Uniform Toroidal Micelles via the Solution Self-Assembly of Block Copolymer–Homopolymer Blends Using a “Frustrated Crystallization” Approach

Multiscale Tunable Nanorings Based on Bi-Component Micellar-Configuration-Transformation Induced by Hydrophobicity

Ringy nanostructures are amazing materials, displaying unique optical, magnetic, and electronic properties highly related to their dimensions. A strategy capable of continuously tailoring the diameter of nanorings is the key to elucidating their structure-function relationship. Herein, a method of bi-component micellar-configuration-transformation induced by hydrophobicity for the synthesis of nanorings with diameters ranging from submicron (≈143 nm) to micron (≈4.8 µm) and their carbonaceous analogs is established. Remarkably, the nanorings fabricated with this liquid phase strategy achieve the record for the largest diameter span. Through varying the molecular lengths of fatty alcohols and copolymers, shortening the molecular length of fatty alcohol can swell the primary micelles, improve the exposure of hydrophobic component and boost the assembly kinetics for ultra-large nanorings is shown here. On the other hand, shortening the molecular length of the copolymer will give rise to ultra-small nanorings by reducing the size of primary micelles and shortening the assembly time. When assembling the nanorings into monolayer arrays and then depositing Au, such substrate displays enhanced surface-enhanced Raman scattering (SERS) performance. This research develops a facile method for the controllable synthesis of ringy materials with multiscale tunable diameters and may inspire more interesting applications in physics, optical, and sensors.

Constructing a Comprehensive Nanopattern Library through Morphological Transitions of Block Copolymer Surface Micelles via Direct Solvent Immersion

This study establishes a comprehensive library of nanopatterns achievable by a single block copolymer (BCP), ranging from spheres to complex structures like split micelles, flower-like clusters, toroids, disordered micelle arrays, and unspecified unique shapes. The ordinary nanostructures of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) surface micelles deposited on a SiOx surface undergo a unique morphology transformation when immersed directly in solvents. Investigating parameters such as immersion solvents, BCP molecular weight, substrate interactions, and temperature, this work reveals the influence of these parameters on the thermodynamics and kinetics governing the morphology transformation. Additionally, the practical application of BCP nanopattern templates for fabricating metal nanostructures through direct solvent immersion of surface micelles is demonstrated. This approach offers an efficient and effective method for producing diverse nanostructures, with the potential to be employed in nanolithography, catalysts, electronics, membranes, plasmonics, and photonics.

Nanoscale polymer discs, toroids and platelets: a survey of their syntheses and potential applications

Polymer self-assembly has become a reliable and versatile workhorse to produce polymeric nanomaterials. With appropriate polymer design and monomer selection, polymers can assemble into shapes and morphologies beyond well-studied spherical and cylindrical micellar structures. Steadfast access to anisotropic polymer nanoparticles has meant that the fabrication and application of 2D soft matter has received increasing attention in recent years. In this review, we focus on nanoscale polymer discs, toroids, and platelets: three morphologies that are often interrelated and made from similar starting materials or common intermediates. For each morphology, we illustrate design rules, and group and discuss commonly used self-assembly strategies. We further highlight polymer compositions, fundamental principles and self-assembly conditions that enable precision in bottom-up fabrication strategies. Finally, we summarise potential applications of such nanomaterials, especially in the context of biomedical research and template chemistry and elaborate on future endeavours in this space.

