Thermal Phase Transition Research Articles

Phototunable Cloud Point Temperatures Stemming from Cyclic Topology: Synthesis and Thermal Phase Transition Behavior of Cyclic Poly(N-acryloylsarcosine methyl ester).

Cyclic polymers possess distinct properties compared with their linear counterparts, such as smaller hydrodynamic volume, lower viscosity, and higher glass-transition temperature, etc. To explore the impact of the cyclic topology on the thermo-induced phase transition behavior of poly(N-acryloylsarcosine methyl ester) (PNASME), the anthracene-terminated telechelic PNASMEs are synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of monomer NASME using a bifunctional chain transfer agent (CTA) with two anthryl groups. Subsequently, cyclic PNASMEs are prepared via UV-induced cyclization under 365nm UV. There are considerable increases (up to 50°C) for the cloud point temperatures (Tcp s) of cyclic PNASMEs compared with the linear counterparts. In view of the increment, the Tcp of PNASME is tuned by varying the cyclic/linear ratio (the molar ratio between cyclic PNASME and linear PNASME in the product) with different irradiation time.

Refining the Design of Diblock Elastin-Like Polypeptides for Self-Assembly into Nanoparticles.

Diblock copolymers based-on elastin-like polypeptide (ELP) have the potential to undergo specific phase transitions when thermally stimulated. This ability is especially suitable to form carriers, micellar structures for instance, for delivering active cargo molecules. Here, we report the design and study of an ELP diblock library based on ELP-[M1V3-i]-[I-j]. First, ELP-[M1V3-i]-[I-j] (i = 20, 40, 60; j = 20, 90) that showed a similar self-assembly propensity (unimer-to-aggregate transition) as their related monoblocks ELP-[M1V3-i] and ELP-[I-j]. By selectively oxidizing methionines of ELP-[M1V3-i] within the different diblocks structures, we have been able to access a thermal phase transition with three distinct regimes (unimers, micelles, aggregates) characteristic of well-defined ELP diblocks.

Prethermalization and thermalization in periodically driven many-body systems away from the high-frequency limit

We investigate a class of periodically driven many-body systems that allows us to extend the phenomenon of prethermalization to the vicinity of isolated intermediate-to-low drive frequencies away from the high-frequency limit. We provide numerical evidence for the formation of a parametrically long-lived prethermal plateau, captured by an effective Floquet Hamiltonian computed using the replica inverse-frequency expansion, and demonstrate its stability w.r.t.~random perturbations in the drive period. Considering exclusively nonintegrable Floquet Hamiltonians, we find that heating rates are non-universal: we observe Fermi's Golden Rule scaling, power-law scaling inconsistent with the Golden Rule, and non-power law scaling, depending on the drive. Despite the asymptotic character of the inverse-frequency expansion, we show that it describes the thermostatic properties of the state all along the evolution up to infinite temperature, with higher-order terms improving the accuracy. Our results suggest a dynamical mechanism to gradually increase temperature in isolated quantum simulators, such as ultracold atoms, and open up an alternative possibility to investigate thermal phase transitions and the interplay between thermal and quantum criticality using Floquet drives.

Modeling the high temperature behavior of all-composite, corrugated-core sandwich panels undergoing ablation

Owing to their structural efficiency, the development of structurally integrated thermal protection systems (SITPS) for the next generation aerospace vehicles is currently of interest. Herein, an all-composite sandwich structure with corrugated core is devised and fabricated. After homogenization of the corrugated core, a one-dimensional (1-D) analytical model is developed. The surface ablation is described by considering thermal decomposition, phase transition and thermochemical ablation. With the thermal loading and moving boundary conditions determined by the surface ablation calculation, a heat transfer analysis is performed. To provide insight into the effect of lateral heat transfer and thermal short through the sandwich structures, a two-dimensional (2-D) finite element model is also presented. In addition, a thermal exposure experimental test with oxyacetylene flame is carried out to validate the proposed models. The 1-D analytical model is found to be of satisfactory accuracy, which is useful for rapid preliminary SITPS design.

