Cage Effect Research Articles

Combustion and pyrolysis behaviors of flame retardant poly (lactic acid) composites containing phosphaphenanthrene and maleimide molecules

To improve the flame retardant performance of poly (lactic acid) (PLA), a phosphaphenanthrene (DOPO) -maleimide derivative (DNPMI) was synthesized. DNPMI based PLA composites were investigated for their flame retardant, thermal and crystalline properties. Moreover, the combustion and pyrolysis behaviors of PLA composites were investigated detailly. The results indicated that the introduction of DNPMI with DOPO and maleimide group in the molecular structure effectively improved the fire safety of PLA composites accompanied with good crystallization ability and transparency properties. With the addition of 7.5 wt% DNPMI, PLA composites reached to UL-94 V-0 grade with a high LOI value of 30.8 %. The excellent flame retardancy performance of PLA/DNPMI composite materials is mainly ascribed to the interplay of quenching and dilution effects in the gaseous phase. The maleimide, and phosphorus-containing radicals generated by the pyrolysis of DNPMI captured the chain radicals and the decomposed inert gases diluted the concentration of the combustion components of PLA. In addition, heat-resistant aromatic structures were generated by the reaction of maleimide radicals and reactive radicals from decomposition of PLA, thereby playing "cage effect" to inhibit the combustion process.

Effect of self and extrinsic encapsulation on electron resilience of porous 2D polymer nanosheets

Despite the exceptional resolution in aberration-corrected high-resolution transmission electron microscope (AC-HRTEM) images of inorganic two-dimensional (2D) materials, achieving high-resolution imaging of organic 2D materials remains a daunting challenge due to their low electron resilience. Optimizing the critical dose (the electron exposure, the material can accept before it is noticeably damaged) is vital to mitigate this challenge. An understanding of electron resilience in porous crystalline 2D polymers including the effect of sample thickness has not been derived thus far. It is assumed, that additional layers of the sample form a cage around inner layers, which are preventing fragments from escaping into the vacuum and enabling recombination. In the literature this so called caging effect has been reported for perylene and pythalocyanine. In this work we determine the critical dose of a porous, triazine-based 2D polymer as function of the sample thickness. The results show that the caging effect should not be generalized to more sophisticated polymer systems. We argue that pore channels in the framework structure serve as escape routes for free fragments preventing the caging effect and thus showing surprisingly a thickness-independent critical dose. Moreover, we demonstrate that graphene encapsulation prevents fragment escape and results in an increase in the critical electron dose and unit-cell image resolution.

Persistent Free Radicals in Petroleum

The persistent free radical content in petroleum is of the order 1018 spins/g (1 μmol/g), with higher and lower values found depending on origin and in different distillation fractions. The field of persistent free radicals in petroleum was reviewed with the aim of addressing and explaining apparent inconsistencies between free radical persistence and reactivity. The macroscopic average free radical concentration in petroleum is persistent over geological time, but individual free radical species in petroleum are short-lived and reactive. The persistent free radical concentration in petroleum can be explained in terms of a dynamic reaction equilibrium of free radical dissociation and association that causes a finite number of species at any given time to be present as free radicals. Evidence to support this description are observed changes in free radical concentration related to change in Gibbs free energy when the bulk liquid properties are changed and responsiveness of free radical concentration to dynamic changes in temperature. Cage effects, solvent effects, steric protection, and radical stabilization affect free radical reaction rate but do not explain the persistent free radical concentration in petroleum. The difference between persistent free radicals in straight-run petroleum and converted petroleum is that straight-run petroleum is an equilibrated mixture, but converted petroleum is not at equilibrium and the free radical concentration can change over time. Based on the limited data available, free radicals in straight-run petroleum appear to be part of the compositional continuum proposed by Altgelt and Boduszynski. Persistent free radical species are partitioned during solvent classification of whole oil, with the asphaltenes (n-alkane insoluble) fraction having a higher concentration of persistent free radicals than maltenes (n-alkane soluble) fraction. Attempts to relate persistent free radical concentration to petroleum composition were inconclusive.

