Phase Transitions In Materials Research Articles

Fabrication and evaluation of eicosane/poly(styrene-co-butylacrylate) microencapsulated phase change materials through ultrasonicated mini-emulsion technique

This study reports the synthesis and characterization of Microencapsulated Phase Change Materials for the pertinence of latent heat storage. Eicosane/ Poly(Styrene-co-Butylacrylate) [ESE/Poly(Sty-co-BA)] microcapsules were synthesized by encapsulating n-Eicosane (n-ESE) with a shell made of Poly(Styrene-co-Butylacrylate) [Poly(Sty-co-BA)] via employing ultrasonic-assistant mini-emulsion polymerization technique. The properties of the synthesized ESE/Poly(Sty-co-BA) microcapsules were analyzed by Differential scanning calorimetry (DSC),Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR)spectroscopy. DSC results indicated that ESE/Poly(Sty-co-BA) exhibited a melting and crystallizing temperature of 35.72 and 32.27 °C, and latent heat of 220.53 and 218.57 J/g, respectively. The ESE/Poly(Sty-co-BA) microcapsules prepared in this work unveiled an effective encapsulation ratio (91.93 %), encapsulation efficiency (91.59 %) and displayed excellent thermal storage capacity (99.63 %). Various models such as Kissinger’s, Augis and Bennett’s approximation, Mahadevan and Arvami theory were employed to determine the effective activation energy value alongside the crystal growth of n-ESE and ESE/Poly(Sty-co-BA). TGA analysis revealed that ESE/Poly(Sty-co-BA) demonstrated three step degradation and exhibited good thermal stability. The findings of the work manifested a novel technique for producing the phase transition materials for TES that can be applied to a wide range of instances, including smart textiles, thermo-sensitized functional coatings, passive space cooling or heating.

Highly switchable photonic spin hall effect in vanadium dioxide grating structure

The enhancement and manipulation of the photonic spin Hall effects are essential for the spin photonic applications. The emergence of the phase transition material, vanadium dioxide (VO2), presents a unique chance to explore its conductivity dependent optical properties. However, the explorations on the PSHEs in VO2 based microstructures are quite rare. Here, we report the enhanced and controllable reflected photonic spin Hall effects under the horizontal or vertical polarized wave by establishing the VO2 grating structure. It can be found that associated with the phase transition of VO2, its changed conductivity not only tunes the magnitude of the reflected spin shift but also changes its sign, which even results in a dramatic modulation of the reflected spin shift from the negative maximum value under the vertical polarized wave to the positive maximum value under the horizontal polarized wave at the specific wavelength. Such features can be attributed to the dramatic changes of the reflectances in the VO2 grating structure under different polarizations induced by the changed conductivity of VO2. Our results allow the actively alternative phase transition material based configurations capable of dramatic manipulation of the reflected spin shifts and it constitutes a significant step toward highly switchable spin photonic devices.

Validation of van der Waals Interface for Enhanced Resistive Switching Performance in Memristor by Using Topotactic Phase Transition Material

Validation of van der Waals Interface for Enhanced Resistive Switching Performance in Memristor by Using Topotactic Phase Transition Material

Toxicity and decomposition activity inhibition of VO2 micro/nanoparticles to white rot fungus Phanerochaete chrysosporium

Vanadium dioxide (VO2) is an excellent phase transition material widely used in various applications, and thus inevitably enters the environment via different routes and encounters various organisms. Nonetheless, limited information is available on the environmental hazards of VO2. In this study, we investigated the impact of two commercial VO2 particles, nanosized S-VO2 and micro-sized M-VO2 on the white rot fungus Phanerochaete chrysosporium. The growth of P. chrysosporium is significantly affected by VO2 particles, with S-VO2 displaying a higher inhibitory effect on weight gain. In addition, VO2 at high concentrations inhibits the formation of fungal fibrous hyphae and disrupts the integrity of fungus cells as evidenced by the cell membrane damage and the loss of cytoplasm. Notably, at 200 μg/mL, S-VO2 completely alters the morphology of P. chrysosporium, while the M-VO2 treatment does not affect the mycelium formation of P. chrysosporium. Additionally, VO2 particles inhibit the laccase activity secreted by P. chrysosporium, and thus prevent the dye decoloration and sawdust decomposition by P. chrysosporium. The mechanism underlying this toxicity is related to the dissolution of VO2 and the oxidative stress induced by VO2. Overall, our findings suggest that VO2 nanoparticles pose significant environmental hazards and risks to white rot fungi.

