“Cross” Supermicelles via the Hierarchical Assembly of Amphiphilic Cylindrical Triblock Comicelles

Self-assembled “cross” architectures are well-known in biological systems (as illustrated by chromosomes, for example); however, comparable synthetic structures are extremely rare. Herein we report an in depth study of the hierarchical assembly of the amphiphilic cylindrical P–H–P triblock comicelles with polar (P) coronal ends and a hydrophobic (H) central periphery in a selective solvent for the terminal segments which allows access to “cross” supermicelles under certain conditions. Well-defined P–H–P triblock comicelles M­(PFS-<i>b</i>-PtBA)-<i>b</i>-M­(PFS-<i>b</i>-PDMS)-<i>b</i>-M­(PFS-<i>b</i>-PtBA) (M = micelle segment, PFS = polyferrocenyldimethylsilane, PtBA = poly­(<i>tert</i>-butyl acrylate), and PDMS = polydimethylsiloxane) were created by the living crystallization-driven self-assembly (CDSA) method. By manipulating two factors in the supermicelles, namely the H segment-solvent interfacial energy (through the central H segment length, <i>L</i>₁) and coronal steric effects (via the PtBA corona chain length in the P segment, <i>L</i>₂ related to the degree of polymerization DP₂) the aggregation of the triblock comicelles could be finely tuned. This allowed a phase-diagram to be constructed that can be extended to other triblock comicelles with different coronas on the central or end segment where “cross” supermicelles were exclusively formed under predicted conditions. Laser scanning confocal microscopy (LSCM) analysis of dye-labeled “cross” supermicelles, and block “cross” supermicelles formed by addition of a different unimer to the arm termini, provided complementary characterization to transmission electron microscopy (TEM) and dynamic light scattering (DLS) and confirmed the existence of these “cross” supermicelles as kinetically stable, micron-size colloidally stable structures in solution

Monodisperse Cylindrical Micelles and Block Comicelles of Controlled Length in Aqueous Media

Cylindrical block copolymer micelles have shown considerable promise in various fields of biomedical research. However, unlike spherical micelles and vesicles, control over their dimensions in biologically relevant solvents has posed a key challenge that potentially limits in depth studies and their optimization for applications. Here, we report the preparation of cylindrical micelles of length in the wide range of 70 nm to 1.10 μm in aqueous media with narrow length distributions (length polydispersities <1.10). In our approach, an amphiphilic linear-brush block copolymer, with high potential for functionalization, was synthesized based on poly­(ferrocenyldimethylsilane)-<i>b</i>-poly­(allyl glycidyl ether) (PFS-<i>b</i>-PAGE) decorated with triethylene glycol (TEG), abbreviated as PFS-<i>b</i>-(PEO-<i>g</i>-TEG). PFS-<i>b</i>-(PEO-<i>g</i>-TEG) cylindrical micelles of controlled length with low polydispersities were prepared in <i>N</i>,<i>N</i>-dimethylformamide using small seed initiators via living crystallization-driven self-assembly. Successful dispersion of these micelles into aqueous media was achieved by dialysis against deionized water. Furthermore, B–A–B amphiphilic triblock comicelles with PFS-<i>b</i>-poly­(2-vinylpyridine) (P2VP) as hydrophobic “B” blocks and hydrophilic PFS-<i>b</i>-(PEO-<i>g</i>-TEG) “A” segments were prepared and their hierarchical self-assembly in aqueous media studied. It was found that superstructures formed are dependent on the length of the hydrophobic blocks. Quaternization of P2VP was shown to cause the disassembly of the superstructures, resulting in the first examples of water-soluble cylindrical multiblock comicelles. We also demonstrate the ability of the triblock comicelles with quaternized terminal segments to complex DNA and, thus, to potentially function as gene vectors

Higher-order assembly of crystalline cylindrical micelles into membrane-extendable colloidosomes

Functional nanoscale objects can be prepared via crystallization-driven self-assembly of diblock copolymers. Here the authors show the self-assembly of crystalline block copolymers into size-specific cylindrical micelles for the hierarchical construction of mechanically robust colloidosomes with a range of membrane textures

Manipulation and Deposition of Complex, Functional Block Copolymer Nanostructures using Optical Tweezers

