Self-organized Materials Research Articles

Social capital and community disaster resilience: post-earthquake tourism recovery on Gili Trawangan, Indonesia

This study examines the hypothesis that social capital can be a foundation for community disaster resilience with an analysis of empirical findings from the August 2018 earthquake recovery on Gili Trawangan, Indonesia, a globally known coastal tourism destination. Positive links between community social capital and community disaster resilience are hypothesized, but the extent to which an iterative and interdependent relationship is co-shaping both is less understood. Social capital can enable collective action, providing self-organized social, psychological, financial and material resources following a disaster, that may otherwise need to be provided externally. In turn, disasters create collective action problems where collective response and recovery process are needed, creating an institutional space where the degree of usefulness, meaning and function of social capital can be shaped, recognized and drawn upon, often where external aid is insufficient. These relationships can be observed following disasters, because individuals and communities are often linked through emotive and meaningful sequences of common experiences, actions and activities. Findings descriptively detail Gili Trawangan’s response and recovery process through the events and activities that occurred, and are then theoretically analyzed with a social capital framework including bonding (within group), bridging (between group) and linking (across power and institutional) ties. Three conclusions can be summarized. (1) Community social capital and disaster resilience are iteratively co-shaped through collective experiences, actions and activities. (2) Understanding context is critical for understanding if and to what degree this relationship exists. (3) The mechanism through which social capital enhances resilience is that it can enable collective action that can lead to the provision of needed aid and services.

Exotic colony formation in Sn-Te eutectic system

Eutectics are self-organized composite materials that exhibit a wide variety of microstructural features. Besides intrinsic materials properties like interfacial energies or diffusivities as well as the nature of the phase diagrams, the process parameters such as magnitude and orientation of the temperature gradient as well as the velocity of the growth interface influence the evolution of the microstructure. Recently, we have observed the evolution of complex patterns due to addition of ternary impurities in the binary Sn-Te system that contains, in addition to (Te), an intermetallic SnTe phase with a cubic crystal structure. This paper examines in detail the origin of such a microstructure that arises due to a two-phase growth instability induced by impurity addition. The binary eutectics (Sn-Te) and ternary eutectics (Sn-Te with an impurity addition) are directionally solidified at different interfacial velocities in order to study the morphological evolution. The binary alloy exhibits a rod-like or an interconnected string of rods morphology while the addition of a third component leads to a diffusive instability (similar to a Mullins-Sekerka instability) that results in the formation of two-phase colonies. The onset of instability depends on both the growth velocity and impurity concentration while the growth direction of the cells is normal to the {0001} planes of (Te) and {111} planes of SnTe. Through the extensive use of multiple characterization techniques, we have explored the morphological characteristics and crystallography of these colonies. The colonies have a complex internal structure that bears a three-fold symmetry reminiscent of the trigonal symmetry of the (Te) crystal, arising possibly because of strong anisotropy in the solid-liquid interfacial energy or in the kinetics of growth. For the different impurity additions (Ag or Sb), the internal eutectic morphology of the colony, due to the addition of Ag is different from that observed for the addition of Sb. The latter leads to the formation of lamellae while a rod-like feature could be observed for impurities like Ag. The complex patterns exhibit a structural hierarchy that provides opportunities for designing novel materials.

Visible-Light-Driven Halogen Bond Donor Based Molecular Switches: From Reversible Unwinding to Handedness Inversion in Self-Organized Soft Helical Superstructures.

Visible-light-driven molecular switches endowing reversible modulation of the functionalities of self-organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room-temperature achiral liquid crystal host 5CB, which also acts as a halogen-bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible-light-driven reversible unwinding, that is, a cholesteric-nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible-light-driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented.