Ultrafast Acoustic Pulses Induced by Femtosecond Pulses and the Dynamics of Materials

Ultrafast acoustic pulses induced by a femtosecond laser can be considered as pure mechanical pressure pulses, excluding energy transitions of electrons caused by photons and thermal energy. This special issue discusses methods for controlling the dynamics of magnetic materials using ultrafast acoustic pulses and outlines the latest research trends. Additionally, it presents potential applications of acoustic pulses not only in magnetic materials but also in phase-transition materials.

Experimental evaluation on the power characteristic of direct-photovoltaic charging for thermal storage equipment

Thermal storage is an essential equipment for storing excessive heat, especially for water heating systems. The present work proposes a preliminary study to maximize the operation of thermal storage using photovoltaics as the primary source for charging the heat storage material. The assessment indicates the concept is feasible, where the output power from photovoltaics can be directly converted to heat using a heating element. The power ratio is considerably high (up to 38.6%), resulting in the maximum temperature of the heat absorber material (water) increasing to 43.2 °C. The final assessment using suitable phase transition material shows that steady phase behavior is essential to maximizing the temperature profile of the material. It is achieved using stabilized-hexadecanoic acid, which shows a transient phase transition at a temperature of 54.2 °C, reducing the possibility of heat loss with an average temperature rate of 0.54 °C/min in the discharge stage. This finding proves the proposed concept is applicable, while further improvement can be done to adjust the suitable power output from photovoltaic and storage tank arrangement for the actual system. Despite that, the result is expected to accelerate the utilization of photovoltaics as reliable solar renewable technology.

Phase Transition Control in Molecular Solids via Complementarity of Hydrogen-Bond Strength.

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H-bonds) in many phase-transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure-property relationship. Here, four high-spin CoII compounds were isolated and systematically investigated by modifying the ligand terminal groups (X=S, Se) and substituents (Y=Cl, Br). S-Cl and Se-Br undergo a reversible structural phase transition near room temperature, triggering the rotation of 15-crown-5 guests and the swing between syn- and anti-conformation of NCX- ligands, accompanied by switchable magnetism. Conversely, S-Br and Se-Cl retain stability in ordered and disordered phases, respectively. H-bonds geometric analysis and ab initio calculations reveal that the electronegativity of X and Y affects the strength of NY-ap-H⋅⋅⋅X interactions. Entropy-driven structural phase transitions occur when the H-bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H-bond strength complementarity - pairing strong acceptor with weak donor and vice versa, which offers a straightforward and effective approach for designing phase-transition molecular solids from a chemical perspective.

Аккумулирование тепловой энергии масла и охлаждающей жидкости дизельного двигателя маневрового тепловоза

Objective: to substantiate the effectiveness of using heat-storing materials to preserve the thermal energy of the oil and coolant of the diesel power plant of a shunting diesel locomotive. To achieve this goal it is necessary: to identify the relevance of the problem of preserving the thermal energy of oil and coolant during the operation of diesel locomotives in conditions of negative ambient temperatures; develop a concept for the use of heat-storing phase transition materials in the oil and water systems of a diesel locomotive; carry out the selection of heat-storing materials based on their physical properties and the operating characteristics of diesel locomotive engine systems; conduct laboratory experimental studies to assess the effectiveness of using a particular heat-storing material. Methods: physical experiment performed in laboratory conditions, which consists of recording the temperature of the working medium (oil and water) and the temperature of the heat-storing material used depending on the cold idle time. Experimental studies make it possible to more accurately select the most preferred materials for accumulating heat from oil and water in diesel locomotive engine systems. Results: an experimental dependence of the temperature of various heat-accumulating materials on the cold idle time was constructed, which makes it possible to justify the use of stearin to accumulate heat from engine oil and cooling system water. Practical importance: the research was carried out as part of the implementation of a grant from Russian Railways JSC for young scientists to conduct scientific research aimed at creating new equipment and technologies for use in railway transport and recommended for use in the locomotive complex. Grant agreement No. 5103675 dated December 26, 2022 “Thermal accumulator for the pre-start preparation system for diesel locomotives in the cold season”

Diffusion-induced stress amplification in phase-transition materials for electrodes of lithium-ion batteries

