Cooperative Phenomena Research Articles

Landau theory for non-symmetry-breaking electronic instability coupled to symmetry-breaking order parameter applied to Prussian blue analog

Different types of ordering phenomena may occur during phase transitions, described within the universal framework of the Landau theory through the evolution of one, or several, symmetry-breaking order parameter h. In addition, many systems undergo phase transitions related to an electronic instability, in the absence of a symmetry-breaking and eventually described through the evolution of a totally symmetric order parameter q linearly coupled to volume change. Analyzing the coupling of a non-symmetry-breaking electronic instability, responsible for volume strain, to symmetry-breaking phenomena is of importance for many systems in nature and here we show that the symmetry-allowed qh2 coupling plays a central role. We use as case study the rubidium manganese hexacyanoferrate Prussian blue analogue, exhibiting phase transitions with hysteresis that may exceed 100 K, and based on intermetallic charge transfer (CT). During the phase transition, the intermetallic CT described through the evolution of q is coupled to cubic-tetragonal ferroelastic symmetry-breaking described through the evolution of h. In this system, the symmetry-breaking and non-symmetry breaking deformations have similar amplitudes but the large volume strain is mainly due to CT. We analyze both the ferroelastic and the CT features of the phase transition within the frame of the Landau theory, taking into account the qh2 coupling, stabilizing concomitant CT and Jahn-Teller distortion. The phase diagrams obtained with this model are in good qualitative agreement with various experimental findings and apply to diverse families of materials undergoing Mott transition, spin-crossover, neutral-ionic transition, for which isostructural electronic instability driving volume strain can couple to symmetry-breaking or not, create phase transition lines and drive cooperative phenomena.

Size-dependent magnetic hardening in CoFe2O4 nanoparticles: effects of surface spin canting

Magnetic cobalt ferrite CoFe2O4 is rich with physical phenomena, owing to its crystalline and magnetic structures. When such a ferrite is produced in a modulated nanoscale size, the increased specific surface area gives rise to even more complex behavior in its magnetism, particularly in relation to magnetic hardening. By correlating nanoparticle size (from 3.5 nm to 80 nm) with crystallite size and magnetic properties, we can observe interesting relations between particle size and magnetic coercivity. On exceeding the superparamagnetic limit of about 10 nm, room-temperature coercivity and remanence values are found to increase with increasing nanoparticle size, up to a maximum value of 4.1 kOe and 52 emu g−1, respectively, at a size of approximately 45 nm. Above this critical size, the nanoparticles are comprised of multiple crystallites, and demonstrate the existence of a cooperative phenomenon, the so-called interaction domains, which leads to a decrease in coercivity and remanence values. More interestingly, the ultrasmall-sized CoFe2O4 nanoparticles (3.5–16 nm) show an anomalous coercivity enhancement and irreversible behavior at low temperatures, as compared to the large-sized nanoparticles, which may be ascribed to enhanced effective magnetic anisotropy due to the surface spin-canting effect. Furthermore, training behavior in the exchange bias field, together with field-dependent blocking behavior, indicate that ultrasmall CoFe2O4 nanoparticles possess highly frustrated surface spins, which rearrange much more slowly than their interior spins, resulting in magnetic hardening at low temperatures.

Platelet adhesion and aggregate formation controlled by immobilised and soluble VWF

