Daoyong Chen

Electrochromatic carbon nanotube/ polydiacetylene nanocomposite fibres

Chromatic materials such as polydiacetylene change colour in response to a wide variety of environmental stimuli, including changes in temperature, pH and chemical or mechanical stress, and have been extensively explored as sensing devices. Here, we report the facile synthesis of carbon nanotube/polydiacetylene nanocomposite fibres that rapidly and reversibly respond to electrical current, with the resulting colour change being readily observable with the naked eye. These composite fibres also chromatically respond to a broad spectrum of other stimulations. For example, they exhibit rapid and reversible stress-induced chromatism with negligible elongation. These electrochromatic nanocomposite fibres could have various applications in sensing.

Nanoscale Tubular and Sheetlike Superstructures from Hierarchical Self‐Assembly of Polymeric Janus Particles

Inspired by hierarchical protein self-assembly in biological systems, the self-assembly of nanoparticles into superstructures has attracted much attention because of potential applications of these superstructures in the fields such as electronic or optical materials and novel nanodevices. Template-free self-assembly of nanoparticles with anisotropic interactions is of particular interest because it can lead to tailor-made complex superstructures. In fact, Janus nanoparticles are nano-objects with anisotropic interactions. The facile preparation, applications, and self-assembly of Janus nanoparticles have attracted extensive interest, and Janus particles with various sizes, structures, and compositions have been recently reported. Several kinds of Janus particles are capable of self-assembling into regular superstructures. For example, M ller and co-workers reported that amphiphilic Janus micelles prepared from ABC triblock copolymers could self-assemble into spherical supermicelles. 20] Granick and co-workers reported that amphiphilic and zwitterionic Janus colloidal spheres could assemble in water to form ordered clusters. In a recent study, we prepared Janus nanoparticles by using hybrid organic/inorganic nanotubes as a desymmetrization tool and the as-prepared amphiphilic Janus nanoparticles self-assembled into narrowly size-distributed flowerlike supermicelles in water. Despite these results, assembly of Janus nanoparticles into superstructures other than spherical supermicelles or clusters, such as nanowires, tubular and sheetlike superstructures, still remains challenging. Herein, we report a novel mechanism for the formation of polymeric Janus particles from mixed-shell micelles (MSMs) and the template-free self-assembly of the Janus particles into tubular superstructures and nanosheets. Micelles with mixed P2 VN/PEO shells were prepared by noncovalent crosslinking of poly(acrylic acid) (PAA) blocks by addition of 1,2-propanediamine (PDA) to a solution of PEO3500-bPAA3800/P2VN38000-b-PAA24000 (1:1 (w/w), PEO = poly(ethylene oxide), P2VN = poly(2-vinyl naphthalene), and the subscripts denote the molecular weights of the respective blocks) in DMF (Figure 1 a). The molar ratio of AA/PDA was 1:5, and the total polymer concentration was 1.0 mgmL . MSMs with PEO/P2VN as the mixed shell and a PDAcross-linked PAA network as the core were thus formed by noncovalent cross-linking. After switching the solvent from DMF to water (pH 7) by using dialysis, P2 VN in the mixed shell collapsed into separated microdomains (Figure 1b). In water, P2VN microdomains were surrounded and protected by solvated PEO chains so that the MSMs were individually dispersed. By decreasing the pH value of the aqueous solution to 3.1, intramicellar complexation occurred between PEO and PAA (Figure 1c), which resulted in an asymmetric intramicellar phase separation between the PEO/PAA complex and P2VN. As a result, amphiphilic Janus nanoparticles with a hydrophobic P2VN domain (formed by aggregation of all the P2VN small domains in a MSM) on one side and a hydrophilic PEO/PAA complex domain on the opposite side were formed (Figure 1d). These Janus nanoparticles were able to self-assemble in water to produce tubular and sheetlike superstructures. The average hydrodynamic radius, hRhi, of MSMs in DMF was 190 nm (Figure 2a, curve 1). In water, MSMs were individually dispersed with an hRhi value of 140 nm (Figure 2a, curve 2) because of the protection of solvated PEO chains in the mixed shell. The decrease in the hRhi value of the MSMs should result from the collapse of P2 VN chains in water. In the transmission electron microscopy (TEM) image of MSMs cast from neutral water stained with RuO4 (Figure 2b), contrast within each MSM was observed. The darker domains were assigned to P2VN microdomains (2–

Hierarchically arranged helical fibre actuators driven by solvents and vapours.

Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles.

