Thermal Collapse Research Articles

Crossover of the effective charge in ionic thermoresponsive hydrogel particles.

We use a generalized nonlinear Poisson-Boltzmann cell model that includes excluded-volume effects to investigate whether the effective charge (Z_{eff}) of charged thermosensitive hydrogel particles increases or decreases upon the hydrogel thermal collapse. We find the existence of a crossover charge, Z^{*}, that separates two regimes. For hydrogel bare charges below Z^{*} the system shows a behavior consistent with theories based on linear approximations, i.e., Z_{eff} increases in the collapsed state. However, for bare charges above Z^{*}, the system enters an anomalous regime, in which Z_{eff} decreases in the collapsed state. We show that diluted hydrogel suspensions at low ionic strength are more likely to follow the anomalous behavior. Our theory provides a full physical justification for the controversial theoretical and experimental results reported in this regard, and describes how the interplay between electrostatic, excluded-volume and entropic effects affects this crossover.

An improved categorization of vapor bubble collapse: Explaining the coupled nature of hydrodynamic and thermal mechanisms

This work presents a numerical and theoretical analysis of the intermediate bubble collapse, where in contrast to the thermally-induced or inertia dominated collapse, both the effects of liquid-vapor interfacial heat transfer and the advection of the surrounding liquid play an important role. A key distinguishing characteristic of this type of collapse is that the interfacial temperature and bubble pressure are continuously changing throughout the collapse process. This behavior is caused by a non-negligible value for the interfacial vapor velocity, which is characterized by a magnitude of the same order as the bubble surface regression rate. This behavior is in contrast to the inertial or thermal collapse, where, in these regimes, the vapor velocity is essentially zero. Incorporating the rate of change of background system pressure, a regime map for bubble collapse is also presented where the parameter space is defined by Bsat and ξ and extends the previous categorization of Florschuetz and Chao (1965) where only Beff was used. Specifically, the present work quantitatively shows that the collapse behavior changes when the process is initiated by a gradual rate of pressurization in the surrounding liquid phase instead of the often used approximation of a step change.

Thermal collapse of a skyrmion

Thermal collapse of an isolated skyrmion on a two-dimensional spin lattice has been investigated. The method is based upon solution of the system of stochastic Landau-Lifshitz equations for up to 104 spins. The recently developed pulse-noise algorithm has been used for the stochastic component of the equations. The collapse rate follows the Arrhenius law. Analytical formulas derived within a continuous spin-field model support numerically-obtained values of the energy barrier. The pre-exponential factor is independent of the phenomenological damping constant that implies that the skyrmion is overcoming the energy barrier due to the energy exchange with the rest of the spin system. Our findings agree with experiments, as well as with recent numerical results obtained by other methods.

Mechanism of rift flank uplift and escarpment formation evidenced by Western Ghats, India

The Western Ghats is one of the largest escarpments on earth, containing Reunion plume derived Deccan Traps, it is an excellent example to probe epeirogenic uplift, extension and subsidence in volcanic continental margins. The most continuous unbiased stratigraphic section of basalt down to the basement within a 1250 m drill hole of the Continental Scientific Deep Drilling Project is a valuable resource to investigate the above aspects. The flows across the entire drill core are geologically subaerial in character with basement exposed ~300 m below the mean sea level; they clearly display more evolved compositions from primary melts of mantle in terms of petrology, and only a single geomagnetic polarity transition in palaeomagnetic data. These results, combined with existing geological and geophysical data, constitute a multi-method approach that demonstrates (a) igneous underplating caused uplift prior to frequently suggested flexural isostasy (b) plume impact and eruption are near-simultaneous and extension/rifting essentially followed soon after volcanism and (c) lithosphere beneath the continental margin, while returning to normal temperatures following the Seychelles-India breakup, experienced thermal collapse and subsidence causing slumping of basalt basement below sea level.

