A Simple Route To Improve Inorganic Nanoparticles Loading Efficiency in Block Copolymer Micelles

Well-Ordered Nanoparticles/Block Copolymer Nanosheets with a Controllable Location of Nanoparticles

Precisely controlling the spatial distributions and arrangements of metal nanoparticles (NPs) into block copolymers is of great importance for fabricating novel nanomaterials with the desired optical and electronic properties. Herein, we develop a simple yet versatile strategy to prepare organic/inorganic nanosheets formed by the coassembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and PS tethered gold nanoparticles (AuNPs@PS) within emulsion droplets. The arrangement of the AuNPs@PS building blocks within the block copolymers (BCP)/AuNPs nanosheets can be adjusted by tuning the effective size ratio (λeff), which can be controlled by the core diameter of the AuNPs and the molecular weight of the PS. Furthermore, the content of the AuNPs is also another essential parameter to manipulate the structures of the nanosheets with the specific λeff. Thus, the BCP/AuNPs hybrid nanosheets with controllable distributions and arrangements of the AuNPs were successfully prepared via tuning of λeff and the content of AuNPs. This study provides a facile way to fabricate well-ordered hybrid nanosheets.

Hybrid Polymer Vesicles: Controllable Preparation and Potential Applications

Hybrid polymer vesicles contain functional nanoparticles (NPs) in their walls, interfaces, coronae, or cavities. NPs render the hybrid vesicles with specific physical properties, while polymers endow them with structural stability and may significantly reduce the high toxicity of NPs. Therefore, hybrid vesicles integrate fascinating multifunctions from both NPs and polymeric vesicles, which have gained tremendous attention because of their diverse promising applications. Various types of delicate hybrid polymeric vesicles with size control and tunable localization of NPs in different parts of vesicles have been constructed via in situ and ex situ strategies, respectively. Their potential applications have been widely explored, as well. This review presents the progress of block copolymer (BCP) vesicle systems containing different types of NPs including metal NPs, magnetic NPs, and semiconducting quantum dots (QDs), etc. The strategies for controlling the location of NPs within hybrid vesicles are discussed. Typical potential applications of the elegant hybrid vesicles are also highlighted.

Poly(vinylpyridine)-Containing Block Copolymers for Smart, Multicompartment Particles

Multicompartment particles generated by the self-assembly of block copolymers (BCPs) have received considerable attention due to their unique morphologies and functionalities. A class of important building blocks for multicomponent particles...

Unveiling the Mechanism of the Location of the Grafted Nanoparticles in a Lamellar-Forming Block Copolymer

Through coarse-grained molecular dynamics simulation of polymer-grafted nanoparticles (NPs) in a lamellar-forming diblock copolymer (BCP), we systematically study the effects of the grafting density (N_g), the compatibility between the grafted chains and the A-block of BCPs (ε_gA), and the NP number (N) on the distance (D) of the NPs from the interface by proposing novel characterization parameters of the orientation and distribution of the grafted chains. The NP gradually migrates away from the interface and into the A-block region with the increase of ε_gA for all studied N_g, while slightly returning toward the interface at high ε_gA and great N_g, which is the first observation of nonmonotonic migration at the molecular level. We ascribe the reason of this to the behavior of the grafted chains that are near the interface. Furthermore, we classify the grafted chains into three types along the normal direction of the interface and the migration process is illustrated by the distribution and orientation of the different types of grafted chains, together with the radial distribution function between the NP and the A-block chains. We observe the formation of the NP layers parallel to the interface for N < 20, and a similar nonmonotonic migration of the layers is as well observed. The D is the largest for a small N because of the excluded volume effects between the NPs. Increasing N_g and N pushes the neighboring NP layers toward the interface due to the mutual repulsion. Generally, this study may shed some light on how to better understand and design high-performance polymer nanocomposites with a tunable location of NPs.

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.

Enantiomer-selective magnetization of conglomerates for quantitative chiral separation

Selective crystallization represents one of the most economical and convenient methods to provide large-scale optically pure chiral compounds. Although significant development has been achieved since Pasteur’s separation of sodium ammonium tartrate in 1848, this method is still fundamentally low efficient (low transformation ratio or high labor). Herein, we describe an enantiomer-selective-magnetization strategy for quantitatively separating the crystals of conglomerates by using a kind of magnetic nano-splitters. These nano-splitters would be selectively wrapped into the S-crystals, leading to the formation of the crystals with different physical properties from that of R-crystals. As a result of efficient separation under magnetic field, high purity chiral compounds (99.2 ee% for R-crystals, 95.0 ee% for S-crystals) can be obtained in a simple one-step crystallization process with a high separation yield (95.1%). Moreover, the nano-splitters show expandability and excellent recyclability. We foresee their great potential in developing chiral separation methods used on different scales.