Localized modes in chiral photonic structures

We discuss chiral structures in self-organizing, artificial, and biological materials. A review of experimental studies and recent advances in the localization of light in chiral structures is given. The behavior of polarized resonant modes in such structures is examined using the example of a one-dimensional photonic crystal containing liquid crystal materials. The anomalous spectral shifts of transmission peaks are interpreted as the contribution of the geometric phase caused by the twisting of the layers of the liquid crystal. The optical Tamm state localized at the boundary between chiral and nonchiral mirrors in the form of a cholesteric layer and a polarization-preserving anisotropic mirror is analytically and numerically described. Considerable attention is paid to the presentation of the properties of localized optical modes in the cholesteric with a resonant metal-dielectric nanocomposite. New possibilities for controlling the properties of the photonic structure are noted, due to the combination of the dispersion of the resonant medium and the intrinsic dispersion of the cholesteric. Attention is focused on controlled hybrid modes in the cholesteric structure formed by the coupling of localized modes. Possible applications and further ways of developing the concept of chiral photonic structures are deliberated.

Nanostructured zeolite with brain-coral morphology and tailored acidity: a self-organized hierarchical porous material with MFI topology

Nano-zeolite with brain-coral morphology formed by self-organization of ultra-small nanospheres, exhibits micro/meso porosity with high surface area, distributed acid sites, and reduced diffusion resistance making it a promising solid acid catalyst.

A numerical investigation of the effect of external resistance and applied potential on the distribution of periodicity and chaos in the anodic dissolution of nickel.

The oscillatory electrodissolution of nickel is one among several reactions utilized as a model-system to study the emergence of oscillations and pattern formation in electrochemical interfaces, in addition to frequently providing experimental proofs for theoretical predictions in synchronization engineering. The reaction was modeled in 1992 by Haim and co-workers [J. Phys. Chem. 1992, 96, 2676] and since then the model has been used with great success. Although some numerical studies have been done in this regard, there is apparently no detailed investigation of the effect of control parameters on the complex dynamics of nickel dissolution. Here, we provide a well-detailed and rigorous analysis of the effect of the external resistance and applied potential by simulating high-resolution phase diagrams based on the calculation of Lyapunov exponents and isospike diagrams. Our findings clearly indicate a strong dependence of the self-similar periodic islands, the so-called shrimps (i.e., periodic islands within chaotic domains in the parameter space), with the control parameters. Overall, we have observed a low density of periodic structures in the phase diagrams, being completely suppressed for large values of resistance and potential. The shrimp-like structures become gradually elongated with an increase of the control parameters to the point where only diagonally aligned periodic bands intertwined with chaotic domains are present. Interestingly, period-doubling cascades were observed not only on the shrimps but also on the periodic bands. The detailed distribution of chaos and periodicity of oscillatory electrodissolution reactions in resistance-potential phase diagrams can bring, for instance, important information to experimentalists to set a desired dynamic behavior and, therefore, to create novel nanostructured self-organized materials.

Kinetic Analysis of the Oscillatory Electrodeposition of Cu/Sn Multilayers: Activation and Diffusion Control

The systematic study of the nonlinear dynamics of different systems can yield important scientific advances. Examples range from the better understanding of living systems, remarkably nonlinear, to the development of new, self-organized materials. In this work, for the first time, quasiperiodic oscillations were observed during the electro-deposition of Cu/Sn multilayers (Figure 1a). Return maps were used to characterize the quasiperiodicity, and the continuous wavelet transform was employed to isolate and determine the oscillation frequencies (Figure 1b and c). To further study the mechanism in play, it was determined the apparent activation energy, by tracking the oscillation frequencies and the currents in the cyclic voltammetry experiments under different temperatures. Two different energy intervals are showed, and those are mainly attributed to: activation barriers (~50 kJ.mol-1) closely related to a fast time scale of the feedback loops responsible for the current oscillations and, diffusional processes (~20 kJ.mol-1) connected with the slow modulations of the oscillation amplitude, giving rise to the quasiperiodic dynamics. As self-organization in chemical systems is quickly developing into a powerful strategy for designing new functional materials, available kinetic parameters become of major interest in a rational design approach. In fact, the quasiperiodic behavior observed during the oscillatory deposition of Cu/Sn yields a material with unique properties and opens the perspective for the synthesis of more intricate morphologies. This work is ready for publication and will be submitted within few days. Figure 1

