Phase Transition Behavior Research Articles

A “turn-on” polymer nanothermometer based on aggregation induced emission for intracellular temperature sensing

Temperature measurements at the nanoscale facilitate the understanding of physiological processes related to heat in cells. Herein, we prepare a tetraphenylethylene-functionalized fluorophore (TPPEBr) with dual characteristics of twisted intramolecular charge transfer (TICT) and aggregation induced emission (AIE). It is polymerized with a thermo-responsive unit NIPAM to construct a fluorescent polymer nanothermometer (PNIPAM-TPPEBr). The phase transition behavior of PNIPAM from dispersed chains to dense spheres in aqueous media promotes the aggregation of TPPEBr fluorophores, which makes the fluorescence of PNIPAM-TPPEBr enhance with increasing temperature. Furthermore, the phase transition of PNIPAM is accompanied by a significant decrease in the polarity of the microenvironment, resulting in a blue shift in the emission wavelength of TPPEBr. Varying the ratio of NIPAM and TPPEBr can regulate the thermo-responsiveness of PNIPAM-TPPEBr in the physiological temperature range (31–38 °C), and the maximum relative thermal sensitivity reaches 13.2 % °C−1. The thermo-responsive performance of this nanothermometer is independent of the intracellular microenvironment, and it is successfully applied in the temperature imaging of A549 cells. Under the stimulation of ionomycin and oxidative phosphorylation inhibitor, the cell temperature increased by ca. 1.5 °C and ca. 1.0 °C, respectively.

Interrogating the Solid–Solid Phase Transition Behavior of a Molecular Crystal with a Diverse Range of Solid-State Analytical Techniques and Computational Predictions

Interrogating the Solid–Solid Phase Transition Behavior of a Molecular Crystal with a Diverse Range of Solid-State Analytical Techniques and Computational Predictions

Phase transition and ionic conductivity of pyrrolidinium-based ionic plastic crystals with magnesium salts

Abstract Despite being safe for use in secondary Mg batteries, solid electrolytes exhibit lower ionic conductivities than those of traditional liquid electrolytes. Organic ionic plastic crystals—soft crystals with excellent thermal and electrochemical stabilities and ionic conductivities—are promising solid electrolytes. Herein, we investigated the effects of various anion species and Mg salt concentrations on the properties of pyrrolidinium-based organic ionic plastic crystals (N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide [[C2epyr][FSA]] and N,N-diethylpyrrolidinium bis(trifluoromethylsulfonyl)amide [[C2epyr][TFSA]]) upon Mg(TFSA)2 addition. The Mg-ion transference number (tMg2+) was measured using the Vincent–Bruce method; ionic conductivity via impedance measurements; and phase transition via differential scanning calorimetry. The phase transition behavior, dissociation state of the Mg salt, and electrochemical properties varied with the organic ionic plastic crystal anionic structure. The FSA system became liquid when the Mg salt concentration exceeded 15 mol%. The ionic conductivity of the pyrrolidinium-based organic ionic plastic crystals increased substantially with the Mg salt concentration. In the solid state, [C2epyr][FSA]/Mg(TFSA)2 (5 mol%) (FT5) showed the highest ionic conductivity (2.9 × 10−4 S cm−1 at 25 °C). The tMg2+ of FT5 at 60 °C was 0.29. Mg exhibited redox behavior in FT5 but not in [C2epyr][TFSA]/Mg(TFSA)2 (5 mol%). The FSA− structure is suitable for Mg electrochemistry and will aid in developing high-performance secondary Mg batteries.

Regulatory effects of cyclodextrins on light-responsive phase transition behaviors of poly(N-isopropylacrylamide-co-N-(4-phenylazophenyl)methylacrylamide)

