Assembly of Semiconductor Nanorods into Circular Arrangements Mediated by Block Copolymer Micelles (original) (raw)
Related papers
Interfacial Assembly of Nanoparticles in Discrete Block-Copolymer Aggregates
Angewandte Chemie International Edition, 2007
The ability to control the assembly structure of nanoscale materials is critical to understand their collective properties and to develop new materials and devices from nanoscale building blocks. In nature, lipid membranes function as structural scaffolds to organize nanoscale intercellular components. This role of lipids originates from their tendency to self-organize into diverse supramolecular aggregates including micelles, bilayers, vesicles, and liquid-crystalline phases. Amphiphilic block copolymers, man-made analogues of lipids, are becoming increasingly important for the synthesis, manipulation, and assembly of nanoparticles. They have been demonstrated to be effective solubilizing agents to transfer organic-phase nanoparticles into water. Preorganized spherical or cylindrical block-copolymer micelles have been actively explored as a type of confined reactor for the controlled synthesis of nanoparticles. However, in most of the solution-phase studies, the nanoparticles were considered as simple solutes, and the efforts in directing the arrangement of nanoparticles using block copolymers have been largely limited to two-dimensional systems. Herein, we describe a novel solution-phase assembly of CdSe quantum dots (QDs) and a prototypical amphiphilic block copolymer, poly(acrylic acid)-block-polystyrene (PAAb-PS). Importantly, this study demonstrates that the interactions between nanoparticles and block copolymers can drastically alter the morphology of block-copolymer aggregates and can lead to a unique three-dimensional assembly structure of nanoparticles (a nanocavity in the present study) with controllable assembly parameters. Coassemblies of PAA-b-PS and organic-phase nanoparticles, including QDs and magnetic particles, have been prepared previously. However, in those studies, the nanoparticles were passively incorporated into the coassemblies by acting as simple solutes, and they were evenly distributed in block-copolymer micelles. Herein, we show a unique example in which nanoparticles act as active components for the assembly formation. Moreover, we demonstrate that one can control the three-dimensional assembly structure of nanoparticles inside discrete blockcopolymer aggregates by manipulating the interfacial energy of the composite system.
Ordering in Polymer Micelle-Directed Assemblies of Colloidal Nanocrystals
Assembly of presynthesized nanocrystals by block copolymer micelles can be rationalized by the incorporation of nanocrystals into micellar coronas of constant width. As determined by quantitative analysis using small-angle X-ray scattering, high loading of small nanocrystals yields composites exhibiting order on two length scales, whereas intermediate loading of nanocrystals larger than the coronal width produces single nanocrystal networks. The resulting structures obey expectations of thermodynamically driven assembly on the nanocrystal length scale, whereas kinetically frozen packing principles dictate order on the polymer micelle length scale.
Macromolecules, 2005
We report several strategies for varying the diameter, the center-to-center spacing, and the areal density of block copolymer micelles, or inorganic nanoclusters synthesized in the cores of the micelles, on planar substrates. The amphiphilic block copolymer, poly(styrene-b-acrylic acid) (PS/PAA), forms micelles in toluene solution that can be spin-coated onto a substrate to create quasi-hexagonal arrays of spherical PAA domains within a PS matrix. The carboxylic acid groups within the PAA domains can be utilized in a nanoreactor synthesis scheme to create inorganic nanocluster arrays, or the PAA domains can be cavitated to expose the carboxylic acid groups to the surface for possible covalent coupling reactions. The strategies we use to vary the planar arrangements include variation of the molecular weight of PS/PAA, variation of the amount of metal loaded into the micellar solution, addition of PS homopolymer into the micellar solution, and the mixing of different micellar solutions. Through these routes, we demonstrate varying the diameter of the inorganic nanoclusters from 4.7 to 16 nm and the areal density from 8 × 10 10 to 6.5 × 10 9 nanoclusters cm-2. We are also able to create arrays of nanoclusters containing more than one inorganic species, with each nanocluster containing either one or all of the inorganic species, depending on the sequence of processing conditions employed. We characterize these arrays using energy-dispersive X-ray analysis on a scanning transmission electron microscope.
Controlled organization of self-assembled rod-coil block copolymer micelles
Polymer, 2009
Spherical micelles of a series of poly (styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS) rod-coil diblock copolymers in a selective solvent can organize into large mono-layered films with a well-ordered hexagonal packing of the spheres after solvent evaporation. Organized domains in the spherical micelle film were observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The core-shell structure of the spherical micelle remained after solvent evaporation. The micelle diameter in the ordered film as observed by TEM and AFM agree. The size of the spherical micelles can be controlled by the length of PMPCS when the length of the PS is fixed. The sphere diameters were varied from several tens of nanometers to more than one hundred nanometers. Solutions of smaller micelle spheres formed less ordered films than those from larger micelle particles. Additionally, monolayer films of cylindrical worm-like micelles were also prepared. Those cylindrical micelles were observed to be end-capped by spherical micelles. The monolayer micelle film from the largest spherical micelles appeared red when observed in optical microscopy in the reflection mode. A broad adsorption peak with a maximum adsorption wavelength of 545 nm was observed via UV-Vis spectroscopy.
