Onsets of Tethered Chain Overcrowding and Highly Stretched Brush Regime via Crystalline−Amorphous Diblock Copolymers

Shape-tunable two-dimensional assemblies from chromophore-conjugated crystallizable poly(L-lactides) with chain-length-dependent photophysical properties

This work reports temperature-dependent shape-changeable two-dimensional (2D) nanostructures by crystallization-driven self-assembly (CDSA) from a chromophore-conjugated poly(L-lactide) (PLLA) homopolymer (PTZ-P1) that contained a polar dye, phenothiazine (PTZ), at the chain-end of the crystallizable PLLA. The CDSA of PTZ-P1 in a polar solvent, isopropanol (iPrOH), by an uncontrolled heating-cooling process, majorly generates lozenge-shaped 2D platelets via chain-folding-mediated crystallization of the PLLA core, leading to the display of the phenothiazines on the 2D surface that confers colloidal stability and orange-emitting luminescent properties to the crystal lamellae. Isothermal crystallization at 60 °C causes a morphological change in PTZ-P1 platelets from lozenge to truncated-lozenge to perfect hexagon under different annealing times, while no shape change was noticed in the structurally similar PTZ-P2 polymer with a longer PLLA chain under similar conditions. This study unveils the complex link between the 2D platelet morphologies and degree of polymerization (DP) of PLLA and the corona-forming dye character. Further, the co-assembly potential of PTZ-P1 with hydrophobic pyrene-terminated PLLAs of varying chain lengths (PY-P1, PY-P2, and PY-P3) was examined, as these two dyes could form a Förster Resonance Energy Transfer (FRET) pair on the 2D surface. The impact of the length of the crystallizable PLLA on the photophysical properties of the surface-occupied chromophores revealed crucial insights into interchromophoric interactions on the platelet surface. A reduction in the propensity for π-stacking with increasing chain-folding in longer PLLAs is manifested in the chain-length-dependent FRET efficiencies and excimer emission lifetimes within the resultant monolayered 2D assemblies. The unconventional "butterfly-shaped" molecular architecture of the tested phenothiazine, combined with its varied functional features and polar character, adds a distinctive dimension to the underdeveloped field of CDSA of chromophore-conjugated poly(L-lactides), opening future avenues for the development of advanced nanostructured biodegradable 2D materials with programmable morphology and optical functions.

Concentric hollow multi-hexagonal platelets from a small molecule

The creation of well-defined hollow two-dimensional structures from small organic molecules, particularly those with controlled widths and numbers of segments, remains a formidable challenge. Here we report the fabrication of the well-defined concentric hollow two-dimensional platelets with programmable widths and numbers of segments through constructing a concentric multiblock two-dimensional precursor followed by post-processing. The fabrication of concentric multi-hexagons two-dimensional platelets is realized by the alternative heteroepitaxial growth of two donor-acceptor molecules. Upon ultraviolet irradiation, one of the two donor-acceptor molecules can be selectively oxidized by singlet oxygen generated during the process, and the oxidized product becomes more soluble due to increased polarity. This allows for selective removal of the oxidized segments simply by solvent dissolution, yielding hollow multiblock two-dimensional structures. The hollow two-dimensional platelets can be utilized as templates to lithograph complex electrodes with precisely controlled gap sizes, thereby offering a platform for examining the optoelectronic performance of functional materials.

Combining Crystallization-Driven Self-Assembly with Reverse Sequence Polymerization-Induced Self-Assembly Enables the Efficient Synthesis of Hydrolytically Degradable Anisotropic Block Copolymer Nano-objects Directly in Concentrated Aqueous Media

Herein we combine the well-known processing advantages conferred by polymerization-induced self-assembly (PISA) with crystallization-driven self-assembly (CDSA) to achieve the efficient synthesis of hydrolytically degradable, highly anisotropic block copolymer nano-objects directly in aqueous solution at 30% w/w solids. This new strategy involves a so-called reverse sequence PISA protocol that employs poly(l-lactide) (PLLA) as the crystallizable core-forming block and poly(N,N'-dimethylacrylamide) (PDMAC) as the water-soluble non-ionic coronal block. Such syntheses result in PDMAC-rich anisotropic nanoparticles. Depending on the target diblock copolymer composition, either rod-like nanoparticles or diamond-like platelets can be obtained. Furthermore, N-Acryloylmorpholine is briefly evaluated as an alternative hydrophilic vinyl monomer to DMAC. Given that the PLLA block can undergo either hydrolytic or enzymatic degradation, such nanoparticles are expected to offer potential applications in various fields, including next-generation sustainable Pickering emulsifiers.