BackgroundIt has been demonstrated that von Willebrand factor (VWF) mediated platelet-endothelium and platelet-platelet interactions are shear dependent. The VWF’s mobility under dynamic conditions (e.g. flow) is pivotal to platelet adhesion and VWF-mediated aggregate formation in the cascade of VWF-platelet interactions in haemostasis.ResultsCombining microfluidic tools with fluorescence and reflection interference contrast microscopy (RICM), here we show, that specific deletions in the A-domains of the biopolymer VWF affect both, adhesion and aggregation properties independently. Intuitively, the deletion of the A1-domain led to a significant decrease in both adhesion and aggregate formation of platelets. Nevertheless, the deletion of the A2-domain revealed a completely different picture, with a significant increase in formation of rolling aggregates (gain of function). We predict that the A2-domain effectively ‘masks’ the potential between the platelet glycoprotein (GP) Ib and the VWF A1-domain. Furthermore, the deletion of the A3-domain led to no significant variation in either of the two functional characteristics.ConclusionsThese data demonstrate that the macroscopic functional properties i.e. adhesion and aggregate formation cannot simply be assigned to the properties of one particular domain, but have to be explained by cooperative phenomena. The absence or presence of molecular entities likewise affects the properties (thermodynamic phenomenology) of its neighbours, therefore altering the macromolecular function.

Dissipation-induced bistability in the two-photon Dicke model

The Dicke model is a paradigmatic quantum-optical model describing the interaction of a collection of two-level systems with a single bosonic mode. Effective implementations of this model made it possible to observe the emergence of superradiance, i.e., cooperative phenomena arising from the collective nature of light-matter interactions. Via reservoir engineering and analogue quantum simulation techniques, current experimental platforms allow us not only to implement the Dicke model but also to design more exotic interactions, such as the two-photon Dicke model. In the Hamiltonian case, this model presents an interesting phase diagram characterized by two quantum criticalities: a superradiant phase transition and a spectral collapse, that is, the coalescence of discrete energy levels into a continuous band. Here, we investigate the effects of both qubit and photon dissipation on the phase transition and on the instability induced by the spectral collapse. Using a mean-field decoupling approximation, we analytically obtain the steady-state expectation values of the observables signaling a symmetry breaking, identifying a first-order phase transition from the normal to the superradiant phase. Our stability analysis unveils a very rich phase diagram, which features stable, bistable, and unstable phases depending on the dissipation rate.

Flagellar length control in biflagellate eukaryotes: time-of-flight, shared pool, train traffic and cooperative phenomena

Flagella of eukaryotic cells are transient long cylindrical protrusions. The proteins needed to form and maintain flagella are synthesized in the cell body and transported to the distal tips. What ‘rulers’ or ‘timers’ a specific type of cells use to strike a balance between the outward and inward transport of materials so as to maintain a particular length of its flagella in the steady state is one of the open questions in cellular self-organization. Even more curious is how the two flagella of biflagellates, like Chlamydomonas reinhardtii, communicate through their base to coordinate their lengths. In this paper we develop a stochastic model for flagellar length control based on a time-of-flight (ToF) mechanism. This ToF mechanism decides whether or not structural proteins are to be loaded onto an intraflagellar transport (IFT) train just before it begins its motorized journey from the base to the tip of the flagellum. Because of the ongoing turnover, the structural proteins released from the flagellar tip are transported back to the cell body also by IFT trains. We represent the traffic of IFT trains as a totally asymmetric simple exclusion process (TASEP). The ToF mechanism for each flagellum, together with the TASEP-based description of the IFT trains, combined with a scenario of sharing of a common pool of flagellar structural proteins in biflagellates, can account for all key features of experimentally known phenomena. These include ciliogenesis, resorption, deflagellation as well as regeneration after selective amputation of one of the two flagella. We also show that the experimental observations of Ishikawa and Marshall are consistent with the ToF mechanism of length control if the effects of the mutual exclusion of the IFT trains captured by the TASEP are taken into account. Moreover, we make new predictions on the flagellar length fluctuations and the role of the common pool.

