Weizhi Wang

Heterogeneous Ultrathin Films of Poly(vinyl alcohol)/Layered Double Hydroxide and Montmorillonite Nanosheets via Layer-by-Layer Assembly

In this paper, Co-Al layered double hydroxide (LDH) and montmorillonite (MMT) have been exfoliated into charged single layers in the solvent of formamide and water, respectively. The structures of individual layers of LDH and MMT were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The delamination mechanisms of LDH and MMT were also discussed. Furthermore, heterogeneous ultrathin films of poly(vinyl alcohol) (PVA)/charged inorganic nanosheets, (PVA/MMT/PVA/LDH)(n), were fabricated by layer-by-layer (LBL) assembly via hydrogen bonding. The LBL assembly process was monitored by UV-vis spectroscopy, and the structures of the heterogeneous ultrathin films were analyzed by XRD.

Aggregation Emission Properties of Oligomers Based on Tetraphenylethylene

A series of eight derivatives based on tetraphenylethylene were prepared, and two of these, i.e., 1,1-bis(4-phenylcarbonyl)-2,2-diphenylethylene (2), 1,1,2,2-tetrakis(4-phenylcarbonyl)phenylethylene (4), were characterized crystallographically. Because the rigidity and steric hindrance in the molecular structure enhanced regularly from sample 5 to 8, UV-visible absorption and PL spectra of 5-8 show the transition from aggregation-induced emission (AIE) to aggregation-induced emission enhancement (AIEE) behavior. Solid fluorescence lifetime characterization shows that samples with less steric hindrance and more interaction in or between molecules will result in a short fluorescence lifetime. All samples 5-8 become more emissive when their chains are induced to aggregate by adding water into their acetonitrile solutions. Cyclic voltammetry measurements taken give the band gap of sample 5-8 as 2.88, 2.70, 2.56, and 2.43 eV, and theoretical calculations also support these bad gap results. Conformational simulations also suggest that the origin of transition from AIE to AIEE behavior is due to the restricted intramolecular rotations of the aromatic rings in samples.

Use of the β-Phase of Poly(9,9-dioctylfluorene) as a Probe into the Interfacial Interplay for the Mixed Bilayer Films Formed by Sequential Spin-Coating

Spin-coating one polymer solution on another spin-cast polymer film is believed to result in unfavorable interfacial mixing. Here, we show some results to demonstrate that some interesting properties will be obtained in such mixed bilayer films formed by sequential spin-coating. Poly(9-vinylcarbazole) and poly(9,9-dioctylfluorene-2,7-diyl) were chosen as the first and second polymer layers, respectively. By varying the initial thickness of the first layer, some interesting variations were observed. The spectroscopic features of beta-phase polyfluorene were utilized to reflect the variations at the complicated interface. Morphologies were also presented to illustrate that the variations of spectroscopic features were accompanied with some interesting morphological changes. On the basis of these results, a schematic model was proposed to gain insight into the mixed interface formed by sequential spin-coating. Polymer light-emitting devices based on such films were also investigated.

Morphology-controlled synthesis of porous polymer nanospheres for gas absorption and bioimaging applications

This paper reports the development of a simple and effective way to prepare novel soluble porous polymer nanospheres (PPSs) by A3B2 catalytic emulsion polymerization using a Suzuki reaction as a one-step, surfactant-free process. The PPSs chemical structures are characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, powder X ray diffraction, dynamical light scattering, and thermogravimetric analysis. The results show that tris(4-bromophenyl)amine (A3) and benzene-1,4-diboronic acid (B2) monomers in a dilute Suzuki system (1 : 20 as the ratio of toluene to water) form a A3 core/B2 shell nano-size micelle in the oil/water template at the early stage. With the reaction processing, the ∼10 nm nanoparticles precipitate in droplets and move into the water phase. The small individual nanoparticles further aggregate and connect into ∼200 nm porous nanoparticles. The controlled second level of porosity is attributed to the uniform individual nanoparticles’ self-assembly. Its porosity is confirmed by N2 sorption isotherms at 77 K. Among the PPS series, PPS3 has a high surface area of 2180 m2 g−1 and adsorbs up to 2.08 wt% hydrogen by mass at 1.13 bar/77 K. Photoluminescence investigations have shown that PPS copolymers with different concentrations of 4,7-dibromo-2,1,3-benzothiadiazole emit blue, green and yellow light, respectively. Preliminary investigations show that PPS displays a low cytotoxicity and can be used as a fluorescence marker in bioimaging.

Crystallization Behavior of Poly(vinylidene fluoride) Nanocomposites Containing Multiwalled Carbon Nanotubes

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loadings of multiwalled carbon nanotubes (CNT) were prepared by a melt compounding technique. The isothermal and nonisothermal crystallization behavior of neat PVDF and PVDF/CNT nanocomposites were studied using differential scanning calorimetry. The crystallization rate of PVDF was significantly increased because of the nucleating effect of CNT. The crystalline morphology of PVDF and its CNT nanocomposites, studied using polarized optical microscopy, indicated that the addition of CNT promoted the crystallization of PVDF and decreased the spherulitic size of PVDF significantly. The isothermal crystallization kinetic behavior was analyzed by Avrami equation and the nonisothermal crystallization kinetics were comparatively studied by the Ozawa method and an Avrami–Ozawa combination method. According to the Kissinger method, the nonisothermal crystallization activation energies of neat PVDF and its nanocomposites were estimated.

