Spontaneous Phenomenon Research Articles

A Comprehensive Study of Effect of Maceral Content on Tendency of Spontaneous Coal Combustion Occurrence

Coal mining has many serious hazards, and the spontaneous combustion phenomenon is one of them. Many factors can influence the tendency for occurrence of this phenomenon. The maceral content is one of the coal inherent characteristics, which has a crucial aspect in the occurrence of this process. Until now, this parameter has not been discussed in a comprehensive study by the scientists. Thus a final conclusion about the effect of maceral content on spontaneous coal combustion is required. Maceral content is directly affected by the growth of coalification and origin of coal formation. This study aimed at developing a new statistical model for predicting the spontaneous coal combustion tendency based on the maceral content. In this work, firstly, 51 coal samples with a variety of maceral contents were collected for training data of the overall underground coal fields in Iran, and the Crossing Point Temperature (CPT) test was carried out on each coal sample. Then the method of regression analysis was used for modeling and predicting the spontaneous coal combustion tendency. For validation and testing, 11 coal samples of another coalfield were collected, the CPT test was carried out on each one of them, and the results obtained were compared using the regression equation. Validation of the developed model was checked by the F test. By examining the experimental results and comparing the CPT test values, it was found that with increase in the vitrinite and liptinite contents and decrease in the inertinite content, the coal samples displayed a higher tendency for spontaneous combustion. The results also showed that the spontaneous combustion tendency could be reliably predicted using the proposed model.

DETERMINATION OF COAL MICROELEMENTS BY INSTRUMENTAL ANALYSIS

In the mineral matter of coal there are microelements chemically bounded to organic matter or mineral impurities in various combinations that catalyzes the evolution / involution of a spontaneous combustion phenomenon as an accelerator in the oxidation reaction or which slows down these processes. Specialised literature analyzes the phenomenon of coal self-heating based on several theories of which we exemplify the theory of coal oxidation, the theory of pyrite and the theory of the microelements role in the process of coal oxidation. For the determination of these microelements in coal, the inductively coupled plasma atomic emission spectrometry method by means of which the mineral concentrations of hard coal and lignite samples were determined. The present paper proposes to perform a comparative analysis of the results obtained by laboratory determinations on samples taken from various coal basins (Valea Jiului, Motru, Jilt, Rovinari, Berbesti).

Putative role of adenosine A2A receptors in promoting remyelination through adult oligodendrogenesis in the EAE Model

