AbstractA facile and electrostatically driven approach has been developed to prepare bicontinuous polymer nanocomposites that is based on the polyoxometalate (POM) macroion induced phase transition of PS-b-P2VP from an initial lamellar phase to a stable bicontinuous phase. The multi-charged POMs can electrostatically cross-link P2VP blocks and give rise to bicontinuous phases in which the POM hybrid conductive domains occupy a large volume fraction of more than 50 %. Furthermore, the POMs can give rise to high proton conductivity and serve as nanoenhancers, endowing the bicontinuous nanocomposites with a conductivity of 0.1 mS cm−1 and a Young's modulus of 7.4 GPa at room temperature; these values are greater than those of pristine PS-b-P2VP by two orders of magnitude and a factor of 1.8, respectively. This approach can provide a new concept based on electrostatic control to design functional bicontinuous polymer materials.

AbstractA facile and electrostatically driven approach has been developed to prepare bicontinuous polymer nanocomposites that is based on the polyoxometalate (POM) macroion induced phase transition of PS-b-P2VP from an initial lamellar phase to a stable bicontinuous phase. The multi-charged POMs can electrostatically cross-link P2VP blocks and give rise to bicontinuous phases in which the POM hybrid conductive domains occupy a large volume fraction of more than 50 %. Furthermore, the POMs can give rise to high proton conductivity and serve as nanoenhancers, endowing the bicontinuous nanocomposites with a conductivity of 0.1 mS cm−1 and a Young's modulus of 7.4 GPa at room temperature; these values are greater than those of pristine PS-b-P2VP by two orders of magnitude and a factor of 1.8, respectively. This approach can provide a new concept based on electrostatic control to design functional bicontinuous polymer materials.

•CSPs were firstly used to fabricate microporous films by the breath figure method.•CSP films with regular pores as small as 260 nm were obtained.•CSPs can efficiently improve the microporous regularity of polystyrene films.Microporous films with tunable honeycomb structures were fabricated based on the self-assembly of a series of clusto-supramolecular star polymers (CSPs) guided by breath figure templates. The CSPs consist of a hydrophilic polyoxometalate cluster core and several hydrophobic polystyrene arms that are electrostatically connected to the core, in which three Keggin-type polyoxometalate clusters [CoW12O40]6-, [SiW12O40]4- and [PW12O40]3- were used as the cores. The dynamic bonding character endows CSPs a rearrangeable amphiphilic conformation that facilities them to accumulate at the oil/water interface to stabilize water droplets. By precisely adjusting the arm number and arm length of CSPs, we revealed the relationship between the structure and the film-forming behavior of CSPs. Regular pores with a small diameter as low as 260 nm were obtained by optimizing the structure of CSPs. Moreover, the CSPs could act as morphological modifiers to efficiently improve the microporous regularity of polystyrene films, even at a low CSP content of 0.8 wt%. To the best of our knowledge, this is the first work using supramolecular star polymers to fabricate microporous films by the breath figure method, which not only introduces a new film-formation material, but also provides a facile way to incorporate inorganic functional components into microporous polymer films.Download high-res image (234KB)Download full-size image

Clusto-supramolecular block copolymers are synthesized by using an anionic cluster [W6O19]2− as an ionic junction to link two cationic terminated polystyrene chains. These polymers exhibit versatile self-assembly behaviours not only dependent on the molecular weight but also adaptive to the concentration and temperature.