Kinetic modeling of ELM-induced tungsten transport in a tokamak plasma

Impurity accumulation in the core plasma leads to fuel dilution and higher radiative losses that can lead to loss of the H-mode, to thermal collapse of the plasma, and eventually even to a disruption in tokamaks. In present experiments, it has been shown that Edge Localized Modes (ELMs) at sufficiently high frequency are required to prevent W accumulation in the core, by expelling impurities from the edge plasma region, thus preventing their penetration into the plasma core. We present a full-orbit particle extension of the MHD code JOREK suitable for simulating impurity transport during ELMs. This model has been applied to the simulation of an ELM crash in ASDEX Upgrade, where we have quantified the displacement of W particles across flux surfaces. The transport mechanism is shown to be the particle E × B-drifts due to the electric field created by the MHD instability underlying the ELM. In- and outward transport is observed as a series of interchange motions, leading to a superdiffusive behavior. This causes not only the particles near the plasma pedestal to move outwards but also the particles outside of the pedestal to move inwards. This has important consequences for operation with W in ITER, where it is expected to be screened in the pedestal, and ELMs are shown here to increase the core W density. A comparison with existing diffusive modeling is made, showing a qualitative agreement and the limitations of this simplified modeling approach.

Compression of a Flapping Mechanophore Accompanied by Thermal Void Collapse in a Crystalline Phase.

Mechanical control of the molecular energy landscape is an important issue in modern materials science. Mechanophores play a unique role in that the mechanical responses are induced against the activation barrier for intramolecular transformation with the aid of external forces. Here we report an unprecedented activation process of a flexible flapping mechanophore. Namely, thermal void collapse in a crystalline phase triggers mechanophore compression in a definite proportion. Unfavored conformational planarization of the flapping mechanophore is compulsorily induced by packing force, leading to a total energy gain in crystal packing. Fluorescence chromism indicates extended π conjugation resulting from the mechanophore compression, giving rise to an energy transfer from the unpressed to compressed conformers.

Relativistic, Viscous, Radiation Hydrodynamic Simulations of Geometrically Thin Disks. I. Thermal and Other Instabilities

Abstract We present results from two-dimensional, general relativistic, viscous, radiation hydrodynamic numerical simulations of Shakura–Sunyaev thin disks accreting onto stellar-mass Schwarzschild black holes. We consider cases on both the gas- and radiation-pressure-dominated branches of the thermal equilibrium curve, with mass accretion rates spanning the range from to 10L Edd/c 2. The simulations directly test the stability of this standard disk model on the different branches. We find clear evidence of thermal instability for all radiation-pressure-dominated disks, resulting universally in the vertical collapse of the disks, which in some cases then settle onto the stable, gas-pressure-dominated branch. Although these results are consistent with decades-old theoretical predictions, they appear to be in conflict with available observational data from black hole X-ray binaries. We also find evidence for a radiation-pressure-driven instability that breaks the unstable disks up into alternating rings of high and low surface density on a timescale comparable to the thermal collapse. Since radiation is included self-consistently in the simulations, we are able to calculate light curves and power density spectra (PDS). For the most part, we measure radiative efficiencies (ratio of luminosity to mass accretion rate) close to 6%, as expected for a nonrotating black hole. The PDS appear as broken power laws, with a break typically around 100 Hz. There is no evidence of significant excess power at any frequencies, i.e., no quasi-periodic oscillations are observed.

Single-Crystalline Particles: An Effective Way to Ameliorate the Intragranular Cracking, Thermal Stability, and Capacity Fading of the LiNi0.6Co0.2Mn0.2O2 Electrodes

The fire incidents triggered by the thermal runaway of Li-ion batteries (LIBs) have aroused widespread concerns, as the instabilities of the delithiated cathode materials are generally accepted as one of the reasons for the ignition of LIBs. Herein, the electrochemical performance and the thermal stability of single-crystal and polycrystalline LiNi0.6Co0.2Mn0.2O2 electrode were investigated, trying to explore a novel, advanced approach for the thermal and cyclic stability of LiNi0.6Co0.2Mn0.2O2. Our results showed that the collapses of the layer structures and the cracks of polycrystalline particles occurred during charge; compared with the polycrystalline materials, the single-crystal particles efficiently improved the thermal stability, cyclic performance, and collapse of the layer structures. Additionally, the single-crystal material could maintain the structure and morphology even under a high charging voltage of 4.95 V. After 800 cycles at 45°C, 92.5% of the initial capacity was maintained for the single-crystal LiNi0.6Co0.2Mn0.2O2, while the capacity retention of the polycrystalline materials was below 90.5% after 300 cycles.