The intranuclear release of a potential anticancer drug from small nanoparticles that are derived from intracellular dissociation of large nanoparticles

Transporting drug-containing nanoparticles into the nucleus of cancer cells through nucleopores and then releasing the drug intranuclearly provide an efficient strategy to overcome the drug resistance mechanisms evolved by cancer cells. However, limited by the diameter of nucleopores, nanoparticles capable of going through nucleopores should be small enough, whereas the nanoparticles with the small size may have short circulation time in blood and low accumulation in solid tumors. We solved this dilemma successfully by preparing kinetically frozen large compound nanoparticles (sized 128 nm) of complex of oligolysine/iridium(III) compound (a potential anticancer drug) that can dissociate into small ones in lysosome environment. The small nanoparticles retain their small size in cytosol after escaping from the lysosomes, so that they can enter the nucleus actively through nucleaopores, with the help of oligolysine segments on the surfaces of nanoparticles acting as the nuclear targeting moieties. It is significant that the nanoparticles can release the contained Ir compound within the nucleus. Further study reveals that the release is triggered by DNA interaction with the nanoparticles, which is responsible for the observation that the release occurs only in the nucleus. We believe that the present study, representing the first example of DNA triggered intranuclear release from nanoparticles, will provide a promising pathway for chemotherapy.

DNA/polymeric micelle self-assembly mimicking chromatin compaction.

Through self-assembly, a large variety of nanomaterials have been fabricated, which are useful in many applied and research fields. However, broader development of nanoscience and nanotechnology requires more complex nanostructures whose fabrication requires precise control of morphology, structural parameters, and distributions of components within the nanomaterials, which remains a great challenge for nanotechnology. Nature is masterful at building nanostructures with great complexity by precisely controlling multi-stage self-assembly processes. One example is the self-assembly of genomic DNA and histone octamers into chromatin in eukaryotic cells. Histone octamers are discshaped nanostructures with positively-charged binding sites specifically distributed on the edge of the disc. In the first stage, a DNA chain organizes histone octamers into a beadson-a-string structure (10 nm chromatin fiber); the bead is a nucleosome composed of one DNA segment wrapping around the edge of one histone octamer, and between neighboring beads is a short DNA linker. In the second stage, histone octamers that are preorganized on the 10 nm chromatin fiber, self-assemble further in a zigzag manner into the 30 nm chromatin fiber with a two-start helical structure. Histone octamers do not self-assemble into the 30 nm fiber until they are preorganized by the first stage of self-assembly; the first stage self-assembly initiates the second stage self-assembly. Inspired by such efficient self-assembly processes from nature, a number of DNA/sphere systems were studied; artificial nanospheres were used in the place of histone octamers. Computer simulation of the interaction between a polyelectrolyte with long DNA-like semi-flexible chains and the spheres with a uniform oppositely-charged surface reveals that the beads-on-a-string structure, similar to the 10 nm chromatin fiber, is the thermodynamic favored structure. However, experimentally, other kinetically trapped structures were inevitably produced in the reported systems because the DNA/sphere interactions were relatively strong. Herein, we prepared thermodynamically optimal structures of a DNA/artificial particle complex by controlling the interaction between DNA and the particles. We selected the block-copolymer micelles with an inert shell and a positively charged core to interact with DNA (Figure 1A); the interaction strength between DNA and the core can be continuously adjusted by the pH value of the medium. It was found that under certain conditions the strings (that are similar to the 10 nm chromatin fibers in both morphology and structure) formed exclusively. Under such conditions, only the thermodynamically favored beads-on-a-string structure can persist, while any kinetically trapped structures cannot. When monodisperse DNA was used, the strings formed were monodisperse, and the earlier-formed long strings evolved to shorter, but also monodisperse, strings; the different strings formed and evolved in a similar manner. Then, in a second stage, the micelles preorganized in the beads-on-a-string structure self-assembled along the strings into core–shell structured solenoidal nanofibers. The preorganization induced and guided the second stage of self-assembly. When monodisperse DNAs are used, the resulting nanostructures are monodisperse. This self-assembly process can be used for synthesis of monodisperse one-dimensional nanostructures with controlled dimensions and various compositions. Poly(ethylene glycol)113-b-poly(4-vinylpyridine)58 (PEG113b-P4VP58, subscripts represent the average degrees of polymerization;Mw/Mn= 1.20) micelles were prepared in a water/ methanol (4:1, v/v) mixture (see Supporting Information, Text S1). The micelles were monodisperse in size with an average hydrodynamic radius hRhi of 16.0 nm, a polydispersity index (PDI) of 0.05, and an average molecular weight of 1.74 10 gmol , based on light scattering (LS) measurements. In the TEM images, the micelles are monodisperse with a size of 17.5 1.5 nm (Figure 1B). The micelles shown have PEG as the shell and P4VP as the core. An aqueous solution of monodisperse linear doublestrandedDNA 5427 bp long (L5427) at 25 8Cwas added to the micelles in the water/methanol mixture to give a DNA/ micelle mass ratio of 1:20. The solution had a pH value of 6.6 in the presence of carbon dioxide (see Experimental Section), which provided the proper strength for the electrostatic interaction between DNA and the micelles (Supporting Information, Text S2). After 0.5 hours incubation, strings with a beads-on-a-string structure formed exclusively (Figure 1C). These strings have a linear structure without any branches, indicating that each string is composed of a single L5427 DNA chain, as detailed below. For each string, the beads were very similar in shape and size to the micelles. Between neighboring beads was a linker, which appears to be a short DNA segment. Additionally, the strings were shown to [*] K. Zhang, Prof. M. Jiang, Prof. D. Chen The State Key Laboratory of Molecular Engineering of Polymers and Department of Macromolecular Science, Fudan University Handan Road 220, Shanghai 200433 (P.R. China) E-mail: chendy@fudan.edu.cn

Preparation of PEO-b-P2VPH+–S2O82− micelles in water and their reversible UCST and redox-responsive behavior

We report here the preparation of PEO-b-P2VPH+-S2O8(2-) micelles and their reversible multi-responsive behavior.