Regulation of Two-Dimensional Platelet Micelles with Tunable Core Composition Distribution via Coassembly Seeded Growth Approach

Seeded growth termed "living" crystallization-driven self-assembly (CDSA) has been identified as a powerful method to create one- or two-dimensional nanoparticles. Epitaxial crystallization is usually regarded as the growth mechanism for the formation of uniform micelles. From this perspective, the unimer depositing rate is largely related to the crystallization temperature, which is a key factor to determine the crystallization rate and regulate the core composition distribution among nanoparticles. In the present work, the coassembly of two distinct crystallizable polymers is explored in detail in a one-pot seeded growth protocol. Results have shown that polylactone containing a larger number of methylene groups (-CH2-) in their repeating units such as poly(η-octalactone) (POL) has a faster crystallization rate compared to poly(ε-caprolactone) (PCL) with a smaller number of -CH2- at ambient temperature (25 °C), thus a block or blocky platelet structure with heterogeneous composition distribution is formed. In contrast, when the crystallization temperature decreases to 4 °C, the difference of crystallization rate between both cores become negligible. Consequently, a completely random component distribution within 2D platelets is observed. Moreover, we also reveal that the core component of seed micelles is also paramount for the coassembly seeded growth, and a unique structure of flower-like platelet micelle is created from the coassembly of PCL/POL using POL core-forming seeds. This study on the formation of platelet micelles by one-pot seeded growth using two crystallizable components offers a considerable scope for the design of 2D polymer nanomaterials with a controlled core component distribution.

Decoding the Pathway-Dependent Self-Assembly of Polymer-Grafted Nanoparticles by Ligand Crystallization

Functional metamaterials can be constructed by assembling nanoparticles (NPs) into well-ordered structures, which show fascinating properties at different length scales. Using polymer-grafted NPs (PGNPs) as a building block, flexible composite metamaterials can be obtained, of which the structure is significantly affected by the property of polymer ligands. Here, it is demonstrated that the crystallization of polymer ligands determines the assembly behavior of NPs and reveal a pathway-dependent self-assembly of PGNPs into different metastructures in solution. By changing the crystallization degree of polymer ligands, the arrangement structure of NPs can be tailored. When the polymer ligands highly crystallize, the PGNPs assemble into diamond-shaped platelets, in which the NPs arrange disorderedly. When the polymer ligands lowly crystallize, the PGNPs assemble into highly ordered 3D superlattices, in which the NPs pack into a body-centered-cubic structure. The structure transformation of PGNP assemblies can be achieved by thermal annealing to regulate the crystallization of polymer ligands. Interestingly, the diamond-shaped platelets remain "living" for seeded epitaxial growth of newly added crystalline species. This work demonstrates the effects of ligand crystallization on the crystallization of NP, providing new insights into the structure regulation of metamaterials.

Precise Control of Two-Dimensional Hexagonal Platelets via Scalable, One-Pot Assembly Pathways Using Block Copolymers with Crystalline Side Chains

Crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) in selective solvents provides a promising route for direct access to two-dimensional (2D) platelet micelles with excellent uniformity, although significant limitations also exist for this robust approach, such as tedious, multistep procedures, and low yield of assembled materials. Herein, we report a facile strategy for massively preparing 2D, highly symmetric hexagonal platelets with precise control over their dimensions based on BCPs with crystalline side chains. Mechanistic studies unveiled that the formation of hexagonal platelets was subjected to a hierarchical self-assembly process, involving an initial stage of formation of kinetically trapped spheres upon cooling driven by solvophobic interactions, and a second stage of fusion of such spheres to the 2D nuclei to initiate the lateral growth of hexagonal platelets via sequential particle attachments driven by thermodynamically ordered reorganization of the BCP upon aging. Moreover, the size of the developed 2D hexagonal platelets could be finely regulated by altering the copolymer concentration over a broad concentration range, enabling scale-up to a total solids concentration of at least 6% w/w. Our work reveals a new mechanism to create uniform 2D core-shell nanoparticles dictated by crystallization and particle fusion, while it also provides an alternative facile strategy for the design of soft materials with precise control of their dimensions, as well as for the scalability of the derived nanostructures.

Cascade Energy Transfer and White-Light Emission in Chirality-Controlled Crystallization-Driven Two-Dimensional Co-assemblies from Donor and Acceptor Dye-Conjugated Polylactides

Achieving predictable and programmable two-dimensional (2D) structures with specific functions from exclusively organic soft materials remains a scientific challenge. This article unravels stereocomplex crystallization-driven self-assembly as a facile method for producing thermally robust discrete 2D-platelets of diamond shape from biodegradable semicrystalline polylactide (PLA) scaffolds. The method involves co-assembling two PLA stereoisomers, namely, PY-PDLA and NMI-PLLA, which form stereocomplex (SC)-crystals in isopropanol. By conjugating a well-known Förster resonance energy transfer (FRET) donor and acceptor dye, namely, pyrene (PY) and naphthalene monoimide (NMI), respectively, to the chain termini of these two interacting stereoisomers, a thermally robust FRET process can be stimulated from the 2D array of the co-assembled dyes on the thermally resilient SC-PLA crystal surfaces. Uniquely, by decorating the surface of the SC-PLA crystals with an externally immobilized guest dye, Rhodamine-B, similar diamond-shaped structures could be produced that exhibit pure white-light emission through a surface-induced two-step cascade energy transfer process. The FRET response in these systems displays remarkable dependence on the intrinsic crystalline packing, which could be modulated by the chirality of the co-assembling PLA chains. This is supported by comparing the properties of similar 2D platelets generated from two homochiral PLLAs (PY-PLLA and NMI-PLLA) labeled with the same FRET pair.

Understanding the Seeded Heteroepitaxial Growth of Crystallizable Polymers: The Role of Crystallization Thermodynamics

Seeded heteroepitaxial growth is a "living" crystallization-driven self-assembly (CDSA) method that has emerged as a promising route to create uniform segmented nanoparticles with diverse core chemistries by using chemically distinct core-forming polymers. Our previous results have demonstrated that crystallization kinetics is a key factor that determines the occurrence of heteroepitaxial growth, but an in-depth understanding of controlling heteroepitaxy from the perspective of crystallization thermodynamics is yet unknown. Herein, we select crystallizable aliphatic polycarbonates (PxCs) with a different number of methylene groups (xCH2, x = 4, 6, 7, 12) in their repeating units as model polymers to explore the effect of lattice match and core compatibility on the seeded growth behavior. Seeded growth of PxCs-containing homopolymer/block copolymer blend unimers from poly(ε-caprolactone) (PCL) core-forming seed platelet micelles exhibits distinct crystal growth behavior at subambient temperatures, which is governed by the lattice match and core compatibility. A case of seeded growth with better core compatibility and a smaller lattice mismatch follows epitaxial growth, where the newly created crystal domain has the same structural orientation as the original platelet substrate. In contrast, a case of seeded growth with better core compatibility but a larger lattice mismatch shows nonepitaxial growth with less-defined crystal orientations in the platelet plane. Additionally, a case of seeded growth with poor core compatibility and larger lattice mismatch results in polydisperse platelet micelles, whereby crystal formation is not nucleated from the crystalline substrate. These findings reveal important factors that govern the specific crystal growth during a seeded growth approach by using compositionally distinct cores, which would further guide researchers in designing 2D segmented materials via polymer crystallization approaches.

