Weijian Xu

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.

Redox-responsive, core-crosslinked degradable micelles for controlled drug release

We developed novel redox-responsive, core-crosslinked micelles (CCLMs) via a simple, one-step click chemistry reaction. CCLMs were prepared by the click reaction between poly(ethylene glycol)-b-poly(5-methyl-5-propargylxycarbonyl-1,3-dioxane-2-one) [PEG-b-poly(MPC)] amphiphilic block copolymer and bis-(azidoethyl) disulfide. The CCLMs not only presented excellent stability under physiological conditions but also achieved the controlled release of DOX in reducing environment (such as DTT, GSH). Furthermore, DOX-loaded CCLMs showed low cytotoxicity in HeLa cells and 4T1 cells by MTT assay as well as enhanced cytotoxicity against drug-resistant ADR/MCF-7 cells in vitro. Confocal laser scanning microscope (CLSM) images show that the DOX-loaded materials were easily taken up by HeLa cells, compared to free DOX as control. With its facile preparation, superior stability, and controlled release, the redox-responsive CCLMs can provide a versatile platform for drug delivery and have great potential for antitumor therapy.

Flame Retardancy and Mechanical Properties of Ethylene-vinyl Acetate Rubber with Expandable Graphite/Ammonium Polyphosphate/Dipentaerythritol System

Ethylene-vinyl acetate thermoset rubber (EVM) with high vinyl acetate content has been widely used in wires and cables for many years. However, the problem of melting drip and efficient flame retardance has not been effectively solved. The combination of expandable graphite (EG), ammonium polyphosphate (APP), and dipentaerythritol (DPER) as a flame retardant system for EVM rubber has been proven to be effective in preventing melting drip and improving flame retardance in this study. This is shown by limiting oxygen index (LOI) and vertical flammability (UL-94) tests. The thermal behavior of EVM treated with this instumescent-flame retardant (IFR) system was investigated by thermogravimetric analysis (TGA) experiments. The results indicated that the char residue of treated samples could reach up to 27.1% at 600°C, which is much higher than that of the untreated EVM. Scanning electron microscopy (SEM) micrographs of residue of treated and untreated EVM showed that the IFR system could promote formation of residual char which imparts the antidripping property to EVM. However, the mechanical properties, such as tensile strength (TS) and elongation at break (EB), decreased gradually with the increase of EG content. Compared to the EVM/APP/DPER system without EG, the TS decreased from 6.55 MPa to 6.13 MPa, while the EB decreased slightly from 570% to 558% when the EG content was 15 wt%.

ROMP of acetoxy-substituted dicyclopentadiene to a linear polymer with a high Tg

A polydicyclopentadiene derivative was obtained via ring-opening metathesis polymerization (ROMP) of acetoxy-substituted dicyclopentadiene (AcO-DCPD) using the Grubbs 1st generation catalyst. Analyses of the polymer microstructures indicate that polymers are linear. The glass transition temperatures (Tg) of the linear polymers range from 136 °C to 159 °C, which are much higher than that of linear polydicyclopentadiene.

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.

Spiropyran-decorated light-responsive amphiphilic poly(α-hydroxy acids) micelles constructed via a CuAAC reaction

Light-responsive amphiphilic poly(α-hydroxy acids) mPEG-b-poly(Tyr)-SP was prepared by the introduction of a spiropyran chromophore into the side chain of poly(ethylene glycol)-modified poly(α-hydroxy acids) (mPEG-b-poly(Tyr)) via a copper-catalysed azide–alkyne cycloaddition (CuAAC) reaction. The resultant copolymer can self-assemble into spherical micelles with an average diameter of 222.7 nm and a critical micelle concentration of 0.0085 mg mL−1. The micelles showed reversible self-assembly and disassembly in aqueous solution under alternative UV and visible light irradiation. The model drug coumarin 102 was then encapsulated into the micelles successfully. Light-controlled release and re-encapsulation behaviours were demonstrated by fluorescence spectroscopy. MTT assay revealed that the mPEG-b-poly(Tyr)-SP micelles exhibited excellent cell compatibility. This study provides a convenient way to construct smart poly(α-hydroxy acids)-based nanocarriers for controlled release and re-encapsulation of hydrophobic drugs.

The preparation and characteristic of robust inorganic/organic IPN nanocomposite hydrogels with fast response rate

In order to prepare a robust thermosensitive hydrogels with ultrarapid response rate, the –Si–O– network was incorporated into the first clay cross-linked poly(N-isopropylacrylamide) network by the simultaneous hydrolytic polycondensation of tetramethoxysilane (TMOS); the two-step freezing polymerization technique was used in polymerization process for guaranteeing the very fast response rate of gels. The properties of resulting hydrogels (T-NC gels) including mechanical properties, hydrophily, swelling and response behavior show an obvious dependency on the content of added TMOS. With the increase of added TMOS, the more integrated and high-density –Si–O– network was formed in gels, which makes the gels become more robust with higher strength and modulus, while the swelling ratio and response rate decreases due to the lapped effect of increased network density and hydrophobicity. Interestingly, T-NC gels show better volume stability than that of NC gels in shrinking process.