Yuanqin Xiong

Photo-responsive reversible micelles based on azobenzene-modified poly(carbonate)s via azide–alkyne click chemistry

Photo-induced reversible amphipathic copolymer PMPC-azo was click conjugated by connecting amphiphilic poly(ethylene glycol)-modified poly(carbonate)s (PEG-b-poly(MPC)) and azide-functional trifluoromethoxy-azobenzene (azo-N3). The resulting copolymer self-assembled into spherical micelles with a hydrophobic azo core stabilized by a hydrophilic PEG corona in aqueous solution. As characterized by time-resolved UV-vis spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM), these micelles showed reversible self-assembly and disassembly in aqueous solution under alternating UV and visible light irradiation. The model drug Nile Red (NR) was then successfully encapsulated into the micelles. Light-controlled release and re-encapsulation behaviors were demonstrated by fluorescence spectroscopy. The cell cytotoxicity of PMPC-azo micelles was also evidenced by MTT assay. This study provides a convenient method to construct smart nanocarriers for controlled release and re-encapsulation of hydrophobic drugs.

High concentration and stable few-layer graphene dispersions prepared by the exfoliation of graphite in different organic solvents

A series of stable graphene dispersions in different organic solvents were prepared by the liquid-phase exfoliation of microcrystalline graphite. The pristine graphite was heat-treated in N-methyl-2-pyrrolidone before it was exfoliated in solvents containing 0.1 mg mL−1 polyvinyl pyrrolidone (PVP). X-ray diffraction and scanning electron microscopy (SEM) results implied that the interlayer spacing of graphite increased after the heat treatment. The increased interlayer spacing makes it favorable for organic molecules to enter the lattice of graphite, and is helpful in the exfoliation of graphite for the production of graphene flakes. High resolution transmission electron microscopy (HRTEM) and Raman spectroscopy indicated that the resulting graphene flakes are high-quality products without any significant structural defects. Atomic force microscopy (AFM) showed that the graphene flakes consist of single-to-few layer graphene, and also demonstrated that the concentration of PVP is an essential factor in the deposition of graphene flakes onto a mica substrate. More importantly, the resulting graphene dispersions can be used to fabricate graphene films and disk arrays on quartz glass. Therefore, it is possible that the graphene dispersions in this study can be used for the preparation of large-area graphene films on different substrates.

Macroscopic, Free-Standing Ag-Reduced, Graphene Oxide Janus Films Prepared by Evaporation-Induced Self-Assembly

A facile, efficient, and unique self-assembly process for the preparation of the macroscopic, free-standing, Ag-reduced, graphene oxide (Ag-RGO) Janus films, which exhibit a unique asymmetry of their two surfaces with macroscopic dimensions, is presented. A novel strategy using an evaporation-induced, self-assembly (EISA) process is shown to be a powerful and flexible method for synthesizing well-defined Janus thin films.

Fabrication of a coumarin-driven switchable superhydrophobic silica surface by photochemistry

A coumarin-driven switchable superhydrophobic silica surface by photochemistry is fabricated and Wenzel–Cassie wetting transition occurs on the surface under UV light (365 nm, 254 nm) irradiation. In addition, the as-prepared sample changes from random nanoparticle aggregates to necklaces (rings) through altering UV light irradiation.

An Hg2+-selective chemosensor based on the self-assembly of a novel amphiphilic block copolymer bearing rhodamine 6G derivative moieties in purely aqueous media

We report on the fabrication of an amphiphilic block copolymer-based colorimetric and fluorescent chemosensor for Hg2+ ions that was prepared by sequential RAFT polymerization of N-isopropylacrylamide (NIPAM) and a novel rhodamine-based Hg2+-recognizing monomer, R6GDM. Because of its amphiphilic properties, the block copolymer P[NIPAM]-b-P[R6GDM] can self-assemble into micelles, which allows it to be used as a chemosensor in aqueous solution. Upon addition of Hg2+ ions to the micelle solution, visual color change and fluorescence enhancement were observed. Moreover, it exhibits high sensitivity and selectivity for Hg2+ ions, relatively. Besides, it can serve as a potential multifunctional sensor to pH and temperature (in a specific temperature range: 25–40 °C or 40–52 °C). The water dispersibility and biocompatibility of these polymer micelles could provide a new strategy for detecting analytes in environmental and biological systems.

Preparation and Characteration of UV-cured EA/MMT Nanocomposites Via In-Situ Polymerization

A long-chain surfactant, enzoylbenzyl-N,N-dimethyl-N-octadecylammonium bromide (BDOB) with a benzophenone group, was synthesized to modify the montmorillonites (MMT) for the preparation of nanocomposites via photo-induced polymerization. The BDOB-modified MMT was characterized by the fourier transform infrared spectrometer (FTIR), thermal gravimetric analyzer (TGA) and X-ray diffraction (XRD), and the results of XRD indicated that the intercalated structures of BDOB-modified MMT was obtained. The conversion of the bisphenol A epoxy diacrylate (EA) was quantified by the FTIR, and the results indicated that conversion increased with an increase in the amount of BDOB-modified MMT. The morphologies of the UV-cured EA/MMT nanocomposites prepared from this organically modified MMT were studied by means of XRD and TEM, and the results showed that all the samples contained an intercalated structure with partial exfoliated structure. The results of TGA and mechanical properties also indicated that the thermal and mechanical properties of UV-cured nanocomposites were significantly enhanced due to the presence of the long chain surfactant organically modified MMT.