Atomic-Scale Corrugations in Crystalline Polypeptoid Nanosheets Revealed by Three-Dimensional Cryogenic Electron Microscopy

Amphiphilic molecules that can crystallize often form molecularly thin nanosheets in aqueous solutions. The possibility of atomic-scale corrugations in these structures has not yet been recognized. We have studied the self-assembly of amphiphilic polypeptoids, a family of bio-inspired polymers that can self-assemble into various crystalline nanostructures. Atomic-scale structure of the crystals in these systems has been inferred using both X-ray diffraction and electron microscopy. Here we use cryogenic electron microscopy to determine the in-plane and out-of-plane structures of a crystalline nanosheet. Data were collected as a function of tilt angle and analyzed using a hybrid single-particle crystallographic approach. The analysis reveals that adjacent rows of peptoid chains, which are separated by 4.5 Å in the plane of the nanosheet, are offset by 6 Å in the direction perpendicular to the plane of the nanosheet. These atomic-scale corrugations lead to a doubling of the unit cell dimension from 4.5 to 9 Å. Our work provides an alternative interpretation for the observed Å X-ray diffraction peak often reported in polypeptoid crystals.

Controlling block copolymer one-dimensional self-assembly in polymeric matrices

The synthesis of one-dimensional (1D) nanostructures in polymeric matrices has become the focus of much research, as the presence of these highly anisotropic domains determines the transport behaviour and mechanical properties of the resulting nanostructured polymers. In this work, 1D PEO nanocrystals were synthesized in situ from polystyrene-b-polyethylene oxide (PS-b-PEO) self-assembly in a polystyrene matrix. For this, three different block copolymers (BCP) were employed: L-BCP (PS = 32 000 Da and PEO = 11 000 Da), M-BCP, (PS = 59 000 Da and PEO = 31 000 Da), and H-BCP, (PS = 102 000 Da and PEO = 34 000 Da). The formation of 1D nanocrystals starts with the reaction-induced microphase separation of BCP during styrene photopolymerization at room temperature. Then, as matrix polymerizes, the primary crystalline micelles aggregate via epitaxial crystallization by end-to-end coupling. The morphology of the resulting nanocrystals was highly dependent on the BCP employed. While L-BCP self-assembles into 1D ribbon-like nanocrystals, M-BCP macro-phase separates and, H-BCP self-assembles into short disk-like nanocrystals. This dissimilar behavior was mainly associated to the length of the stabilizing corona block. In the case of H-BCP, it was found that 1D self-assembly occurred when the conditions for core thickening were given, that is, when a non-reactive period was introduced in the cure cycle. During such a period, core thickening clears the lateral surface of the nanocrystals, allowing end-to-end coupling. The driving force for crystallization was also modified. An increase in undercooling resulted in an elevated nucleation rate and accelerated crystal growth. This led to a narrower size distribution of shorter 1D nanocrystals. This knowledge will enable the synthesis of customized 1D nanocrystals in a thermoplastic matrix, through the precise selection of the BCP formulation and curing conditions.

Polyferrocenylsilane Block Copolymer Spherulites in Dilute Solution

Self-assembly of block copolymers (BCP) into uniform 3D structures in solution is an extremely rare phenomenon. Furthermore, the investigation of general prerequisites for fabricating a specific uniform 3D structure remains unknown and challenging. Here, through a simple one-pot direct self-assembly (heating and cooling) protocol, we show that uniform spherulite-like structures and their precursors can be prepared with various poly(ferrocenyldimethylsilane) (PFS) BCPs in a variety of polar and non-polar solvents. These structures all evolve from elongated lamellae into hedrites, sheaf-like micelles, and finally spherulites as the annealing temperature and supersaturation degree are increased. The key feature leading to this growth trajectory is the formation of secondary crystals by self-nucleation on the surface of early-elongated lamellae. We identified general prerequisites for fabricating PFS BCP spherulites in solution. These include corona/PFS core block ratios in the range of 1-5.5 that favor the formation of 2D structures as well as the development of secondary crystals on the basal faces of platelets at early stages of the self-assembly. The one-pot direct self-assembly provides a general protocol to form uniform spherulites and their precursors consisting of PFS BCPs that match these prerequisites. In addition, we show that manipulation of various steps in the direct self-assembly protocol can regulate the size and shape of the structures formed. These general concepts show promise for the fabrication and optimization of spherulites and their precursors from semicrystalline BCPs with interesting optical, electronic, or biomedical properties using the one-pot direct self-assembly protocol.