Thermal phase transition controlling electromagnetic wave absorption behavior of PAN fiber derived porous magnetic absorber

The increasing excess electromagnetic wave (EMW) energies causes potential electromagnetic radiation pollution. It gives rise to more and more attention on designing environmentally friendly, efficient and suitable for large-scale industrial production of daily EMW absorbers. Carbon matrix composites modified with magnetic particles occupy the majority of these candidate absorbers. However, the preparation is still in its infancy. Here, we creatively mixed Fe(acac)3 with polyacrylonitrile (PAN) spinning solution, and then prepared magnetic carbon-based composites by in-situ pyrolysis of the obtained electrospun fibers (Fe(acac)3/PAN) at different temperatures. The SEM images display a fractured fibrous material with porous structure and uniform distribution of magnetic particles on the outer surface and inside. The XRD and XPS results indicate the composites consist of Fe3O4, Fe3C and carbon matrix. Besides, the thermal phase transition occurs with the pyrolysis temperature increasing from 300 to 1000 °C, and the formed Fe3O4 reacts with the carbon matrix to form Fe3C. As a result, the corresponding magnetic properties and electromagnetic properties improve. MCF-1000 exhibits enhanced EMW absorption performance with a minimum RL ( $${RL}_{\mathrm{min}}$$ ) value of − 29.27 dB at a matching frequency ( $${f}_{m}$$ ) of 11.68 GHz, a matching thickness ( $${t}_{m}$$ ) as low as 1.50 mm, and an effective frequency bandwidth as broad as 4.50 GHz from 13.50 to 18.00 GHz at a fixed thickness as thin as 1.13 mm. Further investigations indicate that such good EMW absorption behavior is attributed to the optimal impedance matching and the weakened eddy current effect which are both benefited by the thermal phase transition effect. The results provide theoretical and practical experience for the industrial large-scale preparation of a kind of EMW absorbers.

High Stability of 1T-Phase MoS2xSe2(1–x) Monolayers Under Ambient Conditions

The phase stability in transition metal dichalcogenides (TMDs) is very significant for their utility in various applications. In particular, the 1T phase of group VI TMDs is of high technological importance owing to its electrically conducting properties and phase stability via strain engineering and chemical functionalization has been reported in the literature. In this regard, alloying with atoms of different sizes is an effective approach to introduce inherent strain in the lattice by modifying bond parameters. In the present study, it has been shown that the 1T polymorph of layered chalcogenides gets stabilized in strained, mixed chalcogen alloys, MoS2xSe2(1–x). The 2H phases of MoS2xSe2(1–x) are amenable for efficient chemical exfoliation to monolayers and successful conversion to metallic 1T phase. The metallic 1T phase of MoS2xSe2(1–x) with inherent strain is found to be very stable for a long duration under ambient conditions. Owing to different Mo–S and Mo–Mo bond lengths in mixed chalcogenides, effective tuning of stability is achieved by changing the S/Se ratio in the compound. The differential scanning calorimetry data reveals a shift in the thermal phase transition with a peak maximum at ∼160 °C in the case of 1T MoSSe which is different from its pristine counterparts. Ex situ XRD and Raman spectroscopic studies suggest the role of inherent strain in retaining the octahedral structure at high temperatures. The alloying approach may be extended to other transition metal chalcogenides to fully explore the potential of metastable polytypes.

Real scalar phase transitions: a nonperturbative analysis

We study the thermal phase transitions of a generic real scalar field, without a Z2-symmetry, referred to variously as an inert, sterile or singlet scalar, or ϕ3 + ϕ4 theory. Such a scalar field arises in a wide range of models, including as the inflaton, or as a portal to the dark sector. At high temperatures, we perform dimensional reduction, matching to an effective theory in three dimensions, which we then study both perturbatively to three-loop order and on the lattice. For strong first-order transitions, with large tree-level cubic couplings, our lattice Monte-Carlo simulations agree with perturbation theory within error. However, as the size of the cubic coupling decreases, relative to the quartic coupling, perturbation theory becomes less and less reliable, breaking down completely in the approach to the Z2-symmetric limit, in which the transition is of second order. Notwithstanding, the renormalisation group is shown to significantly extend the validity of perturbation theory. Throughout, our calculations are made as explicit as possible so that this article may serve as a guide for similar calculations in other theories.