Microstructure and rheology of shear thickening colloidal suspensions under transient flows

Novel measurements of the spatiotemporal microstructure of a continuous shear thickening colloidal suspension under shear cessation and reversal using small angle neutron scattering in a 1–2 shear cell are presented for moderate to high Péclet numbers. In the shear cessation experiments from high Péclet shear flow, two-step relaxation mechanism is found. Particles first readily diffuse on a characteristic timescale of single particle Brownian motion, followed by slower relaxation dynamics on a timescale of short-time self-diffusion when caging effects start dominating. In the shear reversal experiment, the unchanged scattering intensity and the quick flip in anisotropic structure around the shear thickened state suggest the persistence of hydroclusters without transitioning through the equilibrium structure, at least in a time resolution of 0.01 s. Access to the time evolution of microstructure provides valuable insights into the spatiotemporal details of interparticle interactions governing colloidal suspension rheology, such as Brownian, hydrodynamic, and nanotribological forces.

Oil-in-Oil Pickering emulsions stabilized with kaolinite

Oil-oil Pickering emulsions are remarkable systems in pharmaceutical and cosmetic sciences, minimizing oxidation and hydrolysis reactions. Versatile and environmentally friendly clay minerals are poorly discussed in literature as stabilizing particles in these unconventional oil-oil emulsions. We investigated the effect of kaolinite applied in a castor oil/silicone oil emulsion at different oil fractions and kaolinite concentrations. Samples without kaolinite showed a limited and low stability self-emulsification. According to the particle concentration increase, emulsions presented higher emulsified volumes and lower droplet diameter, from 100 to 20 µm. Microscopic images revealed Pickering emulsions, where cage effect started to be observed at 2 wt% kaolinite. Castor oil and silicone oil behaves like liquids, however, in the presence of kaolinite the emulsions formed changed to a solid viscoelastic system, improving long-term stability.

Solvent-Dependent Structural Dynamics in the Ultrafast Photodissociation Reaction of Triiodide Observed with Time-Resolved X-ray Solution Scattering.

Resolving the structural dynamics of bond breaking, bond formation, and solvation is required for a deeper understanding of solution-phase chemical reactions. In this work, we investigate the photodissociation of triiodide in four solvents using femtosecond time-resolved X-ray solution scattering following 400 nm photoexcitation. Structural analysis of the scattering data resolves the solvent-dependent structural evolution during the bond cleavage, internal rearrangements, solvent-cage escape, and bond reformation in real time. The nature and structure of the reaction intermediates during the recombination are determined, elucidating the full mechanism of photodissociation and recombination on ultrafast time scales. We resolve the structure of the precursor state for recombination as a geminate pair. Further, we determine the size of the solvent cages from the refined structures of the radical pair. The observed structural dynamics present a comprehensive picture of the solvent influence on structure and dynamics of dissociation reactions.

Comparative study of the dynamics of colloidal glass and gel.

We investigate and compare the difference in the dynamics of two arrested states: colloidal glass and colloidal gel. Real-space experiments reveal two distinct nonergodicity origins for their slow dynamics, namely, cage effects for the glass and attractive bondings for the gel. Such distinct origins lead to a faster decay of the correlation function and a smaller nonergodicity parameter of the glass than those of the gel. We also find that the gel exhibits stronger dynamical heterogeneity compared with the glass due to the greater correlated motions in the gel. Moreover, a logarithmic decay in the correlation function is observed as the two nonergodicity origins merge, consistent with the mode coupling theory.

