Three-Dimensional Assembly of Gold Nanoparticles in Spherically Confined Microphase-Separation Structures of Block copolymers

Fluorescence Switchable Block Copolymer Particles with Doubly Alternate-Layered Nanoparticle Arrays

The precise self-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) under 3D confinement offers microparticles with programmable nanostructures and functionalities. Here, fluorescence-switchable hybrid microspheres are developed by forming doubly alternating arrays of Au NPs and CdSe/ZnS quantum dots (QDs) within polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP domains. These doubly alternating arrays afford controlled nonradiative energy transfer (NRET) between the QDs and Au NPs that is dependent on the layer-to-layer distance. Solvent-selective swelling of the hybrid particles tunes the distance between layers, modulating their NRET behavior and affording switchable fluorescence. The particle fluorescence is "OFF" in water through strong NRET from the QDs to Au NPs, but is "ON" in alcohols due to the increased distance between the Au NP and QD arrays in the swollen P4VP domains. The experimentally observed NRET intensity as a function of interparticle distance shows larger quenching efficiencies than those theoretically predicted due to the enhanced quenching within a 3D-confined system. Finally, the robust and reversible fluorescence switching of the hybrid particles in different solvents is demonstrated, highlighting their potentials for bioimaging, sensing, and diagnostic applications.

Multicompartment Microparticles with Patchy Topography through Solvent-Adsorption Annealing

We report on the evaporation-induced confinement assembly (EICA) of polystyrene-b-polybutadiene-b-poly(methyl methacrylate) (PS-b-PB-b-PMMA, SBM) triblock terpolymers into multicompartment microparticles and follow their morphological evolution during solvent-adsorption annealing. We initially obtain elliptic microparticles with axially stacked PS/PB/PMMA morphology using cetyltrimethylammonium bromide (CTAB) as surfactant. Exchanging the surfactant to poly(vinyl alcohol) (PVA) during solvent vapor annealing with chloroform (CHCl₃), PMMA preferentially interacts with the interface, and microparticles change their shape into spheres with concentric morphology. Surprisingly, this transformation initiates at both poles of the microparticles simultaneously and then proceeds toward the equator, resulting in particles with inner morphology and patchy topography. We observed this evolution for different PB fractions, suggesting the mechanism to be more general and the EICA process to be a suitable method to generate patchy particle surfaces.

Investigating the cheletropic reaction between sulfur dioxide and butadiene-containing linkers in UiO-66

UiO-66 and a muconic acid functionalized derivative of UiO-66 (UiO-66-MA) were synthesized via the solvothermal method to determine if the muconic acid could undergo a cheletropic reaction in the presence of sulfur dioxide inside the metal-organic framework (MOF). Both MOFs were exposed to a constant flow of sulfur dioxide, and UiO-66-MA was observed to take up three times more sulfur dioxide than unfunctionalized UiO-66. Despite the improved uptake of sulfur dioxide in UiO-66-MA, NMR and IR data indicate that no chemical change occurred to the muconic acid indicating that a cheletropic reaction did not occur. We thus propose that the increased adsorption is due to either an interaction between the sulfur dioxide and unbound carboxylic acid from the muconic acid or a favourable interaction between the butadiene of muconic acid and sulfur dioxide.

3D Lattice Structure Control of Ordered Macroporous Material by Self-Assembly of Liquid Droplets

Microfluidic devices, which can continuously fabricate single emulsion with monodispersed droplets having a pore diameter of more than 100 μm in large numbers, can be applied to manufacture ordered macroporous films. 3D ordered macroporous films with a diameter of more than 100 μm can be fabricated using ordered arrays of the monodispersed droplets as templates of the macropores, which are self-assembled in the space between two parallel flat glass plates. As the gap between the glass plates increases, the number of the layer increases. Furthermore, in the case with two or more layers, the lattice structure of the macroporous films also changes due to the confinement effects.