Effect of Casing Imperfection on the Casing Strength in Steam Injection Wells

In this study, effect of casing imperfection on the casing strength in thermal environment of steam injection wells was investigated. The imperfections were modelled in the form of casing pits which may represent local cavitation, wear or corrosion attacks. Several pits with various depths (C) relative to the casing thickness (t) and different casing diameter to thickness (D/t) ratios were considered in this study. For the purpose of investigation, 3D FE models consisting of defective casing-cement-formation system were developed. N80 casing with the casing length of 3.048 m is analyzed in the numerical study. In the analysis, the combined effects of cyclic thermal stress (from 25 °C to 360 °C), collapse pressure (from formation) and defects on casing were taken into account. From the numerical study, it is found that the casing imperfection greatly affected the casing strength in steam injection wells. The presence of pits markedly reduces the casing collapse strength in comparison to that of non-defective casing. For instance, the collapse strength of casing having 2 pits along its circumferential direction with depth C = 0.5t reduced about 49% and 43% for D/t = 22.09 and D/t = 17.26, respectively. In addition, the combination of high temperature, imperfection factor and formation pressure induces severe deformation on casing, even at lower formation pressure.

Influence of anisotropic stress states on the thermal volume change of unsaturated silt

This study is focused on understanding the influence of anisotropic stress states on the thermal volume change of unsaturated, compacted silt specimens. A thermo-hydro-mechanical true-triaxial cell was used that permits control of the temperature on all six boundaries of a cubical soil specimen as well as control of the suction within the specimen to provide drained conditions during mechanical loading and temperature changes. Six non-isothermal tests were performed as part of this study, each involving suction application, consolidation to a given isotropic or anisotropic stress state, heating and cooling in stages under drained conditions, and unloading. Specifically, tests having minor to major principal stress ratios of 1.0, 0.7, and 0.5 were performed on specimens having initial degrees of saturation of 0.7 and 0.8, complementing tests on the same soil under similar stress states but saturated conditions published in a previous study. Although compressive thermal axial strains were measured in both the major and minor stress directions, a greater thermal axial strain was observed in the direction of the major principal stress for stress ratios less than 1.0. However, similar thermal volumetric strains were observed in all of the tests regardless of the stress state. A small effect of inherent anisotropy was observed due to the formation of the specimens using compaction. Specimens with a lower initial degree of saturation experienced greater thermal volume changes than specimens closer to saturation, possibly due to thermal collapse of the air-filled voids during heating or thermally accelerated creep after application of a given plastic strain during mechanical loading. An empirical relationship to consider the effects of anisotropic stress states and variable saturation was incorporated into an established elasto-plastic model developed for saturated soils under isotropic conditions, and a good fit was obtained between the measurements and predictions.

Payload release by liposome burst: Thermal collapse of microgels induces satellite destruction

We present a smart liposome carrier system for stimulated release, consisting of cationic, thermo-responsive microgels. At low temperature, the swollen microgels adsorb about 200 anionic liposomes, 50 nm in diameter, per microgel. When heated from 39 °C to 41 °C, the microgel–liposome complex particles collapse from approx. 370 nm down to approx. 270 nm. Upon the thermo-induced collapse, the adsorbed liposome satellite layer is squeezed until the initially spherical liposomes explode and release their payload (antitumor drug doxorubicin) into the surrounding. This burst release mechanism, taking place over a narrow temperature range, is newly reported and of possible biomedical importance.

Mysterious Decomposition of Alkoxyphosphonium Chlorides: Postulated Involvement of the HCl2 Anion and Its Capture in the Solid State.

P-Alkoxyphosphonium (AP) chlorides were generated by reacting P-chlorophosphonium chlorides with alcohols. Their well-known spontaneous Arbuzov-type collapse leading to phosphine oxides was studied and its rate found to be dependent on a number of factors in an unexpected fashion: it is inversely proportional to the initial concentration and it shows strong dependence on the acidity of the media but is not very sensitive to the presence of base. To explain these observations, we evoke a self-inhibition model with the formation of the less nucleophilic hydrodichloride anion HCl2 in solution. Detailed analysis of the kinetic data yields the association constant (K=3×102 m-1 ) of the putative HCl2 species in chloroform. Experimental observations for the collapse of highly enriched diastereomeric alkoxyphosphonium (DAP) chlorides are fully analogous to the achiral AP also implying the involvement of HCl2 anions. Moreover, crystallisation of a highly enriched DAP salt derived from (-)-menthol furnished, for the first time, crystals of individual (RP )-DAP hydrodichloride as confirmed by X-ray diffractometry. Importantly, the P-configuration and detailed conformation of the DAP moiety is in good agreement with DFT-level computational results. The thermal collapse of (RP )-DAP⋅HCl2 proceeds with complete retention of the P-configuration furnishing the phosphine oxide of exceptional enantiomeric purity.