The influence of sodium sulphate on sodium aluminosilicate solubility in Bayer liquor aiding the desilication process

The influence of Na2SO4 at chemical equilibrium in the NaOH-Al2O3-SiO2-Na2SO4-H2O system were studied in synthetic Bayer liquors. Sodium aluminosilicate, otherwise referred to as desilication product (DSP) in the alumina industry, was synthesised hydrothermally from kaolin used in a rotating bomb heater. Experiments spanned several days to reach equilibrium at 90 °C, 150 °C and 250 °C and employed Na2SO4 concentration ranging from 0 to 0.4 M. The SO42− incorporation into DSP was best modelled by the mathematical form of Langmuir-type isotherms, and reached maximum occupancy of 85%, primarily displacing OH−, and Al(OH)4− to a lesser degree. The presence of Na2SO4 enhanced desilication (measured by solution SiO2 concentration) by up to 80% compared to sulphate-free tests, with diminishing relative effect with increasing SO42− concentration. Approximate maximum sulphate cage occupancy and effect on desilication were achieved at a Na2SO4 concentration of 0.1 M. Solid residues contained Bayer (alumina)-type cancrinite, sulphate-type cancrinite (vishnevite), hydroxycancrinite, hydroxysodalite and amorphous material as determined by X-ray diffraction. The presence of sulphate led to different transformation pathways for DSP precipitated from kaolin. Sulphate-bearing DSPs exhibited rod-like morphology and presented enhanced thermal stability over their hydroxy counterparts. Valuable new data on the relationship between sulphate ion uptake, and the composition, structure and solubility of DSP are presented, and the results are suitable for the development of kinetic and thermodynamic models describing zeolite equilibria in alumina processing.

Bi-directional crosstalk between gut microbiota and NKT cells

Abstract The gut microbiome interacts with the host, including local and systemic immunity. However, the causal mechanisms are relatively under-explored. In this study, we sought to identify bi-directional crosstalk between gut microbiota and type I and/or type II NKT cells using C57BL/6 WT (wild-type), Traj18-knock out (KO) (lacks only type I NKT cells), or CD1d-KO (lacks both type I and II NKT cells) mice. Mice were co-housed with each other strain in combination from the age of day 30 (9 days after weaning) for 30 days and housed separately again for another 30 days. Fecal pellets collected at the age of days 30, 60, and 90 were sequenced by 16S rRNA (250 bp paired-end, Illumina) sequencing, identifying 1,276 amplicon sequence variants (ASVs) by analysis (QIIME2). Microbes with low frequency (<0.5%) or exhibiting cage effects within a strain at day 30 were filtered out. Comparing the microbial abundances between the different groups (co-housing or not) and time points revealed an interesting phenomenon regarding four ASVs (the closest known species was Muribaculum intestinale strain YL27 (16S pident 86.7–95.6)). They showed differential abundance (limma p-value < 0.05) between strains at day 30 (e.g., an ASV_802 was most abundant in WT mice, then CD1-KO, and lowest in Traj18-KO mice). These closely related bacteria were not transferred to Traj18-KO mice when co-housed with WT or CD1-KO mice. Because the ASV is present in WT and CD1d KO mice, even though the latter also lack type I NKT cells as well as type II, our results suggest the existence of specific microbe(s) that cannot grow well in the presence of unopposed type II NKT cells.

CO-Preserving Photoinduced Transfer of Cymantrenyl Moiety: a Tandem Experimental and Computational Investigation.

Cyclopentadienyl manganese tricarbonyl (cymantrene) is known to undergo photochemical reactions by releasing one of its CO ligands. Here we present the first example of a photorearrangement of a cymantrenylmethyl fragment, where it retains all its three CO ligands. A tandem experimental and DFT (density functional theory)-based computational investigation allows us to explain this unexpected behavior: the rearrangement, indeed, begins with the release of one CO ligand, but cage effect of the solvent captures this CO molecule, allowing it to rapidly reattach once the rearrangement takes place.

