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Three well-defined asymmetric crystalline-coil poly(ferrocenyldimethylsilane-block-2-vinylpyridine) (PFS-b-P2VP) diblock copolymers (PFS 44 -b-P2VP 264 , PFS 75 -b-P2VP 454 , and PFS 102 -b-P2VP 625 ) with similar block ratios (r = N P2VP /N PFS = ca. 6.0 ± 0.1) but different overall molar masses (M n = 38 700, 65 800, and 90 400 g mol −1 ) were synthesized by sequential anionic polymerization, and their solution self-assembly behavior was explored as a function of (i) molar mass and (ii) the ratio of common to selective solvent. When self-assembly was performed in isopropanol (iPrOH), a selective solvent for P2VP, a decrease in the rate of the crystallization-driven transition from the initially formed spheres (with amorphous PFS cores) into cylinders (with crystalline cores) was detected with an increase in molecular weight. This trend can be explained by a decrease in the rate of crystallization for the PFS core-forming block as the chain length increased. In contrast, when a mixture of i-PrOH with increasing amounts of THF, a common solvent for both blocks, was used, spheres, cylinders, and also narrow lenticular platelets consisting of crystallized PFS lamellae sandwiched by two glassy coronal P2VP layers were formed from the same PFS x -b-P2VP 6x sample. The most likely explanation involves the plasticization of the PFS core-forming block which facilitates crystallization, possibly complemented by contraction of the coils of the P2VP coronal block which otherwise limit of the lateral growth of the crystalline PFS core as THF is a poorer solvent for P2VP than i-PrOH. Selected area electron diffraction studies indicated that the PFS cores of the spherical micelles were amorphous but were consistent with those of the cylindrical micelles existing in a state approximating to that of a monoclinic PFS single crystal. In contrast, in the platelets formed in THF/i-PrOH, the PFS cores were found to be polycrystalline. The formation of narrow lenticular polycrystalline platelets rather than a regular, rectangular single crystalline morphology was attributed to a poisoning effect whereby the interference of the long P2VP coronal blocks in the growth of a rectangular PFS single crystalline core introduces defects at the crystal growth fronts. ■ INTRODUCTIONThe self-assembly of block copolymers has attracted growing attention as a result of their ability to form hierarchical ordered structures in either the solid state or solution that possess a wide variety of potential applications in nanoscience and nanomedicine. 1−21 A variety of morphologies can be generated in thin films or the bulk state by controlling the polymer−polymer interaction parameter χ, volume fraction, and molecular weight of the block copolymer. In addition, when diblock copolymers are self-assembled in a selective solvent, a wide range of core− shell micelle morphologies including disks, cylinders, vesicles, and more complex structures have been reported. The resulting block copolymer micelles have attracted attention due to their potential utility a...

Poly(l-lactide) (PLLA)-based nanoparticles have attracted much attention with respect to applications in drug delivery and nanomedicine as a result of their biocompatibility and biodegradability. Nevertheless, the ability to prepare PLLA assemblies with well-defined shape and dimensions is limited and represents a key challenge. Herein we report access to a series of monodisperse complex and hierarchical colloidally stable 2D structures based on PLLA cores using the seeded growth, "living-crystallization-driven self-assembly" method. Specifically, we describe the formation of diamond-shaped platelet micelles and concentric "patchy" block co-micelles by using seeds of the charge-terminated homopolymer PLLA[PPhMe]I to initiate the sequential growth of either additional PLLA[PPhMe]I or a crystallizable blend of the latter with the block copolymer PLLA-b-P2VP, respectively. The epitaxial nature of the growth processes used for the creation of the 2D block co-micelles was confirmed by selected area electron diffraction analysis. Cross-linking of the P2VP corona of the peripheral block in the 2D block co-micelles using Pt nanoparticles followed by dissolution of the interior region in good solvent for PLLA led to the formation of novel, hollow diamond-shaped assemblies. We also demonstrate that, in contrast to the aforementioned results, seeded growth of the unsymmetrical PLLA BCPs PLLA-b-P2VP or PLLA-b-PAGE alone from 2D platelets leads to the formation of diamond-fiber hybrid structures.