Governing Common-Property Assets: Theory and Evidence from Agriculture

This paper introduces a refined approach to conceptualising the commons in order to shed new light on cooperative practices. Specifically, it proposes the novel concept of Common-Property Assets (CPAs). CPAs are exclusively human-made resources owned under common-property ownership regimes. Our CPA model combines quantity (the flow of resource units available to members) and quality (the impact produced on the community by the members’ appropriation of the resource flow). While these two dimensions are largely pre-existing in the conventional case of natural common-pool resources, they directly depend on members’ collective action in CPAs. We apply this theoretical framework to farm machinery sharing agreements—a widespread grassroots cooperative phenomenon in agriculture—using a systematic literature review to generalise the findings from a sample of 54 studies published from 1950 to 2018. Our findings show that in successful CPAs, members endorse and do not deviate from a quantity-quality equilibrium that is collectively agreed upon. Despite the existence of thresholds for both quantity and quality due to (axiological) membership heterogeneity, qualitative changes in respect of the common good are possible in CPAs that promote democratic practices. Our study has potentially strong implications for developing ethics in cooperatives and the sustainable development of communities worldwide.

Evolution of Cooperation in the Presence of Higher-Order Interactions: From Networks to Hypergraphs.

Many real systems are strongly characterized by collective cooperative phenomena whose existence and properties still need a satisfactory explanation. Coherently with their collective nature, they call for new and more accurate descriptions going beyond pairwise models, such as graphs, in which all the interactions are considered as involving only two individuals at a time. Hypergraphs respond to this need, providing a mathematical representation of a system allowing from pairs to larger groups. In this work, through the use of different hypergraphs, we study how group interactions influence the evolution of cooperation in a structured population, by analyzing the evolutionary dynamics of the public goods game. Here we show that, likewise to network reciprocity, group interactions also promote cooperation. More importantly, by means of an invasion analysis in which the conditions for a strategy to survive are studied, we show how, in heterogeneously-structured populations, reciprocity among players is expected to grow with the increasing of the order of the interactions. This is due to the heterogeneity of connections and, particularly, to the presence of individuals standing out as hubs in the population. Our analysis represents a first step towards the study of evolutionary dynamics through higher-order interactions, and gives insights into why cooperation in heterogeneous higher-order structures is enhanced. Lastly, it also gives clues about the co-existence of cooperative and non-cooperative behaviors related to the structural properties of the interaction patterns.

The temperature of maximum density for amino acid aqueous solutions. An experimental and molecular dynamics study

The temperature of maximum density (TMD) for aqueous solutions of seven amino acids has been experimentally determined by means of density measurements versus temperature. The selected amino acids have been arginine, cysteine, glutamic acid, glutamine, lysine, methionine, and threonine. The TMD dependence against composition has been obtained from the experimental data and characterized through the Despretz constant. All amino acids induce a depression in the TMD as compared with that of pure water. If the mole fraction is selected as composition variable, a clear dependence against amino acid molar mass is observed, which disappears when TMDs are represented versus mass fraction; almost all data shrink onto a single straight line. It must be pointed out that the TMD depressions for all studied amino acids are quite larger than those previously observed for proteins. This suggests that TMDs for proteins cannot be explained as a simple, additive result of its constituents, and, therefore complex cooperative phenomena seem to take place. The partial molar volume at infinite dilution has been obtained from density data, and a consistency test between its temperature dependence and that of temperature of maximum density versus composition has been performed, obtaining satisfactory results. A molecular dynamics study for all the studied systems has been also carried out. Amino acids have been modeled through the OPLS-AA force field, whereas the TIP4P/2005 model was used for water. The temperature of maximum density and partial molar volume have been calculated from the simulated density, and the results are compared with experimental data. Although the agreement is only fair, similar qualitative trends were obtained. The simulated Despretz constants are smaller than the experimental ones, a result that was already previously observed for methanol aqueous solutions. A structural analysis of water molecules in solution along the MD trajectories showed no enhancement of ice-like structures in complete agreement with the TMD decrease with concentration.