Event Abstract Back to Event Putative role of adenosine A2A receptors in promoting remyelination through adult oligodendrogenesis in the EAE Model Marta A. Gomes1, 2, Joana M. Mateus1, 2, Ana M. Sebastião1, 2 and Sara Xapelli1, 2* 1 Institute of Pharmacology and Neurosciences, Faculty of Medicine, University of Lisbon, Portugal 2 Institute of Molecular Medicine, Faculty of Medicine, University of Lisbon, Portugal Multiple Sclerosis (MS) is a chronic neuroinflammatory autoimmune demyelinating disease of the central nervous system (CNS). MS pathogenesis begins with an exacerbated inflammatory response that deteriorates the myelin sheath, produced by oligodendrocytes (OLGs) in the CNS, which insulates neuronal axons. Myelinating OLGs result from the differentiation of oligodendrocyte progenitor cells (OPCs) present in the brain parenchyma but also from neural stem cells (NSCs) of the subventricular zone (SVZ) neurogenic niche. Previous studies have reported a spontaneous phenomenon of remyelination in MS, through the migration of OLGs to demyelinated areas. Furthermore, adenosine A2A Receptors (A2AR) have been shown to have a protective role against inflammation in Experimental Autoimmune Encephalomyelitis (EAE), an animal model of MS, attenuating the phenotype of the disease. However, A2AR role in modulating adult oligodendrogenesis under EAE pathogenesis has never been studied. Thus, this project aimed to assess the role of A2AR in promoting OLGs differentiation and myelination under EAE pathogenesis. Female C57BL/6 mice were immunized with MOG35-55 and injected with Pertussis toxin to induce EAE. EAE mice were administered in the lateral ventricle with vehicle or with A2AR agonist (CGS21680, 100 nM) for 26 days using micro-osmotic pumps. Behavioural tests were performed to evaluate EAE model progression, along with cellular and molecular analyses to assess A2AR agonist influence on inflammation, OLG differentiation and de- and remyelination. Overall, EAE disease incidence was of only 40% which constrained the significance of the results. EAE animals showed impaired performance in behavioral tests as EAE phenotype was progressing, although no differences were observed between the vehicle and the CGS21680 groups. Moreover, no tendencies for changes were observed at the molecular level, regarding either inflammatory and cell differentiation signaling pathways. Regarding demyelination, both luxol fast blue assay and immunohistochemical staining for myelin proteins showed that myelin amounts in both EAE vehicle and CGS21680 animals were similar to control animals. Taken together, EAE induction protocol and CGS21680 dose should be optimized to allow further conclusions on A2AR relevance for regenerative therapies in MS. Keywords: Multiple Sclerosis, EAE (experimental autoimmune encephalomyelitis), Adenosine A2A receptor (A2AR), Adult Oligodendrogenesis, remyelination Conference: XVI Meeting of the Portuguese Society for Neuroscience (SPN2019), Lisboa, Portugal, 30 May - 1 Jun, 2019. Presentation Type: Poster presentation Topic: Glia / Neuroinflammation Citation: Gomes MA, Mateus JM, Sebastião AM and Xapelli S (2019). Putative role of adenosine A2A receptors in promoting remyelination through adult oligodendrogenesis in the EAE Model. Front. Cell. Neurosci. Conference Abstract: XVI Meeting of the Portuguese Society for Neuroscience (SPN2019). doi: 10.3389/conf.fncel.2019.01.00008 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Feb 2019; Published Online: 27 Sep 2019. * Correspondence: Dr. Sara Xapelli, Institute of Pharmacology and Neurosciences, Faculty of Medicine, University of Lisbon, Lisbon, Portugal, sxapelli@medicina.ulisboa.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Marta A Gomes Joana M Mateus Ana M Sebastião Sara Xapelli Google Marta A Gomes Joana M Mateus Ana M Sebastião Sara Xapelli Google Scholar Marta A Gomes Joana M Mateus Ana M Sebastião Sara Xapelli PubMed Marta A Gomes Joana M Mateus Ana M Sebastião Sara Xapelli Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Street-art jako nowe zjawisko w sztuce – środek na gentryfikację miejskiego środowiska

The article deals with the genesis of street art, its transformation from a spontaneous phenomenon of the urban environment, to a phenomenon that has been recognized by the people and professionals and attracted the attention of expert artists. Successively, street art has transformed and is transforming into a specific type of contemporary art, in which various movements of international or regional character (graffiti, muralism) can be determined. The spread of street art as a phenomenon of art was promoted by the availability of information technologies and the activity of manufacturers of aerosol paints. In the process of development of street art, thanks to the participation of professional artists, the art techniques have emerged, which have an interconnection with the classical styles of art. Expanding the scope of applica­tion of street art products becomes a significant component of the sphere of spiritual production and requires modern organizational structures and associations, such as art centres and art clusters. It will contribute to the effectiveness of their activities, the popularization of street art as a means of art education of the population, the synthesis of experience. Crystallization of creative processes and thanks to the globalization, their transformation into the directions and styles of street art occur.

Influence of various electrolytes on the interaction of cetyltrimethylammonium bromide with tetradecyltrimethylammonium bromide at different temperatures and compositions: Experimental and theoretical investigation