•A facile strategy to tune block copolymer morphologies is presented by using polyoxometalate macroions as electrostatic additives.•Polyoxometalate macroions can interrupt the regularity of PS-b-P4VP to form disordered bicontinuous morphologies.•The incorporated polyoxometalate macroions can tune the thermal and viscoelastic properties of PS-b-P4VP.Bicontinuous block copolymer morphologies can offer unique transporting properties in catalysis and energy materials, whereas they are difficult to be obtained due to the relatively narrow window in phase diagram. In this work, we present a facile strategy to induce block copolymers to form bicontinuous morphologies by using nanoscale ionic clusters as electrostatic additives. A Keggin-type polyoxometalate cluster, H4SiW12O40 (SiW) was incorporated into the matrices of a series of poly(styrene-b-4-vinylprydine) (PS-b-P4VP) through the electrostatic interaction between SiW and P4VP chains. Upon the increase of SiW content, disordered bicontinuous morphologies were evolved from the PS-b-P4VP with an initial cylindrical phase, accompanying with the disappeared Tg of P4VP and the mechanical reinforcement of PS-b-P4VP/SiW nanocomposites. The bicontinuous structures can also be induced by other polyoxometalate clusters with different charges. However, the PS-b-P4VP with an initial isolating spherical phase retains their spherical structures in spite of loading SiW. These results demonstrate a new concept to obtain bicontinuous polymeric structures by using inorganic macroions to interrupt the regularity of percolating block copolymer phase, which may favor the fabrication of transporting membranes and solid electrolyte materials based on block copolymers.

A noncovalent and phase-transfer-assisted method is developed for the fabrication of polymer-functionalized graphene, in which a series of cluster-cored star polymers (CSPs) containing a polyoxometalate core and polystyrene (PS) arms are used as modifiers. Through the electron transfer interaction between polyoxometalate and graphene, the CSPs can strongly adsorb on graphene nanosheets and transfer them from aqueous media to organic solvents like chloroform, forming individually dispersed graphene. Moreover, the CSP-functionalized graphene is well compatible with additional polymer matrices and can serve as a reinforcing nanofiller for polymer composites. A 0.2 wt% loading of them in PS coating achieves a 98.9% high enhancement in Young’s modulus.

The coassembly of block copolymers (BCPs) with nanoscale inorganic objects is an important route to fabricate nanostructured polymer composites. However, the immiscibility of inorganic/polymeric interface is a recurring challenge to overcome, particularly for inorganic clusters, such as the polyoxometalates (POMs)/BCPs system. In this paper, we present a general method to incorporate POMs into BCP matrices, in which a POM cluster is embedded as a core in a supramolecular star polymer (SSP) whose arms possess the same chemical composition as a BCP segment. Because of the enthalpic interaction between SSP arms and BCP segments, the SSP can carry POM into BCP matrices to realize their coassembly. By this way, we successfully localize a Keggin-type POM cluster [CoW12O40]6– modified with polystyrene (PS) arms into the PS domain of poly(styrene-b-ethylene oxide) micelles, which induces the formation of a series of hybrid micelles with spherical, toroidal, and bicontinuous structures. The morphological transition of micelles can be adjusted by the length of PS arms and the content of cluster cores. The mechanism is studied by both experimental methods and simulations. An unconventional mechanism for toroid formation is disclosed for the first time, which follows a sphere–rosary–toroid pathway. Furthermore, the electrostatically bonded structure of SSP is found to play a crucial role on this pathway. These results not only pave the way for fabricating cluster–polymer nanocomposites with controllable structures but also provide new insights into comprehending the self-assembly behavior of complex polymer systems.

Surfactant-encapsulated polyoxometalate complexes are used as cluster suprasurfactants to transfer reduced graphene oxide (RGO) nanosheets from water to low polar organic solvents, which realizes the single-layer dispersion and the cluster-functionalization of RGO in one step.

A series of hybrid supramolecular star polymers (SSPs) consisting of a polyoxometalate EuW10O369− (EuW10) core and different length of polystyrene arms have been fabricated by a “core-first” method, in which the anionic EuW10 clusters were firstly encapsulated by cationic molecules with trithioester terminal groups and subsequently polystyrene arms were grafted by reversible addition–fragmentation chain-transfer (RAFT) polymerization. The SSPs exhibit structurally dependent self-assembly behaviours in solution, at the air–water interface and solid state. It was found that the SSPs with short arms form large assemblies with a diameter over 100 nm in chloroform, while those with long arms tend to be mono-dispersed. Meanwhile, the distance between the EuW10 cores of adjacent SSPs in Langmuir monolayers and casting films can be precisely adjusted by PS arms, which leads to a tunable colour purity of EuW10 luminescence. This tight structure–property relationship enables the polyoxometalate-cored SSPs to act as potential building blocks for the construction of hybrid polymer materials with controllable functions.

