Temperature-induced Phase Transition Research Articles

Insights into temperature-induced phase transition mechanism of CL-20 using terahertz spectroscopy

Understanding the phase transition mechanism of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is crucial for ensuring its safe applications. In this study, we observed the temperature-induced phase transition of CL-20 using terahertz spectroscopy. Subsequently, quantum chemical calculations were employed to assign the vibrations to experimental absorptions. Finally, the variations of intra- and intermolecular vibrations before and after phase transition were analyzed. The results indicated hydrogen bonds formed by the rotation of 5-nitro promoted hydrogen transfer, resulting in the decrease in thermal stability.

Nanoencapsulation of carotenoid extract via the temperature-induced phase transition of triblock polymer in supercritical carbon dioxide

Abstract Objectives Carotenoids are increasingly explored as nutraceuticals, but their low bioavailability due to poor aqueous solubility limits their applications. This study discusses the development of a novel and organic solvent-free method to develop carotenoid-containing polymeric nanoparticles via temperature-induced phase transition (TIPT) of pluronic F-68 to obtain formulations with the improved dissolution of carotenoids. Methods The nanoencapsulation of carotenoids in pluronic F-68 was performed in supercritical carbon dioxide (scCO2) to avoid oxidative or temperature/solvent-induced degradation. The nanoencapsulates were prepared in scCO2 at 40°C or 60°C and 10 MPa without the aid of any organic solvent. The formulations thereafter were characterised for particle size via dynamic light scattering, particle morphology via scanning electron microscopy and carotenoid content/release via high-performance liquid chromatography (HPLC). Key findings HPLC results showed carotenoid degradation to be negligible in freshly prepared formulations when prepared in scCO2 at 60°C and 10 MPa. The developed particles were spheroidal with sizes ranging between 150 and 250 nm depending on carotenoid content in the preparation. An improvement in the aqueous solubility and storage stability (5°C) of carotenoids was also observed for the formulations prepared in scCO2. Conclusions These results suggest that TIPT under scCO2 can be applied to formulate nanoparticulates with improved dissolution rate and stability of thermosensitive molecules such as carotenoids without causing any degradation during the processing.

Application of upconversion nanoparticles as a thermal sensor for biological tissue

The paper shows the possibility of simultaneous registration of the temperature of nanoparticles embedded in the fat layer and temperature-induced phase transitions in the fat layer. The luminescence spectra of upconversion particles (UCNPs) were measured and analyzed in a wide temperature range: from room to physiological and further to a hyperthermic temperature resulting in tissue morphology change. Typical samples thickness of adipose tissue was 0.5 mm. The sample temperature varied between 25 °C and 60 °C. The temperature dependence of the UCNPs luminescence intensity from UCNPs deposited onto the sample surface (1 layer) and from UCNPs deposited between two layers of abdominal adipose tissue was recorded. In the course of adipocyte heating, lipids of fat droplet first transit from a crystalline form to a liquid crystal form and then to a liquid form, which is characterized by much less scattering. The high-temperature transition is recorded most well. The obtained results confirm a high sensitivity of the luminescent UCNPs to the temperature variations within tissues and show a strong potential for the controllable tissue thermolysis.

Vanadium dioxide thin films-assisted terahertz meta-surface for simultaneous absorption, polarization conversion bi-functional switching, and wavefront operation

Actively switchable metasurfaces are extremely useful for achieving a multifunctional integrated platform. The proposed design enables functional switching through the temperature-induced phase transition features of vanadium dioxide (VO2). The hypothesized metasurface can be considered a broadband absorber when VO2 is in the metallic phase, with an absorption rate approaching 90% in the frequency spectrum of 1.41–2.69 THz, according to numerical simulations. When VO2 is in the insulating phase, the proposed metasurface acts as a half-wave plate with more than 80% polarization conversion rate (PCR) in the frequency range of 0.71–2.72 THz. Furthermore, the dynamic modulation of absorbance and PCR can be achieved when the VO2 conductivity varies within a specific range. Finally, by changing the opening angle of the gold split-ring resonator to introduce an abrupt phase at the interface, the composed metacell can perform arbitrary manipulation of reflected beams in the 1.0–2.2 THz broadband range; we also design 1D and 2D focusing metalenses. Both have good subwavelength focusing characteristics. Therefore, the proposed metasurface can be effectively applied in sixth-generation communication systems, terahertz imaging, and other technologies.