Despite significant development in selective crystallization of chiral compounds this method still lacks high efficiency. Here the authors describe an efficient enantiomer-selective magnetization strategy for quantitatively separating the crystals of conglomerates by using magnetic nano-splitters.

Coordination-induced assemblies of quantum dots in amphiphilic thermo-responsive block copolymer micelles: morphologies, optical properties and applications

Thermo-responsive dual-emitting QD/BCP assemblies with QDs located in the core (CDMs), shell (SDMs) and the interface (IDMs) between the core and the shell of micelles were constructed via coordination-driven assemblies for the selective detection of TNP and Hg²⁺ ions.

Recent progress in the self-assembly of block copolymers confined in emulsion droplets

When the self-assembly of block copolymers (BCPs) occurs within a deformable emulsion droplet, BCPs can aggregate into a variety of nanoscaled particles with unique nanostructures and properties since the confinement effect can effectively break the symmetry of a structure.

In situ formation of luminescent CdSe QDs in a metallohydrogel: a strategy towards synthesis, isolation, storage and re-dispersion of the QDs

A one step, in situ, room temperature synthesis of yellow luminescent CdSe QDs was achieved in a metallohydrogel derived from a facially amphiphilic bile salt, resulting in a QD-gel hybrid. An ordered self-assembly and homogeneous distribution of the CdSe QDs in the hydrogel network was observed from optical and electron micrographs. The different excited state behavior of the CdSe QDs in the hybrid was revealed for the first time using time resolved spectroscopy. We also describe the successful isolation of the photoluminescent CdSe QDs from the gel followed by their re-dispersion in an organic solvent using suitable capping ligands.

Nanocomposites of Highly Monodisperse Encapsulated Superparamagnetic Iron Oxide Nanocrystals Homogeneously Dispersed in a Poly(ethylene Oxide) Melt

Nanocomposite materials based on highly stable encapsulated superparamagnetic iron oxide nanocrystals (SPIONs) were synthesized and characterized by scattering methods and transmission electron microscopy (TEM). The combination of advanced synthesis and encapsulation techniques using different diblock copolymers and the thiol-ene click reaction for cross-linking the polymeric shell results in uniform hybrid SPIONs homogeneously dispersed in a poly(ethylene oxide) matrix. Small-angle X-ray scattering and TEM investigations demonstrate the presence of mostly single particles and a negligible amount of dyads. Consequently, an efficient control over the encapsulation and synthetic conditions is of paramount importance to minimize the fraction of agglomerates and to obtain uniform hybrid nanomaterials.

Anisotropic Self-Assembly of Hairy Inorganic Nanoparticles

Current interest in functional assemblies of inorganic nanoparticles (NPs) stems from their collective properties and diverse applications ranging from nanomedicines to optically active metamaterials. Coating the surface of NPs with polymers allows for tailoring of the interactions between NPs to assemble them into hybrid nanocomposites with targeted architectures. This class of building blocks is termed "hairy" inorganic NPs (HINPs). Regiospecific attachment of polymers has been used to achieve directional interactions for HINP assembly. However, to date anisotropic surface functionalization of NPs still remains a challenge. This Account provides a review of the recent progress in the self-assembly of isotropically functionalized HINPs in both the condensed state and aqueous solution as well as the applications of assembled structures in such areas as biomedical imaging and therapy. It aims to provide fundamental mechanistic insights into the correlation between structural characteristics and self-assembly behaviors of HINPs, with an emphasis on HINPs made from NPs grafted with linear block copolymer (BCP) brushes. The key to the anisotropic self-assembly of these HINPs is the generation of directional interactions between HINPs by designing the surrounding medium (e.g., polymer matrix) or engineering the surface chemistry of the HINPs. First, HINPs can self-assemble into a variety of 1D, 2D, or 3D nanostructures with a nonisotropic local arrangement of NPs in films. Although a template is not always required, a polymer matrix (BCPs or supramolecules) can be used to assist the assembly of HINPs to form hybrid architectures. The interactions between brushes of neighboring HINPs or between HINPs and the polymer matrix can be modulated by varying the grafting density and length of one or multiple types of polymers on the surface of the NPs. Second, the rational design of deformable brushes of BCP or mixed homopolymer tethers on HINPs enables the anisotropic assembly of HINPs (in analogy to molecular self-assembly) into complex functional structures in selective solvents. It is evidenced that the directional interactions between BCP-grafted NPs arise from the redistribution and conformation change of the long, flexible polymer tethers, while the lateral phase separation of brushes on NP surfaces is responsible for the assembly of HINPs carrying binary immiscible homopolymers. For HINPs decorated with amphiphilic BCP brushes, their self-assembly can produce a variety of hybrid structures, such as vesicles with a monolayer of densely packed NPs in the membranes and with controlled sizes, shapes (e.g., spherical, hemispherical, disklike), and morphologies (e.g., patchy, Janus-like). This strategy allows fine-tuning of the NP organization and collective properties of HINP assemblies, thus facilitating their application in effective cancer imaging, therapy, and drug delivery. We expect that the design and assembly of such HINPs with isotropic functionalization is likely to open up new avenues for the fabrication of new functional nanocomposites and devices because of its simplicity, low cost, and ease of scale-up.