The physicochemical properties of light-responsive polymers have attracted widespread attention due to their ability to be precisely and conveniently modulated by light without additives or contact. Here, we report a thermo/light dual-responsive polymer, PNMA, synthesized through the free radical copolymerization of azobenzene derivative (mAzo) and N-isopropylacrylamide (NIPAM) monomers. By switching between 365 nm UV light and 450 nm visible light, the E/Z photoisomerization of the light-responsive mAzo can be reversibly controlled, and thereby adjusting the conformational changes of the PNMA polymer chain. Significantly, the stretching and contraction conformations of PNMA polymer chains can be manipulated by incorporating different types of cyclodextrins. A comprehensive comparative study was conducted to determine the light-controlled binding and dissociation processes between the azobenzene units and CDs (α-CD, β-CD and γ-CD), the influences of CDs on the photoisomerization kinetics and complexation constants of azobenzene with CDs, as well as the effect of CDs on the light-responsive phase transition behaviors of PNMA. Our results highlight the superior advantage of α-CD in constructing light-responsive systems with significant changes in hydrophilicity. Notably, by tuning the concentration of α-CD and the proportion of mAzo in PNMA, the range of light-induced thermosensitive response is significantly expanded. This study is the first to present a comparative study on the effects of three CDs on the thermo/light dual-responsive properties of polymer systems based on PNIPAM and azobenzene, providing new ideas for CD selection in the design and construction of advanced light-responsive materials based on light-responsive guest-host dissociation or hydrophilic changes of azobenzene/CD complexes.

Microstructural evolution and phase transformation behavior of Ni-Ti alloys prepared by accumulative roll bonding-deformation diffusion process

Ni-Ti shape memory alloys were prepared by accumulative roll bonding-deformation diffusion (ARB-DD) process. Effects of deformation heat treatment on the microstructural evolution and phase transition behavior of ARB-DD Ni-Ti alloy were investigated by thermodynamic calculations, and the intrinsic mechanism was revealed. The results show that strong shear is induced by intensified plastic flow of the metal at the interface, resulting the interfaces engage with each other. The simultaneous opening and cross-tangling of multi-directional dislocations leads to the dislocation cells and Taylor lattice interact near the interface, and the compounds are preferentially formed. The ARB-DD treatment resulted in a one-step phase transition for the Ni-Ti alloy. After deformation heat treatment, R-phases appear and the phase transition is transformed into two-step. During heating and cooling the phase transitions are B19’→R→B2 and B2→R→B19’, respectively. The thermal hysteretic temperature increases and reaches 57.0 °C. The microstructure transforms from dislocations to nano-twin. A lattice distortion zone with a width of about 10 nm exists at the interface between precipitates and the matrix. It reduces the energy barrier required for phase transformation, leading to stabilization of the B2 phase and de-stabilization of the B19’ phase. Eventually, a wider temperature interval for the phase transformation is obtained. This process is an effective way to prepare Ni-Ti alloys with favorable shape memory effect.

High-pressure synthesis, crystal structure and anisotropic thermal/compressive behaviors of pseudo-ternary (V,Cr,Mo)P4

Pseudo-ternary CrP4-type (V,Cr,Mo)P4 was successfully synthesized at the conditions of 4 GPa and 900 °C by using a large volume multi-anvil-type press. SEM-EDS and STEM analyses revealed that the synthesized pseudo-ternary (V,Cr,Mo)P4 contains almost equimolar amounts of transition metals. The lattice parameters and unit cell volume of (V,Cr,Mo)P4 yield the average value of its end-members. The low-temperature (133 K–333 K) in-situ synchrotron XRD measurements demonstrated that the c-axis showed the highest coefficient of thermal expansion, followed by the b-axis and the a-axis. These thermal behaviors are the same as the binary end-members and pseudo-binary (V,Cr)P4. While from the high-pressure (P < 10 GPa) in-situ synchrotron XRD measurements, it was found that (V,Cr,Mo)P4 showed no phase transition and compression behaviors in which the c-axis was more compressible than the other two axes (b and a) and the b-axis was slightly compressible more than the a-axis. The zero-pressure bulk modulus of 106 (1) GPa and 122.1 (7) GPa were obtained for (V,Cr)P4 and (V,Cr,Mo)P4, respectively. MoP6 octahedral is highly distorted in comparison with VP4 and CrP4, thus the incorporation of MoP4 greatly yields incompressible behaviors of CrP4-type phosphides with respect to temperature and pressure.