Swarm robotics: Robustness, scalability, and self-X features in industrial applications

Abstract Applying principles of swarm intelligence to the control of autonomous systems in industry can advance our ability to manage complexity in prominent and high-cost sectors—such as transportation, logistics, and construction. In swarm robotics, the exclusive use of decentralized control relying on local communication and information provides the key advantage first of scalability, and second of robustness against failure points. These are directly useful in certain applied tasks that can be studied in laboratory environments, such as self-assembly and self-organized construction. In this article, we give a brief introduction to swarm robotics for a broad audience, with the intention of targeting future industrial applications. We then present a summary of four examples of our recently published research results with simple models. First, we present our approach to self-reconfiguration, which uses collective adjustment of swarm density in a dynamic setting. Second, we describe our robot experiments for self-organized material deployment in structured and semi-structured environments, applicable to braided composites. Third, we present our machine learning approach for self-assembly, motivated as a simple model developing foundational methods, which generates self-organizing robot behaviors to form emergent patterns. Fourth, we describe our experiments implementing a bioinspired model in a robot swarm, where we show self-healing of damage as the robots collectively locate a resource. Overall, the four examples we present concern robustness, scalability, and self-X features, which we propose as potentially relevant to future research in swarm robotics applied to industry sectors. We summarize these approaches as an introduction to our recent research, targeting the broad audience of this journal.

Self-assembled artificial cartilage-hydroxyapatite conjugate for combined articular cartilage and subchondral bone repair

Self-assembled artificial cartilage-hydroxyapatite conjugate for combined articular cartilage and subchondral bone repair

How long does it take a pyrite framboid to form?

Framboids are defined as microscopic, sub-spheroidal clusters of equant and equidimensional microcrystals. The microcrystals are usually constituted of pyrite and framboidal pyrite is one of the most abundant mineral textures in the natural environment. They are of particular interest to geochemists, sedimentologists, paleobiologists and materials scientists because of their potential paleoenvironmental significance, their widespread involvement in fossilization and their potential for the manufacture of self-organizing materials. Here I use a simple diffusion-nucleation model to compute framboid formation times. The results show that pyrite framboids take between 3 h and 3 yr to form depending on framboid size. The time taken for the average sedimentary framboid to form is about 5 days and the average syngenetic framboid forms within 3 days. The shorter formation times for syngenetic compared with diagenetic framboids helps explain the smaller size relative size distributions of syngenetic framboids. This has led to the use of framboid size-frequency measurements as proxies for ancient euxinia. The relatively rapid formation of pyrite framboids explains how pyrite infills and preserves soft tissues before cell lysis and before deformation through burial has been initiated. One unexpected consequence of the model is that it further explains how commonly observed groups of framboids can form contemporaneously.

Diffractive and Refractive Liquid Crystal Devices Based on Multilayer Matrices

Tunable photonic devices based on self-organized materials like liquid crystals are opening new alternatives for photonic applications, especially when several optical functions can be implemented into one device. Beam steering devices based on liquid crystals usually work either as digital beam steerers (phase gratings), or as analog steerers (prisms). Digital steerers move laser beams to fixed positions; they cannot be tuned continuously. Analog beam steerers produce a continuous angular deviation of laser beams but with very limited deviation angles. In this paper, we developed a tunable grating prism, that can work as a prism and as a phase grating at the same time. This combination of refractive and diffractive effects is achieved with multilayer indium tin oxide (ITO) electrode matrices in a liquid crystal device. This solution is completely different from previous approaches, like blaze gratings or Fresnel configurations - the tunability range here is completely continuous, or completely stepped, or a combination of both at the same time - as there are no interpixels or dead areas in the multilayer configuration. The proposed grating prism is able to deviate a light beam to a large fixed angle by diffraction, and then fine tune the beam over small angle ranges by refraction. Additionally, the light losses produced by ITO diffraction in conventional liquid crystal gratings are significantly reduced using the layered configuration.

Multivariate statistical analysis of chemical and electrochemical oscillators for an accurate frequency selection.