Bioresorbable Magnesium-Based Stent: Real-World Clinical Experience and Feasibility of Follow-Up by Coronary Computed Tomography: A New Window to Look at New Scaffolds

(1) Background: The diagnostic accuracy of coronary computed tomography angiography (CCTA) for coronary artery disease (CAD) has greatly improved so CCTA represents a transition in the care of patients suffering from CAD. Magnesium-based bioresorbable stents (Mg-BRS) secure acute percutaneous coronary intervention (PCI) results without leaving, in the long term, a metallic caging effect. The purpose of this real-world study was to assess clinical and CCTA medium- and long-term follow-up of all our patients with implanted Mg-BRS. (2) Methods: The patency of 52 Mg-BRS implanted in 44 patients with de novo lesions (24 of which had acute coronary syndrome (ACS)) was evaluated by CCTA and compared to quantitative coronary angiography (QCA) post-implantation. (3) Results: ten events including four deaths occurred during a median follow-up of 48 months. CCTA was interpretable and in-stent measurements were successful at follow-up without being hindered by the stent strut's "blooming effect". Minimal in-stent diameters on CCTA were found to be 1.03 ± 0.60 mm smaller than the expected diameter after post-dilation on implantation (p < 0.05), a difference not found in comparing CCTA and QCA. (4) Conclusions: CCTA follow-up of implanted Mg-BRS is fully interpretable and we confirm the long-term Mg-BRS safety profile.

The birth and evolution of solvated electrons in the water

The photo-induced radiolysis of water is an elementary reaction in biology and chemistry, forming solvated electrons, OH radicals, and hydronium cations on fast time scales. Here, we use an optical-pump terahertz-probe spectroscopy setup to trigger the photoionization of water molecules with optical laser pulses at ~400 nm and then time-resolve the transient solvent response with broadband terahertz (THz) fields with a ~90 fs time resolution. We observe three distinct spectral responses. The first is a positive broadband mode that can be attributed to an initial diffuse, delocalized electron with a radius of (22 ± 1) Å, which is short lived (<200 fs) because the absorption is blue-shifting outside of the THz range. The second emerging spectroscopic signature with a lifetime of about 150 ps is attributed to an intermolecular mode associated with a mass rearrangement of solvent molecules due to charge separation of radicals and hydronium cations. After 0.2 ps, we observe a long-lasting THz signature with depleted intensity at 110 cm-1 that is well reproduced by abinitio molecular dynamics. We interpret this negative band at 110 cm-1 as the solvent cage characterized by a weakening of the hydrogen bond network in the first and second hydration shells of the cavity occupied by the localized electron.

Stochastic Modelling and Simulation of Free Radical Polymerization of Styrene in Microchannels using a Hybrid Gillespie Algorithm

Most recently, the production of polystyrene by Free Radical Polymerization (FRP) via microchannels has been a subject of core interest due to the efficiency of a micro-or milli-reactor brings. In addition, especially in pilot experimentations, a micro or milli-reactor has been known widely to be efficient in monitoring the microstructural end-use features or properties of the polymer as the chain propagates and ultimately terminates. However, the limitations posed by using micro or milli-reactors in process intensification such as clogging of pores can be a bottleneck when tracking the common phenomena associated with FRP such as cage, gel, and glass effects. In this work, the simulation of the synthesis of polystyrene in FRP via microchannels is computed using a robust and time-efficient hybrid Gillespie Algorithm (GA) or Hybrid Stochastic Simulation Algorithm (HSSA). The obtained results of the end-use properties of polystyrene such as Monomer conversion, Polydispersity Index, Number-Average Molar Mass and Weight Average Molar Mass were compared to experimental data. The simulation results agree well with the experimental results reported in this work. Hence, stochastic simulations prove to be an effective tool in making decisions in the context of process intensification of chain growth polymerization reactions even at a large scale.

The Perfluoro Cage Effect: A Search for Electron-Encapsulating Molecules.

Quantum chemical calculations have for some time predicted that perfluorinated polyhedral organic molecules should exhibit a low-energy LUMO consisting of the overlapping inward-pointing lobes of the C-F σ* orbitals. Accordingly, these molecules should be able to encapsulate an electron within the interior of their cavities. Inspired by the recent confirmation of this prediction for perfluorocubane, we have sought to identify additional perfluorinated cage molecules capable of this remarkable behavior, which we refer to as the perfluoro cage effect (PCE). Using DFT calculations with multiple well-tested exchange-correlation functionals and large STO-QZ4P basis sets, we have identified several systems including [n]prismanes (n = 3-6), [n]asteranes (n = 3-5), twistane, and two norbornadiene dimer cages that clearly exhibit the PCE. In other words, they exhibit a low-energy LUMO belonging to the total symmetric irreducible representation of the point group in question and adiabatic electron affinities ranging from somewhat under 1 eV to over 2 eV. A pronounced size effect appears to hold, with larger cages exhibiting higher electron affinities (EAs). The largest adiabatic EAs, well over 3 eV, are predicted for perfluorinated dodecahedrane and C60. In contrast, the PCE is barely discernible for perfluorinated tetrahedrane and bicyclo[1.1.1]pentane.