Mixed micelle plays an imperative role in the solution chemistry and surface chemical applications. Conductivity measurement technique has been employed for studying the association properties of the mixed systems of two important cationic surfactants (cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB)) in absence/attendance of different electrolytes at varying temperatures. The physicochemical characteristics were examined in H2O and electrolytes solution (NaCl, Na2CO3 and Na3PO4) having identical ionic strength (I=10mmolkg−1) for pure TTAB and CTAB together with their mixture. In occurrence of electrolytes solution, the quantitative values of critical micelle concentration (cmc) are observed below the values obtained from the aqueous medium for pure along with mixed amphiphiles. The anions effectiveness in lowering the cmc value followed the order: PO43−>CO32−>Cl−. The cmcid values are found higher than the experimentally determined cmc values which suggest the subsistence of attractive interaction amid both amphiphiles. CTAB micellar mole fraction was assessed via applying specific recommended models such as Rubingh (X1Rub), Motomura (X1M), Rodenas (X1Rod) and their results suggest that the more contribution of CTAB in mixed micelles, and their values increase by enhance of concentration of CTAB. The activity coefficients (f1 and f2) values were observed to be beneath unity along with the negative β values for the entire cases viewing synergism (attractive) behavior. The negative Gibbs free energy (ΔG°m) values indicated the spontaneous association phenomena.

Magnetomechanical model for coating/substrate interface and its application in interfacial crack propagation length characterization

During the service process of remanufactured components, the stress and crack may occur at the interface between coating and substrate due to their mechanical property mismatch. Based on the spontaneous magnetization phenomenon in ferromagnetic materials, the stress distribution and crack propagation length along the interface can be characterized. In this paper, the magnetomechanical constitutive model for interface is established according to Timoshenko beam theory and Jiles' stress-magnetization model. The distributions of stress and residual magnetization along the interface are analyzed under the effect of typical three-point bending (TPB) load. The results show that the interfacial residual magnetization Mr can reflect the stress distribution very well and its peak value at supporting seat Mr3 is closely related to interfacial crack propagation length. In order to verify the theoretical model, the metal magnetic memory (MMM) technique is used to collect the residual magnetic field along the interface in the TPB testing. The experimental results are consistent with the theoretical predictions. They indicate that the magnetomechanical model for coating/substrate interface established in this paper can provide the theoretical support for magnetic non-destructive testing and the calculation results can be applied to the interfacial crack propagation length characterization in MMM.

Spontaneous formation of spin lattices in semimagnetic exciton-polariton condensates

An exciton-polariton microcavity that incorporates magnetic ions can exhibit a spontaneous self-trapping phenomenon which is an analog of the classical polaron effect. We investigate in detail the full model of a polariton condensate that includes pumping and losses, the spin degree of freedom, external magnetic field and energy relaxation. In the quasi-one-dimensional case, we show that the polaron effect can give rise to a spontaneous lattice of perfectly arranged polarization domains in an antiferromagnetic configuration. We find that partial polarization of the condensate at moderate magnetic field strengths facilitates the formation of such "polaron lattices", which are qualitatively different from self-trapped polarons that appear in a fully polarized condensate. Within the Bogoliubov-de Gennes approximation, we calculate the instability condition which marks the appearance of the patterns. Surprisingly, we find that the stability condition displays a discontinuity at the point of partial-full polarization threshold.

Experimental and theoretical investigation of micellization behavior of sodium dodecyl sulfate with cetyltrimethylammonium bromide in aqueous/urea solution at various temperatures

Mixed micelle formation behavior of cationic surfactant-cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS) in aqueous as well as in urea medium from 303.15 K to 323.15 K at 5 K interval was carried out by conductometric method. The differences between the experimental values of critical micelle concentrations (cmc) and ideal critical micelle concentrations (cmcid) illustrate the interaction between the amphiphiles studied. The values of micellar mole fraction ( $$\text{X}_1^{Rub}$$ (Rubingh), $$\text{X}_1^{M}$$ (Motomura), $$\text{X}_1^{Rod}$$ (Rodenas) and $$\text{X}_1^{id}$$ (ideal) of surfactant CTAB determined by different proposed models and outcome indicate high involvement of CTAB in SDS-CTAB mixed micellization, which enhance by means of the augment of mole fraction of CTAB. The negative value of interaction parameter (β) showed an attractive interaction involving CTAB and SDS. Activity coefficients were less than unity in all case, which also reveals the presence of interaction between CTAB & SDS. The negative $$\Delta{\text{G}}_m^0$$ values imply the spontaneous mixed micellization phenomenon. The attained values of $$\Delta{\text{H}}_m^0$$ were positive at inferior temperature, while negative at superior temperature. The negative $$\Delta{\text{H}}_m^0$$ values in urea (NH2CONH2) medium illustrate exothermic micellization process. The magnitudes of $$\Delta{\text{S}}_m^0$$ were positive in almost all cases. The excess free energy of mixed micelle formation (ΔGex) was found to be negative, which indicates the stability of mixed micelle as compared to the individual’s components micelles.