The effect of experimental parameters on the frequency of chemical oscillators has been systematically studied since the first observations of clock reactions. The approach is mainly based on univariate changes in one specific parameter while others are kept constant. The frequency is then monitored and the effect of each parameter is discussed separately. This type of analysis, however, does not take into account the multiple interactions among the controllable parameters and the synergic responses on the oscillation frequency. We have carried out a multivariate statistical analysis of chemical (BZ-ferroin catalyzed reaction) and electrochemical (Cu/Cu2O cathodic deposition) oscillators and identified the contributions of the experimental parameters on frequency variations. The BZ reaction presented a strong dependence on the initial concentration of sodium bromate and temperature, resulting in a frequency increase. The concentration of malonic acid, the organic substrate, affects the system but with lower intensity compared with the combination of sodium bromate and temperature. On the other hand, the Cu/Cu2O electrochemical oscillator was shown to be less sensitive to changes in the temperature. The applied current density and pH were the two parameters which most perturbed the system. Interestingly, the frequency behaved nonmonotonically with a quadratic dependence. The multivariate analysis of both oscillators exhibited significant differences - while the homogenous oscillator displayed a linear dependence with the factors, the heterogeneous one revealed a more complex dependence with quadratic terms. Our results may contribute, for instance, in the synthesis of self-organized materials in which an accurate frequency selection is required and, depending on its value, different physicochemical properties are obtained.

Thermal assisted self-organization of calcium carbonate

Fabrication of mineral multi-textured architectures by self-organization is a formidable challenge for engineering. Current approaches follow a biomimetic route for hybrid materials based on the coupling of carbonate and organic compounds. We explore here the chemical coupling of silica and carbonate, leading to fabrication of inorganic–inorganic biomimetic structures known as silica-carbonate biomorphs. So far, biomorphic structures were restricted to orthorhombic barium, strontium, and calcium carbonate. We demonstrate that, monohydrocalcite a hydrous form of calcium carbonate with trigonal structure can also form biomorphic structures, thus showing biomorphic growth is not dictated by the carbonate crystal structure. We show that it is possible to control the growth regime, and therefore the texture and overall shape, by tuning the growth temperature, thereby shifting the textural pattern within the production of a given architecture. This finding opens a promising route to the fabrication of complex multi-textured self-organized material made of silica and chalk.

A monitoring device made of an anodic aluminum oxide template for plasma-induced charging potential measurements in the high-aspect-ratio trench structure.

A monitoring device is proposed to investigate the charge accumulation effects in a high-aspect-ratio trench structure. This monitoring device is made of an anodic aluminum oxide (AAO) template, which is a self-organized material with parallel pores, to demonstrate a high aspect ratio trench structure. A top electrode and bottom electrode were formed in the AAO contact structure for measuring electric potentials. These electrodes can be assumed to be electrically floating due to the very high input resistance of the measurement circuit. Therefore, the electric potentials resulting from the charge accumulation can be measured. In this paper, the fabrication process of the proposed device and experimental demonstrations are presented.

Highly Self-Organized Materials: Formation Mechanism and Electrochemical Synthesis

A class of intensively studied materials with application in areas where complex structures with precise geometry are needed (i.e. electronics), are the self-organized nanomaterials. Polymer, metallic and composite self-organized nanomaterials have been in researchers� attention the last decades. They are not only appealing scientifically, by revealing the intrinsic atomic and molecular interactions that might be difficult to detect otherwise but may also hold the key for the development of novel functional structures and devices. The different mechanisms and forces involved in the self-formation of organized nanostructures are discussed in the present manuscript. Further on, key formation fundamentals involved in the fabrication of self-organized nanostructures are described. Between the known manufacturing methods, the electrochemical synthesis is considered extremely simple and cost effective. On the other hand, it involves a wide range of synthesis parameters (e.g. voltage, electrolyte type, temperature, experiment duration, pH etc.) that may lead to the formation of ingenious structures with complex geometries at different length scales. Finally, some representative scientific investigations are mentioned together with applications of self-organized nanomaterials in different engineering and life areas.