This work sheds the light on the stress amplification in active material particles of electrodes caused by the localized lithium concentration inhomogeneity due to phase transitions. This is a significant issue usually neglected in the literature, as generally the ideal Fickian diffusion model is used to describe the lithium diffusion, which particularly fails when dealing with phase change materials, resulting in the underestimation of the stress. In turn, this results in the underestimation of the fracture behavior of the electrode and the battery degradation, ultimately.To overcome these limitations, this work proposes a mechanical-transport model where the lithium transport is modeled according to the non-ideal solution theory with an equivalent diffusion coefficient depending on the potential of the host material vs Li/Li+. The results show that the proposed model correctly describes the concentration distribution within the particle of phase-change materials (graphite is chosen as a case study), in agreement with the existent experimental measurements. The differences with respect to the traditional Fickian diffusion model is substantial as the stress is up to 85% higher with the proposed model and the concentration distribution can capture the inhomogeneity caused by phase transitions.

Numerical analysis is being conducted to investigate the effect of Nano fluids on the melting process of phase change materials (PCMs) in a semi-cylindrical container.

Analytical investigation of the impact of Nano fluids on the melting process of phase change materials (PCM) inside a semi-cylindrical container. In order to analyse the study in a quantitative manner, the combination of enthalpy and porosity was used using the ANSYS/FLUENT 22 programme. This experiment used phase transition materials, namely paraffin wax (RT58). Based on the findings of this research, it is seen that the inclusion of Nano fluid in the PCMs accelerates the dissolving process compared to the PCMs without these materials. The use of nanomaterials results in a reduction in the time needed to complete the melting process by 3 %, 4 %, and 5 % when used at concentrations of 10 %, 20 %, and 30 %, respectively. This study is important for the use of phase-change materials in the cooling of large electronic devices.

Giant Anisotropic Thermal Expansion Phase Transition of Silver Iodide Anionic Organic-Inorganic Hybrid.

Hybrid metal halide materials with charming phase transition behaviors have attracted considerable attention. In former works, much attention has been focused on the phase transition triggered by the order-disorder or displacement motions of the organic component. However, manipulating the variation of the inorganic component to achieve the phase transition has rarely been reported. Herein, two novel organic-inorganic hybrid materials, [THPM]n[AgX2]n (THPM = 3,4,5,6-tetrahydropyrimidin-1-ium, X = I for 1 and Br for 2) with the [AgX2]nn- anionic chain structure, were synthesized. At 293 K, the [AgX2]nn- chains in 1 were constructed by the tetramer units of Ag atoms, while that in 2 was assembled by the dimer structure. Upon heating to 355 K, owing to the variation of the metallophilic interaction between adjacent Ag atoms, a unique transformation process from tetramer to dimer in [AgI2]nn- chains of 1 can be detected and endow 1 with a giant anisotropic thermal expansion with linear strain of ∼7% and shear strain of ∼20%, which can be used as a mechanical actuator for switching. Alternatively, for 2, no phase transition process can be observed upon the temperature variation. This work provides an effective approach to design phase transition materials triggered by the inorganic part.

MEMS-actuated terahertz metamaterials driven by phase-transition materials

The non-ionizing and penetrative characteristics of terahertz (THz) radiation have recently led to its adoption across a variety of applications. To effectively utilize THz radiation, modulators with precise control are imperative. While most recent THz modulators manipulate the amplitude, frequency, or phase of incident THz radiation, considerably less progress has been made toward THz polarization modulation. Conventional methods for polarization control suffer from high driving voltages, restricted modulation depth, and narrow band capabilities, which hinder device performance and broader applications. Consequently, an ideal THz modulator that offers high modulation depth along with ease of processing and operation is required. In this paper, we propose and realize a THz metamaterial comprised of microelectromechanical systems (MEMS) actuated by the phase-transition material vanadium dioxide (VO2). Simulation and experimental results of the three-dimensional metamaterials show that by leveraging the unique phase-transition attributes of VO2, our THz polarization modulator offers notable advancements over existing designs, including broad operation spectrum, high modulation depth, ease of fabrication, ease of operation condition, and continuous modulation capabilities. These enhanced features make the system a viable candidate for a range of THz applications, including telecommunications, imaging, and radar systems.Graphical

Room-Temperature Phase Transition Material with Switchable Second-Order Nonlinear Optical Properties.

