Orientation and stretching of supracolloidal chains of diblock copolymer micelles by spin-coating process

Supracolloidal chains consisting of nano- or micro-scale particles exhibit anisotropic properties not observed in individual particles. The orientation of the chains is necessary to manifest such characteristics on a macroscopic scale. In this study, we demonstrate the orientation of supracolloidal chains composed of nano-scale micelles of a diblock copolymer through spin-coating. We observed separate chains coated on a substrate with electron microscopy, and analyzed the orientation and stretching of the chains quantitatively with image analysis software. In drop-casting, the chains were coated randomly with no preferred orientation, and the degree of stretching exhibited an intrinsic semi-flexible nature. In contrast, spin-coated chains were aligned in the radial direction, and the apparent persistence length of the chain increased, confirming the stretching of the chain quantitatively. Furthermore, by incorporating fluorophores into supracolloidal chains and confirming the oriented chains with confocal fluorescence microscopy, it is demonstrated that oriented chains can be utilized as a template to align functional materials.

Step-growth polymerization of supracolloidal chains from patchy micelles of diblock copolymers

HYPOTHESIS

The formation of supracolloidal chains from the patchy micelles of diblock copolymers bears a close resemblance to traditional step-growth polymerization of difunctional monomers in many aspects, including chain-length evolution, size distribution, and initial-concentration dependence. Thus, understanding the colloidal polymerization based on the step-growth mechanism can offer potential control over the formation of supracolloidal chains in terms of chain structure and reaction rate.

EXPERIMENTS

We analyzed the size evolution of supracolloidal chains of patchy micelles of PS-b-P4VP by investigating a large number of colloidal chains visualized in SEM images. We varied the initial concentration of patchy micelles to achieve a high degree of polymerization and a cyclic chain. To manipulate the polymerization rate, we also changed the ratio of water to DMF and adjusted the patch size by employing PS(25)-b-P4VP(7) and PS(145)-b-P4VP(40).

FINDINGS

We confirmed the step-growth mechanism for the formation supracolloidal chains from patchy micelles of PS-b-P4VP. Based on this mechanism, we were able to achieve a high degree of polymerization early in the reaction by increasing the initial concentration and form cyclic chains by diluting the solution. We also accelerated colloidal polymerization by increasing the ratio of water to DMF in the solution and patch size by using PS-b-P4VP with a larger molecular weight.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

Realizing shape and size control for the synthesis of coordination polymer nanoparticles templated by diblock copolymer micelles

The combination of polymers with nanoparticles offers the possibility to obtain customizable composite materials with additional properties such as sensing or bistability provided by a switchable spin crossover (SCO) core. For all applications, a precise control over size and shape of the nanomaterial is highly important as it will significantly influence its final properties. By confined synthesis of iron(II) SCO coordination polymers within the P4VP cores of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micelles in THF we are able to control the size and also the shape of the resulting SCO nanocomposite particles by the composition of the PS-b-P4VP diblock copolymers (dBCPs) and the amount of complex employed. For the nanocomposite samples with the highest P4VP content, a morphological transition from spherical nanoparticles to worm-like structures was observed with increasing coordination polymer content, which can be explained with the impact of complex coordination on the self-assembly of the dBCP. Furthermore, the SCO nanocomposites showed transition temperatures of T_1/2 = 217 K, up to 27 K wide hysteresis loops and a decrease of the residual high-spin fraction down to γ_HS = 14% in the worm-like structures, as determined by magnetic susceptibility measurements and Mössbauer spectroscopy. Thus, SCO properties close or even better (hysteresis) to those of the bulk material can be obtained and furthermore tuned through size and shape control realized by tailoring the block length ratio of the PS-b-P4VP dBCPs.

Porous self-supporting film of semi-flexible supracolloidal chains of diblock copolymer micelles

Patchy micelles of diblock copolymers can be polymerized into a linear supracolloidal chain. We measure the persistence and contour lengths of supracolloidal chains coated on a solid substrate to evaluate their flexibility. Based on the analysis, the chain is semi-flexible, and the conformation is suitably explained by the worm-like chain model. In addition, utilizing a spin-coating technique with the semi-flexible nature of the chains, we produce a self-supporting film of supracolloidal chains having nanoscale pores essentially from colloidal constituents that tend to form dense packing if there is no prior organization of them into a semi-flexible chain.

