Phase Transition Enthalpy Research Articles

Binary Mixture of Solid-Solid Phase Change Material: Synthesis, Characterization and Experimental Study

In this work, a class of polyol solid-solid phase change material where Neopentyl glycol is mixed in 6 and 2 wt.% of Pentaerythritol and was synthesized by physical blending method to obtain homogeneous mixture and thermally cycled for 500 times. The surface morphology, chemical composition, crystal phase identification, thermal degradation, and phase change phenomena were characterized. The phase transition temperatures and enthalpies upon heating and cooling of 6 and 2 wt.% of Pentaerythritol are found to be 43.1 °C, 133 J g-1, and 28.2 °C, 119 J g-1, and 41.2 °C, 121 J g-1, and 28.5 °C, 106 J g-1, respectively which suits for electronic system to keep under operating zone. Laser Flash Apparatus was used to find the thermal diffusivity and thermal conductivity value was calculated. Further, the effect of heat transfer in binary polyol mixtures were experimentally analysed through conventional heat sink for electronic cooling application.

Vaporization/sublimation enthalpies of mono- and dimethyl-esters estimated by solution calorimetry method

The additive scheme for calculating the solvation enthalpies of aliphatic compounds has been developed for linear mono- and dimethyl-esters. Ester group contribution to the enthalpy of solvation in n-heptane was obtained. Accuracy of the proposed approach for determination of solvation enthalpies of linear mono- and dimethyl-esters was tested by comparison with experimental solvation enthalpies. In most cases, deviations do not exceed 1 kJ·mol−1.It was found that the dependence of the solution enthalpies of mono- and dimethyl-esters on the number of carbon atoms in the molecule can be fitted by power function. This dependence and a group-additivity scheme for solvation enthalpy were used for estimation of the enthalpies of phase transitions of mono- and dimethyl-esters. Evaluated values of sublimation, vaporization, and fusion enthalpies at 298.15 K are in good agreement with experimental data obtained by conventional methods.

Preparation, performances and applications of multi-functional photoluminescence form-stable phase change materials

Up to now, most of the reported phase change materials only show a single application in thermal energy storage and can not satisfy the increasing demand for multifunctional materials. In this study, we first designed and prepared a novel multi-functional photoluminescence form-stable phase change materials (FSPCMs) using photoluminescence side chain liquid crystalline polymers with different flexible spacers length as gelators, and using paraffin as phase change materials. The properties, and the effect of flexible spacer length on the properties of photoluminescence FSPCMs were studied in detail by “tube test” method, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fourier-transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), rheometry test, ultraviolet spectroscopy (UV) and photoluminescence instruments (PL). Experiment results showed that the prepared photoluminescence FSPCMs showed high thermal energy storage density and solid fluorescence quantum yield. The phase transition enthalpy for our prepared photoluminescence FSPCMs can reach 193.1 J g−1 and the solid fluorescence quantum yield can achieve 16.54%. The prepared photoluminescence FSPCMs can also absorb UV light and can be used as UV shielding materials. The properties of photoluminescence FSPCMs varied with the spacer length of polymer gelators. With increasing spacer length, the thermal stability and mechanical property of prepared photoluminescence FSPCMs showed the trend of deterioration. However, the solid fluorescence quantum yield of them increased with the increasing spacer length of polymer gelators.

Investigation on thermal behaviour and optical properties of non-symmetric cholesterol-based twin liquid crystals with thioester linkages

ABSTRACT Herein, a series of novel asymmetric cholesterol-based liquid crystal compounds containing thioester linkage and an analogue containing carboxylate linking unit have been synthesised and characterised. Thermal analyses demonstrated that all desired target compounds possess broad mesophase temperature ranges (ΔT, 91–142.5°C) and high thermal stability (clearing points, 214.9–259.4°C). Due to the increasing chain length of the inner flexible spacer, clearing points and entropy changes (ΔS/R) of the COS-containing dimers showed pronounced parity effects. All dimers exhibited enantiotropic mesophase behaviour with an SmC* phase and a typical cholesteric phase (N*), which were validated by XRD and POM. The effect of structural changes of COO and COS unit in the linking group on the mesomorphic properties was analysed. Comparing C6SAR with C6OAR, it was found that the thioester-containing dimer exhibited more stable mesophase, higher phase transition temperatures (about 20°C higher) and enthalpy values (ΔH). All final products exhibited selective reflection to visible light, produced multiple colours. The higher temperatures led to the shorter pitch, which can further result in shorter reflection wavelengths, and the ‘blue shift’ occurred.

