Self-Assembling a Polyoxometalate–PEG Hybrid into a Nanoenhancer To Tailor PEG Properties

The unique performance of natural materials stems from their hierarchical hybrid structures formed through self-assembly. The self-assembly principles of natural materials have been exploited to create artificial materials. Herein, we demonstrate a bottom-up approach that produces polymer nanocomposites as well as a self-assembled nanoenhancer for tailoring the polymer properties. The polymer is a poly­(ethylene glycol) (PEG), and the nanoenhancer is aggregates formed by self-assembly of a hybrid. The hybrid is prepared through covalent bonding of a surfactant-encapsulated polyoxometalate (S-POM) complex with a PEG chain and can form aggregates composed of an S-POM complex bilayer sandwiched by two PEG layers. The lateral size of aggregates changes, depending on the conditions used in the sample preparation. Hence, we examined four nanostructures in the solid samples of nanocomposites: hybrid self-assembled nanosheets, PEG crystallized lamellae, PEG/hybrid cocrystallized lamellae, and hybrid crystallized lamellae. Because of a strong interaction among the S-POM complexes as well as good miscibility of the PEG layers with the PEG matrix, the stable aggregate homogeneously disperses in the melted PEG matrix, and hence it can enhance the performance of the melted PEG. For instance, the shear storage moduli of nanocomposites are adjustable over many orders of magnitude at temperatures above the PEG melting point. These findings provide a novel approach to generate synthetic nanocomposites with self-assembled enhancers that can tailor the polymer properties

Incorporation of Polyoxometalates into Polymers to Create Linear Poly(polyoxometalate)s with Catalytic Function

Organic polymers have been found widespread commercial applications due to their easy processing and attractive mechanical properties. Concurrently, inorganic polyoxometalates (POMs), a class of metal–oxygen anionic and nanosized clusters of early transition metals, have a wide range of attractive functions and are used in industrial catalysis. In this communication, we report a new approach to creating the first linear poly­(polyoxometalate)­s that combine the advantages of polymers and POM clusters. In the experiment, a POM-containing norbornene monomer was first synthesized by linking a Wells-Dawson-type POM with a norbornene derivative. The monomer was polymerized in the presence of a Grubbs catalyst under mild conditions with yields nearly 100% in a living and controllable manner. The resulting poly­(polyoxometalate)­s have controllable molecular weights and a well-defined hybrid structure of an organic polynorbornene backbone with large pendant groups of the nanosized POM clusters. Thus, they form good films and have a good catalytic performance. Our findings not only pave the way for incorporating the POM clusters into polymers with well-defined structures and high molecular weights, but also offer a competitive strategy for developing more novel catalytic systems by introducing the poly­(polyoxometalate)­s

Tube-<i>graft</i>-Sheet Nano-Objects Created by A Stepwise Self-Assembly of Polymer-Polyoxometalate Hybrids

In this work, we report the preparation of complex nano-objects by means of a stepwise self-assembly of two polymer-polyoxometalate hybrids (PPHs) in solution. The PPHs are designed and synthesized by tethering two linear poly­(ε-caprolactone)­s (PCL) of different molecular weights (MW) on a complex of a Wells-Dawson-type polyoxometalate (POM) cluster and its countraions. The higher MW PCL–POM self-assembled into nanosheets, while the lower MW PCL–POM assembled into nanotubes just by altering the ratio of water in the DMF–water mixed solvent system. The two nano-objects have a similar membrane structure in which a PCL layer is sandwiched by the two POM-based complex layers. The PCL layer in the nanosheets is semicrystalline, while the PCL layer in the nanotubes is amorphous. We further exploited this MW-dependence to self-assemble the nanotubes on the nanosheet edges to create complex tube-<i>graft</i>-sheet nano-objects. We found that the nanotubes nucleate on the four {110} faces of the PCL crystal and then further grow along the crystallographic <i>b</i>-axis of the PCL crystal. Our findings offer hope for the further development of nano-objects with increasing complexity

Mesoscale Graphene-like Honeycomb Mono- and Multilayers Constructed via Self-Assembly of Coclusters

Honeycomb structure endows graphene with extraordinary properties. But could a honeycomb monolayer superlattice also be generated via self-assembly of colloids or nanoparticles? Here we report the construction of mono- and multilayer molecular films with honeycomb structure that can be regarded as self-assembled artificial graphene (SAAG). We construct fan-shaped molecular building blocks by covalently connecting two kinds of clusters, one polyoxometalate and four polyhedral oligomeric silsesquioxanes. The precise shape control enables these complex molecules to self-assemble into a monolayer 2D honeycomb superlattice that mirrors that of graphene but on the mesoscale. The self-assembly of the SAAG was also reproduced via coarse-grained molecular simulations of a fan-shaped building block. It revealed a hierarchical process and the key role of intermediate states in determining the honeycomb structure. Experimental images also show a diversity of bi- and trilayer stacking modes. The successful creation of SAAG and its stacks opens up prospects for the preparation of novel self-assembled nanomaterials with unique properties

POM–Organic–POSS Cocluster: Creating A Dumbbell-Shaped Hybrid Molecule for Programming Hierarchical Supramolecular Nanostructures

We report the construction of dumbbell-shaped hybrid molecules for programming their hierarchical supramolecular nanostructures through a synergetic self-assembly. Our first dumbbell-shaped hybrid molecule is a POM–organic–POSS cocluster produced by covalently coupling a POM cluster and a POSS cluster together through an organic tether. Structural analyses demonstrated a highly ordered lamellar morphology with a 4.9 nm periodicity, indicating a strong thermodynamic force driving a nanoscale phase separation of the POM and POSS blocks. The POM clusters were arranged in an orderly fashion within the POM-containing layer with a 1.38 nm periodicity because of fixed shape and size of the cluster. This investigation provides in-depth understanding of how to construct hierarchical supramolecular nanostructures at a nanoscale less than 5 nm by manipulating and controlling the topological shape of hybrid molecules