Biosorption of cationic dye onto "Phragmites australis" fibers: Characterization and mechanism

The problem of industrial wastewater pollution especially the textile industry is becoming more and more crucial and is pushing researchers to try to develop new, low cost and efficient industrial wastewater treatment processes. We present in this work the biosorption of a cationic model dye "Methylene Blue" by the fibers of a Tunisian biomass "Phragmites Australis" in batch system. It was shown that the highest dye removal was found at pH 8. The dye uptake was achieved by increasing the biomass assay up to 0.1 g for an initial dye concentration 10 mg/L. The results showed that the biosorved amount increases when the amount of biomass increases from 60% for 0.1 g of biomass to 72.25% for 0.5 g of biomass. The kinetic rate of pseudo-second order and Brouers-Sotolongo isotherm modeling is the most appropriate to describe the present biosorption phenomenon, thus assuming the fractal character of the process. The thermodynamic study reveals a spontaneous phenomenon of biosorption and confirms the chemisorption shown in desorption tests. The morphology of the different compounds of Phragmites australis fibers was studied by Boehm titration, FTIR, SEM and explained with different mechanisms reactions. The mechanism proposed involved hydrogen-bonding formations, electrostatic interactions and π-π interaction that show the importance of the carboxylic groups in the biosorption process.

Effectiveness of Hypnosis Techniques to Quit Smoking

Background: The main reason for carrying out this study was to realize that tobacco addicted are more than their beliefs, family, social life, religion, profession, and paradigms. Aim: The objective of this project was to help patients quit smoking through hypnosis techniques and, consequently, to help them face quitting methods more comfortably and safely and also avoid relapse. Methods: This project started with a biographical questionnaire, identification of smoker phases and some suggestion hypnotics are also evaluated through classic tests (vigils suggestions) and the Tellegen Absorption Scale. After collecting the data, we proceeded to an intervention plan that in synthesis had the following phases: sessions 3 and 4 aimed at obtaining a hypnotic trance with sufficient stability and depth, we value the state achieved as a medium-deep trance and spontaneous hypnotic phenomena. The next sessions, 5 and 6, we apply as ego strengthening and suggestions to demystify previously recorded thoughts, feelings and, consequently, behavior. Sessions 7 we explain the concept and importance of self-hypnosis. Results: The quantitative results will be presented here to show the effectiveness of the project developed. The most important information is the number of people who interrupted tobacco dependence: 16 (80%) out of 20 quit smoking, of which 10 (50%) were men and 10 (50%) were women. Four patients (20%) did not complete the treatment, 2 men and 2 women. Conclusion: It was possible to verify that quitting smoking through hypnosis is effective, because the smokers can transform their cognitive system and, thereby, they can change, naturally, their biopsychological paradigms in all contexts of their lives.

Optimization of techniques for the extinction and prevention of coal fires produced in final walls as a result of spontaneous combustion in the Cerrejón mine-Colombia.

The Cerrejón mine has identified fires in its coal production seams for a few years in its operation. Fires are produced as a result of spontaneous combustion phenomena. Coal spontaneous combustion is a phenomenon that occurs naturally during coal oxidation when exposed to atmospheric conditions, due to erosion processes, geological and mining practices. This phenomenon is a subject of great concern in the world's coal mines, as it causes environmental problems, generating emissions of polluting gases into the atmosphere and economic losses due to reserve consumption. In this work, we seek to optimize the prevention and extinction processes used by the company. In terms of prevention, the current state was evaluated and alternatives, such as diluted bitumen and brine (combustion inhibitor), cement/slaked lime, fine sand cement, and clinker/slaked lime were developed to avoid ignition. As far as extinction is concerned, an additional methodology for medium magnitude fires was determined, in order to improve extinction times through the use of cooling. It was determined that the bitumen/brine has better adhesion and durability properties in the coal seam. Extinction through reagent cooling is quicker, thus improving the backhoe's productivity and minimizing costs.