Shape-stabilized hydrated salt/paraffin composite phase change materials for advanced thermal energy storage and management

Thermal energy storage and management have attracted considerable interest in the field of sustainable control and utilization of energy. Thermal energy storage materials with excellent thermal properties and shape stability are in high demand. Herein, we developed a simple and effective method to fabricate hydrated salt / paraffin composite (HPC) shape-stabilized phase change materials (SSPCMs). Hydrated salt was emulsified into paraffin by an inverse emulsion template method to obtain HPC. Owing to its low volatility, paraffin enhanced the thermal stability of the hydrated salt by preventing its direct contact with the environment. Furthermore, after its crystallization, paraffin provided nucleation sites and functioned as a nucleating agent to promote the crystallization of the hydrated salt. The HPC was then simultaneously impregnated into cellulose sponge (CS), forming the SSPCMs, which exhibited excellent thermal stability, high energy storage density with a phase transition enthalpy of 227.3 J/g, and a reduced supercooling degree. Besides, there was negligible leakage during the test. The efficiency of the SSPCMs as temperature management materials was then tested by using them as a lining in a fully enclosed protective clothing.

Molecular simulation of energy storage of R1234yf, R1234ze(z), R32, and their mixtures in Co-MOF-74 materials

The heat capacity of working fluid can be enhanced through the mutual transformation between thermal energy and surface energy during the absorption and separation process of fluid molecules in porous materials. In this paper, molecular simulation (molecular dynamics and grand canonical Monte Carlo) methods were used to study the absorption and energy storage properties of R1234yf, R1234ze(z), R32 and their mixtures in Co-MOF-74. In order to evaluate the properties of thermal energy storage of metal organic heat carriers (MOHCs), the enthalpy difference (Δ h MOHCs) of MOHCs was calculated. Δ h MOHCs consists of the enthalpy of pure organic fluid (∆ h Fluid), the energy change of metal organic framework (MOF) nanoparticles (( ∫c p d T )MOFs) and the enthalpy of desorption (∆ h desorption). It can be inferred that MOHCs can strengthen the energy storage capacity of basic fluid when the sum of ( ∫c p d T )MOFs and ∆ h desorption is larger than ∆ h Fluid, and vice versa. For the purpose of calculating the energy change of metal organic framework nanoparticles (( ∫c p d T )MOFs), molecular dynamics simulation was adopted. Furthermore, grand canonical Monte Carlo methods were used to calculate the enthalpy of desorption (∆ h desorption). The results suggested that the adsorption amount of R32 in Co-MOF-74 is higher than that of R1234yf and R1234ze(z). The saturated adsorption pressure of R1234yf and R1234ze(z) is lower than that of R32. Besides, the saturated absorption amount of R1234ze(z) is higher than that of R1234yf. And the desorption heat of R32 is lower than that of R1234yf and R1234ze(z). As a result of phase transition, the enthalpy of organic fluid significantly increases at the temperature of phase transition. However, the enthalpy of phase transition of R32 is higher than that of R1234yf and R1234ze(z). The addition of Co-MOF-74 nanoparticles could enhance the energy storage capacity of the studied pure refrigerants. R1234yf and R1234ze(z) nanofluids have superior enhancement effect to that of R32 nanofluid. Nonetheless, the energy storage capacity of R32 nanofluid is depressed at the temperature of phase transition. This can be attributed to that the enthalpy of phase transition of R32 (∆ h Fluid) is higher than the sum of the energy of Co-MOF-74 nanoparticles (( ∫c p d T )MOFs) and the enthalpy of desorption (∆ h desorption) of R32 in Co-MOF-74. Moreover, due to the temperature of phase transition increases with the pressure increasing, the lowest point of energy storage enhancement appears at higher temperature. Besides, the absorption amount of R1234ze(z) and R1234yf is lower than that of R32 in the refrigerant mixture adsorption. What’s more, the absorption amount of R1234ze(z) in R1234ze(z)/R32 mixture is lower than that of R1234yf in R1234yf/R32 mixture. And this result is different from the adsorption of pure working fluid. Also, with the increase in temperature, the adsorption amount of R1234ze(z) and R1234yf shows a gradually increasing trend, while that of R32 gradually decreases. The desorption heat of R1234ze(z) and R1234yf is higher than that of R32 in the mixture adsorption. In general, this study is of great significance for theoretical analysis of adsorption characteristics of refrigerant molecules in porous media. And it can provide reliable basis for selecting appropriate refrigerant working mediums and MOFs to form optimal MOHCs in engineering.