Order-Disorder Phase Transition and Ionic Conductivity in a Li2B12H12 Solid Electrolyte.

Temperature-induced phase transitions and ionic conductivities of Li2B12H12 and LiCB11H12 were simulated with the use of machine learning interatomic potentials based on van der Waals-corrected density functional theory (rev-vdW-DF2 functional). The simulated temperature of order-disorder phase transition, lattice parameters, diffusion, ionic conductivity, and activation energies are in good agreement with experimental data. Our simulations of Li2B12H12 uncover the importance of the reorientational motion of the [B12H12]2- anion. In the ordered α-phase (T < 625 K), these anions have well-defined orientations, while in the disordered β-phase (T > 625 K), their orientations are random. In vacancy-rich systems, its complete rotation was observed, while in the ideal crystal, the anions display limited vabrational motion, indicating the static nature of the phase transition without dynamic disordering. The use of machine learning interatomic potentials has allowed us to study large systems (>2000 atoms) in long (nanosecond-scale) molecular dynamics runs with ab initio quality.

Temperature-dependent Raman spectra and thermal expansion of MgP2O6

The Raman spectra and thermal expansion of MgP2O6 metaphosphate were investigated at various temperatures up to 1073 K at ambient pressure. No temperature-induced phase transition was observed in this study. The effect of temperature on the Raman active vibrations and unit cell parameters was determined. All the observed Raman active bands of MgP2O6 showed linear temperature dependences in the range of −2.61 × 10−2 ∼ −0.49 × 10−2 cm−1 K−1. The thermal expansion coefficient of MgP2O6 was estimated to be 3.21(2) × 10−5 K−1. An axial anisotropic thermal expansion exists and the c-axis shows the smallest thermal expansion. The isobaric mode Grüneisen parameters of MgP2O6 were calculated. The obtained results were compared with other compounds in the MgO-P2O5 system.

Systemic approach in the study of the properties and pressure-induced structural transformations in TaN: First-principles molecular dynamics simulations

First-principles molecular dynamics simulations were used to investigate pressure- and temperature-induced phase transitions in different TaN polymorphs. The driving forces and intermediate structures were established for the CoSn-like TaN (ε phase) to WC-type TaN (θ phase) and ε to NaCl type-TaN (δ phase) structural transformations that were observed in experiments and for the θ to hP4-194, θ to cP2-221, δ to cP2-221 and δ to tP4-129 phase transitions that were predicted in this investigation. Other possible TaN polytypes were systematically investigated and five new prospective phases were found: oP8-25, oP12-25, hP8-194, tP8-105 and tI8-109. All new structures are thermodynamically, dynamically and mechanically stable, and their formation energy is only slightly higher than that of the θ phase (by 0.014–0.032 eV/atom). The relative stability, electronic structure, chemical bonding, vibrational spectra, elastic moduli and their spatial anisotropy, Vickers hardness, fracture toughness, Debye temperature and optical properties (real and imaginary parts of the dielectric function, reflectivity spectrum) of the tantalum mononitrides mentioned above were systematically calculated and discussed. The oP12-25, tP8-105 and tI8-109 novel phases exhibit the Vickers hardness (33.1–34.2 GPa), fracture toughness (5.52–5.59 MPa m1/2) and Debye temperatures (609.7–616.1 K) that are higher compared to those of the known TaN structures. The TaN polytypes with the strong Ta-N bonds with minimal fraction of ionicity were found to possess the best mechanical properties. Further experimental investigations are highly desirable to confirm the results presented in this paper.