On the decay of strong magnetization in global disc simulations with toroidal fields

Strong magnetization in accretion discs could resolve a number of outstanding issues related to stability and state transitions in low-mass X-ray binaries. However, it is unclear how real discs become strongly magnetized and, even if they do, whether they can remain in such a state. In this paper, we address the latter issue through a pair of global disc simulations. Here, we only consider cases of initially purely toroidal magnetic fields contained entirely within a compact torus. We find that, over only a few tens of orbital periods, the magnetization of an initially strongly magnetized disc, $P_\mathrm{mag}/P_\mathrm{gas} \ge 10$, drops to $\lesssim 0.1$, similar to the steady-state value reached in initially weakly magnetized discs. This is consistent with recent shearing box simulations with initially strong toroidal fields, the robust conclusion being that strongly magnetized toroidal fields can not be locally self-sustaining. These results appear to leave net poloidal flux or extended radial fields as the only avenues for establishing strongly magnetized discs, ruling out the thermal collapse scenario.

Solid-state synthesis of Nd-doped glass: thermal collapse of Nd3+-incorporated NaY zeolites

A new solid-state synthesis route to fabricate a new type of thermal resistant Nd-glass from Nd3+-incorporated NaY zeolites has been developed by our research, in which Nd3+ cations are well and rationally dispersed after being heated beyond 1278 K.

Thickening vs. extension in the Variscan belt: P–T modelling in the Central Iberian autochthon

The Variscan tectonothermal structure of the NW and Central Iberian Massif shows an important thickening during the Early Carboniferous, prior to its thermal weakening and gravitational collapse in the Middle Carboniferous, triggering the uplift of its orogenic roots. Pseudosections modelling of selected samples from Somosierra, in the Barrovian metamorphic area of Central Iberia, yield P–T conditions of at least 6kbar and 500–540°C for a micaschist of the garnet zone, 5.0–9.7kbar and 580–620°C for a psammitic schist of the staurolite zone, above 9.0kbar and 680°C for a kyanite micaschist of the sillimanite zone, and 4.0–9.0kbar and 750–800°C for a migmatitic paragneiss structurally beneath the Barrovian sequence. These data, together with previous metamorphic and structural data, imply the near-parallel emplacement of a >9km-thick allochthonous nappe over the Central Iberian foreland during the Early Carboniferous. Emplacement was probably related to the lateral extension of a mid-European orogenic plateau in the form of a channel between opposite-verging collisional wedges. This orogen-parallel extension flow can be traced from the Bohemian Massif through the French Massif Central, South Domain of the Armorican Massif and NW of the Iberian Massif, to the Central Iberian area. The highly oblique emplacement of the thick allochthonous nappe explains the orogen-parallel stretching lineations, the development of Barrovian and subsequent low-pressure metamorphisms, and it could also explain the massive granitic magmatism located in the NW and central areas of the Central Iberian Zone.

Thermal Volume Change of Unsaturated Silt under Different Stress States and Suction Magnitudes

This paper presents an evaluation of the thermal volume change of compacted specimens of the same type of silt under a wide range of stress states, initial void ratios, and suction magnitudes. Stress states include both isotropic and anisotropic conditions with varying principal stress ratios, as well as normally consolidated and overconsolidated conditions. Initial void ratios range from 0.60 to 0.86, spanning very dense to loose conditions. Suctions evaluated range from saturated conditions, to low suctions in the funicular range, to suctions corresponding to residual saturation conditions. For the same soil, wide variations in thermal volume change are observed. Thermal contraction is observed for normally consolidated conditions regardless of the initial degree of saturation. Different mechanisms of thermal volume change can be used to explain the results, ranging from thermally-induced pore water pressure dissipation, to thermal collapse, to thermally-accelerated creep.

Effect of Micellization on the Thermoresponsive Behavior of Polymeric Assemblies.