Antibacterial phase change microcapsules obtained with lignin as the Pickering stabilizer and the reducing agent for silver

This paper provides a novel and facile method to synthesize antibacterial phase change microcapsules (microPCMs) decorated with silver particles, where lignin was acting as both the Pickering stabilizer and the reducing agent for silver. First lignin Pickering emulsions at various oil-to-water ratios and lignin loading were prepared. Then, n-eicosane encapsulated in polyurea (PU) shells was prepared via interfacial polymerization of isophorone diisocyanate (IPDI) and ethylene diamine/diethylene triamine (EDA/DETA) in a Pickering emulsion stabilized by lignin particles. The results showed that the lignin particles were embedded in the microPCMs shell. These lignin particles were utilized to reduce silver ions, resulting in silver particles decorated microPCMs (Ag/lignin microPCMs). The resulting Ag/lignin microPCMs exhibited a well-defined core-shell spherical morphology with high phase-transition enthalpy (177.6 J/g), high encapsulation efficiency (69.0%) and good thermal durability. As well, the Ag/lignin microPCMs presented good antibacterial activity, showing great potential in industrial applications such as biomedical, textile and construction areas.

Behavior of thermal properties of AgCu1−xFexS compounds under non-isothermal conditions

AgCu[Formula: see text]Fe[Formula: see text]S compounds were synthesized by partial Cu[Formula: see text][Formula: see text][Formula: see text]Fe replacement in the AgCuS crystal at a concentration range of 0[Formula: see text][Formula: see text][Formula: see text]x[Formula: see text][Formula: see text][Formula: see text]0.03. In the differential thermal analysis spectrum obtained at a temperature range of 300 K[Formula: see text][Formula: see text][Formula: see text]T[Formula: see text][Formula: see text][Formula: see text]1300 K, endoeffect corresponding to the structural phase transition in the AgCuS compound was observed at the temperature T[Formula: see text]=[Formula: see text]938 K. It has been determined that this result is also observed in the AgCu[Formula: see text]Fe[Formula: see text]S compound obtained by partial replacement of Cu atoms by Fe atoms. However, in the compound of AgCu[Formula: see text]Fe[Formula: see text]S this effect was observed at higher temperatures. The thermal capacities and enthalpies of phase transitions were calculated for the given compounds.

Thermophysical properties of Inconel 718 alloy

The thermal diffusivity (a), linear thermal expansion coefficient (α), isobaric heat capacity (Cp) and phase transition enthalpy (ΔH) of Inconel 718 superalloy were determined by laser flash method, dilatometric method and differential scanning calorimetry in the temperature range of 298–1375…1473 К. The thermal conductivity (λ) has been calculated from the measurement results. The estimated errors of the obtained data were 2–5%, 3–5%, 2–3% and (1.5–2)×10−7 K−1 for a, λ, Cp and α, respectively. The approximation equations and a table of reference values for the studied properties have been obtained.