Strain-induced continuous transition from orthorhombic to hexagonal-like phase in Ti-36Zr-6Nb alloy with abnormally high strain hardening

The deformation mechanism of the α″-type Ti-36Zr-6Nb alloy exhibiting an abnormal strain hardening behavior was investigated using in-situ high-energy X-ray diffraction and ex-situ transmission electron microscopy under tensile tests. It was discovered that the orthorhombic α″ phase distorts successively toward hexagonal symmetry during tension through coupled atomic shear and shuffle, and the successive distortion of the α″ lattice contributes to the abnormally high strain hardening of the Ti-36Zr-6Nb alloy. Notably, the orthorhombic α″ phase does not transform into an ideal hexagonal phase during tension but instead transforms into a hexagonal-like phase. The hexagonal-like phase exhibits shear and shuffle components that are very close to those of the ideal hexagonal phase. Additionally, the strain-induced α″ to hexagonal-like martensitic transition was found to be partially reversible during unloading. The present study offers an in-depth understanding of the abnormal strain hardening behavior and the strain-induced phase transition behavior of the α″-type titanium alloys.

Revealing the role of B-site cations in the antiferroelectricity of NaNbO3-based perovskites

The promising prospects of antiferroelectric perovskite oxides in the realm of energy storage applications hinge on the unique field-induced phase transitions. Once the transition is triggered by the application of an electric field, characteristic double polarization loops appear. However, NaNbO3-based materials that exhibit a reversible phase transition are still rare, which hinders the practical applications of lead-free antiferroelectrics. Here, the impact of materials chemistry on the competition between antiferroelectric and ferroelectric states is demonstrated in a series of NaNbO3-based solid solutions with varying perovskite B-site cations, while the A-site is fixed as strontium. The crystal structure is analyzed on the basis of Rietveld refinement of high-energy X-ray diffraction data. The phase transition behavior as well as the antiferroelectric and ferroelectric properties are probed by a series of electrical measurements. The antiferroelectric phase is universally observed for all investigated materials in the virgin state. The SrTiO3-substituted system shows an irreversible phase transition similar to that of pure NaNbO3. In contrast, double polarization hysteresis loops are observed in the SrHfO3-, SrZrO3-, and SrSnO3-substituted systems. It is confirmed that compounds that can reduce the tolerance factor of the system contribute to the stabilization of the antiferroelectric order, while those that can reduce the electronegativity difference lead to more pronounced double loops. The competition between antiferroelectricity and ferroelectricity is linked to the competition between covalent and ionic bonding in perovskites.

A numerical model for evaluating the long-term migration and phase transition behavior of foam-assisted injection of CO2 in saline aquifers

Geological Carbon Storage (GCS) is a rapidly developing technology with the potential to mitigate the environmental impact of excessive greenhouse gas emissions. Foam-assisted injection of CO2 can effectively alter fluid rheological properties, thereby enhancing sweep efficiency. In this paper, a numerical model to evaluate the long-term migration behavior of foam-assisted injected CO2 in saline aquifers is developed. It is found that foam-assisted injection improves storage efficiency and reduces the plume migration distance compared to direct CO2 injection. This creates higher demands on the injection pressure but minimizes the risk of leakage. The effects of injection strategy, volume fraction of foam, and reservoir heterogeneity were investigated. Modeling results show that the injection strategy with a high foam volume fraction enhances the sweep efficiency and improves the transition rate of injected CO2 to the dissolved state. This can effectively enhance the long-term security of the sequestration. Simulations of layered formations indicates that foams can potentially inhibit the rapid migration of plumes along high-permeability zones. Our study provides insights for foam-assisted injection to enhance reservoir storage efficiency and long-term safety for GCS.

Fabricating highly stable and reliable vanadium dioxide thin films: Insights from radio frequency magnetron sputtering

This study establishes an optimization protocol to fabricate a stoichiometric VO2 thin film onto the glass substrate using a single process step in RF magnetron sputtering. An interplay between the substrate temperature and the oxygen-to-argon ratio in process gas is shown to achieve a range of VOx composition (from oxygen-rich to oxygen-deficient phases). The re-sputtering phenomenon is found to be crucial at higher temperature (T ≥ 873 K), leading to a shift in stoichiometry from V2O5 to V2O3. Moreover, a process model for the fabrication of various VOx compounds in thin film form is also established in this study. The crystal structure transformation from M1 to R phase for these VO2 thin films deposited over a range of process conditions is found to be 339 ± 1 K, in close agreement with the reported value for the bulk VO2. In spite of the microstructural variations, these films are found to show consistent phase transition behavior, excellent stability, and reliability in repeated thermal cycles. These films show a semiconductor-to-metal transition, which is correlated to their structural phase transformation temperature. Moreover, this study also establishes a correlation between various external stimuli, widening the usage of this material in a range of applications.