Photosensitized activation of diazonium derivatives for C–B bond formation

Aryl diazonium salts are ubiquitous building blocks in chemistry, as they are useful radical precursors in organic synthesis as well as for the functionalization of solid materials. They can be reduced electrochemically or through a photo-induced electron transfer reaction. Here we provide a detailed picture of the ground and excited-state reactivity of a series of 9 rare and earth abundant photosensitizers with 13 aryl diazonium salts, which also included 3 macrocyclic calix[4]arene tetradiazonium salts. Nanosecond transient absorption spectroscopy confirmed the occurrence of excited-state electron transfer and was used to quantify cage-escape yields, i.e. the efficiency with which the formed radicals separate and escape the solvent cage. Cage-escape yields were large; increased when the driving force for photo-induced electron transfer increased and also tracked with the C-N2 + bond cleavage propensity, amongst others. A photo-induced borylation reaction was then investigated with all the photosensitizers and proceeded with yields between 9 and 74%.

Structural and dynamic heterogeneity in associative networks formed by artificially engineered protein polymers.

This work investigates static gel structure and cooperative multi-chain motion in associative networks using a well-defined model system composed of artificial coiled-coil proteins. The combination of small-angle and ultra-small-angle neutron scattering provides evidence for three static length scales irrespective of protein gel design which are attributed to correlations arising from the blob length, inter-junction spacing, and multi-chain density fluctuations. Self-diffusion measurements using forced Rayleigh scattering demonstrate an apparent superdiffusive regime in all gels studied, reflecting a transition between distinct "slow" and "fast" diffusive species. The interconversion between the two diffusive modes occurs on a length scale on the order of the largest correlation length observed by neutron scattering, suggesting a possible caging effect. Comparison of the self-diffusive behavior with characteristic molecular length scales and the single-sticker dissociation time inferred from tracer diffusion measurements supports the primarily single-chain mechanisms of self-diffusion as previously conceptualized. The step size of the slow mode is comparable to the root-mean-square length of the midblock strands, consistent with a single-chain walking mode rather than collective motion of multi-chain aggregates. The transition to the fast mode occurs on a timescale 10-1000 times the single-sticker dissociation time, which is consistent with the onset of single-molecule hopping. Finally, the terminal diffusivity depends exponentially on the number of stickers per chain, further suggesting that long-range diffusion occurs by molecular hopping rather than sticky Rouse motion of larger assemblies. Collectively, the results suggest that diffusion of multi-chain clusters is dominated by the single-chain pictures proposed in previous coarse-grained modeling.

Limited predatory effects on infaunal macrobenthos community patterns in intertidal soft-bottom of Arctic coasts.

Predation shapes marine benthic communities and affects prey species population dynamics in tropic and temperate coastal systems. However, information on its magnitude in systematically understudied Arctic coastal habitats is scarce. To test predation effects on the diversity and structure of Arctic benthic communities, we conducted caging experiments in which consumers were excluded from plots at two intertidal sedimentary sites in Svalbard (Longyearbyen and Thiisbukta) for 2.5months. Unmanipulated areas served as controls and partial (open) cages were used to estimate potential cage effects. At the end of the experiment, we took one sediment core from each plot and quantified total biomass and the number of each encountered taxon. At both sites, the experimental exclusion of predators slightly changed the species composition of communities and had negligible effects on biomass, total abundance, species richness, evenness, and Shannon Index. In addition, we found evidence for cage effects, and spatial variability in the intensity of the predation effects was identified. Our study suggests that predators have limited effects on the structure of the studied intertidal macrobenthic Arctic communities, which is different from coastal soft-bottom ecosystems at lower latitudes.