Crystallization-Driven Controlled Two-Dimensional (2D) Assemblies from Chromophore-Appended Poly(L-lactide)s: Highly Efficient Energy Transfer on a 2D Surface

A rational approach towards precision two-dimensional (2D) assemblies by crystallization-driven self-assembly (CDSA) of poly(L-lactides) (PLLAs), end-capped with dipolar dyes like merocyanine (MC) or naphthalene monoimide (NMI) and hydrophobic pyrene (PY) or benzene (Bn) is described. PLLA chains crystallize into diamond-shaped platelets in isopropanol, which forces the terminal dyes to assemble into a 2D array on the platelet surface by either dipolar interactions or π-stacking and exhibit tunable emission. Dipolar dyes play a critical role in imparting colloidal stability and structural uniformity to the 2D crystals, which is partly compromised for hydrophobic ones. Co-crystallization between NMI- and PY-labeled PLLAs yields similar diamond-shaped co-platelets with highly efficient (≈80 %) Förster Resonance Energy Transfer on the 2D surface. Further, the "living" CDSA method confers enlarged, segmented block co-platelets using one of the homopolymers as "seed" and the other as "unimer".

The role of cooling rate in crystallization-driven block copolymer self-assembly

Self-assembly of crystalline-coil block copolymers (BCPs) in selective solvents is often carried out by heating the mixture until the sample appears to dissolve and then allowing the solution to cool back to room temperature. In self-seeding experiments, some crystallites persist during sample annealing and nucleate the growth of core-crystalline micelles upon cooling. There is evidence in the literature that the nature of the self-assembled structures formed is independent of the annealing time at a particular temperature. There are, however, no systematic studies of how the rate of cooling affects self-assembly. We examine three systems based upon poly(ferrocenyldimethylsilane) BCPs that generated uniform micelles under typical conditions where cooling took pace on the 1–2 h time scale. For example, several of the systems generated elongated 1D micelles of uniform length under these slow cooling conditions. When subjected to rapid cooling (on the time scale of a few minutes or faster), branched structures were obtained. Variation of the cooling rate led to a variation in the size and degree of branching of some of the structures examined. These changes can be explained in terms of the high degree of supersaturation that occurs when unimer solutions at high temperature are suddenly cooled. Enhanced nucleation, seed aggregation, and selective growth of the species of lowest solubility contribute to branching. Cooling rate becomes another tool for manipulating crystallization-driven self-assembly and controlling micelle morphologies.

In the self-assembly of crystalline-coil block copolymers in solution, heating followed by different cooling rates can lead to different structures.

Self-assembly of polymer-tethered nanoparticles with uniform and Janus surfaces in nanotubes

In this study, a coarse-grained molecular simulation was performed to investigate the morphologies and phase diagrams of self-assembled polymer-tethered nanoparticles (NPs) confined in nanotubes (NTs). Unlike ordinary NPs, polymer-tethered NPs have two distinct characteristic lengths, which are key factors that determine their self-assembly. Herein, two distinct types of NT walls and three types of polymer-tethered NPs were considered: hydrophilic and hydrophobic walls, and hydrophilic, hydrophobic, and Janus surfaces. First, the qualitative phase diagrams of the axial pressure, Pz, versus the ratio of the NT radius to the NP radius, L, were derived. The results revealed that diverse self-assembled morphologies, which are not formed in non-tethered NPs, were observed in the polymer-tethered NPs. For example, three types of ordered structures with different structural characteristic lengths, depending on Pz, were obtained. In addition, the effect of the chemical nature of the polymer-tethered NP surface on the self-assembled morphology confined in NTs was investigated. Clusters of water molecules were formed, particularly in the hydrophobic polymer-tethered NPs, and these clusters caused the structural distortion of the NP. Moreover, in the polymer-tethered NPs with the Janus amphiphilic surface, the hydrophobic and hydrophilic polymer tethered NPs assembled in the axial direction to form an ordered structure, and a double-helix structure was formed at L = 3.0 in the hydrophobic NT. The results of these simulations indicate that the self-assembly behaviours of polymer-tethered NPs can be qualitatively predicted based on the chemical nature of the NT walls and the surface design of the polymer-tethered NP.