Phase transition and internal friction behaviors in Mn-doped Co-V-Ga shape memory alloys

Shape memory alloys with a high abundance of mobile interfaces exhibit remarkable internal friction (IF) behaviors, which can be utilized for the reduction of noise and vibration. In this study, we systematically investigate the martensitic transformation and internal friction behaviors in the Mn-doped Co53V35–xGa12Mnx (x = 0 - 10) polycrystalline alloys. Our findings indicate that using Mn to replace V results in decreased transformation temperatures but increased thermal hysteresis. The addition of Mn enhances magnetic exchange interaction, leading to a gradual enhancement in magnetization difference across martensitic transformation, thereby compromising the transformation entropy change and arresting the martensitic transformation. At a frequency of 0.4 Hz, the intensity of transformation IF peak is enhanced from 0.124 to 0.178 with increasing the Mn content from 0 to 4.5 %, as a result of deteriorated geometrical compatibility between austenite and martensite due to the addition of Mn. Furthermore, hydrogenation treatments substantially improve both the peak intensity and frequency dependence of peak position for the relaxation-type IF, demonstrating the great contribution from hydrogen-twin boundary interaction.

A Thermosensitive Ionic Hydrogel for Thermotropic Smart Windows With Integrated Thermoelectric Energy Harvesting Capability

AbstractHarvesting low‐grade waste heat into electrical energy is recognized as a promising solution for sustainable energy supply. In parallel, thermotropic smart windows have emerged as an efficient way to reduce building energy consumption. It is posit that thermotropic smart windows with inherent thermoelectric property may offer unique advantages for practical applications. Herein, the preparation and characterization of a series of ionic hydrogels that exhibit temperature‐sensitive phase transition behavior is reported, which are suitable for both thermotropic smart windows and thermoelectric generators. Notably, the lower critical solution temperature (LCST) of this ionic hydrogels can be feasibly modulated, and the thermoteopic phase transition also induces a sharp increase in their Seebeck coefficient, reaching up to 39.03 mV K−1 with a power factor (PFi) value up to 0.838 mW m−1 K−2. A prototype dual functional thermotropic smart window that simultaneously works as an ionic thermoelectric generator is further demonstrated, achieving both efficient phase transition driven by solar heat at ≈26 °C and an energy density up to 250 mJ m−2. This study offers new opportunity for the development of smart materials that can bridge the gap between thermal comfort and energy sustainability for energy harvesting and smart building applicat.

Intrinsically Flexible Phase Change Fibers for Intelligent Thermal Regulation

AbstractOwing to the significant latent heat generated at constant temperatures, phase change fibers (PCFs) have recently received much attention in the field of wearable thermal management. However, the phase change materials involved in the existing PCFs still experience a solid–liquid transition process, severely restricting their practicality as wearable thermal management materials. Herein, we, for the first time, developed intrinsically flexible PCFs (polyethylene glycol/4,4′‐methylenebis(cyclohexyl isocyanate) fibers, PMFs) through polycondensation and wet‐spinning process, exhibiting an inherent solid‐solid phase transition property, adjustable phase transition behaviors, and outstanding knittability. The PMFs also present superior mechanical strength (28 MPa), washability (&gt;100 cycles), thermal cycling stability (&gt;2000 cycles), facile dyeability, and heat‐induced recoverability, all of which are highly significant for practical wearable applications. Additionally, the PMFs can be easily recycled by directly dissolving them in solvents for reprocessing, revealing promising applications as sustainable materials for thermal management. Most importantly, the applicability of the PMFs was demonstrated by knitting them into permeable fabrics, which exhibit considerably improved thermal management performance compared with the cotton fabric. The PMFs offer great potential for intelligent thermal regulation in smart textiles and wearable electronics.