2014
Block copolymers (BCPs) with a short crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming block self-assemble in selective solvents to afford cylindrical micelles, the ends of which are active to further growth via a process termed living crystallization-driven self-assembly (CDSA). We now report studies of the CDSA of a series of crystalline-brush BCPs with C 6 (BCP 6), C 12 (BCP 12), and C 18 (BCP 18) n-alkyl branches that were prepared by the thiol−ene functionalization of PFS-b-PMVS (PMVS = poly(methylvinylsiloxane)). Although the increased n-alkyl brush length of BCP 12 and BCP 18 hindered micelle growth, the increased intercoronal chain repulsion could be alleviated by their coassembly with linear PFS-b-PMVS. When the coassembly was initiated by short cylindrical seed micelles, monodisperse block comicelles of controllable length with "patchy" coronal nanodomains were accessible. TEM and AFM analysis of micelles prepared from BCP 18 and PFS-b-PMVS were found to provide complementary characterization in that the OsO 4-stained PMVS coronal domains were observed by TEM, whereas the brush block domains of BCP 18 (which displayed greater height) were detected by tapping mode AFM. The results showed that the coassembly afforded a gradient structure, with an initial bias for the growth of the linear BCP over that of the more sterically demanding brush BCP, which was gradually reversed as the linear material was consumed. This represents the first example of living gradient CDSA, a process reminiscent of a living covalent gradient copolymerization of two different monomers. Although other possible explanations exist, simulations based on a statistical model indicated that the coronal nanodomains detected likely result from a segmented, gradient comicelle architecture that arises as a consequence of: (i) different rates of addition of BCP unimer to the micelle termini, and (ii) a cumulative effect resulting from steric hindrance associated with the brush block.
Block Copolymer Micelles as Nanoreactors for Self-Assembled Morphologies of Gold Nanoparticles
New micelle-like organic supports for single site catalysts based on the self-assembly of polystyrene-b-poly(4-vinylbenzoic acid) block copolymers have been designed. These block copolymers were synthesized by sequential atom transfer radical polymerization (ATRP) of styrene and methyl 4-vinylbenzoate, followed by hydrolysis. As evidenced by dynamic light scattering, self-assembly in toluene that is a selective solvent of polystyrene, induced the formation of micelle-like nanoparticles composed of a poly(4-vinylbenzoic acid) core and a polystyrene corona. Further addition of trimethylaluminium (TMA) afforded in situ MAO-like species by diffusion of TMA into the core of the micelles and its subsequent reaction with the benzoic acid groups. Such reactive micelles then served as nanoreactors, MAO-like species being efficient activators of 2,6-bis[1-{(2,6-diisopropylphenyl)imino}ethyl]pyridinyl iron toward ethylene polymerization. These new micelle-like organic supports enabled the production of polyethylene beads with a spherical morphology and a high bulk density through homogeneous-like catalysis.
Hierarchical self-organization of soft patchy nanoparticles into morphologically diverse aggregates
Current Opinion in Colloid & Interface Science
We present a concise review of the large variety of self-assembly scenarios observed in solutions of diblock copolymer stars with a solvophilic inner block and a solvophobic outer block. A variety of modeling approaches and simulation techniques at different levels of detail reveals that individual molecules assume configurations akin to patchy colloids, but with a patchiness that depends on physical parameters and can adjust to external stimuli such as temperature and pH. These soft, patchy building blocks inter-associate at finite concentrations into micellar or gel-like solutions, including spherical and wormlike micelles, or they display macroscopic phase separation. The connections between single-molecule conformation and the structure of the concentrated solution are discussed, and coarse-grained strategies for these novel molecular entities are critically compared to one another.
Block Copolymer Micelles Generated by Crystallization-Driven Self-Assembly in Polymer Matrices
Science Reviews - from the end of the world
In this review, we show how Crystallization-Driven Self-Assembly (CDSA), a method originally employed for the self-assembly of block copolymers in solution, was extended to the synthesis of elongated micellar nanostructures in polymer matrices. By highlighting some of the works published by our group in this area, the conditions to synthesize nanostructured polymers by CDSA are discussed. The knowledge of these conditions will allow developing a new generation of nanomaterials with tailored architecture based on a given application.
Assembly of colloidal semiconductor nanorods in solution by depletion attraction
2010
Arranging anisotropic nanoparticles into ordered assemblies remains a challenging quest requiring innovative and ingenuous approaches. The variety of interactions present in colloidal solutions of nonspherical inorganic nanocrystals can be exploited for this purpose. By tuning depletion attraction forces between hydrophobic colloidal nanorods of semiconductors, dispersed in an organic solvent, these could be assembled into 2D monolayers of close-packed hexagonally ordered arrays directly in solution. Once formed, these layers could be fished onto a substrate, and sheets of vertically standing rods were fabricated, with no additional external bias applied. Alternatively, the assemblies could be isolated and redispersed in polar solvents, yielding suspensions of micrometersized sheets which could be chemically treated directly in solution. Depletion attraction forces were also effective in the shape-selective separation of nanorods from binary mixtures of rods and spheres. The reported procedures have the potential to enable powerful and cost-effective fabrication approaches to materials and devices based on self-organized anisotropic nanoparticles.