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. ABSTRACT: Rectangular platelets formed by the self-assembly of block copolymers in selective solvents are of interest for a range of applications. Recently we showed that the seeded growth of crystallizable blends of a block copolymer and homopolymer yields well-defined, low dispersity examples of these two-dimensional (2D) structures. The key feature was the use of the same crystallizable polymer segment in the seed and blend components to enable an efficient homoepitaxial growth process. Herein we demonstrate that this 2D crystallization-driven self-assembly approach can be extended to heteropitaxial growth by the use of different crystallizable polymers with compatible crystal structures. This allows the formation of well-defined "patchy" rectangular platelets and platelet block comicelles with different core chemistries. The use of scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy provided key information on the spatial location of the components in the resulting assemblies and thereby valuable insight into the 2D heteroepitaxial growth process.

Square-planar platinum(II) complexes often stack cofacially to yield supramolecular fiber-like structures with interesting photophysical properties. However, control over fiber dimensions and the resulting colloidal stability is limited. We report the self-assembly of amphiphilic Pt(II) complexes with solubilizing ancillary ligands based on polyethylene glycol [PEG, where n = 16, 12, 7]. The complex with the longest solubilizing PEG ligand, Pt-PEG, self-assembled to form polydisperse one-dimensional (1D) nanofibers (diameters <5 nm). Sonication led to short seeds which, on addition of further molecularly dissolved Pt-PEG complex, underwent elongation in a "living supramolecular polymerization" process to yield relatively uniform fibers of length up to ca. 400 nm. The fiber lengths were dependent on the Pt-PEG complex to seed mass ratio in a manner analogous to a living covalent polymerization of molecular monomers. Moreover, the fiber lengths were unchanged in solution after 1 week and were therefore "static" with respect to interfiber exchange processes on this time scale. In contrast, similarly formed near-uniform fibers of Pt-PEG exhibited dynamic behavior that led to broadening of the length distribution within 48 h. After aging for 4 weeks in solution, Pt-PEG fibers partially evolved into 2D platelets. Furthermore, self-assembly of Pt-PEG yielded only transient fibers which rapidly evolved into 2D platelets. On addition of further fiber-forming Pt complex (Pt-PEG), the platelets formed assemblies via the growth of fibers selectively from their short edges. Our studies demonstrate that when interfiber dynamic exchange is suppressed, dimensional control and hierarchical structure formation are possible for supramolecular polymers through the use of kinetically controlled seeded growth methods.

Transition metal dichalcogenides (TMDs) have attracted considerable attention in a diverse array of applications due to the breadth of possible property suites relative to other low-dimensional nanomaterials (e.g., graphene, aluminosilicates). Here, we demonstrate an alternative methodology for the exfoliation of bulk crystallites of group V-VII layered TMDs under quiescent, benchtop conditions using mild redox chemistry. Anionic polyoxometalate species generated from edge sites adsorb to the TMD surface and create Coulombic repulsion that drives layer separation without the use of shear forces. This method is generalizable (MS, MSe, and MTe) and effective in preparing high-concentration (>1 mg/mL) dispersions with narrow layer thickness distributions more rapidly and with safer reagents than alternative solution-based approaches. Finally, exfoliation of these TMDs is demonstrated in a range of solvent systems that were previously inaccessible due to large surface energy differences. These characteristics could be beneficial in the preparation of high-quality films and monoliths.

Solid-state complexes of flexible polymers with surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology. Because the surf molecules are strongly associated with the polymer backbone, the ordered packing of the alkyl tails should be cooperative with the chain packing in the polymer layers which is influenced by chain topology. In this study, the supramolecular structure and thermal properties of the complexes of a highly branched poly(ethylenimine) (PEI) with dodecylbenzenesulfonic acid (DBSA) were investigated. Polarized optical microscopy and small-angle X-ray scattering (SAXS) revealed the presences of mesomorphic phases and microphase-separated lamellar morphology in the complexes. The ordered supramolecular structure was observed not only for the stoichiometric composition but over a wide composition range. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. The surf layer thickness varied with complex composition. The glass transition temperature of polymer layers was raised by complexation because of the stiffening of polymer chains. Complexation with DBSA also enhanced the thermal stability of PEI, where the thermal decomposition temperature can be raised by as much as 50 °C.