Multilevel Resistance Switching and Enhanced Spin Transition Temperature in Single- and Double-Molecule Spin Crossover Nanogap Devices

Spin crossover (SCO) molecules are promising bi-stable magnetic switches with applications in molecular spintronics. However, little is known about the switching effects of a single SCO molecule when it is confined between two metal electrodes. Here we examine the switching properties of a [Fe(III)(EtOSalPet )(NCS)] SCO molecule that is specifically tailored for surface deposition and binding to only one gold electrode in a nanogap device. Temperature dependent conductivity measurements on SCO molecule containing electromigrated gold break junctions show voltage independent telegraphic-like switching between two resistance states at temperature below 200 K. The transition temperature is very different from the transition temperature of 83 K that occurs in a bulk film of the same material. This indicates that the bulk, co-operative SCO phenomenon is no longer preserved for a single molecule and that the surface interaction drastically increases the temperature of the SCO phenomenon. Another key finding of this work is that some devices show switching between multiple resistance levels. We propose that in this case, two SCO molecules are present within the nanogap with both participating in the electronic transport and switching.

Coexistence of a charge density wave and superconductivity in the cluster compound K2Mo15Se19

The competition between charge density wave (CDW) and superconductivity is a central theme in condensed-matter physics with ramifications to correlated electron systems and high-temperature superconductivity. While the emergence of superconductivity is often observed upon suppressing the CDW transition by tuning the chemical composition or the external pressure, their coexistence has been reported in only a handful of materials, with the cuprates being the most prominent example. Here, we demonstrate that both cooperative electronic phenomena coexist in the cluster compound ${\mathrm{K}}_{2}\mathrm{M}{\mathrm{o}}_{15}\mathrm{S}{\mathrm{e}}_{19}$. The CDW transition sets in at ${T}_{\mathrm{CDW}}=\phantom{\rule{0.16em}{0ex}}114\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, accompanied by a commensurate periodic modulation of the crystal lattice along the $c$ axis evidenced by electron diffraction. Bulk type-II superconductivity develops upon further cooling below ${T}_{c}=\phantom{\rule{0.16em}{0ex}}2.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The presence of similar signatures of CDW ordering in other ${\mathrm{A}}_{2}\mathrm{M}{\mathrm{o}}_{15}\mathrm{S}{\mathrm{e}}_{19}$ compounds shows that this electronic instability may be ubiquitous in these compounds, providing a novel family where the interplay between CDW and superconductivity may be systematically investigated.

Synergetics: The cooperative phenomenon in multi-compressions S-CO2 power cycles

Abstract Mature power plant uses regenerative steam Rankine cycle to achieve excellent performance, but there is a lack of general approach for gas Brayton cycle. Here, synergetics is introduced to construct multi-compressions S-CO2 cycle for the first time. Our work starts from the analysis of recompression cycle (RC). RC is decoupled into two simple Brayton cycles (SCs). We show that at the optimal split ratio of flow rate, the mixing stream coming from the two subsystems does not generate exergy destruction, and the heat transfer induced exergy destruction is controlled to an acceptable level. Thus, the two subsystems are synergistic to have the efficiency reinforcing feedback. This finding inspires us to construct multi-compressions cycle. For example, the tri-compressions cycle (TC) is built by cooperation between RC and SC, and the four-compressions cycle (FC) is formed based on TC and SC. At the main vapor parameters 550 °C/20 MPa, thermal efficiencies are increased from 47.43% for RC to 49.47% for TC. A regime map is presented to select multi-compressions cycle based on main vapor parameters. We state that both of multi-compressions and reheating are effective. The combination of both approaches further improves system performance, but multi-compressions are preferable because the high temperature induced heat transfer issue can be avoided. This work fills the gap on how to reach excellent performance for gas Brayton cycle driven by various heat sources such as nuclear energy, solar energy and fossil energy etc.