Uniform 1D Micelles and Patchy & Block Comicelles via Scalable, One-Step Crystallization-Driven Block Copolymer Self-Assembly

Fiber-like (1D) core-crystalline micelles of uniform length can be obtained in protocols involving multiple steps from block copolymers (BCPs) in which crystallization of the core-forming polymer drives the self-assembly. Here we report a systematic study that shows that adding small amounts (<5 w/w%) of a homopolymer corresponding to the core-forming block of the BCP enables uniform 1D micelles (mean lengths L_n = 0.6 to 9.7 μm) to be obtained in a single step, simply by heating the mixture in a selective solvent followed by slow cooling. A series of poly(ferrocenyldimethylsilane) (PFS) BCPs with different corona-forming blocks and different compositions as well as PFS homopolymers of different lengths were examined. Dye labeling and confocal fluorescence microscopy showed that the homopolymer ends up in the center of the micelle, signaling that it served as the initial seed for epitaxial micelle growth. The rate of unimer addition was strongly enhanced by the length of the PFS block, and this enabled more complex structures to be formed in one-pot self-assembly experiments from mixtures of two or three BCPs with different PFS block lengths. Furthermore, BCP mixtures that included PFS-b-PI (PI = polyisoprene) and PFS-b-PDMS with similar PFS block lengths resulted in simultaneous addition to growing micelles, resulting in a patchy block that could be visualized by staining the vinyl groups of the PI with Pt nanoparticles. This approach also enabled scale up, so that uniform 1D micelles of controlled architecture can be obtained at concentrations of 10 w/w % solids or more.

Spherulite-Like Micelles

One-dimensional (1D) and 2D structures by crystallization-driven self-assembly of block copolymers (BCPs) can form fascinating hierarchical structures through secondary self-assembly. But examples of 3D structures formed via hierarchical self-assembly are rare. Here we report seeded growth experiments in decane of a poly(ferrocenyldimethylsilane) BCP with an amphiphilic corona forming block in which lenticular platelets grow into classic spherulite-like uniform colloidally stable structures. These 3D objects are spherically symmetric on the exterior, but asymmetric near the core, where there is a more open structure consisting of sheaf-like leaves. The most remarkable aspect of these experiments is that growth stops at different stages of growth process, depending upon how much unimer is added in the seeded growth step. The system provides a model for studying spherulitic growth where real-time observations on their growth at different stages remains challenging.

Surface Patterning of Uniform 2D Platelet Block Comicelles via Coronal Chain Collapse

The formation of colloids with anisotropically patterned surfaces is of growing interest for the creation of hierarchical structures and the templating of nanoparticles. We have recently shown that well-defined two-dimensional platelets with low areal dispersities can be formed by the seeded growth of a blend of homopolymers and block copolymers. Herein we form rectangular platelets containing two block copolymers with different coronal chemistries. On addition of a solvent that is only able to solvate the corona of one block, we were able to form colloidally stable micelles with patterned surfaces via coronal collapse. Scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy and atomic force microscopy were employed to provide information on the structure and size of the patches decorating the micelle surfaces.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm^-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Solvent effects leading to a variety of different 2D structures in the self-assembly of a crystalline-coil block copolymer with an amphiphilic corona-forming block

