Functional materials and devices by self-assembly
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Introduction For the past century, the atom has been the building block of chemistry. Small atomic assemblies, aka molecules, remain the most fundamental and important concept in chemistry.1 However, organized structures can form spontaneously, not only from atoms and small molecules, but also from various other types of building blocks. This process called “selfassembly” allows expanding and generalizing the concepts of bottom-up design and synthesis of structures, materials and devices. Self-assembly creates an opportunity to develop new paradigms for chemistry and material science, where various, typically nanometer-sized, objects with precisely engineered sizes, shapes, compositions, and concomitant properties serve as “meta-atoms” or superatomic building blocks for hierarchically assembled materials and devices. Just as atoms combine to form molecules with dramatically different properties than the atomic constituents, self-assembly of “meta-atoms” can create “meta-molecules,” and “meta-crystals.” Ultimately, self-assembly should contribute to the development and manufacturing of materials and devices for real-world applications (Figure 1). This issue of MRS Bulletin discusses examples of the successful adaption of self-assembly principles to the needs of electronics,2 photonics,3 energy storage,4 chemical separations,5 and complex structure formation.6 Self-assembly also plays a central role in biological systems and living organisms.
These strong conceptual ties between self-assembly and biology open a wide design space for biomimetic materials.
What is self-assembly good for? Self-assembly adds several unique features to our existing toolset of chemical and physical methods for the synthesis and processing of functional materials. First, self-assembly allows making materials with structural features on the length scales of several nanometers, in not only two dimensions, but also in three dimensions, which is too large for traditional (atomby-atom) chemical synthesis but too small to be efficiently approached by top-down techniques, such as photolithography (Figure 2a). Self-assembly is particularly useful to synthesize hierarchically organized materials with structures independently engineered on different scales. For example, a variety of macromolecules containing two or more covalently bonded blocks of different polymers can be prepared by conventional chemical synthesis. These block copolymers spontaneously self-assemble into ordered structures with ∼10 nm features (Figure 2b). The type of self-assembling structure and feature size can be rationally engineered by controlling the block size of individual molecules.7,8 A similar hierarchical design is achieved for nanocrystal solids that can be engineered at the level of individual nanocrystals and then self-assembled into
Dmitri V. Talapin, Department of Chemistry, James Franck Institute, and Pritzker School of Molecular Engineering, University of Chicago, USA; [email protected] Michael Engel, Department of Chemical and Biological Engineering, Frie
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