Tuning Transition-Metal Dichalcogenide Field-Effect Transistors by Spontaneous Pattern Formation of an Ultrathin Molecular Dopant Film.

Spontaneous pattern formation is an energetically favorable process and is shown in nature in molecular-scale assembly, biological association, and soft material organizations. The opposite regime, the artificial process, which is widely applied to the fabrication of semiconducting devices, such as lithographic techniques, requires enormous amounts of energy. Here, we propose a concept of tuning the properties of semiconducting MoS2 and WSe2 devices using the spontaneous pattern formation of adjacent molecular films. The film used was a 10 nm thick ultrathin film of a molecular electron dopant, which exhibited spontaneous pattern formation and dynamically transformed the morphology of tiny holes, a network, a maze, and dots on substrates, including SiO2, MoS2, and WSe2. These patterns were exhibited only when the film came in contact with water and was tuned with temperature and time. The specific lengths of the patterns were less than 200 nm, which is sufficiently smaller than the exfoliated ∼10 μm semiconducting MoS2 and WSe2 flakes. The properties of the field-effect devices of MoS2 and WSe2 were found to be modified according to the pattern formation process of the ultrathin molecular film on the device. This concept applies the spontaneous patterning phenomena shown in nature to the fabrication and optimization of electronic devices by using molecular films and their responses to the external environment.

Two Birds with One Stone: Spontaneous Size Separation and Growth Inhibition of Femtosecond Laser-Generated Surfactant-Free Metallic Nanoparticles via ex Situ SU-8 Functionalization.

Laser ablation in liquids (LAL) offers a facile technique to develop a large variety of surfactant-free nanomaterials with high purity. However, due to the difficulty in the control of the particle synthesis process, the as-prepared nanomaterials always have a broad size distribution with a large polydispersity (σ). Surfactant-free properties can also cause problems with particle growth, which further increases the difficulty in size control of the colloids. Therefore, searching for strategies to simultaneously unify the sizes of colloids and inhibit particle growth has become significantly important for LAL-synthesized nanomaterials to be extensively used for biological, catalytic, and optical applications, in which fields particle size plays an important role. In this work, we present a facile way to simultaneously realize these two goals by ex situ SU-8 photoresist functionalization. Ag nanoparticles (NPs) synthesized by femtosecond laser ablation of silver in acetone at laser powers of 300 and 600 mW were used as starting materials. The synthesized Ag NPs have a broad size distribution between 1 and 200 nm with an average size of ca. 5.9 nm and σ of 127–207%. After ex situ SU-8 functionalization and 6 months storage, most particles larger than 10 nm become aggregates and precipitate, which makes the size distribution narrow with an average diameter of 4–5 nm and σ of 48–78%. The precipitation process is accompanied by the decrease in colloid mass from the initial ∼0.2 to 0.10–0.11 mg after ex situ SU-8 functionalization and 6 months colloid storage. Morphology analysis indicates that ex situ SU-8 functionalization inhibits the particle growth into polygonal nanocrystals. Radical polymerization of SU-8 on Ag NPs is considered to be the reason for both spontaneous size separation and growth inhibition phenomena. Benefiting from Ag NPs embedment and acetone dissolution, the glass-transition temperature of SU-8 photoresist increased from 314 to 331 °C according to thermogravimetric analysis. The universality of ex situ SU-8 functionalization-induced growth inhibition and size separation behaviors is further proved using the Au colloids generated by LAL in acetone. This work is expected to provide a new route for better size control of LAL-synthesized colloids via ex situ photoresist functionalization, although a half of colloidal mass is wasted due to radical polymerization-induced colloidal precipitation.

