Self-assembly of charged, equally sized metal nanoparticles of two types (gold and silver) leads to the formation of large, sphalerite (diamond-like) crystals, in which each nanoparticle has four oppositely charged neighbors. Formation of these non-close-packed structures is a consequence of electrostatic effects specific to the nanoscale, where the thickness of the screening layer is commensurate with the dimensions of the assembling objects. Because of electrostatic stabilization of larger crystallizing particles by smaller ones, better-quality crystals can be obtained from more polydisperse nanoparticle solutions.C rystalline aggregates composed of one or more types of metallic and/or semiconductor nanoparticles (NPs) are of great interest for the development of new materials with potential applications in areas such as optoelectronics (1), high-density data storage (2), catalysis (3), and biological sensing (4). To date, methods for the crystallization of two-dimensional (2D) and 3D NP superlattices have relied on the differences in the sizes of component particles and on attractive van der Waals or hard-sphere interactions between them. This strategy has been successful in preparing several types of lattices Esuch as AB (5), AB 2 (6), AB 5 (7), and AB 13 (6)^, but the all-attractive nature of the interparticle potentials limits its applicability to relatively few and usually (8) close-packed structures.To overcome this limitation, we and others (8, 9) have focused on systems of NPs interacting via electrostatic forces; such forces provide a basis for ionic, colloidal (9), or even macroscopic (10) crystals, but, despite promising attempts (8, 11), have not been successfully exploited for controllable or predictable long-range organization of matter at the nanoscale. Here, we report electrostatic self-assembly (10) (ESA) of oppositely charged, nearly equally sized metallic NPs of different types into large 3D crystals characterized by sphalerite (diamond-like) (12) internal packing, and of overall morphologies identical to those of macroscopic diamond or sphalerite crystals (Figs. 1 to 4). Formation of these nonclose-packed structures results from the change in electrostatic interactions in the nanoscopic regime, where the thickness of the screening layer becomes commensurate with the dimensions of the assembling particles, and is facilitated by the presence of smaller, charged NPs in the crystallizing solutions that stabilize larger NPs by what can be termed a nanoscopic counterpart of Debye screening.We used Ag and Au NPs coated with w-functionalized alkane thiols (13): HS(CH 2 ) 10 COOH (MUA) and HS(CH 2 ) 11 NMe 3 þ Cl j (TMA) (Fig. 1A). These NPs were prepared according to a modified procedure (14) Esee Supporting Online Material (15)^and had average diameters of 5.1 nm (with dispersity s 0 20%) for Au and 4.8 nm (s 0 30%) for Ag (Fig. 1B). We chose this pair as a model system, because the average sizes of Au NPs passivated with MUA Eself-assembled monolayer (SAM) thickness 0 1.63 nm (16)^and Ag NPs cov...

Dynamic self-assembly (DySA) processes occurring outside of thermodynamic equilibrium underlie many forms of adaptive and intelligent behaviors in natural systems. Relatively little, however, is known about the principles that govern DySA and the ways in which it can be extended to artificial ensembles. This article discusses recent advances in both the theory and the practice of nonequilibrium self-assembly. It is argued that a union of ideas from thermodynamics and dynamic systems' theory can provide a general description of DySA. In parallel, heuristic design rules can be used to construct DySA systems of increasing complexities based on a variety of suitable interactions/potentials on length scales from nanoscopic to macroscopic. Applications of these rules to magnetohydrodynamic DySA are also discussed.

Revealing the chemical and physical mechanisms underlying symmetry breaking and shape transformations is key to understanding morphogenesis. If we are to synthesize artificial structures with similar control and complexity to biological systems, we need energy- and material-efficient bottom-up processes to create building blocks of various shapes that can further assemble into hierarchical structures. Lithographic top-down processing allows a high level of structural control in microparticle production but at the expense of limited productivity. Conversely, bottom-up particle syntheses have higher material and energy efficiency, but are more limited in the shapes achievable. Linear hydrocarbons are known to pass through a series of metastable plastic rotator phases before freezing. Here we show that by using appropriate cooling protocols, we can harness these phase transitions to control the deformation of liquid hydrocarbon droplets and then freeze them into solid particles, permanently preserving their shape. Upon cooling, the droplets spontaneously break their shape symmetry several times, morphing through a series of complex regular shapes owing to the internal phase-transition processes. In this way we produce particles including micrometre-sized octahedra, various polygonal platelets, O-shapes, and fibres of submicrometre diameter, which can be selectively frozen into the corresponding solid particles. This mechanism offers insights into achieving complex morphogenesis from a system with a minimal number of molecular components.