Programming self-organizing multicellular structures with synthetic cell-cell signaling.

A common theme in the self-organization of multicellular tissues is the use of cell-cell signaling networks to induce morphological changes. We used the modular synNotch juxtacrine signaling platform to engineer artificial genetic programs in which specific cell-cell contacts induced changes in cadherin cell adhesion. Despite their simplicity, these minimal intercellular programs were sufficient to yield assemblies with hallmarks of natural developmental systems: robust self-organization into multidomain structures, well-choreographed sequential assembly, cell type divergence, symmetry breaking, and the capacity for regeneration upon injury. The ability of these networks to drive complex structure formation illustrates the power of interlinking cell signaling with cell sorting: Signal-induced spatial reorganization alters the local signals received by each cell, resulting in iterative cycles of cell fate branching. These results provide insights into the evolution of multicellularity and demonstrate the potential to engineer customized self-organizing tissues or materials.

Light‐Driven Reversible Transformation between Self‐Organized Simple Cubic Lattice and Helical Superstructure Enabled by a Molecular Switch Functionalized Nanocage

Self-organized stimuli-responsive smart materials with adjustable attributes are highly desirable for a plethora of device applications. Simple cubic lattice is quite uncommon in soft condensed matter due to its lower packing factor. Achieving a stable simple cubic soft lattice and endowing such a lattice with dynamic reconstruction capability solely by a facile light irradiation are of paramount significance for both fundamental studies and engineering explorations. Herein, an elegant stable self-organized simple cubic soft lattice, i.e., blue phase II, in a chiral liquid crystal (LC) system is disclosed, which is stable down to room temperature and exhibits both reversible lattice deformation and transformation to a helical superstructure, i.e., cholesteric LC, by light stimulation. Such an amazing trait is attained by doping a judiciously designed achiral photoresponsive molecular switch functionalized polyhedral oligomeric silsesquioxane nanocage into a chiral LC host. An unprecedented reversible collapse and reconstruction of such a high symmetric simple cubic blue phase II driven by light has been achieved. Furthermore, a well-defined conglomerate micropattern composed of simple cubic soft lattice and helical superstructure, which is challenging to fabricate in organic and inorganic crystalline materials, is produced using photomasking technology. Moreover, the promising photonic application based on such a micropattern is demonstrated.

Nano-Architecture of nitrogen-doped graphene films synthesized from a solid CN source

New synthesis routes to tailor graphene properties by controlling the concentration and chemical configuration of dopants show great promise. Herein we report the direct reproducible synthesis of 2-3% nitrogen-doped ‘few-layer’ graphene from a solid state nitrogen carbide a-C:N source synthesized by femtosecond pulsed laser ablation. Analytical investigations, including synchrotron facilities, made it possible to identify the configuration and chemistry of the nitrogen-doped graphene films. Auger mapping successfully quantified the 2D distribution of the number of graphene layers over the surface, and hence offers a new original way to probe the architecture of graphene sheets. The films mainly consist in a Bernal ABA stacking three-layer architecture, with a layer number distribution ranging from 2 to 6. Nitrogen doping affects the charge carrier distribution but has no significant effects on the number of lattice defects or disorders, compared to undoped graphene synthetized in similar conditions. Pyridinic, quaternary and pyrrolic nitrogen are the dominant chemical configurations, pyridinic N being preponderant at the scale of the film architecture. This work opens highly promising perspectives for the development of self-organized nitrogen-doped graphene materials, as synthetized from solid carbon nitride, with various functionalities, and for the characterization of 2D materials using a significant new methodology.

Study of the Tribotechnical Properties of a Cutting Tool Made of Sintered Powder Tool Materials

The research results on the wear of cutting tools made by sintering high-speed steel powders have been presented. It has been shown that powder tool materials based on high-speed steel additionally alloyed with titanium carbide have high wear resistance and can be classified as a new class of self-organized tool materials. As has been shown by the research, the wear resistance of these tools is 2–3.5 times higher than the wear resistance of standard high-speed steel tools.

Self-organizing materials built with DNA

Abstract