Superposition of conventional and spontaneous exchange bias in a Ni50Mn34In13Fe3 magnetic shape memory alloy

The conventional exchange bias and spontaneous exchange bias are two interesting but fundamentally different effects in Mn rich Ni-Mn-Z magnetic shape memory alloys. Previous investigations show that these two phenomena appear separately. Here, we report that the conventional and spontaneous exchange bias phenomena coexist in a Ni50Mn34In13Fe3 alloy and the superposition of them increases the total exchange bias of the alloy. Our results suggest that the canonical spin glass and super spin glass may coexist and are embedded in the antiferromagnetic matrix of the martensite, through properly tuning the temperature-field history, which further results in the superposition of conventional and spontaneous exchange bias for this alloy. The interfacial interaction between the canonical spin glass and the antiferromagnetic matrix forms during field cooling process, which results in the conventional exchange bias. Moreover, the application of large magnetic field during the isothermal magnetization process changes the superspin glass into a superferromagnetic state, which interacts with the antiferromagnetic matrix at the interface, causing the spontaneous exchange bias. The superposition of exchange bias provides an effective way to achieve large exchange bias in materials.

Spontaneous growth of gauge fields in gravity through the Higgs mechanism

We introduce gravity theories featuring spontaneously growing gauge fields where the growth is due to the Higgs mechanism. The underlying physics is inspired by the spontaneous scalarization phenomena in scalar-tensor theories. The tachyonic instability that causes the growth in spontaneous scalarization and its analog for vector fields is introduced not as an explicit potential term, but through a scalar coupling using a Higgs field. The resulting theories are distinct from previous examples of spontaneous tensorization in that they respect the gauge symmetry at the level of the action. Our results are valid for both Abelian and non-Abelian gauge theories, and this is the first study of the spontaneous growth of the latter. We discuss astrophysical implications of these theories and argue their relevance especially in the strong gravity regime.

The misunderstanding of Clausius statement of the second law of thermodynamics and its aftermath

As with the first law of thermodynamics, the second law of thermodynamics has been proven by countless examples. The Clausius statement of the second law of thermodynamics given in most of the literatures is “heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time”. After carefully studying Clausius’ mechanical theory of heat published from 1850 to 1865, we found that this is not true. Actually, Clausius already clearly stated that the second law of thermodynamics is “Theorem of the equivalence of the transformation of work to heat and the transformation of heat at a higher to a lower temperature”. The former statement is only a basic principle that can lead to the theorem of the equivalence of transformations. In addition, all processes in derivation of the theorem of the equivalence of transformations and proof of the equivalence between Clausius statement and Kelvin statement are reversible processes. The statement “Heat can never pass from a colder to a warmer body without some other change” only illuminates the spontaneous natural phenomenon in opposite direction that heat flows from high temperature to low temperature, which tells that heat at different temperatures are nonequivalent. Admittedly, Clausius discussed the process irreversibility and thereby obtained Clausius Inequality. But he only used the state change to measure the process irreversibility, which did not involve the concept of space, time and speed. Clausius just expressed that the process irreversibility will reduce heat efficiency and did not focus exclusively on the laws of process irreversibility. The misunderstanding of viewing Clausius statement as “Heat can never pass from a colder to a warmer body without some other change”, easily produces such a viewpoint that the second law of thermodynamics is the rule about process direction and irreversibility, consequently leading to the faulty assumption that the minimum entropy generation principle can be used to derive the transport law of heat conduction and optimize the heat transfer process. However, theory and practice analyses have proven that it is problematic. The action of heat conduction process is just half of entransy dissipation, whose variation points to the linear Fourier’s heat conduction law, which thereby has a better application for the optimization of heat transfer process. Transfer process has different laws from conversion process, so they should be treated distinguishingly and analyzed with different methods and indexes. It is not advisable to simply put heat transfer issues into category of non-equilibrium thermodynamics.

Spontaneous Shape Alteration and Size Separation of Surfactant-Free Silver Particles Synthesized by Laser Ablation in Acetone during Long-Period Storage.