Origin of structural and dynamic heterogeneity in thymol and coumarin-based hydrophobic deep eutectic solvents as revealed by molecular dynamics.

Hydrophobic deep eutectic solvents (HDESs) have recently emerged as a class of water-immiscible solvents with greener starting materials and inherent hydrophobic character, opening the gates to various new promising applications. Herein, we have carried out all-atom molecular dynamics simulations to comprehend the bulk phase structural organization and dynamic behavior of thymol and coumarin-based HDESs at two molar ratios of the constituent components. The simulated X-ray and neutron scattering structure functions (S(q)s) indicate a prepeak signifying that these HDESs possess nanoscale heterogeneity or intermediate range ordering. The decomposition of the total S(q)s based on polarity reveals that clustering of the polar group present in thymol and coumarin leads to the presence of the prepeak which also has small contributions from the apolar-apolar correlations. The intermolecular hydrogen bonding network between thymol-coumarin and thymol-thymol mainly guides the arrangement of the HDESs. We find a stronger hydrogen bond between the carbonyl oxygen of coumarin and the hydroxyl hydrogen of thymol, marked by the longer hydrogen bond lifetime. In contrast, the shorter lifetime of the hydrogen bond between the hydroxyl oxygen and the hydroxyl hydrogen of thymol suggests a weaker hydrogen bonding. On changing the thymol : coumarin molar ratio from 1 : 1 to 2 : 1, the average lifetimes of both the hydrogen bonds decrease, suggesting stronger hydrogen bonds in the 1 : 1 HDES. The translational dynamics of thymol and coumarin become faster in the 2 : 1 thymol : coumarin HDES. A slightly stronger caging effect is observed for coumarin in comparison to thymol molecules. From the analysis of the non-Gaussian parameter, we observe the presence of heterogeneity in the translational displacements of thymol and coumarin molecules. Furthermore, the computed self-van Hove correlation functions reveal that thymol and coumarin molecules cover more distances than the ideal diffusive displacements, confirming the presence of dynamic heterogeneity.

Recent Progress on the Rheology of Giant Molecules

AbstractGiant molecules are a new class of precise macromolecules whose constructing blocks are molecular nanoparticles, such as polyhedral oligomeric silsesquioxane (POSS), fullerene (C60), etc., connected by different types of links with various molecular topologies in soft matter. These blocks are connected in 3D instead of chain‐like. Thus, the dynamics of giant molecules cannot be described by the entanglement‐dominated “reptation” dynamics, nor by the volume‐fraction‐determined caging effect as in the colloidal domain. Instead, they demonstrate different kinetics which are highly dependent on their sizes (diameters), bridging the conventional polymeric and colloidal systems. Further investigations into its unique dynamics will not only offer new properties for developing novel materials, but will also provide a deeper insight into the general principles of glass formation. In this review, the definition of giant molecules, their assemblies as well as their structural features are first introduced. The general dynamics of other systems, including the conventional polymeric and colloidal systems are briefly summarized. The recent progress of the rheological study of giant molecules is then focused upon. Finally, perspectives on this direction are proposed.

Homogenization of Helmholtz equation in a periodic layer to study Faraday cage-like shielding effects

The work is motivated by the Faraday cage effect. We consider the Helmholtz equation over a 3D domain containing a thin heterogeneous interface of thickness . The layer has a δ-periodic structure in the in-plane directions and is cylindrical in the third direction. The periodic layer has one connected component and a collection of isolated regions. The isolated region in the thin layer represents air or liquid, and the connected component represents a solid metal grid with a δ thickness. The main issue is created by the contrast of the coefficients in the air and in the grid and that the zero-order term has a complex-valued coefficient in the connected faze while a real-valued in the complement. An asymptotic analysis with respect to is provided, and the limit Helmholtz problem is obtained with the Dirichlet condition on the interface. The periodic unfolding method is used to find the limit.