Monte Carlo Study of Degenerate Behavior of AB Diblock Copolymer/Nanoparticle under Cylindrical Confinement

Degenerate behavior (i.e., forming different self-assembled structures for a given block copolymer (BCP) under the same confinement) commonly exists in various confined systems. Understanding degenerate behavior is crucial for precise control over the structures formed by self-assembly systems under confinement. In this study, the degenerate behavior of a self-assembled AB diblock copolymer/nanoparticle (NP) mixture in a cylindrical pore is studied using Monte Carlo simulation. We find that the degenerate behavior of such a mixture depends on the introduction of the NP. Under different pore sizes, four typical degenerate structures [i.e., single helices (S-helices), double helices (D-helices), parallel cylinders, and stacked toroids] can be obtained if the NP content is zero. However, when the NP content in the mixture is increased, it is found that the number of degenerate structures decreases, that is, only blocky structures can be obtained in the case of high NP content. Moreover, the probability of forming S-helices decreases, whereas the probability of forming D-helices increases with increase in the NP content. Analysis of the interactive enthalpy densities and the chain conformation of the systems indicates that entropy plays an important role in the degenerate structure formation. This study provides some new insights into the degenerate behavior of a BCP/NP mixture under confinement, which can offer a theoretical reference for further experiments.

Frustrated phases under three-dimensional confinement simulated by a set of coupled Cahn-Hilliard equations

We numerically study a set of coupled Cahn-Hilliard equations as a means to find morphologies of diblock copolymers in three-dimensional spherical confinement. This approach allows us to find a variety of energy minimizers including rings, tennis balls, Janus balls and multipods among several others. Phase diagrams of confined morphologies are presented. We modify the size of the interface between microphases to control the number of holes in multipod morphologies. Comparison to experimental observation by transmission electron microtomography of multipods in polystyrene-polyisoprene diblock copolymers is also presented.

Facile synthesis of thermo-responsive episulfide group-containing diblock copolymers as robust protecting ligands of gold nanoparticles for catalytic applications

Well-defined novel thermo-responsive diblock copolymers containing episulfide ligand stabilized Au NPs show interesting assembly morphologies, excellent colloidal stability and high catalytic activity for the reduction of 4-nitrophenol.

How does dense phase CO2 influence the phase behaviour of block copolymers synthesised by dispersion polymerisation?

Using a CO₂ continuous phase for dispersion synthesis of block copolymers can provide a useful handle to control phase behaviour.

Block copolymer synthesis by controlled/living radical polymerisation in heterogeneous systems

We review the range of CLRP-controlled syntheses of block copolymer particles in dispersed systems, which are being exploited to create new opportunities for the design of nanostructured soft materials.

Block copolymer self-assembly for nanophotonics

The ability to control and modulate the interaction of light with matter is crucial to achieve desired optical properties including reflection, transmission, and selective polarization. Photonic materials rely upon precise control over the composition and morphology to establish periodic interactions with light on the wavelength and sub-wavelength length scales. Supramolecular assembly provides a natural solution allowing the encoding of a desired 3D architecture into the chemical building blocks and assembly conditions. The compatibility with solution processing and low-overhead manufacturing is a significant advantage over more complex approaches such as lithography or colloidal assembly. Here we review recent advances on photonic architectures derived from block copolymers and highlight the influence and complexity of processing pathways. Notable examples that have emerged from this unique synthesis platform include Bragg reflectors, antireflective coatings, and chiral metamaterials. We further predict expanded photonic capabilities and limits of these approaches in light of future developments of the field.

Frustrated phases: polymeric self-assemblies in a 3D confinement

This paper reviews recent progress concerning polymeric self-assemblies in confined spaces, including phase-separated structures of polymer blends and block copolymers. Although a wide variety of polymer self-assemblies have been studied in terms of conventional parameters, such as blend ratio, interaction of constituent polymers, block ratio, and molecular weight, a series of unique structures appear when the systems are self-assembled under confined conditions. Due to the limited space for phase separation, the polymers in the confinement are frustrated, and the resulting morphologies are distinctly different from those formed in free space. We give an overview of experimental and theoretical studies of the frustrated morphologies. We begin by defining confinement with respect to dimensionality and surface properties, and then introduce methods for producing various shapes and sizes of three-dimensional confinement. Finally, we present morphological and application-oriented studies and discuss the prospects for this research area.

