Construction aims to build systems that are structurally stable after assembly, as well as throughout their functional operations. This objective inherently prompts to the thermodynamic control of self-assembly, prototypically represented by crystallization processes. The thermodynamic i. Under thermodynamic control, the target structure is designed to univocally coincide with the global minimum of the free energy landscape associated with its building blocks.
Given the negligible mobility of typical mesoscopic building blocks, kinetic energy is injected from an external source to stir the system along its thermodynamic trajectory.
The purposeful provision of surrogate high temperature and Brownian motion is temporary, and the final structure withstands its extinction unaffected. The self-assembling system needs to be posed under the effect of potential or force gradients only as long as it takes to be correctly locked into its most stable state. The latter state is path-independent, and can be reached from a variety of initial conditions.
The minimal energy state may be degenerate, which improves self-assembly yield. A structure of high designability can be equivalently assembled out of multiple or redundant sets of building blocks Hogg, Static self-assembly has been successfully used in pioneering proofs of concepts and applied to the fabrication of mesoscopic systems of technological relevance Mastrangeli et al.
Purely stochastic self-assembly approaches, deliberately inspired by chemical reactions and modeled through reaction network formalisms Mastrangeli et al.
New method inverts the self-assembly of liquid crystals
This requires the introduction of programmable force fields, biasing Chung et al. More recently, and after an initial sprawl of directions of investigation, research in mesoscopic self-assembly has been manifesting the tendency to converge to a scenario whereby a subset of mature methods, tailored to driving applications, is surrounded by a fertile cloud of explorative forays.
Accordingly, the core of mesoscopic static self-assembly eminently includes 1 the fabrication of two- and three-dimensional colloidal crystalline structures with low-defect densities and long-range order, suitable for, e. As for the latter, fluidic self-assembly Crane et al. The convergence to the aforementioned scenario arguably results from a selection among the available options — a selection based upon performance and, where applicable, upon the challenges facing the development of laboratory demonstrations into potential staples of industrial practice.
Capillary self-alignment Arutinov et al. Is the current situation in mesoscopic self-assembly here to stay, or should it rather be considered a trend susceptible of further developments? In arguing in favor of the latter option, we remind that, besides notable exceptions Fialkowski et al. Most of the achievements of mesoscopic self-assembly thus far have indeed involved only a limited number of types of homogeneous building blocks mostly, a single one , a subset of the possible interactions, and exogenous ways to bring the blocks together, typically in close packing or direct contact.
Therefore, even before turning to technological outputs, there is still a lot more to demonstrate, achieve, and fundamentally learn about self-assembly — particularly at the mesoscale, and both inside and outside its static realm. Steps toward higher complexity may be pursued by shifting the focus of research toward the static self-assembly of three-dimensional structures. At mesoscale, three-dimensional building blocks are successfully and deterministically self-assembled through the folding of two-dimensional nets of panels, whose deterministic wrapping, mediated by flexible hinges, extrinsic stresses, or elastocapillary effects, is algorithmically preset by conformational constraints Shenoy and Gracias, The resulting structures are nonetheless essentially hollow shells, whose core is more easily occupied by a fluid than by a solid payload.
Alternative to constrained folding is the puzzle approach Cademartiri and Bishop, , whereby the target structure results from the coordination of building blocks upon close contact Gracias et al. The puzzle approach is, however, liable to the curse of dimensionality, i. Keeping at bay the surge of configurations accessible to a self-assembling system in its potential landscape represents a major, standing reason of caution along this self-assembly strategy. This issue can nonetheless be normalized and faced in several ways.
Systems with higher levels of structural and functional sophistication can be produced, for instance, through programmability and reconfigurability. Programmability amount to partitioning the progression of the construction into stages by presetting the sequence of allowed assembly steps. This approach can be practiced by the controlled enablement and selective structural coding of binding events, and subsumes hierarchical self-assembly techniques Cademartiri and Bishop, Reconfigurability consists instead in resetting the morphology of the system Mattia and Otto, In static self-assembly, this is only possible by perturbing the potential landscape through changes in boundary conditions Mao et al.