Phase transition materials with switchable second-order nonlinear optical (NLO) properties have attracted extensive attention because of their great application potential in photoelectric switches, sensors, and modulators, while metal-free organics with NLO switchability near room temperature remain scarce. Herein, we report a hydrogen-bonded metal-free organic crystal, 2-methylpropan-2-aminium 2,2-dimethylpropanoate (1), exhibiting a room-temperature phase transition and favorable NLO switchability. Through investigations on its thermal anomalies, dielectric properties, and crystal structures, we uncover that 1 holds a near-room-temperature phase transition at 303 K from noncentrosymmetric point group C2v to centrosymmetric one D2h, which is attributed to the order-disorder transformations of both tert-butylamine cations and dimethylpropionic acid anions. Accompanied by symmetry change during the phase transition, 1 exhibits reversible and repeatable NLO "on-off" switchability with a desirable switching contrast ratio of ca. 19 between high and low NLO states. This discovery demonstrates a metal-free organic crystal with NLO switching behavior near room temperature, serving as a promising candidate in smart and ecofriendly photoelectric functional materials and devices.

Tunable polarization-independent and angle-insensitive ultra-broadband terahertz absorber with vanadium dioxide

In this paper, a tunable ultra-broadband terahertz metamaterial absorber is proposed based on the phase transition material of vanadium dioxide (VO2). The absorber cell consists of a petal-like monolayer vanadium dioxide, a dielectric layer, and a metal layer. The terahertz absorption bandwidth of more than 90% absorptance reaches 4.2 THz, which covers from 1.99 to 6.19 THz, and a relative bandwidth attains to 102.7%. By changing the conductivity of VO2, the absorbance of this structure can be dynamically adjusted from 2.4% to 98.96%. The physical mechanism of the perfect absorption in this paper is investigated by the impedance matching theory and electric field distributions. The results show that the strong coupling effect in the petal-like structure contributes to the broadening of the absorption spectrum, and the absorber is polarization-insensitive and wide-angle incidence-insensitive due to the symmetry of the cell structure. The metamaterial absorber designed in this paper is expected to have a wide range of applications in the fields of terahertz imaging, stealth, sensing and detection.

CONCENTRATION OF NANO FLUID/BASE FLUID SUSPENSION ENHANCE SURFACE CHARGE WITH PH STABILITY FOR LOW TO MEDIUM TEMPERATURE PHASE CHANGE MATERIALS

Zeta potential and poly-dispersivity are used to characterize the samples that is obtained using absorption refrigeration system for low to medium temperature phase transition materials. Salicyclic acid, Benzanilide, Hydroquinone, Potassium thiocyanates, D-mannitol, Alunimium oxide, Iron oxide, and ZnO active concentration with base fluid, aspects including the influence of the PCMs property based on their phase transition mutual interaction are explored. In order to comprehend their behavior and improve their performance, functional materials synthesis and characterization depend heavily on the isoelectric point. Understanding the material surface charge role of the medium's pH stability to the many liquid-phase procedures involved in the synthesis of materials, since it conduct the processes like agglomeration, coagulation, peptization to form solid particles materials. Zeta potential measure, which commonly use concentration of volume fraction methods, electrophoretic migration techniques, are hence a valuable source of data.

Large relative cooling power in van der Waals room-temperature ferromagnet Fe5GeTe2

Due to the unique structures, van der Waals (vdW) materials have advantages over traditional magnetothermal materials in manipulating magnetothermal properties through structural modification and in cooling applications in nanodevices. Here, we study the magnetothermal properties of vdW ferromagnet Fe5GeTe2 with Curie temperature around room temperature. The results show that Fe5GeTe2 is a second-order magnetic phase transition material, and its in-plane and out-of-plane values of relative cooling power are large up, respectively, to 299.3 and 269.2 J/kg for a field change of 5 T. Compared to other vdW materials reported, Fe5GeTe2 has the greatest potential for room-temperature magnetic cooling applications.