The block copolymers (BCs), as structure-directing agents, co-assembling with nanoscale inorganic additives is an important route to fabricate nanostructured hybrid materials. In this work, we present a facile approach to fabricate hybrid micelles composed of BCs and polyoxometalates (POMs), in which the POM clusters are premodified with the groups that can specifically interact with a certain BC block. A representative POM (NH4)42[Mo132O372(CH3COO)30(H2O)72] (Mo132) is chosen as the example and encapsulated with cationic molecules containing carboxyphenyl groups through electrostatic interactions, and then the resulting hybrid complex can further co-assemble with poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) through hydrogen bonding with the pyridine groups, which leads to the formation of hybrid micelles and the localization of Mo132 in the micelle cores. The micelles exhibit a high stability despite time and dilution. Furthermore, the fusion of the micelles can be readily adjusted by varying the length of PS blocks, which is promising to be used in constructing polymer–POM hybrid materials with discrete or continuous hybrid domains. This work is based on the electrostatic premodification of POMs and thus its concept is generally suitable for the whole anionic POM system, which may create a large class of BC–POM nanocomposites with tunable structures.

•Graphene oxide has been successfully photoreduced by polyoxometalates.•The influence of the energy level of polyoxometalates on their photoreduction capabilities has been elucidated.•The saturable absorption of the reduced graphene oxide has been studied by Z-scan method.We investigated the photocatalytic abilities of three Keggin-type polyoxometalate (POM) clusters, H3PW12O40 (PW), H4SiW12O40 (SiW), and H3PMo12O40 (PMo) to reduce graphene oxide (GO) under UV-irradiation in water. UV–vis absorption and X-ray photoelectron spectroscopy were performed and show that PW and SiW can photoreduce GO effectively, in contrast to PMo. We conclude that the LUMO levels of POMs should be located energetically above the work function of GO to enable electron transfer from POM to GO. We also investigated the saturable absorption of GO and reduced GO by means of z-scan experiments at 532 nm. The POM-assisted photoreduction of GO can greatly enhance the saturable absorber properties of GO, which appears useful for modelocking in ultrafast laser systems.Graphical abstract

A new type of organic–inorganic hybrid supramolecular polymer has been prepared by using the base group modified polyoxometalate clusters as monomers, where the hydrogen bonds between the complementary base pairs act as the driving force.

An organically pyridyl-grafted Anderson-type POM complex (TBA–Py–MnMo6) bearing counterions of tetrabutylammonium (TBA) was found to form supramolecular gels instantaneously through mixing with appropriate dicarboxylic acid additives in acetonitrile. In the gelation process, TBA–Py–MnMo6 was confirmed to self-assemble into supramolecular polymer chains through unidirectional hydrogen bonding between the pyridyl groups of POMs and the carboxylic groups of dicarboxylic acids, which drove the complexes into one-dimensional fibers. The fibers were demonstrated to further intertwine together through the lateral hydrogen bonding between polymer chains under the support of excess acid, forming three-dimensional networks. The distance between TBA–Py–MnMo6 units secluded by dicarboxylic acid was proved to be a criterion for the formation of gels, which is related to the TBA density along the supramolecular polymer chains and the solvent–fiber interfacial energy. The gelation behaviour of the hybrid POM complex can be simply controlled through adjusting the length of dicarboxylic acids. More interestingly, the POM hybrid gels exhibited a quick response to organic bases and diacids reversibly.