A much wider realm of possibilities may, furthermore, be approached by shifting from a strictly static self-assembly framework to a dynamic one Table 1 Warren et al. Dynamic self-assembly stems from the kinetic control of systems that are thermodynamically metastable or far from equilibrium Lehn, ; Fialkowski et al. Metastable systems are kinetically trapped within local minima of the free energy landscape Mattia and Otto, The specific self-assembly pathway traversed does select the actual morphology of these systems Whitelam and Jack, Seeds Saitou, and catalysts Miyashita et al.
Out of equilibrium or self-organizing systems are instead posed in steady-state by the balance of opposing interactions, such as global attraction and local repulsion or other instances of, respectively, synthetic and dissipative reactions Mattia and Otto, A constant energy input, sustaining constant energy dissipation and entropy production, is required to preserve the transient order of such systems, which gets lost upon interruption of the exogenous input. Foreshadowed by early demonstrations Fialkowski et al. In the specific mesoscale case, though, such conceivable move may entail a more radical revision: should the foremost role of self-assembly remain building thermodynamically stable structures, or rather become fostering programmable matter Warren et al.
Analogies with systems chemistry, and elucidation through artificial replication of mechanisms possibly at the origin of life Nicolis and Prigogine, ; Schneider and Kay, ; Pross, , are also driving motives. It may be inspiring also to remind that energy dissipation does play a fundamental role in the physics of computation Bennett, ; and, more pragmatically, that all active devices of daily use absolve their functions only when transiently posed out of thermodynamic equilibrium through an external supply of energy, ultimately dissipated into heat. A standing key challenge remains devising efficient ways to implement and tune energy input and dissipation in mesoscopic self-organizing systems.
In this respect, progress is nevertheless being made. Colloidal systems are witnessing a rapid increase of demonstrations of self-organization and dynamic self-assembly Snezhko, ; Kokot et al. Along the way, this may provide important additional hints toward a comprehensive theory of dissipative systems Nicolis and Prigogine, ; Tretiakov et al. Table 1.
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Representative instances of mesoscopic self-assembly in their static versus dynamic manifestations. While not dismissing the persistent development of alternative approaches able to leverage or complement current manufacturing practices, self-assembly should ultimately concentrate on its unicity and target achievements that are exclusively accessible to itself.
This will let self-assembly thrive securely guarded from applicative competition. Complexity — declined through collective interactions of large sets of heterogeneous components, structures with fully three-dimensional architectures, and kinetically controlled systems — holds the promise to light up the road ahead. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Arutinov, G. In-plane mode dynamics of capillary self-alignment.
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Design and Control of Self-Assembly
Bishop, K. Nanoscale forces and their uses in self-assembly. Small 5, — Cademartiri, L. Programmable self-assembly. Using shape for self-assembly. Either by signing into your account or linking your membership details before your order is placed. Your points will be added to your account once your order is shipped. Click on the cover image above to read some pages of this book! Mechanical Self-Assembly: Science and Applications introduces a novel category of self-assembly driven by mechanical forces.
The mechanical self-assembly process is inherently quick, simple, and cost-effective, as well as accessible to a large number of materials, such as curved surfaces for forming three-dimensional small structures. Mechanical self-assembly is complementary to, and sometimes offer advantages over, the traditional micro- and nano-fabrication. Country of Publication: US Dimensions cm : Help Centre. Because the negative and positive order liquid crystal rubbers act in opposite ways, this opens for interesting ways to combine the two, to make a more effective composite actuator, for instance for soft robotics.
When the positive-order actuator responds slowly, the negative-order one actuates quickly, and vice versa. From a fundamental physics point of view, the physical existence of the previously only theoretically predicted anti-ordered liquid crystal state opens for many interesting experiments as well as theory development for the behavior of self-organizing soft matter.
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Design and Control of Self-Assembly | Mechanical and Aerospace Engineering
Science News. Story Source: Materials provided by University of Luxembourg. Journal Reference : V. Jampani, R. Volpe, K. Reguengo de Sousa, J. Ferreira Machado, C. Yakacki, J. Liquid crystal elastomer shell actuators with negative order parameter. Science Advances , ; 5 4 : eaaw DOI: ScienceDaily, 12 April