Competitive devitrification and metastable phase selection in amorphous Al–Sm

Competitive phase selection during devitrification of Al–Sm glassy alloys is investigated for compositions ranging from 9.0 to 14.1 at% Sm. The crystallization response under isothermal and constant-heating-rate treatments is observed to involve metastable phases that lie well beneath (energetically above) the equilibrium landscape. Certain phases have also been shown to contain particular sub-crystalline atomic motifs that may be present and even dominant in the undercooled liquid and glass. Experimentally observed structures and associated chemical variations are investigated within the context of comprehensive solution-based thermodynamic models and the corresponding relationship between driving force and chemical partitioning. It is found that initial selection of complex large-unit-cell intermetallic phases is largely governed by the energetics of the partitionless or nearly partitionless crystallization transition. Evidence from transmission electron microscopy and small-angle X-ray scattering further suggests that cooperative precipitation phenomena may be operative and instrumental in alleviating the excess solute burden, as might be expected under conditions of limited atomic transport.

Collapse and cavitation during the drying of water-saturated PDMS sponges with closed porosity.

In this paper, we study the drying of water-saturated porous polydimethylsiloxane (PDMS) elastomers with closed porosity in which the evaporation of water is possible only via the diffusion across PDMS. Starting from water/PDMS emulsions, we fabricate soft macroporous samples with different pore diameter distributions and average diameters ranging from 10 to 300 μm. In these materials, the drying may lead to either a collapsed state with low porosity or the cavitation and reopening of a fraction of the pores. Using optical microscopy and porosity measurements, we showed the influence of the pore diameters and interactions on the result of drying. At pore diameters lower than 30 μm, the majority of pores remain collapsed. We attribute the permanence of the collapse of most small pores to a low probability of cavitation and to the adhesion of the pore walls. Pores with diameters larger than 100 μm reopen via cavitation of the water they contain. The behavior of pores with diameters ranging from 30 to 100 μm depends on the porosity and drying temperature. We also visualize collective cavitation upon the drying of sponges initially saturated with sodium chloride solution. In this case, the cavitation in the largest pores leads to the reopening of small pores in a neighboring zone of the sample. To our knowledge, our results present the first experimental proof of the pore-size-dependent and cooperative nature of the response of soft sponges with closed porosity to drying.

Using light intensity to control reaction kinetics and reversibility in photomechanical crystals.

4-Fluoro-9-anthracenecarboxylic acid (4F-9AC) is a thermally reversible (T-type) photomechanical molecular crystal. The photomechanical response is driven by a [4 + 4] photodimerization reaction, while the photodimer dissociation determines the reset time. In this paper, both the chemical kinetics of dimer dissociation (using a microscopic fluorescence-recovery-after-photobleaching experiment) and mechanical reset dynamics (by imaging bending microneedles) for single 4F-9AC crystals are measured. The dissociation kinetics depend strongly on the initial concentration of photodimer, slowing down and becoming nonexponential at high dimer concentrations. This dose-dependent behavior is also observed in the mechanical response of bending microneedles. A new feature in the photomechanical behavior is identified: the ability of a very weak control beam to suppress dimer dissociation after large initial dimer conversions. This phenomenon provides a way to optically control the mechanical response of this photomechanical crystal. To gain physical insight into the origin of the nonexponential recovery curves, the experimental results are analyzed in terms of a standard first-order kinetic model and a nonlinear Finke–Watzky (FW) model. The FW model can qualitatively reproduce the transition from exponential to sigmoidal recovery with larger initial conversions, but neither model can reproduce the suppression of the recovery in the presence of a weak holding beam. These results highlight the need for more sophisticated theories to describe cooperative phenomena in solid-state crystalline reactions, as well as demonstrating how this behavior could lead to new properties and/or improved performance in photomechanical materials.

Observation and Active Control of a Collective Polariton Mode and Polaritonic Band Gap in Few-Layer WS2 Strongly Coupled with Plasmonic Lattices.