Hypo-Osmotic Stress and Pore-Forming Toxins Adjust the Lipid Order in Sheep Red Blood Cell Membranes.

Lipid ordering in cell membranes has been increasingly recognized as an important factor in establishing and regulating a large variety of biological functions. Multiple investigations into lipid organization focused on assessing ordering from temperature-induced phase transitions, which are often well outside the physiological range. However, particular stresses elicited by environmental factors, such as hypo-osmotic stress or protein insertion into membranes, with respect to changes in lipid status and ordering at constant temperature are insufficiently described. To fill these gaps in our knowledge, we exploited the well-established ability of environmentally sensitive membrane probes to detect intramembrane changes at the molecular level. Our steady state fluorescence spectroscopy experiments focused on assessing changes in optical responses of Laurdan and diphenylhexatriene upon exposure of red blood cells to hypo-osmotic stress and pore-forming toxins at room temperature. We verified our utilized experimental systems by a direct comparison of the results with prior reports on artificial membranes and cholesterol-depleted membranes undergoing temperature changes. The significant changes observed in the lipid order after exposure to hypo-osmotic stress or pore-forming toxins resembled phase transitions of lipids in membranes, which we explained by considering the short-range interactions between membrane components and the hydrophobic mismatch between membrane thickness and inserted proteins. Our results suggest that measurements of optical responses from the membrane probes constitute an appropriate method for assessing the status of lipids and phase transitions in target membranes exposed to mechanical stresses or upon the insertion of transmembrane proteins.

Phase-Controlled Cobalt Catalyst Boosting Hydrogenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran.

The search for non-noble metal catalysts for chemical transformations is of paramount importance. In this study, an efficient non-noble metal catalyst for hydrogenation, hexagonal close-packed cobalt (HCP-Co), was synthesized through a simple one-step reduction of β-Co(OH)2 nanosheets via a temperature-induced phase transition. The obtained HCP-Co exhibited several-times-higher catalytic efficiency than its face-centered cubic cobalt (FCC-Co) counterpart in the hydrogenation of the C=C/C=O group, especially for the 5-hydroxymethylfurfural (HMF) hydrogenation (8.5-fold enhancement). Density functional theory calculations demonstrated that HMF molecules were adsorbed more firmly on the (112_0) facet of HCP-Co than that on the (111) facet of FCC-Co, favoring the activation of the C=O group in the HMF molecule. The stronger adsorption on the (112_0) facet of HCP-Co also led to lower activation energy than that on the (111) facet of FCC-Co, thereby resulting in high activity and selectivity. Moreover, HCP-Co exhibited outstanding catalytic stability during the hydrogenation of HMF. These results highlight the possibility of fabricating hydrogenation catalysts with satisfactory catalytic properties by precisely tuning their active crystal phase.

Functional properties and shape memory effect of Nitinol manufactured via electron beam powder bed fusion

Ti-rich Nitinol (NiTi) is characterized by its functional properties to restore its original shape after deformation due to a temperature-induced reversible martensitic phase transition. In this study, dense Ti-rich Nitinol free of cracks is successfully produced by means of Electron Beam Powder Bed Fusion (PBF-EB). The martensitic phase transition behavior of the as-built NiTi parts and powder is analyzed using Differential Scanning Calorimetry (DSC) analysis. To gain a deep understanding of the DSC results, segregation during solidification is thermodynamically studied (CALPHAD). The PBF-EB-fabricated NiTi shows a microstructure containing fine columnar grains and numerous precipitates, whose influence on the tensile properties at room temperature is discussed. Furthermore, the one-way and two-way shape memory effects of PBE-EB-produced NiTi are investigated using an innovative experimental setup based on thermomechanical training.

Insight into Eu3+-Doped Phase-Change K3Lu(PO4)2 Phosphate toward Data Encryption.