In situ conversion from crew-cut to hairy micelles by surface-initiated polymerization

Whether spherical micelles of block copolymers have short or long coronas is intrinsically determined by the molecular weight of the corona-forming block with respect to that of the core block before the micelles are assembled. Because of the inherent conditions of packing copolymer chains into a micelle, the core diameter is altered when we assemble a micelle from a block copolymer having a long corona block, compared to that having a short corona block with the same length of the core block. However, micelles with the same core diameter but having various corona lengths can be guaranteed when the corona is extended upon surface-initiated polymerization on the micelles. Herein, we demonstrated in situ conversion from crew-cut to hairy micelles by selectively extending a corona block while maintaining the spherical shape of block copolymer micelles. We first synthesized block copolymers having a chain transfer agent (CTA) positioned at the end of the corona block and then assembled them into a crew-cut micelle. Employing this micelle as an assembly of macro-CTAs, we conducted surface-initiated polymerization on the micelle by photo-induced energy/electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Since PET-RAFT enables the polymerization at room temperature, the corona block was selectively extended with preservation of the core diameter, thereby converting a crew-cut micelle to a hairy one. In addition, by applying the same polymerization protocol to a worm-like micelle, we could selectively extend the coronas, leading to the formation of a worm-like micelle with a long corona. If such copolymer chains were assembled into a micelle, we would obtain a spherical micelle instead of a worm-like micelle having a hairy corona, which is difficult to assess because of the inherent packing problem.

Hierarchical self-assembly of miktoarm star copolymers with pathway complexity

The self-assembly of amphiphilic miktoarm star copolymers shows hierarchical pathway complexity from molecular building blocks to miktoarm stars to micellar nano-objects to complex hierarchical assemblies.

Versatile surface-active ionic liquid: construction of microemulsions and their applications in light harvesting

This article outlines a sustainable method towards the synthesis of advanced materials such as core/shell Quantum Dots (QDs) and their in situ stabilization using microemulsions (MEs). QDs are versatile materials which show unusual optical properties. We have constructed MEs consisting of an Ionic Liquid (IL) based surfactant i.e. choline dioctylsulfosuccinate, [Cho][AOT] as an emulsifier, toluene as a nonpolar phase and water as a polar phase. The system forms a large single-phase region in the phase diagram without any co-surfactant. Spontaneous formation of micelles has been observed and studied through tensiometry and fluorescence and isothermal titration calorimetry (ITC). The exceptional swelling behaviour of the MEs was studied using Dynamic Light Scattering (DLS) and small angle neutron scattering (SANS). In ME droplets, i.e. Reverse Micelles (RMs), we successfully synthesized spherical core/shell QDs (size ∼3 to ∼6 nm) with precise control over the size and morphology. The QDs have been characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Powder X-ray Diffraction (PXRD). QDs stabilized in MEs exhibited excellent optical properties and can be suitably used as light harvesting materials for diverse applications.

Colloidal molecules and patchy particles: complementary concepts, synthesis and self-assembly

About the latest developments regarding self-assembly of textured colloids and its prospects.

Polymer-guided assembly of inorganic nanoparticles

The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.

Phase-Separated Molecular Assembly of a Nanotube Composed of Amphiphilic Polypeptides Having a Helical Hydrophobic Block

Amphiphilic block polypeptides of poly(sarcosine)-b-(l- or d-Leu-Aib)₆ (SL12OMe or SD12OMe) and poly(sarcosine)-b-(l-Leu-Aib)₇ (SL14OMe) were reported to self-assemble into a nanotube morphology. Herein, we tried to construct a phase-separated nanotube by sticking two different kinds of nanotubes. SD12OMe nanotubes were found to stick to SL14OMe nanotubes with a heat treatment at 50 °C, but the sticking yield was limited. The amphiphilic polypeptides were functionalized by replacement of methyl ester with aromatic groups of N-ethylcarbazole (SL12Ecz) and naphthalimide (SD12NpiTEG), but they lost the ability to form homogeneous nanotubes. A fraction of the functionalized amphiphilic polypeptides mixing in the nanotube-forming amphiphilic polypeptides, a mixture of SL12OMe and SL12Ecz (9:1) as well as a mixture of SD12OMe and SD12NpiTEG (9:1), allowed nanotube formation. These two kinds of nanotubes partly stuck together with a heat treatment at 15 °C to maintain a segregated state of two kinds of aromatic groups along the nanotube, resulting in the formation of a phase-separated nanotube.

Painting Supramolecular Polymers in Organic Solvents by Super-resolution Microscopy

Despite the rapid development of complex functional supramolecular systems, visualization of these architectures under native conditions at high resolution has remained a challenging endeavor. Super-resolution microscopy was recently proposed as an effective tool to unveil one-dimensional nanoscale structures in aqueous media upon chemical functionalization with suitable fluorescent probes. Building upon our previous work, which enabled photoactivation localization microscopy in organic solvents, herein, we present the imaging of one-dimensional supramolecular polymers in their native environment by interface point accumulation for imaging in nanoscale topography (iPAINT). The noncovalent staining, typical of iPAINT, allows the investigation of supramolecular polymers' structure in situ without any chemical modification. The quasi-permanent adsorption of the dye to the polymer is exploited to identify block-like arrangements within supramolecular fibers, which were obtained upon mixing homopolymers that were prestained with different colors. The staining of the blocks, maintained by the lack of exchange of the dyes, permits the imaging of complex structures for multiple days. This study showcases the potential of PAINT-like strategies such as iPAINT to visualize multicomponent dynamic systems in their native environment with an easy, synthesis-free approach and high spatial resolution.