The technique of laser ablation in liquids (LAL) has already demonstrated its flexibility and capability for the synthesis of a large variety of surfactant-free nanomaterials with a high purity. However, high purity can cause trouble for nanomaterial synthesis, because active high-purity particles can spontaneously grow into different nanocrystals, which makes it difficult to accurately tailor the size and shape of the synthesized nanomaterials. Therefore, a series of questions arise with regards to whether particle growth occurs during colloid storage, how large the particle size increases to, and into which shape the particles evolve. To obtain answers to these questions, here, Ag particles that are synthesized by femtosecond (fs) laser ablation of Ag in acetone are used as precursors to witness the spontaneous growth behavior of the LAL-generated surfactant-free Ag dots (2–10 nm) into different polygonal particles (5–50 nm), and the spontaneous size separation phenomenon by the carbon-encapsulation induced precipitation of large particles, after six months of colloid storage. The colloids obtained by LAL at a higher power (600 mW) possess a greater ability and higher efficiency to yield colloids with sizes of <40 nm than the colloids obtained at lower power (300 mW), because of the generation of a larger amount of carbon ‘captors’ by the decomposition of acetone and the stronger particle fragmentation. Both the size increase and the shape alteration lead to a redshift of the surface plasmon resonance (SPR) band of the Ag colloid from 404 nm to 414 nm, after storage. The Fourier transform infrared spectroscopy (FTIR) analysis shows that the Ag particles are conjugated with COO– and OH– groups, both of which may lead to the growth of polygonal particles. The CO and CO2 molecules are adsorbed on the particle surfaces to form Ag(CO)x and Ag(CO2)x complexes. Complementary nanosecond LAL experiments confirmed that the particle growth was inherent to LAL in acetone, and independent of pulse duration, although some differences in the final particle sizes were observed. The nanosecond-LAL yields monomodal colloids, whereas the size-separated, initially bimodal colloids from the fs-LAL provide a higher fraction of very small particles that are <5 nm. The spontaneous growth of the LAL-generated metallic particles presented in this work should arouse the special attention of academia, especially regarding the detailed discussion on how long the colloids can be preserved for particle characterization and applications, without causing a mismatch between the colloid properties and their performance. The spontaneous size separation phenomenon may help researchers to realize a more reproducible synthesis for small metallic colloids, without concern for the generation of large particles.

Pressure-driven spontaneous ion concentration polarization using an ion-selective membrane

In this study, the spontaneous ion concentration polarization phenomenon induced by pressure via a cation-selective membrane was theoretically and experimentally investigated. Unlike conventional electrokinetic ion concentration polarization, which uses electric current as a driving flux of cations through the membrane, advection caused by pressure is used as a transmembrane driving flux of cations to spontaneously and stably form an ion depletion zone in the present ion concentration polarization technique. The ion depletion zone produced in a simple experimental setup was used to filter electrolyte and preconcentrate ions and microparticles. Different from the general assumption of the negligible thickness of the electric double layer in microchannels, the low concentration in the ion depletion zone considerably increased the length of the electric double layer. This enhanced the formation of the ion depletion zone. The present results can improve the understanding on ion transport in the ion concentration polarization system and can be utilized to develop a portable water desalination device for rural/remote areas and for preconcentrating biomolecules.

Biomimetic, Flexible, and Self-Healable Printed Silver Electrode by Spontaneous Self-Layering Phenomenon of a Gelatin Scaffold

Organic-inorganic hybrid layer-by-layer (LBL) composite structures can not only increase the strength and ductility of materials but also well disperse nanomaterials for better-conducting pathways. Here, we discovered the self-assembly process of an organic and silver (Ag) LBL hybrid structure having excellent sustainability during the long-term bending cycle. During the assembly process, the organic and Ag hybrid structure can be self-assembled into a layered structure. Unlike other conventional LBL fabrication processes, we applied the hydrogel scaffold of a biological polymer, which can spontaneously phase separate into an LBL structure in a water/alcohol solvent system. This new hydrogel-based Ag LBL patterns can successfully be printed on a flexible polyimide film without nozzle-clogging problem. Although these Ag LBL patterns cracked during the bending cycle, carbonized organic compounds between the Ag layers help to self-heal within few minutes at a low temperature (<80 °C). On the basis of our new hydrogel-based Ag ink, we could fabricate a fully printed reliable microscale flexible heater. We expect that our self-layering phenomenon can expand to the broad research field of flexible electronics in the near future.

Introduction: Solidarity and Utopia

Introduction: Solidarity and Utopia