Adjusting the local coordination environment of lanthanide luminescent ions can modulate their crystal-field splittings and broaden their applications in the relevant optical fields. Here, we introduced Eu3+ ions into the phase-change K3Lu(PO4)2 phosphate and found that the temperature-induced reversible phase transitions of K3Lu(PO4)2 (phase I ⇆ phase II and phase II ⇆ phase III, below room temperature) give rise to an obvious photoluminescence (PL) difference of Eu3+ ions. The Eu3+ emission mainly focused on the 5D0 → 7F1 transition in phase III but manifested comparable 5D0 → 7F1,2 transitions in the two low-temperature phases. On this basis, the change of Eu3+-doped concentration led to the phase evolution in Eu3+:K3Lu(PO4)2, which could stabilize two types of low-temperature polymorphs to the specific temperature by controlling the doping content. Finally, we proposed a feasible information encryption strategy based on the PL modulation of Eu3+:K3Lu(PO4)2 phosphors, which was caused by the temperature hysteresis of the relevant phase transition, exhibiting good stability and reproducibility. Our findings pave an avenue for exploring the optical application of lanthanide-based luminescent materials by introducing phase-change hosts.

A large modulation of spin pumping using magnetic phase transitions in single crystalline dysprosium

We report a large modulation of spin pumping using temperature-induced magnetic phase transitions in c-axis oriented single crystalline dysprosium (Dy). From the temperature variation of the magnetic susceptibility, transitions from paramagnetic (PM) to ferromagnetic (FM) phases via antiferromagnetic (AFM) phase are clearly observed in the Dy. Unlike polycrystalline Dy, the spin pumping of both PM- and AFM-Dy are strongly suppressed owing to the increased non-dissipative backflow of spin current by the long-range spin transport, although two orders of magnitude difference exist between FM- and AFM-phases.

Liquid metal-filled phase change composites with tunable stiffness: Computational modeling and experiment

Liquid metal-filled phase change composites have promising applications as tunable stiffness components and reconfigurable structures in soft robotics, actuators, and metamaterials. At present, there is a lack of mechanistic understanding on the microscale-macroscale correlation of their mechanical behaviors. To fill this knowledge gap, we employ computational micromechanics modeling to simulate and reproduce the macroscopic mechanical behaviors of these liquid metal composites. Specifically, the liquid metal composites are simulated using representative volume elements and the particle-matrix interfaces are modeled as cohesive surfaces. The model is able to predict not only the stress-strain curves of the composites with temperature-induced phase transition but also progressive debonding between the particles and the polymer matrix. Moreover, the computational model also reproduces the debonding-induced Mullins effect of the liquid metal composites. The simulation results agree well with our experimental data by calibrating the modeling parameters carefully.

High performance composition-tailored PVDF triboelectric nanogenerator enabled by low temperature-induced phase transition

Polyvinylidene difluoride (PVDF) polymers are widely used in triboelectric nanogenerators (TENGs) due to their excellent dielectric and piezoelectric properties. To design a high-performance TENG, it is essential to investigate the individual contributions of these properties on contact electrification (CE). In this work, a range of PVDF, co- and terpolymers are used to assess the distinct contributions of dielectric and piezoelectric properties on the TENG’s output. As elucidated by a modified overlapped electron cloud model (OEC) supported with Kelvin Probe Force Microscopy (KPFM) measurements, the high dielectric constant in terpolymers hinders electron backflow after CE, while piezoelectric polarization in β-phase PVDF shifts its electron energy levels before CE. Notably, in PVDF polymers, the dielectric and piezoelectric enhancements to TENGs come at the expense of one another. To verify this phenomenon, the terpolymers are cooled to alter their phases from relaxor to regular ferroelectrics, diminishing their dielectric constants while increasing their piezoelectric polarizations. Initially, the output is high (10.2 W/m2) at room temperature during the relaxor ferroelectric phase which is due to the high dielectric constant. Upon cooling, the output decreased to its lowest during the phase transition (4.3 W/m2 at 0 °C), as a result of the tradeoff between dielectric and piezoelectric enhancement. When the temperature was further tuned down to − 40 °C, the output reaches the maximum of 16 W/m2, which is attributed mainly to the ferroelectric phase. For the first time, the phase transition is observed and evidenced by electric field-induced dielectric and ferroelectric measurements, proving the piezoelectric polarization of PVDF terpolymers. These findings therefore provide guidelines on material selection and pave the way for potential low-temperature TENG applications.