A new kind of organic–inorganic hybrid complexes based on polyoxometalate were synthesized through symmetrically grafting two adeninyl groups onto Anderson-type MnMo6 clusters and encapsulating the clusters by organic surfactants. The resultant complexes exhibited thermal-induced dynamic self-assembly behaviors which greatly depended on the ambient temperature and the chain length of cationic surfactants. With the encapsulation of a short surfactant tetrabutyl ammonium, the complex assembled into fibrous, rod-like, and tubular architectures respectively upon heating; while for the case of using a long surfactant dimethyldioctadecyl ammonium as counter ions, the assemblies of the complex transformed from fibers to spheres with the increased temperature. Moreover, the two types of transformations were both reversible during a cooling process. The related mechanism was investigated by combining multiple characterization methods including X-ray crystallography, XPS, FT-IR and temperature-dependent 1H NMR, which indicated that such a thermal-induced morphological transformation resulted from a synergy effect of the variation of the multiple hydrogen bonds among the complexes and the rearrangement of the surfactants surrounding the MnMo6 clusters. These results demonstrated a new concept that hydrogen bonds can be rationally employed as the driving force for the fabrication of polyoxometalate-based materials with smart responsive properties.

In this paper, four organic–inorganic hybrid complexes were prepared using a cationic surfactant dimethyldioctadecylammonium (DODA) to replace the counter cations of four Keggin-type polyoxometalate (POM) clusters with gradually increased negative charges, PW12O403–, SiW12O404–, BW12O405–, and CoW12O406–. The formed surfactant-encapsulated POM (SEP) complexes showed typical amphiphilic properties and can be spread onto the air–water interface to form Langmuir monolayers. The interfacial behavior of the SEP monolayer films was systemically studied by multiple in situ and ex situ characterization methods including Brewster angle microscopy (BAM), atomic force microscopy (AFM), reflection–absorption infrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We found that the increasing alkyl chain density of SEPs leads to an enhanced stability and a higher collapse pressure of SEP Langmuir monolayers. Moreover, a second layer evolved as patterns from the initial monolayers of all the SEPs, when the surface pressures approached the collapse values. The rational combination of alkyl chain density and surface pressure can precisely control the size and the morphology of SEP patterns transforming from disk-like to leaf-like structures on a micrometer scale. The pattern formation was demonstrated to be driven by the self-optimized surface energy of SEP monolayers. This finding can direct a new strategy for the fabrication of POM-hybrid films with controllable patterns, which should be instructive for designing POM-based thin film devices.

Polyoxometalates can serve as active components to induce and modulate the micellization behavior of polystyrene-block-poly(4-vinylpyridine).

Polyoxometalates can serve as active components to induce and modulate the micellization behavior of polystyrene-block-poly(4-vinylpyridine).

A new type of organic–inorganic hybrid supramolecular polymer has been prepared by using the base group modified polyoxometalate clusters as monomers, where the hydrogen bonds between the complementary base pairs act as the driving force.

A new kind of organic–inorganic hybrid complexes based on polyoxometalate were synthesized through symmetrically grafting two adeninyl groups onto Anderson-type MnMo6 clusters and encapsulating the clusters by organic surfactants. The resultant complexes exhibited thermal-induced dynamic self-assembly behaviors which greatly depended on the ambient temperature and the chain length of cationic surfactants. With the encapsulation of a short surfactant tetrabutyl ammonium, the complex assembled into fibrous, rod-like, and tubular architectures respectively upon heating; while for the case of using a long surfactant dimethyldioctadecyl ammonium as counter ions, the assemblies of the complex transformed from fibers to spheres with the increased temperature. Moreover, the two types of transformations were both reversible during a cooling process. The related mechanism was investigated by combining multiple characterization methods including X-ray crystallography, XPS, FT-IR and temperature-dependent 1H NMR, which indicated that such a thermal-induced morphological transformation resulted from a synergy effect of the variation of the multiple hydrogen bonds among the complexes and the rearrangement of the surfactants surrounding the MnMo6 clusters. These results demonstrated a new concept that hydrogen bonds can be rationally employed as the driving force for the fabrication of polyoxometalate-based materials with smart responsive properties.

Surfactant-encapsulated polyoxometalate complexes are used as cluster suprasurfactants to transfer reduced graphene oxide (RGO) nanosheets from water to low polar organic solvents, which realizes the single-layer dispersion and the cluster-functionalization of RGO in one step.