Neuromorphic one-shot learning utilizing a phase-transition material

Design of hardware based on biological principles of neuronal computation and plasticity in the brain is a leading approach to realizing energy- and sample-efficient AI and learning machines. An important factor in selection of the hardware building blocks is the identification of candidate materials with physical properties suitable to emulate the large dynamic ranges and varied timescales of neuronal signaling. Previous work has shown that the all-or-none spiking behavior of neurons can be mimicked by threshold switches utilizing material phase transitions. Here, we demonstrate that devices based on a prototypical metal-insulator-transition material, vanadium dioxide (VO2), can be dynamically controlled to access a continuum of intermediate resistance states. Furthermore, the timescale of their intrinsic relaxation can be configured to match a range of biologically relevant timescales from milliseconds to seconds. We exploit these device properties to emulate three aspects of neuronal analog computation: fast (~1 ms) spiking in a neuronal soma compartment, slow (~100 ms) spiking in a dendritic compartment, and ultraslow (~1 s) biochemical signaling involved in temporal credit assignment for a recently discovered biological mechanism of one-shot learning. Simulations show that an artificial neural network using properties of VO2 devices to control an agent navigating a spatial environment can learn an efficient path to a reward in up to fourfold fewer trials than standard methods. The phase relaxations described in our study may be engineered in a variety of materials and can be controlled by thermal, electrical, or optical stimuli, suggesting further opportunities to emulate biological learning in neuromorphic hardware.

Intermolecular Forces Regulating the Phase-Transition Temperatures in Organic-Inorganic Hybrid Materials.

Organic-inorganic hybrid phase-transition materials have attracted widespread attention in energy storage and sensor applications due to their structural adaptability and facile synthesis. However, increasing the phase-transition temperature (Tc) effectively remains a formidable challenge. In this study, we employed a strategy to regulate intermolecular interactions (different types of hydrogen bonds and other weak interactions), utilizing bismuth chloride as an inorganic framework and azetidine, 3,3-difluoro azetidine, and 3-carboxyl azetidine as organic components to synthesize three compounds with different Tc values: [C3H8N]2BiCl5 (1, 234 K), [C3H6NF2]3BiCl6 (2, 256 K), and [C4H8O2N]3BiCl6 (3, 350 K). 1 is a one-dimensional chain structure and 2 and 3 are zero-dimensional structures. Analysis of the crystal structure and the Hirshfeld surface and 2D fingerprints further suggests that the intermolecular forces are efficiently modulated. These findings emphasize the efficacy of our strategy in enhancing Tc and may facilitate further research in this area.

A Numerical Study of the Effect of Water Speed on the Melting Process of Phase Change Materials Inside a Vertical Cylindrical Container

The present work offers a thorough analysis of the impact of water velocity on phase change material (PCM) melting in a vertical cylindrical container. A detailed quantitative analysis uses sophisticated numerical techniques, namely the ANSYS/FLUENT 16 program, to clarify the complex relationship between enthalpy and porosity during the melting process. The experimental focus is on phase transition materials based on paraffin wax, particularly Rubitherm RT42. This study’s primary goal is to evaluate the effects of different water velocities (that is, at velocities of 0.01 m/s, 0.1 m/s, and 1 m/s) on the PCM’s melting behavior at a constant temperature of 333 K. This work intends to make a substantial contribution to the development of thermal energy storage systems by investigating new perspectives on PCM behavior under various flow circumstances. The study’s key findings highlight the possible ramifications for improving PCM-based thermal energy storage devices by revealing significant differences in melting rates and behavior that correlate to changes in water velocities. Future research is recommended to explore the impact of temperature variations, container geometries, and experimental validation to improve the accuracy and practicality of the results and to advance the creation of sustainable and effective energy storage solutions.

Evaluation of various phase-transition materials for steep switching super-low power application in the latest technology node

Recently, a phase-transition field effect transistor (phase-FET) integrated with a phase-transition material (PTM) is attracting attention as a steep switching device, and attempts to solve the power consumption limitation of conventional CMOS using various PTMs are continuing. In order to utilize the phase-FET, it is essential to design an appropriate device and circuit characteristics by carefully considering the close correlation between the baseline-FET and the PTM and the hysteresis characteristics caused by the phase-transition. In this work, by integrating various PTMs according to the baseline FETs in various technology nodes, the logic and SRAM characteristics implemented the phase-FET were investigated, and the appropriate PTM and the electrical characteristic target required for the PTM were presented through systematic analysis. As a result, it was confirmed that single crystalline vanadium di-oxide (SC VO2) has characteristics suitable for constructing phase-FETs compared to other candidate PTMs in 32 nm planar FET, 7 nm Fin-FET, and 3 nm gate-all-around FET technology nodes. As a result of benchmarking with conventional-FET at each technology node, in the case of logic, the speed is 26.15% (32 nm), 20.26% (7 nm), and 20.05% (3 nm), and in the case of memory, standby power, read stability and write time are improved.