Intrinsically Flexible Phase Change Fibers for Intelligent Thermal Regulation.

Owing to the significant latent heat generated at constant temperatures, phase change fibers (PCFs) have recently received much attention in the field of wearable thermal management. However, the phase change materials involved in the existing PCFs still experience a solid-liquid transition process, severely restricting their practicality as wearable thermal management materials. Herein, we, for the first time, developed intrinsically flexible PCFs (polyethylene glycol/4,4'-methylenebis(cyclohexyl isocyanate) fibers, PMFs) through polycondensation and wet-spinning process, exhibiting an inherent solid-solid phase transition property, adjustable phase transition behaviors, and outstanding knittability. The PMFs also present superior mechanical strength (28 MPa), washability (>100 cycles), thermal cycling stability (>2000 cycles), facile dyeability, and heat-induced recoverability, all of which are highly significant for practical wearable applications. Additionally, the PMFs can be easily recycled by directly dissolving them in solvents for reprocessing, revealing promising applications as sustainable materials for thermal management. Most importantly, the applicability of the PMFs was demonstrated by knitting them into permeable fabrics, which exhibit considerably improved thermal management performance compared with the cotton fabric. The PMFs offer great potential for intelligent thermal regulation in smart textiles and wearable electronics.

Topological equivalence and phase transition rate in holographic thermodynamics of regularized Maxwell theory

Utilizing the holographic dictionary from the proposal that treats Newton’s constant as a thermodynamic variable, we establish a thermodynamic topological equivalence between the AdS black holes in the bulk and the thermal states in the dual CFT. The findings further reveal that the thermodynamic topological characteristics of the RegMax AdS black holes are strongly influenced by the characteristic parameter of the regularized Maxwell theory. Additionally, we investigate the phase transition between low and high entropy thermal states within a canonical ensemble in the dual CFT. Our observations indicate that the phase transition behavior of the thermal states mirrors that of the black holes. By modeling the phase transition process as a stochastic process, we are able to calculate the rates of phase transition between the thermal states. This result enhances our understanding of the dominant processes involved in the phase transition of the thermal states in the dual CFT.

A novel ionic liquids phase change absorption system for carbon dioxide capture and utilization

In order to achieve low cost, and reduce energy consumption during regeneration, a novel ionic liquid phase change absorbent composed of tetraethylenepentamine [TEPA] imidazole [Im] and diethylene glycol dimethyl ether (DGME) and water was designed for CO2 capture applications. The absorbent [TEPAH][Im]+DM+H2O can achieves a CO2 absorption capacity of 2.08 mol CO2/mol ILs, the rich phase volume accounts for 15.6 vol%, and the mass fraction of CO2 is 99 %, this greatly reduces the regenerative volume of the absorption system, showing the potential of energy saving and emission reduction. After five absorption–desorption cycles, the regeneration efficiency of the system remained above 96 %. The CO2 capture mechanism was analyzed using both 13C NMR spectroscopy and density functional theory (DFT) calculations to elucidate its underlying processes. The cation [TEPAH]+ and the anion [Im]- each undergo a reaction with CO2 to produce carbamate, followed by hydrolysis of carbon dioxide to yield carbonate. The absorption system’s phase transition behavior primarily arises from variations in CO2 product solubility across solvents. Moreover, the ionic liquid facilitated the conversion of CO2 into quinazoline-2,4 (1H, 3H)-dione with a remarkable yield of 98 %. Even after five cycles, the ILs maintained substantial catalytic activity.