In situ synthesis of the Ag/poly(4-vinylpyridine)-block-polystyrene composite nanoparticles by dispersion RAFT polymerization

A new method for the synthesis of metal/block-copolymer nanocomposites of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS) and Ag nanoparticles by dispersion RAFT polymerization is proposed.

Self-Organization of Gold Nanoparticle Assemblies with 3D Spatial Order and Their External Stimuli Responsiveness

Gold nanoparticles (AuNP) with pyridyl end-capped polystyrenes (PS-4VP) as "quasi-monodentate" ligands self-assemble into ordered PS-4VP/AuNP nanostructures with 3D hexagonal spatial order in the dried solid state. The key for the formation of these ordered structures is the modulation of the ratio AuNP versus ligands, which proves the importance of ligand design and quantity for the preparation of novel ordered polymer/metal nanoparticle conjugates. Although the assemblies of PS-4VP/AuNP in dispersion lack in high dimensional order, strong plasmonic interactions are observed due to close contact of AuNP. Applying temperature as an external stimulus allows the reversible distortion of plasmonic interactions within the AuNP nanocomposite structures, which can be observed directly by naked eye. The modulation of the macroscopic optical properties accompanied by this structural distortion of plasmonic interaction opens up very interesting sensoric applications.

Clustering of CdSe/CdS Quantum Dot/Quantum Rods into Micelles Can Form Bright, Non-blinking, Stable, and Biocompatible Probes

We investigate clustered CdSe/CdS quantum dots/quantum rods, ranging from single to multiple encapsulated rods within amphiphilic diblock copolymer micelles, by time-resolved optical spectroscopy. The effect of the clustering and the cluster size on the optical properties is addressed. The clusters are bright and stable and show no blinking while retaining the fundamental optical properties of the individual quantum dots/quantum rods. Cell studies show neither unspecific uptake nor morphological changes of the cells, despite the increased sizes of the clusters.

Hairy Core-Shell Polymer Nano-objects from Self-Assembled Block Copolymer Structures

Fabrication of core-shell polymer nano-objects with well-defined shape and hairy shell has been a subject of immense interest in polymer chemistry for more than two decades now. Different approaches such as those involving synthesis (grafting approaches) and block copolymer self-assembly (solution as well as bulk) have been used for the preparation of such nano-objects. Of these approaches that involving bulk self-assembled structures of block copolymers have been of special interest because of the simplicity and range of shape and structures possible. The present review focuses on the advances which have been made in this direction using diblock and triblock self-assembled structures. It will be shown that this approach allows to fabricate hairy nano-objects of not only simple shapes such as spheres, rods, and sheets but also those with more complex shape and morphology such as multicompartment micelles, which are not possible to obtain with synthetic or solution self-assembly approaches. Furthermore, interesting structures such as Janus nano-objects could also be fabricated using this approach. The review further highlights the use of such nano-objects for templating applications.

Strategies for interfacing inorganic nanocrystals with biological systems based on polymer-coating

A representative set of nanocrystals made of semiconductors, Au and iron oxide, surface-capped with polymer ligands presenting various metal-coordinating groups.