Folded three-dimensional graphene with uniformly distributed mesopores for high-performance supercapacitors

Folded three-dimensional graphene (FTG) is prepared through self-assembly of graphite oxide (GO) and liquid-phase exfoliation graphene (LG), followed by sonication and reduction processes. The obtained FTG consists of few-layer graphene. And it possesses a high degree of crystallinity, three-dimensional architecture and uniformly distributed mesopores. A supercapacitor based on an FTG electrode exhibits enhanced electrochemical performance. The FTG electrode exhibits high specific capacitance of 195.4 F g−1 at a scan rate of 1 mV s−1 and excellent cycling stability with 93.9% of its initial capacitance at a large scan rate of 500 mV s−1 after 8000 cycles. The supercapacitor fabricated with the FTG electrode delivers a high energy density of 27.1 W h kg−1 at a power density of 97.7 W kg−1. These results suggest that FTG is a promising material for high-performance supercapacitor applications.

UV-Curable Hybrids of Hyperbranched and Linear Polyurethane Dispersions

A series of UV-curable hybrids of hyperbranched and linear polyurethane dispersions (HLPUDs) were synthesized by a three-step process. Hybrids of HLPUDs were obtained by mixing acrylated hyperbranched polyurethane (HBPUA) with linear acrylated polyurethanes (LPUAs) and then being dispersed with water. The high density of acrylic groups on the surface of the HBPUA is very useful for the post UV curing. The synthesis of HBPUA and the effects of the HBPUA loading on the particle size (PS) of the HLPUDs as well as the thermal and the mechanical properties of the resulting cured films were characterized by Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering particle analysis, differential scanning calorimetry (DSC), dynamic mechanical analysis, thermal gravimetric analysis, and tensile measurements. The PS of the hybrids of HLPUDs were found to increase slightly from 38 to 76 nm with increase of the HBP content. Compared with the pure LPUA, the mechanical properties of the hybrids were enhanced dramatically, which could be correlated to the microstructure of the hybrids.

Flowability and Mechanical and Thermal Properties of Nylon 6/Ethylene bis-Stearamide/Carboxylic Silica Composites

Nylon 6 (PA 6)/ethylene bis-stearamide (EBS)/SiO2- carboxylic acid-functionalized silica nanoparticles (COOH) composites were prepared by in-situ polymerization of caprolactam. SiO2-COOH was used to enhance the compatibility between SiO2 and PA 6 matrix. For comparison, pure PA 6 and PA 6/EBS composites were also prepared via the same method. The PA 6/EBS/SiO2-COOH composites with low content of EBS and SiO2-COOH had greater melt-flow index (MFI) (the value of MFI increased by 50%–80%) than the pure PA 6. The results of mechanical properties showed almost no decrease in the tensile strength of PA 6/EBS/SiO2-COOH composites, with the bending strength decreasing by 17%–21%. However, the Izod impact strength of the PA 6/EBS/SiO2-COOH composites was greatly improved compared with pure PA 6, which indicated that the toughness of PA 6/EBS/SiO2-COOH had been greatly improved. The morphology of Izod impacted fractured surfaces of PA 6/EBS/SiO2-COOH was observed by scanning electron microscopy. The results revealed that the PA 6/EBS/SiO2-COOH composites presented a typical ductile fracture behavior with large amounts of long and large strip-like cracks. When the content of SiO2-COOH was 0.2 wt%, the SiO2-COOH particles were uniformly dispersed over the entire body of the PA 6 matrix. The results from differential scanning calorimetry indicated that the melting point (Tm), degree of crystallinity (Xc), and crystallization temperatures (Tc) of PA 6/EBS/SiO2-COOH composites were lower than the pure PA 6.

Synthesis of Polymethyl Methacrylate Grafted Styrene-butadiene-Styrene Triblock Polymer via Atom Transfer Radical Polymerization and its Characterization

Grafting of poly (methyl methacrylate) (PMMA) onto styrene–butadiene–styrene (SBS) triblock copolymer (SBS-g-PMMA) was synthesized by atom transfer radical polymerization (ATRP). The hydroxylated SBS (SBS-OH) was synthesized firstly by the reaction of SBS and formic acid/peroxide hydrogen. After esterification reactions between α-chloroacetic chloride and hydroxyl side groups, the chlorinated SBS (SBS-Cl) was obtained. Then the SBS-Cl was used as a macroinitiator to initiate the graft polymerization of MMA in the presence of CuBr and N,N,N’,N’,N”-Pentamethyldiethyltriamine (PMDETA) to get SBS-g-PMMA. The structure of SBS-g-PMMA was characterized by fourier transform infrared spectrometer (FTIR) and proton nuclear magnetic resonance (1H-NMR), and the results confirmed that MMA was grafted. The properties of the product were characterized by gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and atomic force micrograph (AFM). The molecular weight distribution of SBS-g-PMMA was as narrow as 1.17 measured by GPC. TGA data showed that the thermal stability of SBS-g-PMMA was improved. By AFM images, the structure of micro-phase separation could be observed obviously.