possess a layered structure with periodicities of 3.8 and 5.05 nm, respectively. Alkyl chains in SEC-2 are disordered, but SEC-3 is indicative of well-ordered alkyl chains. According to the simplified structural analysis for SEC-2 and SEC-3, DODAs occupy areas of 1.12 and 0.589 nm(2) on the surface of the POMs, which are characteristic of the liquid-like and crystalline-like phases for DODA, respectively. The different conformations of DODAs then lead to the different packing structures of SECs. This work is aiming to control the organizational structures of the POM-based materials by selecting the appropriate POMs.

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PubMed2003

Measuring the swelling behavior of polymer microspheres with different cross-linking densities and the medium-dependent color changes of the resulting latex crystal films.

We measured the size changes of cross-linked polymer microspheres of narrow size distribution with different cross-linking densities by the in situ swelling method. The swelling behavior of these cross-linked polymer microspheres revealed that their maximal swelling degree linearly decreased as a function of the cross-linker content from 6.65 at 1.36 mol% to 2.43 at 3.25 mol%. By means of UV-vis spectra, we observed the spectral changes of the latex crystal films composed of these cross-linked polymer microspheres when we filled the interstices of the latex crystal films with different fluid media. Some succeeding peak shifts were observed, which may have resulted from the movement or the swelling of the polymer microspheres in the latex crystals.

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PubMed2002

Hydrogen-bonded 1,2-bis(4-pyridyl)ethylene and maleic acid.

The title compound (systematic name: 4,4'-ethylenedipyridinium dimaleate), C(12)H(12)N(2)(2+).2C(4)H(3)O(4)(-), is a 1:2 adduct of 1,2-bis(4-pyridyl)ethylene (BPE) and maleic acid (MA). The interaction between the two components in the molecular complex is due to intermolecular hydrogen bonding via an N(+)-H.O(-) hydrogen bond.

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PubMed2002

Investigation on solvent casting films of surfactant-encapsulated clusters.

The surfactant-encapsulated cluster (SEC) composed of a hydrophobic dimethyl dioctadecyl ammonium (DODA) shell and an encapsulated hydrophilic polyoxoanion core can form casting films. The structure of the casting film is influenced by evaporation rates of organic solvent. When the casting films are prepared by slow evaporation of chloroform, the alkyl chains are considered to possess a partial interdigitation, and the interdigitated length is 1.6 nm. The casting film structure is characterized by scanning force microscopy (SFM), Fourier transformation infrared (FT-IR), wide-angle X-ray diffraction, and differential scanning calorimetry (DSC).

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