Single Monomer for Multiple Tasks: Polymerization Induced Self-Assembly, Functionalization and Cross-Linking, and Nanoparticle Loading

Efficient preparation of multifunctional nano-objects with controlled morphologies in one step at high concentrations is synthetically challenging, yet is highly desirable, in a broad range of materials applications. Herein, we address this synthetic hurdle by introducing a single commodity monomer 2-(acetoacetoxy)ethyl methacrylate (AEMA) to realize multiple functions. Facile preparation of both nanospheres and vesicles via polymerization induced self-assembly at concentrations of 20-30% provided defined polymeric nanomaterials with reactive handles inherent to the AEMA units. High-yielding keto-alkoxylamine chemistry was utilized to decorate and cross-link the nano-objects. Nanoparticle loading into the designated location within both nano-objects was exemplified with in situ formation of silver nanoparticles. The concept of using a single monomer capable of both morphology control and multifunctionalization is expected to offer significant opportunities in functional nanomaterials.

Correction: Hood, M.A., et al. Synthetic Strategies in the Preparation of Polymer/Inorganic Hybrid Nanoparticles. Materials 2014, 7, 4057-4087

In [1], several sentences were repeated three times on pages 4062, 4063 and 4065. In addition, many references were incorrect. The errors were introduced by the editorial office during the editing process. We apologize for this mistake and any inconvenience this may have caused to authors and readers. The corrected manuscript is given below.[...].

Colloidal micelles of block copolymers as nanoreactors, templates for gold nanoparticles, and vehicles for biomedical applications

Target drug delivery methodology is becoming increasingly important to overcome the shortcomings of conventional drug delivery absorption method. It improves the action time with uniform distribution and poses minimum side effects, but is usually difficult to design to achieve the desire results. Economically favorable, environment friendly, multifunctional, and easy to design, hybrid nanomaterials have demonstrated their enormous potential as target drug delivery vehicles. A combination of both micelles and nanoparticles makes them fine target delivery vehicles in a variety of biological applications where precision is primarily required to achieve the desired results as in the case of cytotoxicity of cancer cells, chemotherapy, and computed tomography guided radiation therapy.

Ultralong cylindrical micelles precisely located with semiconductor nanorods by solvent evaporation-driven self-assembly

We demonstrate the efficient incorporation of PS-tethered cadmium sulfide nanorods (PS-CdS NRs) into polystyrene-block-poly(ethylene oxide) (PS-b-PEO) ultralong cylindrical micelles by solvent evaporation-driven self-assembly. The hexadecyl trimethyl ammonium bromide (CTAB) was used as the surfactant in chloroform-in-water emulsions. It is a prerequisite to improve the enthalpic compatibility between the CdS NRs and the PS block of PS-b-PEO to accomplish their cooperative assembly. We investigated the effects including the concentration of CTAB in the aqueous solution ([CTAB]), the weight fraction of CdS NRs (f), the volume ratio of the organic solvent to water and the magnetic stirring rate on the cooperative assembly behaviors. The different morphologies of hybrid assemblies formed at varied [CTAB] were rationalized in view of the adsorption of the aqueous surfactant and block copolymer at the oil-water interfaces, thereby leading to the disparate mechanisms by which the organic-water interfacial instabilities proceeded. This work presents an extremely precise location of the CdS NRs in the centers of the cylindrical micelles, i.e. 95.2% of the CdS NRs were distributed in the central ca. 4 vol% regions of the cylinders and all of them were dispersed in the central ca. 38% radial spans. The length of the hybrid cylindrical micelles can reach tens of micrometers. The ultralong cylindrical micelles functionalized by the CdS NRs in the central cores can lower the toxicity of the CdS NRs and improve the biocompatibility, which have potential applications in fluorescence probes, labels and many others.

Polymer-assisted self-assembly of superparamagnetic iron oxide nanoparticles into well-defined clusters: controlling the collective magnetic properties

The combination of superstructure-forming amphiphilic block copolymers and superparamagnetic iron oxide nanoparticles produces new nano/microcomposites with unique size-dependent properties. Herein, we demonstrate the controlled clustering of superparamagnetic iron oxide nanoparticles (SPIOs) ranging from discretely encapsulated SPIOs to giant clusters, containing hundreds or even more particles, using an amphiphilic polyisoprene-block-poly(ethylene glycol) diblock copolymer. Within these clusters, the SPIOs interact with each other and show new collective properties, neither obtainable with singly encapsulated nor with the bulk material. We observed cluster-size-dependent magnetic properties, influencing the blocking temperature, the magnetoviscosity of the liquid suspension, and the r2 relaxivity for magnetic iron oxide nanoparticles. The clustering methodology can be expanded also to other nanoparticle materials [CdSe/CdS/ZnS core/shell/shell quantum dots (QDs), CdSe/CdS quantum dots/quantum rods (QDQRs), gold nanoparticles, and mixtures thereof].

