Block copolymer (BCP) self-assembly has attracted considerable attention for many decades because it can yield ordered structures in a wide range of morphologies, including spheres, cylinders, bicontinuous structures, lamellae, vesicles, and many other complex or hierarchical assemblies. These aggregates provide potential or practical applications in many fields. The present tutorial review introduces the primary principles of BCP self-assembly in bulk and in solution, by describing experiments, theories, accessible morphologies and morphological transitions, factors affecting the morphology, thermodynamics and kinetics, among others. As one specific example at a more advanced level, BCP vesicles (polymersomes) and their potential applications are discussed in some detail.

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Self-assembly of block copolymers

Just as nanoparticles display properties that differ from those of bulk samples of the same material, ensembles of nanoparticles can have collective properties that are different to those displayed by individual nanoparticles and bulk samples. Self-assembly has emerged as a powerful technique for controlling the structure and properties of ensembles of inorganic nanoparticles. Here we review different strategies for nanoparticle self-assembly, the properties of self-assembled structures of nanoparticles, and potential applications of such structures. Many of these properties and possible applications rely on our ability to control the interactions between the electronic, magnetic and optical properties of the individual nanoparticles. Self-assembly is a powerful technique for controlling the structure and properties of ensembles of inorganic nanoparticles. This article reviews the properties and potential applications of self-assembled structures made from nanoparticles.

Properties and emerging applications of self-assembled structures made from inorganic nanoparticles

Engineering applications of synthetic polymers are widespread due to their availability, processability, low density, and diversity of mechanical properties (Figure 1a). Despite their ubiquitous nature, modern polymers are evolving into multifunctional systems with highly sophisticated behavior. These emergent functions are commonly described as “smart” characteristics whereby “intelligence” is rooted in a specific response elicited from a particular stimulus. Materials that exhibit stimuli-responsive functions thus achieve a desired output (O, the response) upon being subjected to a specific input (I, the stimulus). Given that mechanical loading is inevitable, coupled with the wide range of mechanical properties for synthetic polymers, it is not surprising that mechanoresponsive polymers are an especially attractive class of smart materials. To design materials with stimuli-responsive functions, it is helpful to consider the I-O relationship as an energy transduction process. Achieving the desired I-O linkage thus becomes a problem in finding how to transform energy from the stimulus into energy that executes the desired response. The underlying mechanism that forms this I-O coupling need not be a direct, one-step transduction event; rather, the overall process may proceed through a sequence of energy transduction steps. In this regard, the network of energy transduction pathways is a useful roadmap for designing stimuli-responsive materials (Figure 1b). It is the purpose of this review to broadly survey the mechanical to chemical * To whom correspondence should be addressed. Phone: 217-244-4024. Fax: 217-244-8024. E-mail: jsmoore@illinois.edu. † Department of Chemistry and Beckman Institute. ‡ Department of Materials Science and Engineering and Beckman Institute. § Department of Aerospace Engineering and Beckman Institute. Chem. Rev. XXXX, xxx, 000–000 A

Mechanically-induced chemical changes in polymeric materials

Directing the self-assembly of block copolymers

Block copolymers consist of two or more chemically different polymers connected by covalent linkages. In solution, repulsion between the blocks leads to a variety of morphologies, which are thermodynamically driven. Polyferrocenyldimethylsilane block copolymers show an unusual propensity to forming cylindrical micelles in solution. We found that the micelle structure grows epitaxially through the addition of more polymer, producing micelles with a narrow size dispersity, in a process analogous to the growth of living polymer. By adding a different block copolymer, we could form co-micelles. We were also able to selectively functionalize different parts of the micelle. Potential applications for these materials include their use in lithographic etch resists, in redox-active templates, and as catalytically active metal nanoparticle precursors.

https://science.sciencemag.org/content/sci/317/5838/644.full.pdf

Cylindrical Block Copolymer Micelles and Co-Micelles of Controlled Length and Architecture

The preparation of a new type of cylindrical micelle architecture with an A-B-A triblock structure bearing spatially controlled coronal charge is reported. This was achieved by extending the living supramolecular polymerization approach to block copolymers with hydrophilic blocks and to polar solvents. Electrostatic interactions can be used to selectively functionalize the new nanomaterials with Au and PbS NPs in a spatially selective manner to afford novel composite structures.

Cylindrical Block Co-Micelles with Spatially Selective Functionalization by Nanoparticles

Detailed studies of a new approach to the synthesis and encapsulation of silver and silver halide nanoparticles inside shell-cross-linked cylindrical block copolymer polyisoprene-block-polyferrocenyldimethylsilane (PI-b-PFS) micelles (1) through in situ redox reactions are reported. The cylindrical nanostructures 1 were prepared by the solution self-assembly of the PI-b-PFS diblock copolymer in the PI-selective solvent hexane followed by Pt(0)-catalyzed PI shell-cross-linking hydrosilylation reactions. The partial preoxidation of the swollen PFS core using tris(4-bromophenyl)aminium hexachloroantimonate [p-BrC6H4)3N][SbCl6] (2, Magic Blue) followed by redox reaction between the remaining Fe(II) centers in the PFS core and Ag+ cations led to the formation of silver nanoparticles. High-resolution scanning transmission electron microscopy images of the resulting peapod structures provided a clear indication that the nanoparticles were encapsulated inside the micelles. The composition of the nanoparticles was...

Redox-mediated synthesis and encapsulation of inorganic nanoparticles in shell-cross-linked cylindrical polyferrocenylsilane block copolymer micelles.

A new approach to encapsulate silver nanoparticles inside block copolymer nanotubes is reported and involves an in situ redox reaction between a polyferrocenylsilane (PFS) inner wall and silver ions. Partial preoxidation of the PFS domains was found to be a key step for the efficient formation of one-dimensional arrays of silver nanoparticles confined within the nanotubes.

Hai Wang

Papers

Cylindrical Block Copolymer Micelles and Co-Micelles of Controlled Length and Architecture

Cylindrical Block Co-Micelles with Spatially Selective Functionalization by Nanoparticles

Redox-mediated synthesis and encapsulation of inorganic nanoparticles in shell-cross-linked cylindrical polyferrocenylsilane block copolymer micelles.

Redox-Induced Synthesis and Encapsulation of Metal Nanoparticles in Shell-Cross-Linked Organometallic Nanotubes

Fabrication of Continuous and Segmented Polymer/Metal Oxide Nanowires Using Cylindrical Micelles and Block Comicelles as Templates