Two-dimensional semiconductors host excitons with very large oscillator strengths and binding energies due to significantly reduced carrier screening. Two-dimensional semiconductors integrated with optical cavities are emerging as a promising platform for studying strong light-matter interactions as a route to explore a variety of exotic many-body effects. Here, in few-layered WS2 coupled with plasmonic nanoparticle lattices, we observe the formation of a collective polaritonic mode near the exciton energy and the formation of a complete polariton band gap with energy scale comparable to the exciton-plasmon coupling strength. A coupled oscillator model reveals that the collective mode arises from the cooperative coupling of the excitons to the plasmonic lattice diffraction orders via exciton-exciton interactions, leading to ultrastrong coupling. The emergence of the collective mode is accompanied by a superlinear increase of the polariton mode splitting as a function of the square root of the exciton oscillator strength. The presence of these many body effects, which are enhanced in systems which lack bulk polarization, not only allows the formation of a collective mode with periodically varying field profiles, but also further enhances the exciton-plasmon coupling. By integrating the hybrid WS2-plasmonic lattice device with a field-effect transistor, we demonstrate active tuning of the collective mode and the polariton band gap. We also report electrically tunable waveguiding in the polariton band gap region through a line defect, which can be turned off with gate bias that can extinguish the collective mode and the polariton band gap. These systems provide new opportunities for obtaining a deeper and systematic understanding of many body cooperative phenomena in two-dimensional materials coupled with periodic photonic systems and for designing more complex and actively controllable polaritonic devices including switchable polariton lasers, waveguides, and optical logical elements.

Cooperative evolution in pedestrian room evacuation considering different individual behaviors

Cooperative phenomenon is common in pedestrian evacuation, though in some cases the evacuation environment is competitive. Knowing how the cooperation evolves is of considerable importance since it plays an essential role in the understanding of the entire evacuation process. In this work, we study the evolution of cooperation in pedestrian room evacuation mixed with different individual behaviors by means of a cellular automaton (CA) model coupled with a spatial game. In the game, each agent interacts with its immediate neighbors and plays for the expected evacuation time which depends on its surroundings. Agents have one of the two possible modes of strategy to choose that lead to be either patient or impatient. Agents’ strategies are updated in parallel according to two kinds of individual behaviors: cherry-picking behavior and imitation behavior. This model shows how evacuation conditions and agents’ individual behaviors affect the evolution of cooperation during the evacuation process.

Direct Visualization of Local Spin Transition Behaviors in Thin Molecular Films by Bimodal AFM.

Thin films of the molecular spin-crossover complex [Fe(HB(1,2,4-triazol-1-yl)3 )2 ] undergo spin transition above room temperature, which can be exploited in sensors, actuators, and information processing devices. Variable temperature viscoelastic mapping of the films by atomic force microscopy reveals a pronounced decrease of the elastic modulus when going from the low spin (5.2 ± 0.4 GPa) to the high spin (3.6 ± 0.2 GPa) state, which is also accompanied by increasing energy dissipation. This technique allows imaging, with high spatial resolution, of the formation of high spin puddles around film defects, which is ascribed to local strain relaxation. On the other hand, no clustering process due to cooperative phenomena was observed. This experimental approach sets the stage for the investigation of spin transition at the nanoscale, including phase nucleation and evolution as well as local strain effects.