Nano-assemblies of phosphonium-functionalized diblock copolymers with fabulous antibacterial properties and relationships of structure-activity

As a novel antimicrobial material, quaternary phosphonium salts (QPSs) have been drawing close attention because of their excellent antimicrobial capacity with high activity and low bacterial survivability. Polymeric QPSs (PQPSs) also exhibit selectivity and long-term stability, however the polymerization of QPSs is severely challenged by low controllability and narrow selectivity of cation type. In this study, high-conversion RAFT polymerization is employed to prepare innovative phosphonium-functionalized diblock copolymers (PFDCs) with desired molecular weights and particle sizes. The excellent antibacterial activity of the PFDCs achieves lowest MIC values of 40 and 60 μg mL^-1 (i.e., 1.4 and 2.2 μmol L^-1) against E. coli and S. aureus, respectively. Mixing with an ink, dye, and latex coating does not weaken the antibacterial activity of the PFDCs, which inhibited 99.9% E. coli, showing broad applicability in different media. The effects of the cation type, synthesis medium, crosslinking content, and particle size on the morphology and antibacterial activity are studied. In summary, the RAFT polymerization of QPSs through the versatile design of ionic liquid monomers and the polymerization-induced self-assembly (PISA) method for constructing nano-assemblies with various micromorphology and particle size provides an exceedingly efficient way to build up multifunctional and multi-morphological polymeric nano-objects that open up vast possibilities in the fields of antibiotics, drug delivery, templated synthesis, and catalysis.

Unexpected toroidal micelles formed from St/MMA gradient copolymers

Toroidal micelles are of great interest and rarely observed in gradient copolymer systems. Herein, we report massive toroidal micelles formed from styrene (St)/methyl methacrylate (MMA) gradient copolymers using a common solvent mixing method followed by a cooling-heating procedure. Furthermore, we demonstrate that the obtained toroidal morphology is sensitively dependent on a heat treatment procedure. Solely spherical micelles are obtained by a common solvent mixing method. These spherical micelles could be transformed into toroidal micelles via vesicles during a cooling-heating process. When a reverse heating-cooling process is adopted, no toroidal micelles formed. Thus, these results add new members to the family of toroidal micelles and reveal pathway dominating morphologies in gradient copolymer micelles.

In situ generation and evolution of polymer toroids by liquid crystallization-assisted seeded dispersion polymerization

An effective method is presented for preparing high solid content azobenzene-containing triblock copolymer toroidal assemblies by liquid crystallization-assisted seeded dispersion polymerization. Vesicles are prepared via polymerization-induced self-assembly (PISA), and used as seeds for further chain extension. By introducing smectic liquid crystalline (LC) ordering into the core-forming block, toroids are formed in situ during the polymerization. The morphological transformation from toroids to barrels is observed under ultraviolet irradiation due to the photo-isomerization of the azobenzene mesogens. This strategy expands the scope of tunable anisotropic morphologies for potential functional nanomaterials based on a LC copolymer by seeded dispersion polymerization.

Bottom-up supramolecular assembly in two dimensions

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. Attracted by the interesting properties of two-dimensional inorganic analogues, monomers of different chemical natures are being explored for the assembly of dynamic 2D systems. Although many important discoveries have been already achieved, great challenges are still to be addressed in this field. Hierarchical multicomponent assembly, directional non-covalent growth and internal structural control are a just a few of the examples that will be discussed in this perspective about the exciting present and the bright future of two-dimensional supramolecular assemblies.

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. This perspective discusses the main strategies to direct the supramolecular self-assembly of organic monomers in 2D.

Fluorescent homopolypeptide toroids

Toroids are important ring-like nanostructures in living systems; intrinsically luminogenic toroids are promising in bioimaging but it is challenging to synthesize such nanoparticles. Herein, we report a fluorescent toroid that...

Pathway-Dependent Co-Assembly of Elastin-Like Polypeptides

In natural systems, temperature-induced assembly of biomolecules can lead to the formation of distinct assembly states, created out of the same set of starting compounds, based on the heating trajectory followed. Until now it has been difficult to achieve similar behavior in synthetic polymer mixtures. Here, a novel pathway-dependent assembly based on stimulus-responsive polymers is shown. When a mixture of mono- and diblock copolymers, based on elastin-like polypeptides, is heated with a critical heating rate co-assembled particles are created that are monodisperse, stable, and have tunable hydrodynamic radii between 20 and 120 nm. Below this critical heating rate, the constituents separately form polymer assemblies. This process is kinetically driven and reversible in thermodynamically closed systems. Using the co-assembly pathway, fluorescent proteins and bioluminescent enzymes are encapsulated with high efficiency. Encapsulated cargo shows unperturbed function even after delivery into cells. The pathway-dependent co-assembly of elastin-like polypeptides is not only of fundamental interest from a materials science perspective, allowing the formation of multiple distinct assemblies from the same starting compounds, which can be interconverted by going back to the molecularly dissolved states. It also enables a versatile way for constructing highly effective vehicles for the cellular delivery of biomolecular cargo.

