Themed issue: self-assembly

Much of self-assembly's (SA) appeal derives from its ability to arrange simple components into complex structures with an almost magical ease. One must remember, however, that even simple demonstrations of SA are almost never as effortless as they might appear and are usually preceded by months of experimental and/or theoretical work through which one learns how to control the intercomponent forces and find experimental conditions that lead to the desired structures. As it stands now, SA is very elegant a posteriori but not yet very practical a priori, as evidenced by relatively few (though constantly growing in number!) technologies based on self-assembly.

The problem facing SA is the lack of universal principles available for the rational design (“engineering”) of self-assembly. As a result, virtually all but the most primitive systems one wishes to design have to be treated on a case-by-case basis. On the other hand, the preponderance of self-assembly in nature and its manifestations on scales from the molecular to the macroscopic hint that such principles do—or, at least, should—exist.

The motivation for this themed issue is therefore not only to review the current status of the SA field, but also stimulate the search for the unifying rules that govern it across different length scales.

The issue contains a Tutorial Review (DOI: 10.1039/b819321p) that systematizes the concepts used in SA research, discusses its relationship to thermodynamics (both in equilibrium and in non-equilibrium regimes), and provides illustrative examples of self-assembly at work. Expert theorists highlight some new, exciting theoretical approaches to SA. Whitelam and colleagues (DOI: 10.1039/b810031d) discuss efficient computational methods with which to model many-particle SA systems. Torquato's review (DOI: 10.1039/b814211b) focuses on the challenging topic of reverse-engineering—that is, of identifying interparticle interactions needed to evolve isolated components into desired assemblies. Balazs and co-workers (DOI: 10.1039/b805245j) consider SA in polymeric systems which can be modeled by continuum equations. Tretiakov et al. (DOI: 10.1039/b811254a) consider some theoretical aspects of SA in systems displaced from thermodynamic equilibrium.

The non-equilibrium theme ties neatly with two outstanding reviews from Ingber's (DOI: 10.1039/b806442c) and Weibel's (DOI: 10.1039/b812146J) groups. These papers illustrate the richness of non-equilibrium/dynamic self-assembly processes in cells and in cell populations, where multiple SA processes are orchestrated in space and time to give rise to emergent and collective behaviors. Some of these biological examples are nothing short of breathtaking and are probably the best inspiration for SA research. Biology does show us how sophisticated self-assembly can be!

The rest of the issue is devoted to artificial SA systems. The contributions are from the leading groups in their fields and cover the scales on which self-assembly occurs. We thus progress from the level of macromolecues (Huskens (DOI: 10.1039/b811873f) and Tschierske (DOI: 10.1039/b818871h)), through nanoparticles (Rotello (DOI: 10.1039/b808494g), Pochan (DOI: 10.1039/b811619a), Kotov (DOI: 10.1039/b812115j), Stupp (DOI: 10.1039/b819002j), and Aggeli (DOI: 10.1039/b815558e)), to colloids (Xia (DOI: 10.1039/b811021b), Velegol (DOI: 10.1039/b810882j), Doyle (DOI: 10.1039/b807389a)), and then macroscopic systems (Velev (DOI: 10.1039/b814304h), Whitesides (DOI: 10.1039/b813590h)). Some of the contributions are reports of new, exciting research, others review the progress in a specific subfield of SA (e.g., Kotov's Review of nanoscale self-assembly and Xia's Highlight on colloidal systems). The collective knowledge of this distinguished group of authors is a testament to how vibrant self-assembly research is and how applicable is SA to both small and large things.

Curiously, the SA strategies used at all these scales share some similarities, like the requirement for both attractive and repulsive interactions in all self-assembling systems, the competition between entropy and enthalpy, and more. As the field of self-assembly further matures, these commonalities will have to be systematized and formalized further until they form a coherent description of SA. All in all, SA is more than a set of disjoint “phenomena” but rather a general and very powerful approach to manipulate matter at all scales.

Plate1 Bartosz A. Grzybowski, Guest Editor

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