Frustration-induced incommensurate solids in the extended Bose-Hubbard model

We study the extended Bose-Hubbard model with nearest-neighbor and next-nearest-neighbor $(V, V')$ repulsive interactions on a square lattice by using the quantum Monte Carlo method. Unlike the case of strong $V'$ where the ground states can be striped solids or striped supersolids, we focus on weak $V' < V/2$ and small hoppings and find that, in the thermodynamic limit, incommensurate solids of fractional densities varying from 1/4 to 1/2 can be stabilized. We also show that the incommensurate solids, which are characterized by a continuous set of wave vectors changing from $(\pi,\pi/2)$ (or $(\pi/2,\pi)$) to $(\pi,\pi)$, can be understood by a mechanism of domain wall formation. The related ground-state phase diagram and thermal phase transitions are also discussed.

L‐Carnitine‐Based Bio‐Ionic Liquids as Antioxidants

AbstractThe purpose of this research was to determine the antioxidant properties of ionic liquids containing an anion showing antioxidant activity and a cation of natural origin derived from L‐carnitine. Formation methods of ionic liquids based on direct protonation of an L‐carnitine zwitterion form were evaluated with the selected phenolic acids and L‐ascorbic acid. All received compounds were characterized, and the physicochemical properties significant to ionic liquid uses were measured (thermal stability and phase transitions). All research on antioxidant activity was conducted using commonly applied spectrophotometric methods, allowing for assessment of the neutralization ability of compounds regarding various radicals. The ferrous and cupric ion reduction ability and ferrous ion chelation of the ionic liquids were also examined. Furthermore, ionic liquid activity toward the enzyme xanthine oxidase responsible for the formation of reactive oxygen species in the body was determined.

Reconfinement, localization, and thermal monopoles in SU(3) trace-deformed Yang-Mills theory

We study, by means of numerical lattice simulations, the properties of the reconfinement phase transition taking place in trace deformed $SU(3)$ Yang-Mills theory defined on $\mathbb{R}^3\times S^1$, in which center symmetry is recovered even for small compactification radii. We show, by means of a finite size scaling analysis, that the reconfinement phase transition is first-order, like the usual $SU(3)$ thermal phase transition. We then investigate two different physical phenomena, which are known to characterize the standard confinement/deconfinement phase transition, namely the condensation of thermal magnetic monopoles and the change in the localization properties of the eigenmodes of the Dirac operator. Regarding the latter, we show that the mobility edge signalling the Anderson-like transition in the Dirac spectrum vanishes as one enters the reconfined phase, as it happens in the standard confined phase. Thermal monopoles, instead, show a peculiar behavior: their density decreases going through reconfinement, at odds with the standard thermal theory; nonetheless, they condense at reconfinement, like at the usual confinement transition. The coincidence of monopole condensation and Dirac mode delocalization, even in a framework different from that of the standard confinement transition, suggests the existence of a strict link between them.

Ultrafast Thermal Melting in Nonequilibrium Warm Dense Copper.

The ultrafast dynamics of the loss of crystalline periodicity is investigated in femtosecond laser heated warm dense copper, by the original use of x-ray absorption near-edge specific structures just above the L3 edge. The characteristic time is observed near 1ps, for specific energy density ranging from 1 to 5 MJ/kg, using ps-resolution x-ray absorption spectroscopy. The overall experimental data are well reproduced with two-temperature hydrodynamic simulations, supporting a thermal phase transition.

Machine learning transition temperatures from 2D structure

A priori knowledge of physicochemical properties such as melting and boiling could expedite materials discovery. However, theoretical modeling from first principles poses a challenge for efficient virtual screening of potential candidates. As an alternative, the tools of data science are becoming increasingly important for exploring chemical datasets and predicting material properties. Herein, we extend a molecular representation, or set of descriptors, first developed for quantitative structure-property relationship modeling by Yalkowsky and coworkers known as the Unified Physicochemical Property Estimation Relationships (UPPER). This molecular representation has group-constitutive and geometrical descriptors that map to enthalpy and entropy; two thermodynamic quantities that drive thermal phase transitions. We extend the UPPER representation to include additional information about sp2-bonded fragments. Additionally, instead of using the UPPER descriptors in a series of thermodynamically-inspired calculations, as per Yalkowsky, we use the descriptors to construct a vector representation for use with machine learning techniques. The concise and easy-to-compute representation, combined with a gradient-boosting decision tree model, provides an appealing framework for predicting experimental transition temperatures in a diverse chemical space. An application to energetic materials shows that the method is predictive, despite a relatively modest energetics reference dataset. We also report competitive results on diverse public datasets of melting points (i.e., OCHEM, Enamine, Bradley, and Bergström) comprised of over 47k structures. Open source software is available at https://github.com/USArmyResearchLab/ARL-UPPER.