Evolution of conductive network and properties of nanorod/polymer composite under tensile strain

In this work, the conductive network, probability, and percolation threshold of nanorod/polymer composites under tensile strain are investigated using the molecular dynamics simulation. The internal interactions, including polymer-polymer, polymer-nanorod, and nanorod-nanorod interactions, are taken into account in simulations. In particular, the influence of polymer induced depletion force on the orientation of nanorods is analyzed. Under a constant strain, the conductive stability firstly declines and then rises with the increasing concentration of fillers, and the minimum corresponds to the percolation threshold. As strain increases, the result exhibits a strong anisotropy in the stability of conductive property.

Bottom-up approach to creating three-dimensional nanoring arrays composed of Au nanoparticles

A bottom-up approach to creating 3D assemblies of Au nanorings by drying aqueous dispersions of PS colloidal particles and Au NPs is shown. The evaporation of water from the dispersion allowed for the formation of hexagonally assembled colloidal crystals and nanorings composed of Au nanoparticles among the PS colloidal particles. The size of the nanorings could be controlled on a scale of tens to hundreds of nanometers. After sintering, the Au NPs formed Au nanorings. This simple approach supplies a potentially useful path to novel plasmonic materials and unique metamaterials for the visible light region.

Thermally sensitive block copolymer particles prepared via aerosol flow reactor method: Morphological characterization and behavior in water

This work describes properties of thermo-sensitive submicron sized particles having the same chemical composition but different morphologies. These particles have been prepared with an aerosol technique using dimethylformamide solutions of linear polystyrene-block-poly(N-isopropylacrylamide-block-polystyrene, PS-b-PNIPAM-b-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block-copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly(N-isopropylacrylamide) matrix and physically cross-linking polystyrene domains. The particles were dispersed in aqueous media and their behavior in water was studied both below and above the lower critical solution temperature of poly(N-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering experiments showed that the particles gradually aggregate and precipitate with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron density to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph analysis that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degradation scheme is proposed to explain these results.

Hierarchically structured materials from block polymer confinement within bicontinuous microemulsion-derived nanoporous polyethylene

The self-assembly behavior of block polymers under strong two-dimensional and three-dimensional confinement has been well-studied in the past decade. Confinement effects enable access to a large suite of morphologies not typically observed in the bulk. We have used nanoporous polyethylene, derived from a polymeric bicontinuous microemulsion, as a novel template for the confinement of several different cylinder-forming block polymer systems: poly(isoprene-b-2-vinylpyridine), poly(styrene-b-isoprene), and poly(isoprene-b-dimethylsiloxane). The resultant materials exhibit unique hierarchical arrangements of structure with two distinct length scales. First, the polyethylene template imparts a disordered, microemulsion-like periodicity between bicontinuous polyethylene and block polymer networks with sizes on the order of 100 nm. Second, the block polymer networks display internal periodic arrangements produced by the spontaneous segregation of their incompatible constituents. The microphase-separated morphologies observed are similar to those previously reported for confinement of block polymers in cylindrical pores. However, at present, the morphologies are spatially variant in a complex manner, due to the three-dimensionally interconnected nature of the confining geometry and its distribution in pore sizes. We have further exploited the unique structure of the polyethylene template to generate new hierarchically structured porous monoliths. Poly(isoprene-b-2-vinylpyridine) is used as a model system in which the pyridine block is cross-linked, post-infiltration, and the polyethylene template is subsequently extracted. The resultant materials possess a three-dimensionally continuous pore network, of which the pore walls retain the unique, microphase-separated morphology of the confined block polymer.