Fluorescent Supracolloidal Chains of Patchy Micelles of Diblock Copolymers Functionalized with Fluorophores

By selective attachment of fluorescent dyes to the core-forming block, we produced patchy micelles of diblock copolymers with fluorophores localized in the micellar cores. From these patchy micelles functionalized with dyes, fluorescent supracolloidal chains in a few micrometers were polymerized by combining the patches in neighboring micelles, indicating that selective modification of the core-forming block delivered the functionality into the supracolloidal chain without altering the polymerization of patchy micelles. Thus, with the same polymerization condition, we were able to produce red-, green-, and blue-emitting supracolloidal chains by varying the fluorescent dyes attached to the core-forming block. In addition, we directly visualized individual supracolloidal chains by fluorescence confocal microscopy as well as by transmission electron microscopy.

Supracolloidal chains of patchy micelles in water

This work describes the programmable self-assembly of ABC triblock terpolymers into patchy micelles and further to supracolloidal chains in water.

Supracolloidal chains of patchy micelles of diblock copolymers with in situ synthesized nanoparticles

Supracolloidal chains of diblock copolymer micelles were functionalized with gold and silver nanoparticles (NPs). Both NPs were independently synthesized in situ in the core of spherical micelles which were then converted to patchy micelles. With these patchy micelles as colloidal monomers, supracolloidal chains were polymerized by combining the patches of neighboring micelles. Since all micelles contained NPs, NPs were incorporated in every repeat unit of chains. In addition, a single gold NP was synthesized in the micellar core in contrast to several silver NPs so that we differentiated the chains with Au NPs from those with Ag NPs by the number of NPs in the repeat unit as well as by plasmonic bands in UV-Vis spectra.

Stepwise self-assembly of a block copolymer-platinum(ii) complex hybrid in solvents of variable quality: from worm-like micelles to free-standing sheets to vesicle-like nanostructures

The self-assembly process of formation of worm-like micelles of a block copolymer-platinum(ii) complex hybrid is investigated with respect to the influence of solvent quality. When the solvent quality is moderately weakened, unilamellar free-standing sheets are achieved, in which the worm-like micelles snap off to form star micelles together with a few short worms. Extremely worsened solvent quality leads to unilamellar vesicle-like nanostructures, onto which only star micelles emerged. With the intermediate solvent quality, the sheets coexist with the vesicle-like nanostructures. This is well correlated with mechanistic insights regarding the morphological transition from sheet- to vesicle-like nanoassemblies. In these aggregates, short worms and star micelles still hold their core-shell structures. Furthermore, these unconventional superstructures are well interrelated with their luminescence properties. This result challenges the conventional paradigm of the amphiphilic self-assembly of surfactants and block copolymers in selective solvents, where they form bilayered nanostructures and are required universally to be rearranged during the morphological transition from micelles to vesicles.

Hybrid Nanoscopy of Hybrid Nanomaterials

The combination of complementary techniques to characterize materials at the nanoscale is crucial to gain a more complete picture of their structure, a key step to design and fabricate new materials with improved properties and diverse functions. Here it is shown that correlative atomic force microscopy (AFM) and localization-based super-resolution microscopy is a useful tool that provides insight into the structure and emissive properties of fluorescent β-lactoglobulin (βLG) amyloid-like fibrils. These hybrid materials are made by functionalization of βLG with organic fluorophores and quantum dots, the latter being relevant for the production of 1D inorganic nanostructures templated by self-assembling peptides. Simultaneous functionalization of βLG fibers by QD655 and QD525 allows for correlative AFM and two-color super-resolution fluorescence imaging of these hybrid materials. These experiments allow the combination of information about the topography and number of filaments that compose a fibril, as well as the emissive properties and nanoscale spatial distribution of the attached fluorophores. This study represents an important step forward in the characterization of multifunctionalized hybrid materials, a key challenge in nanoscience.

Colloidal Random Terpolymers: Controlling Reactivity Ratios of Colloidal Comonomers via Metal Tipping

We report on a versatile synthetic method of preparing colloidal copolymers and terpolymers composed of dipolar Au@Co core-shell nanoparticles (NPs) in the backbone, along with semiconductor CdSe@CdS nanorod (NR), or tetrapod (TP) side chain groups. A seven-step colloidal total synthesis enabled the synthesis of well-defined colloidal comonomers composed of a dipolar Au@CoNP attached to a single CdSe@CdS NR, or TP, where magnetic dipolar associations between Au@CoNP units promoted the formation of colloidal co- or terpolymers. The key step in this synthesis was the ability to photodeposit a single AuNP tip onto CdSe@CdS NR or TP that enables selective seeding of a dipolar CoNP onto the AuNP seed. We show that the variation of the AuNP size directly controlled the size and dipolar character of the CoNP tip, where the size modulation of the Au and Au@CoNP tips is analogous to control of comonomer reactivity ratios in classical copolymerization processes.

Branched and crosslinked supracolloidal chains with diblock copolymer micelles having three well-defined patches

We report controlled branching and eventual crosslinking in supracolloidal chains by introducing well-defined trifunctional patchy micelles.