Preface

Conference on Theoretical Physics and Nonlinear Phenomena 2018 (CTPNP2018)Conference on Theoretical Physics and Nonlinear Phenomena is an annual conference of the Indonesian Theoretical Physicist Group (Grup Fisika Teoretik Indonesia = GFTI). The conference has been an effective gathering place for theorists from Indonesia and neighboring countries to exchange and share ideas. The conference is mainly intended to motivate young physicists to actively do research in the fields. The first meeting (academic gathering) in the form of workshop commenced in 2004, held in Indonesia University. Since 2010, the workshop developed into a conference and named as CTPNP (Conference on Theoretical Physics Nonlinear Phenomena). This annual conference has been held in various major cities of Indonesia, such as Jakarta, Surabaya, Bandung and Jogyakarta. It is for the first time for this year (2018), the conference is held outside Java, here in Makassar, the capital city of South Sulawesi, on the 2nd July 2018, in conjunction with National Physics Seminar on 3rd July 2018, hosted by Physics Department of Hasanuddin University.As a phyiscs community in this university, we are happy that this important event finally comes to Hasanuddin University. We believe that having this event in Makassar will inspire our physics community in this region. The conference is aimed to strengthen the collaboration and networking among researchers in theoretical physics and nonlinear phenomena, so that members of this group could increase their academic productivity. We hope that this aim can be enlightened by this year CTPNP’s main theme: Cooperative phenomena in small and large scale world. Cooperative phenomena are ubiquitous in nature, emphasizing the importance of research collaboration.As organizer and editor of this proceeding, we would like to take this opportunity to thank all people and institutions who have give significant contribution for realizing this conference, in particular Hasanuddin university for having been a main sponsor. We thank our plenary speakers and all contributive presenters and audiences, coming from different universities and research institutes. Our appreciation is extended to the Head of Physics Department and Dean of Science Faculty for fully support this conference.We also would like to thank the Theoretical Physics division of the Indonesian Physical Society (IPS) who have given the opportunity to the Department of Physics, Hasanuddin University to host this conference.We wish all participants with a very pleasant and enjoyable time during the conference day and staying in Makassar, which is the gate city for eastern part of Indonesia.Faithfully,On behalf of the organizer and EditorsTasrief Surungan, PhDChairman and Chief Editor of CTPNP 2018

Halloysite nanoclay supported adsorptive removal of oxytetracycline antibiotic from aqueous media

Halloysite nanoclay was utilized to retain aqueous oxytetracycline (OTC) which is extensively used in the veterinary industry. The micro-structure and functionality of the nanoclay were characterized through spectroscopic techniques before and after adsorption. The OTC removal experiments were performed at different pH conditions (pH 3.0–9.0), ionic strengths (0.001, 0.01, 0.1 M NaNO3) and contact time (up to 32 h) at an initial 25 mg/L OTC concentration with 1.0 g/L halloysite. Oxytetracycline adsorption was pH dependent, and the best pH was observed in the range of pH 3.5–5.5 at a 0.001 M ionic strength. At pH 3.5, the maximum OTC adsorption amount was 21 mg/g which translated to 68% removal of the initial OTC loading. Positively charged inner lumen and negatively charged outer lumen of the tubular halloysite structure led to form inner-sphere complexes with the anionic and cationic forms of OTC, respectively. A rapid adsorption of OTC was observed in the kinetic study where 62% OTC was adsorbed in 90 min.. Pseudo-second order equation obeyed by the kinetic data indicated that the adsorption was governed by chemisorption, whereas Hill isotherm equation was the most fitted with a maximum adsorption capacity of 52.4 mg/g indicating a cooperative adsorption phenomenon.

Perylene-Based Covalent Organic Frameworks for Acid Vapor Sensing.

Traditionally, the properties and functions of covalent organic frameworks (COFs) are defined by their constituting building blocks, while the chemical bonds that connect the individual subunits have not attracted much attention as functional components of the final material. We have developed a new series of dual-pore perylene-based COFs and demonstrated that their imine bonds can be protonated reversibly, causing significant protonation-induced color shifts toward the near-infrared, while the structure and crystallinity of the frameworks are fully retained. Thin films of these COFs are highly sensitive colorimetric acid vapor sensors with a detection limit as low as 35 μg L-1 and a response range of at least 4 orders of magnitude. Since the acidochromism in our COFs is a cooperative phenomenon based on electronically coupled imines, the COFs can be used to determine simultaneously the concentration and protonation strength of nonaqueous acid solutions, in which pH electrodes are not applicable, and to distinguish between different acids. Including the imine bonds as function-determining constituents of the framework provides an additional handle for constructing multifunctional COFs and extending the range of their possible applications.