Synthesis and mesomorphic properties of coumarin derivatives with chalcone and imine linkages

We report here design and synthesis of two new mesogenic homologous series of coumarin derivatives consisting of chalcone and imine central linkages along with terminal n-alkoxy chain. All the compounds were synthesized and characterized by combination of elemental analysis and standard spectroscopic methods. All compounds were screened under polarising optical microscope (POM) for liquid crystalline properties, thermogram of all compounds were studied using differential scanning calorimetry (DSC) to get phase transition temperatures, enthalpy and entropy. X-ray single crystal study of n-octyloxy coumarin derivative 16 g was resolved with imine central linkage, which showed linear rod like geometry.

The Design and Manufacture of a Multilayer Low-Temperature Protective Composite Fabric Based on Active Heating Materials and Passive Insulating Materials

Based on active heating materials (the phase change microcapsules (microPCMs)) and passive insulating materials (SiO2 aerogel), a new-type multilayer low temperature protective composite fabric (MPF) was designed and manufactured to meet the demands of protection and operation in a short time under a low-temperature environment. Results showed that the MPF consisted of three layers including the fabric layer, the microPCM function layer, and the SiO2 aerogel thermal insulation layer. The differential scanning calorimeter (DSC) results demonstrated that the phase transition enthalpy of the composite was 96.2 J/g during the cooling process. The low-temperature resistance and thermal insulation performance at −50 °C were investigated. The results also demonstrated that the low-temperature resistance time of the MPF was 660 s and the power consumption of the MPFs needed to maintain 37 °C for 10 and 20 min were 629 J and 1872 J, respectively. Compared with the microPCM function layer and the thermal insulation layer, which have the same thickness as the MPF, the low-temperature resistance time of the MPF was prolonged for about 2 and 3 min, respectively. The MPF could provide effective protection of the low-temperature work in a short time and could be applied as potential materials in low-temperature protection.

Experimental investigations on the thermal stability of Na2CO3–K2CO3 eutectic salt/ceramic composites for high temperature energy storage

In this study, eutectic salt/ceramic composites with MgO serving as supportingmaterial and Na2CO3–K2CO3 eutectic salt acting as thermal absorbing materials were prepared by the form-stable technique. As additives, effects of both Kaolin and graphite on the thermal stability of composites were investigated. The microstructures of the composites before and after thermal cycling tests were detected by X-ray diffraction and scanning electron microscope techniques. The thermal stability and thermal properties including latent heat, specific heat capacity, thermal conductivity, etc. were measured using differential scanning calorimetry, laser thermal instrument and thermogravimetric analysis, etc. The results showed the composite phase change materials had good thermal reliability and chemical stability. No obvious damages were found in the samples with thermal cycles reaching 1500 times. Kaolin can improve the stability of the sample by restraining the volatilization of molten salt, but it can reduce the phase transition enthalpy of the composite. In comparison with kaolin, carbon can improve thermal cycle life due to its favorable shock resistance. But it suffers severe oxidation at high temperature, which might be a possible reason for its decay in thermal cycling life. These studies suggest the thermal life of the composite can be controlled by adding proper materials.

Contribution of headgroup and chain length of glycerophospholipids to thermal stability and permeability of liposomes loaded with calcein

Biological membranes are complex systems that are composed of lipids, proteins and carbohydrates. They are difficult to study, so it is established practice to use lipid vesicles that consist of closed ‘shells’ of phospholipid bilayers as model systems to study various functional and structural aspects of lipid organisation. To define the effects of the structural properties of lipid vesicles on their phase behaviour, we investigated their headgroup and chain length, and the chemical bonds by which their acyl chains are attached to the glycerol moiety of glycerophospholipid species, in terms of phase transition temperature, enthalpy change and calcein permeability. We used differential scanning calorimetry to measure the temperature and enthalpy changes of phase transition, and fluorescence to follow calcein release through the bilayer structure. Our data show that longer acyl chains increase the stability of the lipid bilayers, whereas higher salt concentrations decrease the thermal stability and widen the phase transitions of these lipid bilayers. We discuss the possible reasons for the observed phase transition behaviour.