Magnetic Lovelock black holes with a cloud of strings and quintessence

We consider a model of exponential electrodynamics as a source of gravitational field and worked for the solution describing magnetic black hole surrounded by a quintessence and cloud of strings. In this set up, a new family of Lovelock black hole solutions of the gravitational field equations are constructed. The thermodynamics of these black holes is also studied and the mass as well as the other associated thermodynamic quantities such as Hawking temperature and heat capacity in terms of horizon radius are computed. These quantities are dependent on the parameters of exponential electrodynamics, cloud of strings and quintessential dark energy, which have been used for the identification of the regions corresponding to thermal phase transitions and thermodynamic stability of black holes. Furthermore, the effects of thermal fluctuations are also discussed and modified thermodynamic quantities associated to logarithmic correction in entropy are calculated. The Hawking radiations corresponding to these black holes are briefly discussed as well.

Dilaton black holes with logarithmic source in gravity’s rainbow

Starting from the suitable action of four-dimensional Einstein gravity, which is coupled to a scalar dilaton field and logarithmic nonlinear electrodynamics, the related field equations have been solved in a spherically symmetric and energy-dependent spacetime. It has been found that the scalar potential, as the exact solution of the scalar field equations, must be written as the linear combination of two Liouville-type potentials. Three families of novel exact black holes have been introduced as the exact solutions to the gravitational equations, which are asymptotically non-flat and non-AdS. It has been illustrated that our solutions, recover their corresponding quantities in the Einstein–Maxwell-dilaton gravity theory when the nonlinearity parameter of electrodynamics is chosen very large. The thermodynamic and conserved quantities of the black holes have been calculated under the influence of the rainbow function. Then, through calculation of the Smarr mass formula, we have shown that the first law of black hole thermodynamics remain valid for all of the new dilatonic black holes. Thermal stability or phase transition of the black holes have been investigated by use of the canonical ensemble and thermodynamic geometry approaches, separately. By comparison of the results of these two alternative approaches, it has been found that they lead to the same results provided that the thermodynamic metric of HPEM is used.

On Einstein-non linear-Maxwell-Yukawa de-Sitter black hole thermodynamics

We investigate the thermodynamics of the Einstein-non linear-Maxwell-Yukawa black hole solution in de Sitter spacetime. After presenting the black hole solution and its horizons, we use different thermodynamical points of view to probe the phase structure of such a black hole, ranging from local, global thermodynamics to effective thermodynamical formalism with two horizons. Our analysis showed that the black hole can undergo a thermal phase transition between an unstable phase and stable phase. These results are consolidated by our proposal of generalizing effective thermodynamics to three horizons. As a remarkable byproduct, we find that the effective temperatures behave as an association of ohmic resistances in an electric circuit, which may reveal a possible analogy between the electric and thermodynamic systems.

Composition, Thermal Expansion and Phase Transitions in Framework Silicates: Revisitation and Review of Natural and Synthetic Analogues of Nepheline-, Feldspar- and Leucite-Mineral Groups

Framework silicates form about 70% of the Earth’s crust, mainly feldspars ~50–60% and quartz ~10–15%. Less-abundant feldspathoids include nepheline-, leucite-, and sodalite-group minerals, rich in structurally challenging properties. This review paper deals with anhydrous feldspar-, nepheline-, and leucite/pollucite groups, emphasising the importance of parallel studies on natural and synthetic samples. Four topics are covered. For decades, petrologists have analysed nephelines and recalculated their compositions as endmember molecules but, by not following rules of stuffed-tridymite crystal chemistry, have not estimated reliably the excess SiO2 present in solid solution. Some materials scientists make similar mistakes, and a new approach is described here. Synthesis studies of analogue feldspars, nephelines, and leucite/pollucites led to collaborative studies, mainly using laboratory and synchrotron X-ray powder diffraction methods at room and elevated temperatures, to study thermal expansion and displacive phase transitions. Such work was recently expanded to address the spontaneous strain relations. Topics covered here include work on nepheline/kalsilite analogues in the system SrAl2O4—BaAl2O4; thermal expansion of (K,Na)Al-, RbAl-, RbGa-, and SrAl-feldspars; and thermal expansion and phase transitions in analogue leucites KGaSi2O6 (tetragonal to cubic) and K2MgSi5O12 (monoclinic to orthorhombic). Results are reviewed in the context of research published in mineralogical and more-widely in physical sciences journals.