Optimizing energy storage performance of lead zirconate-based antiferroelectric ceramics by a phase modulation strategy

Dielectric energy storage has gained considerable significance owing to the high energy requirements of human society. Lead zirconate-based (PZ) antiferroelectric materials have received much attention due to their fast discharge rate, high power density, and low cost. Nevertheless, their low energy storage density seriously limits their practical applications. To overcome this limitation, the phase modulation strategy via chemical modification was adopted to optimize the breakdown strength and phase switching field. Specifically, the antiferroelectric ceramics of (Pb0.97−xGd0.02Srx)(Zr0.87Sn0.12Ti0.01)O3 were prepared by the tape-casting method. An apparent multistage phase transition behavior revealed for x ≥ 0.05 is rarely discussed in reported Sr2+ modified PZ system. This is attributed to the coexistence of the main orthorhombic phase and the tetragonal phase. Although the transition near the lower field reduces the energy storage slightly, the disruption of the long-range order stabilizes the antiferroelectricity of the orthorhombic phase, hence elevating its transition field. In addition, the tetragonal phase with lower polarization suppresses the electrostrain thus improving the breakdown strength. Consequently, an ultrahigh recoverable energy storage density of 14.5 J/cm3 with a high energy efficiency of 81 % is achieved at a high electric field of 717 kV/cm for (Pb0.92Gd0.02Sr0.05)(Zr0.87Sn0.12Ti0.01)O3. Moreover, the fatigue resistance of this composition is excellent within 26,000 fatigue cycles. Besides, it exhibits a high discharge energy density of 9.4 J/cm3 and a great power density of 387 MW/cm3. These results confirm that the energy storage properties of PZ-based antiferroelectric materials can be effectively optimized via a phase modulation strategy.

Exploring the Premelting Transition through Molecular Simulations Powered by Neural Network Potentials

The premelting layer on crystal surfaces significantly affects the stability, surface reactivity, and phase transition behaviors of crystals. Traditional methods for studying this layer—experimental techniques, classical simulations, and even first-principle simulations—have significant limitations in accuracy and scalability. To overcome these challenges, we employ molecular dynamic simulations based on neural network potentials to investigate the structural and dynamic behavior of the premelting layer on ice. This approach matches the accuracy of first-principle calculations while greatly improving computational efficiency, allowing us to simulate the ice–vapor interface on a much larger scale. In this study, we conducted a one-nanosecond simulation of the ice–vapor interface involving 1024 water molecules. This significantly exceeds the time and size scales of previous first-principle studies. Our simulation results indicate complete surface melting. Furthermore, our simulation results reveal dynamic heterogeneity within the premelting layer, with molecules segregated into clusters of low and high mobility.

Phase transitions in Pb0.96La0.04(Zr0.95Ti0.05)O3 capacitors by in-situ AC-HRTEM

Antiferroelectrics (AFEs) undergo reversible antiferroelectric-ferroelectric (AFE-FE) phase transitions under external electric fields, and show great promise in modern electronic devices. The real-time phase transition behavior of pure PZO has been detected, while the dynamic studies of complex incommensurately modulated structure have never been addressed. Here, with the strong support of in-situ aberration corrected high resolution transmission electron microscopy (AC-HRTEM), the structural evolutionary behaviors in Pb0.96La0.04(Zr0.95Ti0.05)O3 (PLZT) film excited by energetic electron beams is decoded. The AFE-to-FE phase transition occurs via a 90° reorientation and a rapid expansion of domain boundary region at the expense of the initial AFE matrix. At the same time, the modulation periods experience a monotonic increase in the reorientation region. The observation is of certain significance to establish the deep-seated phase transition mechanism, which will facilitate the development of antiferroelectric-based nanoelectronics.

Holographic entanglement properties in the QCD phase diagram from Einstein-Maxwell-dilaton models

In this study, we investigate the behavior of entanglement properties in the QCD phase diagram using holographic Einstein-Maxwell-dilaton models. We consider two representative holographic QCD models and examine various entanglement measures, including entanglement entropy, conditional mutual information, and the entanglement of purification. We find that the entanglement entropy obtained using the direct UV-cutoff renormalization method shows significant dependence on the specific model being used. However, the outcomes of other nondivergent entanglement measures, such as cutoff-independent entanglement entropy, conditional mutual information, and the entanglement of purification, exhibit congruence in our calculations. When we focus specifically on the temperature range below 300 MeV, we observe a similar behavior among the three entanglement measures. This may suggest that within this temperature range, the entanglement of QCD matter decreases with increasing temperature. Additionally, we observe distinct phase transition behaviors of entanglement properties at the critical end point and first-order phase transitions. This observation highlights the potential of entanglement properties as effective order parameters for QCD matter phase transitions. Published by the American Physical Society 2024