Phase transitions in higher-melting imidazolium-based ionic liquids: Experiments and advanced data analysis

As thermal energy storage becomes an increasingly important topic, good knowledge of properties of phase-change materials (PCM) is essential. Among other properties, a good PCM should show a large enthalpy of melting, reproducible melting/solidification cycles, and long-term thermal stability. Temperatures and enthalpies of fusion should be determined at a possibly large range of conditions to allow for a critical evaluation of the experimental data and assessment of the material application potential.In this work, imidazolium-based ionic liquids (ILs) with long alkyl chain substituents 1-hexadecyl-3-methylimidazolium chloride and 1-hexadecyl-3-methyl-imidazolium saccharinate were studied in view of their possible use as phase-change materials. Differential scanning calorimetry (DSC) and the heat-leak modulus (HLM) methods were used to determine the temperatures and the enthalpies of phase transitions in the studied ILs, enabling us to study the influence of the heating and cooling rates on the measured properties. Enthalpies of fusion near to or larger than 100 J·g−1 were found in the studied ionic liquids, making them promising candidates for thermal energy storage. Peaks corresponding to possible liquid crystalline phases in the DSC traces of 1-hexadecyl-3-methylimidazolium saccharinate were observed, pointing to more complex phase behaviour of the studied ionic liquids.Finally, to critically evaluate the experimental data measured in this work, methods based on mathematical gnostics were used. Repeatability of measurements and the degree of mutual agreement between the methods used in this work could thus be determined.

Evidence for ATP Interaction with Phosphatidylcholine Bilayers.

ATP is a fundamental intracellular molecule and is thought to diffuse freely throughout the cytosol. Evidence obtained from nucleotide-sensing sarcolemmal ion channels and red blood cells, however, suggest that ATP is compartmentalized or buffered, especially beneath the sarcolemma, but no definitive mechanism for restricted diffusion or potential buffering system has been postulated. In this study, we provide evidence from alterations to membrane dipole potential, membrane conductance, changes in enthalpy of phospholipid phase transition, and from free energy calculations that ATP associates with phospholipid bilayers. Furthermore, all-atom molecular dynamics simulations show that ATP can form aggregates in the aqueous phase at high concentrations. ATP interaction with membranes provides a new model to understand the diffusion of ATP through the cell. Coupled with previous reports of diffusion restriction in the subsarcolemmal space, these findings support the existence of compartmentalized or buffered pools of ATP.

Synthesis and properties of antiferroelectric and/or ferroelectric compounds with the –CH2O group close to chirality centre

ABSTRACTNovel chiral three-ring compounds with the –CH2O group close to chirality centre were synthesised and their properties were studied. The phase transitions and phase sequences were observed using a polarising optical microscope. The phase transition temperatures and enthalpies were checked by differential scanning calorimetry. A broad-frequency dielectric spectroscopy was also used to confirm the phase transition temperatures as well as the phase sequence. The helical pitch was measured by the spectrophotometry method. It was found that the compounds differing only in one lateral substituted fluorine atom create two different chiral tilted smectic phases, one a ferroelectric phase (SmC*) and the other an antiferroelectric phase (SmCA*).

Microstructural characterization of the as-cast and annealed Pu-10Zr alloy

Phase diagrams constructed for the Pu-Zr binary system report the existence of θ-(Pu,Zr), δ-(Pu,Zr), γ-Pu, α-Pu, β-Pu, and ζ-Pu28Zr phases in Pu-enriched region, when Pu concentrations exceed 75 at.% (equivalent to 89 wt% Pu). The compound θ-(Pu,Zr) has been said to occur at about 20 at.% Zr, but the regions for θ-(Pu,Zr) on the Pu-rich side have not been well defined. In an effort to understand the phases formed in Pu-Zr binary alloys and define the boundary between θ-(Pu,Zr), (θ+δ), and δ-(Pu,Zr) regions, Pu-10Zr (in wt.%, equivalent 23 at.%) alloys were scrutinized in this contribution. This manuscript details microstructural characterization and phase identification results obtained using electron microscopy-based techniques for a Pu-10Zr alloy before and after annealing at 550 °C. In contradiction with predicted phase diagrams, no θ-(Pu,Zr) was detected in any of the examined specimens. The phases present in as-cast fuel included a δ-(Pu,Zr) matrix with a number of smaller, randomly distributed α-Zr, ZrO2, Zr3O, PuO, and κ-PuZr2 inclusions. Heat treatment annealed out the intermetallic κ-PuZr2 phase and resulted in formation of small δ′-Pu and β-Pu inclusions. Similar to the as-cast alloys, the matrix of the annealed alloys was consistent with δ-(Pu,Zr) phase and contained small α-Zr, ZrO2, and PuO2 inclusions. Two different microscopy-based techniques were used for phase identification, but neither identified any θ-(Pu,Zr) phase. Differential scanning calorimetry was then used to determine the phase transition temperatures and enthalpies of transition for the identified phases. While our data is similar to the existing phase diagrams, a number of discrepancies are reported that call for a careful re-examination of the Pu-Zr system. This contribution discusses different scenarios that could explain the discrepancies between obtained and historical data, and provides the most logical conclusion that could be reached based on the obtained results.