Highly mismatched antiferroelectric films: Transition order and mechanical state

Epitaxial ${\mathrm{PbZrO}}_{3}/{\mathrm{SrRuO}}_{3}/{\mathrm{SrTiO}}_{3}$ heterostructures are among the most widely studied thin-film antiferroelectrics. This paper explores their temperature-induced phase transitions and the characteristics of the domain structure by means of high-resolution synchrotron x-ray diffraction. The antiferroelectric transition order appears to change from the first to the second; peculiar in-plane $M$-point superstructures develop at high temperatures, manifesting a new phase; the $R$- and $\mathrm{\ensuremath{\Sigma}}$-point superstructure reflections demonstrate much reduced splitting as compared to the demands of the mechanical compatibility. We discuss the energetics of the reduced around-the-normal antiferroelectric domain tilts, its relation to the observed changes in phase transitions, and point to the possible contribution to the observed effect from an unusual diffraction mechanism related to the partial coherence between domains in a random nanodomain structure.

Cyclic versus Linear Alkylammonium Cations: Preventing Phase Transitions at Operational Temperatures in 2D Perovskites.

Two-dimensional lead halide perovskites offer numerous attractive features for optoelectronics owing to their soft, deformable lattices and high degree of chemical tunability. While alteration of the metal and halide ions gives rise to significant modification of the bandgap energy, the organic spacer cations offer in-roads to tuning phase behavior and more subtle functionalities in ways that remain to be understood. Here, we study six variations of 2D perovskites changing only the organic spacer cations and demonstrate that these components intrinsically impact material response in important ways such as altering crystallographic structure, temperature-induced phase transitions, and photoluminescence emission. Two-dimensional perovskites containing commonly utilized aliphatic linear spacers, such as butylammonium, undergo phase transitions near room temperature. These transitions and temperature changes induce spacer-dependent variations in the emission spectra. Conversely, 2D perovskites comprising cyclic aliphatic spacers, such as cyclobutylammonium, are found to lack first-order phase transitions. These cyclic molecules are more sterically hindered within the crystal lattice, leading to temperature-induced contraction or expansion along certain crystallographic planes but no other significant thermal effects; additionally, they undergo changes in their emission spectra that cannot be explained by simple thermal expansion. Given the similarities in the dielectric and chemical makeup of this set of six alkylammonium molecules, these results are unexpected and suggest a large structural and thermal phase space via spacer manipulation that could lead to improved 2D perovskite functionalization.

Reversible Transition between Discrete and 1D Infinite Architectures: a Temperature-Responsive Cu(I) Complex with a Flexible Disilane-bridged Bis(pyridine) Ligand.

Thermoresponsive molecular structure based on a disilane-bridged bis(pyridine) ligand and CuI is reported. Single-crystal X-ray analysis revealed that there are two polymorphs in the Cu(I) complex: octanuclear copper(I) complex at 20 °C and 1D staircase copper(I) polymer complex at -196 °C. The formation of these polymorphs is due to the flexibility of ligand. Cu-I bond formation is observed upon cooling the sample from -10 °C to -170 °C. The temperature-induced phase transition progression was clarified by DSC, VT-PXRD, and VT-photoluminescence measurements and indicated a reversible temperature-controlled crystal-to-crystal phase transition. Observation on a VT-stage using a high-speed camera showed crystal cracking during single-crystal to single-crystal transitions between these polymorphic forms.