Large-Area Fabrication of Vertical Silicon Nanotube Arrays via Toroidal Micelle Self-Assembly

We present a highly scalable, room-temperature strategy for fabricating vertical silicon nanotube arrays derived from a toroidal micelle pattern via a water vapor-induced block copolymer (BCP) self-assembly mechanism. A polystyrene-b-poly(ethylene oxide) (PS-b-PEO) BCP system can be self-assembled into toroidal micelle structures (diameter: 400-600 nm) on a PS-OH-modified substrate in a facile manner contrasting with other complex processes described in the literature. It was found that a minimum PS-b-PEO thickness of ∼86 nm is required for the toroidal self-assembly. Furthermore, a water vapor annealing treatment at room conditions (∼25 °C, 60 min) is shown to vastly enhance the ordering of micellar structures. A liquid-phase infiltration process was used to generate arrays of iron and nickel oxide nanorings. These oxide structures were used as templates for pattern transfer into the underlying silicon substrate via plasma etching, resulting in large-area 3D silicon nanotube arrays. The overall simplicity of this technique, as well as the wide potential versatility of the resulting metal structures, proves that such room-temperature synthesis routes are a viable pathway for complex nanostructure fabrication, with potential applicability in fields such as optics or catalysis.

Formation of 2D and 3D multi-tori mesostructures via crystallization-driven self-assembly

The fabrication of three-dimensional (3D) objects by polymer self-assembly in solution is extremely challenging. Here, multi-tori mesostructures were obtained from the crystallization-driven self-assembly of a coil-crystalline block copolymer (BCP) in mixed solvents. The formation of these structures follows a multistep process. First, the BCP self-assembles into amorphous micrometer-large vesicles. Then, the BCP confined in these mesosized vesicles crystallizes. This second step leads to the formation of objects with shapes ranging from closed 3D multi-tori spherical shells to 2D toroid mesh monolayers, depending on the solvent mixture composition. This approach demonstrates how topological constraints induced by the specific interactions between coil-crystalline BCP and solvents can be used to prepare mesostructures of complex morphologies.

Systematic study on evolution of self-assembly morphologies of CABC tetrablock terpolymers with varied segment lengths

The self-assembly structures of PEEA-PMMA-PGLMMA-PEEA CABC-type tetrablock terpolymers with a fixed length of the PGLMMA (red colour) segment and varied lengths of the PMMA (blue) and PEEA (green) segments were systematically studied.

Moebius strips of chiral block copolymers

The Moebius topology (twisted, single-sided strip) is intriguing because of its structural elegance and distinct properties. Here we report the generation of block copolymer Moebius strips via a fast self-assembly of chiral block copolymer polystyrene-block-poly(D-lactide acid) (PS-b-PDLA) in tetrahydrofuran/water mixed solvents. The Moebius strip is formed by morphological evolution from large compound micelle (LCM) to spindle-like micelle (SLM) and then to toroid with a 180° twist along the ring. Mechanism insight reveals that a subtle balance of crystallization of PDLA and microphase separation between PS and PDLA chains dominates the formation of Moebius strips. An intriguing helix-helix transition occurs during the chiral transfer from microphase to assemblies, which is driven by relaxation of the internal stress within SLM related to orientated stretching of PS chains. Mesoporous chiral channels can be generated within Moebius strips after removal of PDLA, which are interesting in chiral recognition, separation and asymmetric catalysis.