Synthetic Strategies in the Preparation of Polymer/Inorganic Hybrid Nanoparticles

This article reviews the recent advances and challenges in the preparation of polymer/inorganic hybrid nanoparticles. We mainly focus on synthetic strategies, basing our classification on whether the inorganic and the polymer components have been formed in situ or ex situ, of the hybrid material. Accordingly, four types of strategies are identified and described, referring to recent examples: (i) ex situ formation of the components and subsequent attachment or integration, either by covalent or noncovalent bonding; (ii) in situ polymerization in the presence of ex situ formed inorganic nanoparticles; (iii) in situ precipitation of the inorganic components on or in polymer structures; and (iv) strategies in which both polymer and inorganic component are simultaneously formed in situ.

Crafting threads of diblock copolymer micelles via flow-enabled self-assembly

Hierarchically assembled amphiphilic diblock copolymer micelles were exquisitely crafted over large areas by capitalizing on two concurrent self-assembling processes at different length scales, namely, the periodic threads composed of a monolayer or a bilayer of diblock copolymer micelles precisely positioned by flow-enabled self-assembly (FESA) on the microscopic scale and the self-assembly of amphiphilic diblock copolymer micelles into ordered arrays within an individual thread on the nanometer scale. A minimum spacing between two adjacent threads λmin was observed. A model was proposed to rationalize the relationship between the thread width and λmin. Such FESA of diblock copolymer micelles is remarkably controllable and easy to implement. It opens up possibilities for lithography-free positioning and patterning of diblock copolymer micelles for various applications in template fabrication of periodic inorganic nanostructures, nanoelectronics, optoelectronics, magnetic devices, and biotechnology.

Selective confinement of oleylamine capped Au nanoparticles in self-assembled PS-b-PEO diblock copolymer templates

Amphiphilic polystyrene-block-polyethylene oxide (PS-b-PEO) block copolymers (BCPs) have been demonstrated to be effective in directing organization of colloidal Au nanoparticles (NPs). Au NPs have been incorporated into the polymer and the different chemical affinity between the NP surface and the two blocks of the BCP has been used as a driving force of the assembling procedure. The morphology of the nanocomposites, prepared and fabricated as thin films, has been investigated by means of atomic force and scanning electron microscopies as a function of the NP content and BCP molecular weight. NPs have been effectively dispersed in PS-b-PEO hosts at any investigated content (up to 17 wt%) and a clear effect of the BCP properties on the final nanocomposite morphology has been highlighted. Finally, electrostatic force microscopy has demonstrated the conductive properties of the nanocomposite films, showing that the embedded Au NPs effectively convey their conductive properties to the film. The overall investigation has confirmed the selective confinement of the as-prepared surfactant-coated metal NPs in the PS block of PS-b-PEO, thus proposing a very simple and prompt assembling tool for nanopatterning, potentially suitable for optoelectronic, sensing and catalysis applications.

A general approach toward polymer-coated plasmonic nanostructures

A generic method for the preparation of polymer-coated plasmonic nanostructures with tunable thickness of the hydrophobic polymer spacer.

A multifunctional amphiphilic polymer as a platform for surface-functionalizing metallic and other inorganic nanostructures

We designed a new set of polymer ligands that combine multiple metal-coordinating groups and short polyethylene glycol (PEG) moieties in the same structure. The ligand design relies on the controlled grafting of a large number of amine-terminated histamines and PEG short chains onto a poly(isobutylene-alt-maleic anhydride) backbone,viaa one-step nucleophilic addition reaction. This addition reaction is highly efficient, can be carried out in organic media and does not require additional reagents. We show that when imidazole groups are used the resulting polymer ligand can strongly ligate onto metal nanostructures such as nanoparticles (NPs) and nanorods (NRs) made of gold cores. The resulting polymer-coated NPs and NRs exhibit good colloidal stability to pH changes and added electrolytes. This constitutes a departure from the use of thiol-based ligands to coordinate on Au surfaces. The present chemical approach also opens up additional opportunities for designing hydrophilic and reactive platforms where the polymer coating can be adjusted to various metal and metal oxide surfaces by simply modifying or combining the addition reaction with other metal coordinating groups. These could include iron oxide NPs and semiconductor QDs. These polymer-capped NPs and NRs can be used to develop biologically-active platforms with potential use for drug delivery and sensing.