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Reaction-diffusion (RD) processes are common throughout nature, which uses them routinely to build and control structures on length scales from molecular to macroscopic. At the same time, despite a long history of scientific research and a significant level of understanding of the basic aspects of RD, reaction-diffusion has remained an unrealized technological opportunity. This review suggests that RD systems can provide a versatile basis for applications in micro-and nanotechnology. Straightforward experimental methods are described that allow precise control of RD processes in complex microgeometries and enable fabrication of small-scale structures, devices, and functional systems. Uses of RD in sensory applications are also discussed.

The general mechanisms of structure and form generation are the keys to understanding the fundamental processes of morphogenesis in living and non-living systems. In our recent study (Denkov et al., Nature 528 (2015) 392) we showed that micrometer sized n-alkane drops, dispersed in aqueous surfactant solutions, can break symmetry upon cooling and "self-shape" into a series of geometric shapes with complex internal structure. This phenomenon is important in two contexts, as it provides: (a) new, highly efficient bottom-up approach for producing particles with complex shapes, and (b) remarkably simple system, from the viewpoint of its chemical composition, which exhibits the basic processes of structure and shape transformations, reminiscent of morphogenesis events in living organisms. In the current study, we show for the first time that drops of other chemical substances, such as long-chain alcohols, triglycerides, alkyl cyclohexanes, and linear alkenes, can also evolve spontaneously into similar non-spherical shapes. We demonstrate that the main factors which control the drop "self-shaping", are the surfactant type and chain length, cooling rate, and initial drop size. The studied surfactants are classified into four distinct groups, with respect to their effect on the "self-shaping" phenomenon. Coherent explanations of the main experimental trends are proposed. The obtained results open new prospects for fundamental and applied research in several fields, as they demonstrate that: (1) very simple chemical systems may show complex structure and shape shifts, similar to those observed in living organisms; (2) the molecular self-assembly in frustrated confinement may result in complex events, governed by the laws of elasto-capillarity and tensegrity; (3) the surfactant type and cooling rate could be used to obtain micro-particles with desired shapes and aspect ratios; and (4) the systems studied serve as a powerful toolbox to investigate systematically these phenomena.

Nanoactuators and nanomachines have long been sought after, but key bottlenecks remain. Forces at submicrometer scales are weak and slow, control is hard to achieve, and power cannot be reliably supplied. Despite the increasing complexity of nanodevices such as DNA origami and molecular machines, rapid mechanical operations are not yet possible. Here, we bind temperatureresponsive polymers to charged Au nanoparticles, storing elastic energy that can be rapidly released under light control for repeatable isotropic nanoactuation. Optically heating above a critical temperature T c = 32°C using plasmonic absorption of an incident laser causes the coatings to expel water and collapse within a microsecond to the nanoscale, millions of times faster than the base polymer. This triggers a controllable number of nanoparticles to tightly bind in clusters. Surprisingly, by cooling below T c their strong van der Waals attraction is overcome as the polymer expands, exerting nanoscale forces of several nN. This large force depends on van der Waals attractions between Au cores being very large in the collapsed polymer state, setting up a tightly compressed polymer spring which can be triggered into the inflated state. Our insights lead toward rational design of diverse colloidal nanomachines.ctuators are needed to turn energy sources into physical movement. These can be for microrobotics, sensing, storage devices, smart windows and walls, or more general functional and active materials. Such artificial muscles have gained rapidly increasing interest (1, 2) leading to micropropellers (3, 4), gas jets from catalytic surfaces (5), and DNA machines (6). However, the actuation methods, delivery of energy, and forces obtained (typically 10 fN/nm 2 ) are limited so far (7): Magnetic fields are inconvenient to apply locally for actuation, as is >200°C heating to actuate polymer fibers; the nanocatalysis of chemical fuels lacks controllability, whereas DNA machines rely on "fuel" DNA strands to competitively bind and operate on very slow (second) timescales. Piezoelectric-type materials used in high-end instrumentation (such as atomic force microscopy or nanopositioning stages) provide short travel but with inorganic materials that are dense, delicate, expensive, hard to fabricate, and demand high voltages (150-300 V), as is also true for electrostrictive rubbers and relaxor ferroelectrics (8, 9). Many biological systems such as Escherichia coli (10), cilia (11), or nematocysts (12) provide sophisticated models for nanomachines (13). Although molecular motors and artificial muscles from hydrogels (14, 15), colloids (16), or liquid crystalline elastomers (17, 18) successfully mimic such behaviors, they are very slow (on the order of seconds) and the forces generated are very small (∼ pN). This is because either the energy density stored in the system is low or the energy release is inefficient.To overcome this we design a colloidal actuating transducer system with high-energy storage (1,000 k B T/cycle) and fast (>MHz) release mechanism....

We review the most promising design strategies for enhanced conducting polymer-based supercapacitors, summarizing the challenges and recent progress in optimizing each of the most important metrics of supercapacitor performance.