Targeting PPM1D by lentivirus-mediated RNA interference inhibits the tumorigenicity of bladder cancer cells

Protein phosphatase magnesium/manganese-dependent 1D (PPM1D) is a p53-induced phosphatase that functions as a negative regulator of stress response pathways and has oncogenic properties. However, the functional role of PPM1D in bladder cancer (BC) remains largely unknown. In the present study, lentivirus vectors carrying small hairpin RNA (shRNA) targeting PPM1D were used to explore the effects of PPM1D knockdown on BC cell proliferation and tumorigenesis. shRNA-mediated knockdown of PPM1D significantly inhibited cell growth and colony forming ability in the BC cell lines 5637 and T24. Flow cytometric analysis showed that PPM1D silencing increased the proportion of cells in the G0/G1 phase. Downregulation of PPM1D also inhibited 5637 cell tumorigenicity in nude mice. The results of the present study suggest that PPM1D plays a potentially important role in BC tumorigenicity, and lentivirus-mediated delivery of shRNA against PPM1D might be a promising therapeutic strategy for the treatment of BC.

Ladder-type conjugated oligomers prepared by the Scholl oxidative cyclodehydrogenation reaction: synthesis, characterization and application in field effect transistors

Two novel well defined ladder-type conjugated oligomers have been successfully designed and synthesized through a solution processing method in an excellent yield. The field effect transistors (FETs) fabricated by these ladder-type oligomers with a nice planar structure exhibit excellent charge carrier mobilities, up to 0.10 cm2 V−1 s−1 and 0.33 cm2 V−1 s−1; furthermore, the devices can work well with a low gate voltage. The ladder-type oligomers are both converted from two precursor co-oligomers, poly(2,7-(1,2,-diphenylethene)-9,9-dioctylfluorene) (PDPF), via an anhydrous FeCl3 oxidative cyclodehydrogenation. The pronounced red shift shown in the preliminary photoluminescence spectra and the changes of band gaps measured by electrochemical analysis both testify that the better electronic transmission capacity in the FET performance is due to the expanded molecular chain planarization after the chemical cyclodehydrogenation. Interestingly, the precursor oligomers having a linear-type chain and a zigzag-type chain (L-PDPF and Z-PDPF, respectively) show many characteristic differences in their thermal, optical and electrochemical properties. The differences caused by the different types of main chains demonstrate that the macromolecular configurations have a tremendous impact on the functioning of the oligomers.

Studies on non-linear optical properties of Langmuir-Blodgett films formed from azobenzocrown ether derivatives

Azobenzocrown ether derivatives, a novel type of non-linear optical (NLO) material, were synthesized. The structure and conditions for the formation of their Langmuir films have been studied with pressure-area isotherms. These compounds can form monolayers on the subphase and be transferred onto a glass substrate to form multilayers consisting of over 100 monolayers. The construction of multilayer LB films was also studied with X-ray diffraction which proved that the designed molecules were consistent with the CPK molecular model. The X-ray diffraction measurement of the same samples after 2 months showed that the films were quite stable. The second harmonic generation of these compounds was examined and found to be in the order of 10−28–10−29 esu.

Boronate ester post-functionalization of PPEs: versatile building blocks for poly(2,2′-(1-(4-(1,2-di(thiophen-2-yl)vinyl)phenyl)-2-(2,5-dioctylphenyl)ethene-1,2-diyl)dithiophene) and application in field effect transistors

A convenient and scalable strategy for post-functionalization of poly(phenylene-ethynylene)s and phenylene-ethynylene arrays from boronate ester derivatives using the thienyl group as an example. Furthermore, poly(2,2′-(1-(4-(1,2-di(thiophen-2-yl)vinyl)phenyl)-2-(2,5-dioctylphenyl)ethene-1,2-diyl)dithiophene) showed good field-effect transistor performance with an excellent mobility up to 0.723 cm2 V−1 s−1 and an on–off ratio of 104.

Emission-Tunable Multicolor Graphene Molecules with Controllable Synthesis, Excellent Optical Properties, and Specific Applications

Series of graphene molecules with varied emission colors have been prepared by oxidative cyclodehydrogenation using anhydrous ferric chloride (FeCl3) as the catalyst under mild conditions. By controlling the oxidation time in the initial step only, molecules with different fluorescence colors are conveniently obtained. New colors can be recorded evidently because of the stepwise and controllable process, which highly related to the conjugation length. Blue emissive starting compounds in the solid state can be transformed into orange upon brief oxidation, whereas green emissive oligomers are varied to red with an emission wavelength redshift about 123 nm. Cyclic voltammetry measurements performed can give the corresponding data, which verify the results drawn from the UV and PL spectroscope. The gradual change of conjugation length with tunable emission is confirmed in the MALDI-TOF study as well. Further characterizations indicate that the graphene molecules possess satisfactory optical properties, which are highly emissive both in solution and in the solid state because of the alkyl group. In addition, the good thermal stability and the self-assembly of graphene molecules suggest that they are promising candidates for high-tech applications. Furthermore, the fabricated field-effect transistors possess the nice performance, whose mobilities are about 0.57 cm(2) V(-1) s(-1) with an on-off ratio of 1 × 10(4) and 0.81 cm(2) V(-1) s(-1) with an on-off ratio of 1 × 10(3), respectively.