We describe a polyferrocenyldimethylsilane (PFS) block copolymer (BCP), PFS27-b-P(TDMA65-ran-OEGMA69) (the subscripts refer to the mean degrees of polymerization), in which the corona-forming block is a random brush copolymer of hydrophobic tetradecyl methacrylate (TDMA) and hydrophilic oligo(ethylene glycol) methyl ether methacrylate (OEGMA). Thus, the corona is amphiphilic. This BCP generates a remarkable series of different structures when subjected to crystallization-driven self-assembly (CDSA) in solvents of different polarity. Long ribbon-like micelles formed in isopropanol, and their lengths could be controlled using both self-seeding and seeded growth protocols. In hexanol, the BCP formed more complex structures. These objects consisted of oval platelets connected to long fiber-like micelles that were uniform in width but polydisperse in length. In octane, relatively uniform rectangular platelets formed. Finally, a distinct morphology formed in a mixture of octane/hexanol, namely uniform oval structures, whose height corresponded to the fully extended PFS block. Both long and short axes of these ovals increased with the initial annealing temperature and with the BCP concentration. The self-seeding protocol also afforded uniform two-dimensional structures. Seeded growth experiments, in which a solution of the BCP in THF was added to a colloidal solution of the oval micelles led to a linear increase in area while maintaining the aspect ratio of the ovals. These experiments demonstrate the powerful effect of the amphiphilic corona chains on the CDSA of a core crystalline BCP in solvents of different hydrophilicity.

Phase Behavior and Phase Diagram of Polystyrene-b-Poly(Perfluorooctylethyl Acrylates)

Fluorocontaining polymers bearing special properties are unique and important materials in modern society. In this work, we focused on the phase behavior and phase diagram of poly(styrene-block-perfluorooctylethyl acrylate) with a volume fraction varying from 0.2 to 0.8. Small-angle X-ray scattering and transmission electron microscopy showed the phase formation in the sequence of hexagonally packed cylinders (HEX) to lamellar layers (LAM) to inverse hexagonally packed cylinders (iHEX) in this series of block polymers. Wide-angle X-ray diffraction experiments proved that the fluorodomains of the LAM phases and the matrix of iHEX phases contained layered structures formed by the crystallization of fluorosegments. During heating, the self-assembled lattice remained intact even after the melting of fluorodomain, with barely changed lattice parameters. Such hierarchical structural formation was understood by chain conformation and domain interaction, which may provide new insight into the molecular design of advanced materials.

Single-step self-assembly to uniform fiber-like core-crystalline block copolymer micelles

Accessing uniform fiber-like micelles by single-step crystallization-driven co-self-assembly of a block copolymer with a trace of homopolymer.

Interfacial self-assembly of amphiphilic conjugated block copolymer into 2D nanotapes

In the present work, the evaporation-induced interfacial self-assembly behavior of an amphiphilic conjugated polymer, poly(3-hexylthiophene)-b-poly(acrylic acid) (P3HT-b-PAA), at the oil-water interface is explored. Novel 2D nanotapes of P3HT-b-PAA are prepared via the interfacial self-assembly. It is inferred that P3HT segments adopt a special conformation at the oil-water interface, which facilitates the packing of alkyl side chains and π-π interaction. The UV-vis spectrum further confirms that the ordering degree of P3HT segments is increased while transmission IR and Raman spectroscopic studies suggest that the P3HT chains adopt a more planar conformation at the oil-water interface. It is proposed that the formation of the nanotapes is driven by the ordered packing of the P3HT chains at the oil-water interface. Finally, the packing model of the P3HT chains inside the nanotapes is roughly proposed.

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.

Characterizing Polymer-Grafted Nanoparticles: From Basic Defining Parameters to Behavior in Solvents and Self-Assembled Structures

Polymer-grafted nanoparticles, often called hairy nanoparticles (HNPs), are an intriguing class of nanostructured hybrid materials with great potential in a variety of applications, including advanced polymer nanocomposite fabrication, drug delivery, imaging, and lubrication. This Feature provides an introduction to characterization of various aspects of HNPs, from basic defining parameters to behavior of HNPs in solvents and self-assembled structures of multicomponent brush nanoparticles, by using a broad range of analytical tools.