Block copolymer self-assembly has enabled the creation of a range of solution-phase nanostructures with applications from optoelectronics and biomedicine to catalysis. However, to incorporate such materials into devices a method that facilitates their precise manipulation and deposition is desirable. Herein we describe how optical tweezers can be used to trap, manipulate, and pattern individual cylindrical micelles and larger hybrid micellar materials. Through the combination of TIRF imaging and optical trapping we can precisely control the three-dimensional motion of individual cylindrical block copolymer micelles in solution, enabling the creation of customizable arrays. We also demonstrate that dynamic holographic assembly enables the creation of ordered customizable arrays of complex hybrid block copolymer structures. By creating a program which automatically identifies, traps, and then deposits multiple assemblies simultaneously we have been able to dramatically speed up this normally slow process, enabling the fabrication of arrays of hybrid structures containing hundreds of assemblies in minutes rather than hours

Dimensional control and morphological transformations of supramolecular polymeric nanofibers based on cofacially-stacked planar amphiphilic platinum(II) complexes

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_<i>n</i>, where <i>n</i> = 16, 12, 7]. The complex with the longest solubilizing PEG ligand, <b>Pt-PEG</b>_<b>16</b>, self-assembled to form polydisperse one-dimensional (1D) nanofibers (diameters <5 nm). Sonication led to short seeds which, on addition of further molecularly dissolved <b>Pt-PEG</b>_<b>16</b> complex, underwent elongation in a “living supramolecular polymerization” process to yield relatively uniform fibers of length up to <i>ca</i>. 400 nm. The fiber lengths were dependent on the <b>Pt-PEG</b>_<b>16</b> 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 <b>Pt-PEG</b>_<b>12</b> exhibited dynamic behavior that led to broadening of the length distribution within 48 h. After aging for 4 weeks in solution, <b>Pt-PEG</b>_<b>12</b> fibers partially evolved into 2D platelets. Furthermore, self-assembly of <b>Pt-PEG</b>_<b>7</b> yielded only transient fibers which rapidly evolved into 2D platelets. On addition of further fiber-forming Pt complex (<b>Pt-PEG</b>_<b>16</b>), the platelets formed assemblies <i>via</i> 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

Non-covalent synthesis of supermicelles with complex architectures using spatially confined hydrogen-bonding interactions

Nature uses orthogonal interactions over different length scales to construct structures with hierarchical levels of order and provides an important source of inspiration for the creation of synthetic functional materials. Here, we report the programmed assembly of monodisperse cylindrical block comicelle building blocks with crystalline cores to create supermicelles using spatially confined hydrogen-bonding interactions. We also demonstrate that it is possible to further program the self-assembly of these synthetic building blocks into structures of increased complexity by combining hydrogen-bonding interactions with segment solvophobicity. The overall approach offers an efficient, non-covalent synthesis method for the solution-phase fabrication of a range of complex and potentially functional supermicelle architectures in which the crystallization, hydrogen-bonding and solvophobic interactions are combined in an orthogonal manner

Exploring the Tunable Optical and Mechanical Properties of Multicomponent Low-Molecular-Weight Gelators

A class of amino acid-based low-molecular-weight gelators (LMWGs) was used for single and multicomponent gel studies to investigate their tunable optical properties and their self-assembly process. The optical properties of multicomponent gels were found to be easily tuned by changing the proportion of the components, varying from opaque to highly transparent gels as analyzed using ultraviolet–visible spectroscopy. This phenomenon allows tunability without introducing another variable into the system. Scanning electron microscopy, differential scanning calorimetry, and small-angle X-ray scattering (SAXS) were used to investigate the structures of the gels. It was found that because of the structural similarities of the molecules, the gelators favor coassembly packing over self-sorting. The emergence of transparency was ascribed to changes in the fiber diameters. Moreover, analysis of the SAXS data allowed us to compare the molecular order present in the gel phase with single-crystal X-ray diffraction (SCXRD) data. Our analysis suggests that the packing of molecules seen in the crystalline phase is translated into the gel network. This reveals that the structure of the crystalline phase seen through SCXRD is a useful tool to aid in understanding the molecular packing in the gel phase

Fluorous Cylindrical Micelles of Controlled Length by Crystallization-Driven Self-Assembly of Block Copolymers in Fluorinated Media

Fluorous solvents have recently found broad applications in medical treatments as well as catalytic transformations, yet the controlled self-assembly of nanomaterials in fluorinated media has remained a challenge. Herein, we report the synthesis of block copolymers containing a crystalline polyferrocenylsilane metalloblock and a highly fluorinated coil block and their controlled self-assembly in fluorinated media. Using the crystallization-driven self-assembly approach, cylindrical micelles have been prepared with controlled lengths and narrow length polydispersities by self-seeding. Finally, by partial functionalization of these block copolymers with fluorescent dye molecules, we show that well-defined, functional nanomaterials can be obtained in the fluorous phase