Conformation Transformation Determined by Different Self-Assembled Phases in a DNA Complex with Cationic Polyhedral Oligomeric Silsesquioxane Lipid

In this work, a novel cube-shaped cationic lipid based on the imidazolium salt of polyhedral oligomeric silsesquioxane (POSS) was complexed with double-stranded DNA. Because of the negative spontaneous curvature of the cationic POSS imidazolium lipid, an inverted hexagonal phase resulted above the melting point of POSS crystals. Depending on the competition between the crystallization of POSS molecules and the negative spontaneous curvature of cationic POSS imidazolium lipids, different self-assembled phase morphologies were obtained. A lamellar phase was obtained when the POSS crystallization was relatively slow. When the POSS crystallization was fast, an inverted hexagonal phase was obtained with POSS lamellar crystals grown in the interstitials of DNA cylinders. On the basis of a circular dichroism study, double-stranded DNA adopted the B-form helical conformation in the inverted hexagonal phase, whereas the helical conformation was largely destroyed in the lamellar phase.

Water in Oil Emulsion Stabilized by Tadpole-like Single Chain Polymer Nanoparticles and Its Application in Biphase Reaction

In this study, tadpole-like single chain polymer nanoparticles (TSCPNs) were efficiently synthesized by intramolecularly cross-linking P4VP block of commercial block polymer of PMMA2250-b-P4VP286 in N,N-dimethylformamide using propargyl bromide as cross-linking agent. The intramolecular cross-linking reaction led to the production of TSCPNs with a linear tail and a cross-linked head. The as-prepared TSCPNs were then applied as emulsifier to stabilize water in chlorobenzene emulsion, and an extremely stabilized water in oil (W/O) emulsion was generated at a low TSCPNs concentration. The TSCPNs concentration was as low as 0.0075 wt % versus total weight of water and chlorobenzene for emulsion formation. The emulsifying performance of TSCPNs was better than that of low molecular surfactant, such as Span-80. The generated W/O emulsion provided an ideal medium for the reduction of oil-soluble p-nitroanisole by water-soluble sulfide to p-anisidine, an effective contact problem between the two reactants with different solubility was well solved through interfacial reaction.

Biologically Inspired, Sophisticated Motions from Helically Assembled, Conducting Fibers

A hierarchically helical organization of carbon nanotubes into macroscopic fibers enables sophistication while controlling three-dimensional electromechanical actuations, e.g., an artificial swing and tail. The actuation generates a stress of more than 260 times that of a typical natural skeletal muscle and an accelerated velocity of more than 10 times that of a cheetah at low electric currents with high reversibility, good stability, and availability to various media.

Macrocellular polymer foams from water in oil high internal phase emulsion stabilized solely by polymer Janus nanoparticles: preparation and their application as support for Pd catalyst

In this study, the preparation of styrene/divinylbenzene-based macrocellular polymers of high internal phase emulsions (polyHIPEs) with interconnected open-cell structure as well as their application as support for Pd nanoparticles are presented. Firstly, water in oil high internal phase emulsions (HIPEs) were generated by adding the water stepwise to the oil phase (styrene and divinylbenzene) containing Janus polymer nanoparticles that consist of a linear poly(methyl methacrylate) “tail” and a cross-linked poly(4-vinylpyridine) “head”. The generated water in oil HIPEs stabilized solely by Janus polymer nanoparticles were then converted to polyHIPEs foams by polymerizing the external continuous oil phase, followed by the extraction with methanol and the drying under the reduced press. Scanning electron microscopy observation revealed that the as-produced macrocellular polyHIPEs were foam structure with closed and/or partially open-cells. Partial cells covered by a thin polymer film were peeled off during the post-treatment. Some key factors influencing the polyHIPEs morphologies, including emulsifier particles content, the mole ratio of styrene to divinylbenzene and the internal phase volume fraction were investigated, and macrocellular polyHIPEs with interconnected open-cell morphologies could be achieved under optimal conditions. Benefited from the strong interaction between the emulsifier particles embedded in the polyHIPEs and H2PdCl4 precursor, Pd nanoparticles were facilely supported in situ within the macrocellular polyHIPEs without any functional monomers or post-functionalization requirement. The obtained Pd@macrocellular polymer hybrid foams were then applied for the heterogeneous Suzuki–Miyaura carbon–carbon coupling reactions between iodobenzene and benzeneboronic acid, and a high catalytic activity with a good recyclability were demonstrated.