Effect of Composition and Molecular Structure of Poly(l-lactic acid)/Poly(ethylene oxide) Block Copolymers on Micellar Morphology in Aqueous Solution

The effect of the hydrophobic block length in diblock (PLLA _x- b-PEO₁₁₃, x = 64, 166, 418) and triblock (PLLA _y- b-PEO₉₁- b-PLLA _y, y = 30, 52, 120) copolymers of l-lactic acid and ethylene oxide on the structure of micelles prepared by dialysis was studied by wide- and small-angle X-ray scattering in dilute aqueous solution, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and force spectroscopy. It was found that the size of the crystalline PLLA core is weakly dependent on the PLLA block length. In addition to individual micelles, a number of their micellar clusters were detected with characteristic distance between adjacent micelle cores decreasing with an increase in PLLA block length. This effect was explained by the change in the conformation of PEO chains forming the micellar corona because of their overcrowding. Force spectroscopy experiments also reveal a more stretched conformation of the PEO chains for the block copolymers with a shorter PLLA block. A model describing the structure of the individual micelles and their clusters was proposed.

Surface Density Variation within Cyclic Polymer Brushes Reveals Topology Effects on Their Nanotribological and Biopassive Properties

While topology effects by cyclic polymers in solution and melts are well-known, their translation into the interfacial properties of polymer "brushes" provides new opportunities to impart enhanced surface lubricity and biopassivity to inorganic surfaces, above and beyond that expected for linear analogues of identical composition. The impact of polymer topology on the nanotribological and protein-resistance properties of polymer brushes is revealed by studying linear and cyclic poly(2-ethyl-2-oxazoline) (PEOXA) grafts presenting a broad range of surface densities and while shearing them alternatively against an identical brush or a bare inorganic surface. The intramolecular constraints introduced by the cyclization provide a valuable increment in both steric stabilization and load-bearing capacity for cyclic brushes. Moreover, the intrinsic absence of chain ends within cyclic adsorbates hinders interpenetration between opposing brushes, as they are slid over each other, leading to a reduction in the friction coefficient (μ) at higher pressures, a phenomenon not observed for linear grafts. The application of cyclic polymers for the modification of inorganic surfaces generates films that outperform both the nanotribological and biopassive properties of linear brushes, significantly expanding the design possibilities for synthetic biointerfaces.

Crystallization-Driven Two-Dimensional Self-Assembly of Amphiphilic PCL-b-PEO Coated Gold Nanoparticles in Aqueous Solution

This Letter reports the first formation of free-standing plasmonic monolayer nanosheets by the self-assembly of AuNPs without assistance from a planar interface. The strategy involves the coating of poly(caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) diblock copolymers on AuNPs, followed by two-dimensional (2D) self-assembly of the resultant amphiphilic AuNPs in aqueous phase. The crystallization of the PCL blocks, affected by their grafting density and radius of gyration, drives the formation of the AuNP nanosheets, which undergoes a growth process of individual micelles to small nanosheets and eventually to large sheets. Due to the plasmonic coupling of AuNPs in close proximity, the AuNP nanosheets exhibit near-infrared (NIR) absorption with the maximum at about 700 nm. This study not only brings a new approach toward polymer-AuNP hybrid superstructures in solution, but also provides a new system for fundamental study on 2D self-assembly of AuNPs.

Monitoring Collapse of Uniform Cylindrical Brushes with a Thermoresponsive Corona in Water

We generated rod-like micelles of uniform length by living crystallization-driven self-assembly of a polyferrocenylsilane (PFS) block copolymer PFS₂₆-b-POEGMA₁₆₃ in a methanol-ethanol mixture and then transferred these micelles to water. The corona chains consisted of poly(oligoethylene glycol methacrylate) that had a lower critical solution temperature (LCST) of 40.5 °C in water. We used a combination of static (SLS) and dynamic (DLS) multiangle light scattering to determine the dimensions of these cylindrical brush micelles in solution. Measurements carried out in dilute solution in water over a series of temperatures from 23 to 50 °C showed that the collapse transition was broad and continuous, upon both heating and cooling. This response is different from the collapse transition of POEGMA₁₆₃ homopolymer in water, which occurs over a very narrow temperature range. Thus, we show that the collapse transition of a cylindrical brush has important features in common with the collapse of a brush of thermoresponsive polymers on a planar surface.