The chain density of polymer micelles, dictated by their aggregation number (Nagg), is an often overlooked parameter that governs the macroscopic behavior of responsive assemblies. Using a combination of variable-temperature light scattering, turbidimetry, and microcalorimetry experiments, the cloud point and thermal collapse of micellar poly(N-isopropylacrylamide) (pNIPAM) corona chains at lower temperatures than the cloud point were found to be largely independent of the micelle's Nagg. By controlling the core composition, the degree of hysteresis associated with the thermal transition was found to increase as a function of core hydrophobicity. We performed this study on well-characterized micelles with tunable Nagg values, composed of a thermoresponsive corona (pNIPAM) and a nonresponsive core block poly(n-butyl acrylate-co-N,N-dimethylacrylamide) (p(nBA-co-DMA)), which were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. This allowed for a distinction to be made between thermoresponsive behavior at both the molecular and macroscopic level. The study of the subtle differences between these behaviors was made possible using a combination of complementary techniques. These results highlight the critical need for consideration of the effect that self-assembly plays on the responsive behavior of polymer chains when compared with free unimers in solution.

Preparation and Characterization of Porous Titania Ceramic Scaffolds

Biocompatible ceramics have recently attracted increasing attention as porous scaffolds that stimulate and guide natural bone regeneration. Due to excellent biocompatibility of titania (titanium dioxide or TiO2) porous three-dimensional (3D) TiO2 structures have been proposed as promising scaffolding materials for inducing bone formation from the surrounding environment and for enhancement of vascularisation after implantation. In this paper, 3D porous TiO2 ceramic scaffolds were produced via polymer foam replica method. This work deals with several important issues that are considered to be important for 3D scaffolds applied to regenerate bone tissue: pore size, porosity and mechanical strength. TiO2 ceramic scaffolds with pore size 300 μm − 700 μm and porosity > 90 % were obtained. Scaffolds showed fully open and interconnected pore structure that remained after recoating them with low viscosity TiO2 slurry. By optimising thermal treatment conditions grain growth and collapse of struts could be controlled in a way that resulted in higher compressive strength. Recoating greatly improved compressive strength and it reached 0.74±0.08 MPa after two coatings without causing changes in the open porestructure.

Thermal collapse and hierarchy of polymorphs in a faujasite-type zeolite and its analogous melt-quenched glass.

We examine the route of structural collapse and re-crystallization of faujasite-type (Na,K)-LSX zeolite. As the first step, a rather stable amorphous high density phase HDAcollapse is generated through an order-disorder transition from the original zeolite via a low density phase LDAcollapse, at around 790 °C. We find that the overall amorphization is driven by an increase in the bond angle distribution within T-O-T and a change in ring statistics to 6-membered TO4 (T = Si(4+), Al(3+)) rings at the expense of 4-membered rings. The HDAamorph transforms into crystalline nepheline, though, through an intermediate metastable carnegieite phase. In comparison, the melt-derived glass of similar composition, HDAMQ, crystallizes directly into the nepheline phase without the occurrence of intermediate carnegieite. This is attributed to the higher structural order of the faujasite-derived HDAcollapse which prefers the re-crystallization into the highly symmetric carnegieite phase before transformation into nepheline with lower symmetry.

Thermo- and UV Photo-Triggerable Monoolein Cubic Phase Bearing Poly(Hydroxyethyl Acrylate-co-Coumaryl Acrylate-co-Octadecyl Acrylate)

Thermo- and UV photo-triggerable monoolein (MO) cubic phases were developed by incorporating poly(hydroxyethyl acrylate-co-coumaryl acrylate-co-octadecyl acrylate) (P(HEA-CA-ODA)) in the cubic phases. P(HEA-CA-ODA)s, for which the HEA/CA/ODA molar ratio was 98.6:0:1.4, 96.7:2.0:1.3, 96.2:2.6:1.2, 95:3.8:1.2, and 92.8:6.1:1.1, calculated on the 1H NMR spectra, were prepared by a free radical reaction. The air–water interfacial tension was inversely proportional to the CA content of the copolymer. The copolymers for which the CA content was 2.6%, 3.8%, and 6.1% exhibited their phase transition temperature in an aqueous solution in the temperature range from 25°C to 40°C. As the CA content was more, the temperature sensitivity was higher and the phase transition temperature was lower. The UV light (254 nm, 6 W)-induced dimerization degree of CA was proportional to its content in the copolymers. The release of fluorescein isothiocyanate-dextran from cubic phases containing P(HEA/CA/ODA)s was promoted by UV light irradiation, possibly due to the photo-induced collapse of the copolymer chains. The release from cubic phases incorporating copolymers, for which the CA content was 3.8% and 6.1%, was enhanced by increasing the releasing medium temperature from 23°C to 37°C, possibly due to the thermal collapse of the copolymer chains.