Probing the physicochemical interactions between thermo-thickening polymers and clay fluids for improve rheological performance

The field of thermo-thickening polymer interacting with clay has long been shrouded in mystery and ambiguity. Despite numerous studies and investigations, the complex interactions, underlying mechanism and binding forces remain elusive, imposing further exploration and elucidation. In this study, three thermo-thickening polymers such as poly(acrylamide methylpropane sulfonic acid-co-N-vinylcaprolactam) (PNV), poly(acrylamide methylpropane sulfonic acid-co-N,N-dimethylacrylamide) (PDM), and poly(acrylamide methylpropane sulfonic acid-co-N-isopropylacrylamide) (PNP) with clay fluids (CFs) were investigated to gain deeper understanding of the underlying physicochemical interactions. Techniques such as Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and elemental analysis (EA) elucidated the structural properties, whereas turbidimetry and rheometric analysis elucidated the temperature-induced phase transitions. The interactions between the different polymer side chains and clay double-sheets were investigated through isothermal adsorption testing, probing chemisorption and hydrogen bonding tuned the chemical properties, whereas electrostatic forces (ionic/van der Waals) bind the physical properties as demonstrated by Zeta (ζ) potential, XRD, high-resolution spectroscopy (XPS), and scanning electron microscopy (SEM) imaging. The addition of 0.2–1.5 wt% of the polymers induced significant effect on the rheological properties of CFs, with increase in low shear viscosity and plastic viscosity, attributed to the formation of gel-like structures at high temperatures. PNV/Clay (NVBF)-modified fluid demonstrated exceptional fluid thickening and suspension behaviors compared to linear PDM/Clay (DMBF) and PNP/Clay (NPBF)-modified fluids. In addition, NVBF exhibited significantly higher adsorption energies and basal spacings, along with more crystalline patterns suited to embed clay particles. Overall, the synergistic effect of the different polymer side chains with clay particles provides valuable insights on the mechanistic and enhancement of rheological properties of CFs effective as shale inhibition, viscosifier and wellbore stabilization.

Impact of the uniaxial strain on terahertz modulation characteristics in flexible epitaxial VO2 film across the phase transition.

Exploring flexible electronics is on the verge of innovative breakthroughs in terahertz (THz) communication technology. Vanadium dioxide (VO2) with insulator-metal transition (IMT) has excellent application potential in various THz smart devices, but the associated THz modulation properties in the flexible state have rarely been reported. Herein, we deposited an epitaxial VO2 film on a flexible mica substrate via pulsed-laser deposition and investigated its THz modulation properties under different uniaxial strains across the phase transition. It was observed that the THz modulation depth increases under compressive strain and decreases under tensile strain. Moreover, the phase-transition threshold depends on the uniaxial strain. Particularly, the rate of the phase transition temperature depends on the uniaxial strain and reaches approximately 6 °C/% in the temperature-induced phase transition. The optical trigger threshold in laser-induced phase transition decreased by 38.9% under compressive strain but increased by 36.7% under tensile strain, compared to the initial state without uniaxial strain. These findings demonstrate the uniaxial strain-induced low-power triggered THz modulation and provide new insights for applying phase transition oxide films in THz flexible electronics.

LCST-UCST Transition Property of a Novel Retarding Swelling and Thermosensitive Particle Gel

Super absorbent resin particles used as profile control and water plugging agent remains a deficiency that the particles swells with high speed when absorbing water, resulting in low strength and limited depth of migration. To address this issue, we proposed a thermosensitive particle gel possessing the upper critical solution temperature (UCST), which was synthesized from hydrophobically modified poly(vinyl alcohol)s (PVA) with glutaraldehyde (GA) as a cross-linker. The structure of the hydrogel was characterized by Fourier transform infrared spectrophotometer (FTIR) and nuclear magnetic resonance (NMR). The thermosensitive-transparency measurement and swelling experiment show that the hydrophobic-modified PVA solutions and corresponding hydrogels exhibited thermosensitive phase transition behaviors with lower critical solution temperature (LCST) and UCST. The results indicated that the temperature-induced phase transition behavior of CHPVA hydrogels leads to their retarding swelling property and great potential as an efficient water plugging agent with excellent temperature and salt resistance.