Sintering behaviors and properties of porous ceramics derived from artificially cultured diatom frustules

AbstractBimodal porous ceramics with high strength have been fabricated by conventional powder metallurgy utilizing artificially cultured diatom frustules (DFs). The effect of sintering temperature on thermal behaviors, phase transition, and pore structures features of DFs‐based porous ceramics is investigated between 800 and 1200°C. The phase evolution of DFs powders is investigated with thermal analysis (DIL and DSC‐TG). Phase transition behaviors analyzed with XRD, Raman, and FT‐IR spectra confirm the transformation of quartz into cristobalite phases occurs under 1050°C. Sintering under 950°C could bind DFs powders tightly into high strength porous ceramics while maintain the multilayer pore structures simultaneously, having porosity of 56.4%, compressive strength of 15.0 MPa and surface area of 50.9 m2/g, respectively. Slit‐shaped microstructures and mesopores (2‐50 nm) are observed in DFs‐based porous ceramics sintered under 1050°C. Collapse and blockage of pore structures as well as partial fusion of DFs particles happened at the temperature of 1100°C, indicating the presence of diminished multilayers and particle agglomeration.

Thermal characterization of halloysite materials for porous ceramic preforms

Purpose: The aim of the study was to investigate the possibility of sintering raw (natural) halloysite and pure halloysite to produce porous ceramic preforms, and determination of sintering temperature based on the results of investigations into thermal effects, linear changes and phase transitions. Design/methodology/approach: Due to mullitisation ability of halloysite at high temperature, alternative applications based on the sintering technology (including the production of reinforcement of metal matrix composites) are being searched for. Pure halloysite and Dunino halloysite were selected for the study. Findings: Pure halloysite, characterized by low impurities, dimensional stability during sintering, softening temperature above 1500ºC and ability to transform into mullite at temperatures above 950ºC could be used as a base for the production of sintered, porous mullite preforms. Research limitations/implications: Presence of impurities in Dunino halloysite, contribute to the shift of the sintering temperature towards lower temperatures and caused a rapid and uncontrolled shrinkage of the sample and the appearance of the softening temperature at 1300ºC. Practical implications: Based on the research of thermal (DTA/TG, linear changes in high-temperature microscopy) and XRD studies it is possible to determine the sintering temperature of pure halloysite to manufacture the porous mullite preforms with open porosity. Originality/value: The received results show the possibility of obtaining the new mullite preforms based on pure halloysite.

Solid-state behaviors of imines: colossal biaxial positive thermal expansion, motion capability, and phase transitions

The torsional flexibility of imines affects solid-state packing and properties. Behaviors including colossal thermal expansion, pedal motion, and phase transitions in imine-containing solids are described.

Sinteza i karakterizacija pH-osetljivih poliuretanskih hidrogelova modifikovanih saharidima - uticaj poliola, umreživača i kiselinskog produživača lanca

Biodegradable polyurethanes can be the basis for drug delivery systems that are sensitive to external changes. pH-sensitive polyurethanes (PUs) have been used successfully as intravaginal rings and specific drug delivery systems for the colon. In this study, a series of pH-sensitive polyurethane hydrogels with a change of the polyol component (poly(ethylene glycol) 400/poly(propylene glycol) 2000/poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) 1100), saccharides as crosslinkers (melibiose/raffinose/starch) and a-hydroxy carboxylic acids as chain extenders (dimethylol propionic acid/lactic acid) were synthesized. Structural characterization of the synthesized polyurethane hydrogels was performed using Fourier transform infrared spectroscopy (FTIR), which showed that the polyurethane synthesis reaction was achieved with successful crosslinking with saccharides and, despite the change of starting components, FTIR spectra for all investigated samples are almost identical. The degree of swelling of the hydrogels was monitored at 25 °C in solutions of pH values 4.5 and 7.4. In samples with the polyol component block1100, the degree of swelling at pH 7.4 (16.09%) was up to 9 times higher than at pH 4.5 (1.82%). The effects of variable parameters on the thermal properties and phase transitions of PUs hydrogels were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that by varying the saccharide as a crosslinker, the acid chain extender and the chain length of the polyols, the stated properties of polyurethane hydrogels as potential drug delivery carriers can be influenced.