Modified Al@Al2O3 phase change materials by carbon via in-situ catalytic decomposition of methane

The microencapsulated phase change materials (MEPCMs) are very promising in thermal storage due to the shape-stable structure that can prevent the leakage of liquid phase change materials during the solid-liquid phase transformation. However, the relatively low thermal conductivity significantly lowers the heat exchange efficiency. Herein, we proposed a new strategy to improve the stability and thermal conductivity by depositing carbon on the surface of Al@Al2O3 composite via in-situ catalytic methane decomposition. In this method, the Al spheres (20–50 μm) are firstly coated by a thin layer of nano Ni species which can promote the oxidation of the surface layer of Al to Al2O3 during the calcination in air. Thereafter, the carbon is produced on the surface of Al@Al2O3 composite when it is submitted to CH4 flow at relatively high temperature (e.g., 650 °C) due to the catalytic methane decomposition by Ni species, obtaining the Al@Al2O3–C composite. The Al@Al2O3–C composite exhibits high phase transition enthalpy (266 J g−1), high thermal conductivity (8 W (m K)−1), and low degree of supercooling in the exothermic process during cooling. In addition, the nesting of the deposited carbon on the surface of phase change material also contributes to obtain dense shell, owning excellent stability in multiple heating/cooling cycles.

Manganese-based layered perovskite solid–solid phase change material: Synthesis, characterization and thermal stability study

In this paper, a new class of Manganese based Layered Perovskite Solid–Solid Phase Change Materials (1-C9H19NH3)2MnCl4 and (1-C10H21NH3)2MnCl4 (SS-PCM) were synthesized by a liquid phase reaction method, and the effect of thermal cycling was compared for 0, 500, 1000 cycles. The crystal morphology, elemental compositions, thermal degradation, and phase transition phenomena were characterized and compared. It was noted from DSC that the phase transition temperatures and enthalpies upon heating and cooling for (1-C9H19NH3)2MnCl4 is 293.80 K, 64.75 kJ/kg, and 285.57 K, 65.49 kJ/kg, and for (1-C10H21NH3)2MnCl4 is 311.54 K, 73.83 kJ/kg, and 304.24 K, 79.79 kJ/kg, respectively. During the transition period, the synthesized material possesses increased thermal conductivity and thermal diffusivity which eliminates the need for thermal conductivity enhancers. Additionally, we found through characterization that the SS-PCMs were thermally and chemically stable for around 1000 cycles because of the presence of the metal substrate. Hence, the synthesized SS-PCMs are desirable for various low-temperature thermal energy storage applications.

Liquid crystals for IR: Part II synthesis and properties of perfluoroalkyl- or perfluoroalkoxy-terminated tolanes

ABSTRACT This article is a continuation of previously published ‘Liquid crystals for IR: Part I’ article. Several homologous series of laterally halogenated and perfluoroalkyl- or perfluoroalkoxy-terminated tolanes derivatives have been synthesised. Obtained compounds were divided into three families, i.e. tolanes, phenyltolanes, bistolanes and their mesomorphic properties, phase transition temperatures and enthalpies were determined. The influence of the length of the core, type and position of substituents in the molecular core has been analysed. The lack of aliphatic protons in molecular structure generates unique infrared properties of presented materials and their mixtures.