Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage

Polyethylene Glycol/Rice Husk Ash Shape-Stabilized Phase Change Materials: Recovery of Thermal Energy Storage Efficacy via Engineering Porous Support Structure

This study focuses on modifying the porous structure of acid-treated rice husk ash (ARHA) to enhance the thermal energy storage capacity of poly(ethylene glycol) (PEG) confined within shape-stabilized phase change materials. The modification process involved a cost-effective sol-gel method in which ARHA was initially dissolved in an alkaline solution and subsequently precipitated in an acidic environment. ARHA, being a mesoporous SiO2-based material with a high surface area but low pore volume, had limited capacity to adsorb PEG (50%). Furthermore, it hindered the crystallinity of impregnated PEG by fostering abundant interfacial hydrogen bonds (H-bonds), resulting in a diminished thermal energy storage efficiency. Following modification of the porous structure, the resulting material, termed mARHA, featured a three-dimensional macroporous network, providing ample space to stabilize a significant amount of PEG (70%) without any leakage. Notably, mARHA, with a reduced surface area, effectively mitigated interfacial H-bonds, consequently enhancing the crystallinity of impregnated PEG. This modification led to the recovery of thermal energy storage efficacy from 0 J/g for PEG/ARHA to 109.3 J/g for PEG/mARHA. Additionally, the PEG/mARHA composite displayed improved thermal conductivity, reliable thermal performance, and effective thermal management when used as construction materials. This work introduces a straightforward and economical strategy for revitalizing thermal energy storage in PEG composites confined within RHA-based porous supports, offering promising prospects for large-scale applications in building energy conservation.

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Experimental Study and Mechanism Analysis of Paraffin/Sisal Composite Phase Change Energy Storage Fiber Prepared by Vacuum Adsorption Method

Sisal fiber exhibits a fibrous and porous structure with significant surface roughness, making it highly suitable for storing phase change materials (PCMs). Its intricate morphology further aids in mitigating the risk of PCM leakage. This research successfully employs vacuum adsorption to encapsulate paraffin within sisal fiber, yielding a potentially cost-effective, durable, and environmentally friendly phase change energy storage medium. A systematic investigation was carried out to evaluate the effects of sisal-to-paraffin mass ratio, fiber length, vacuum level, and negative pressure duration on the loading rate of paraffin. The experimental results demonstrate that a paraffin loading rate of 8 wt% can be achieved by subjecting a 3 mm sisal fiber to vacuum adsorption with 16 wt% paraffin for 1 h at -0.1 MPa. Through the utilization of nano-CT imaging enhancement technology, along with petrographic microscopy, this study elucidates the mechanism underlying paraffin storage within sisal fiber during vacuum adsorption. The observations reveal that a substantial portion of paraffin is primarily stored within the pores of the fiber, while a smaller quantity is firmly adsorbed onto its surface, thus yielding a durable phase change energy storage medium. The research findings contribute to both the theoretical foundations and the available practical guidance for the fabrication and implementation of paraffin/sisal fiber composite phase change energy storage mediums.

Self-assembled boron nitride nanosheet-based aerogels as support frameworks for efficient thermal energy storage phase change materials

Phase change materials (PCMs) are promising in many fields related to energy utilization and thermal management. However, the low thermal conductivity and poor shape stability of PCMs restrict their direct thermal energy conversion and storage. The desired properties for PCMs are not only high thermal conductivity and excellent shape stability, but also high latent heat retention. In this study, the boron nitride nanosheets (BNNSs) were bridged by small amounts of GO nanosheets and successfully self-assembled into BNNS/rGO (BG) aerogels by hydrothermal and freeze-drying processes. The BG aerogels with interlaced macro-/micro-pores have been proven to be ideally suited as support frameworks for encapsulating polyethylene glycol (PEG). The obtained composite PCMs exhibit high thermal conductivity (up to 1.12 W m-1 K-1), excellent shape stability (maintain at 90 °C for 10 min), and high latent heat (187.2 J g-1) with a retention of 97.3% of the pure PEG, presenting great potential applications in energy storage systems and thermal management of electronic devices.

Novel PEG6000-Silica-MWCNTs Shape-Stabilized Composite Phase-Change Materials (ssCPCMs) for Thermal-Energy Storage

This paper describes the preparation of new PEG₆₀₀₀-silica-MWCNTs composites as shape-stabilized phase change materials (ssPCMs) for application in latent heat storage. An innovative method was employed to obtain the new organic-inorganic hybrid materials, in which both a part of the PEG chains, used as the phase change material, and a part of the hydroxyl functionalized multiwall carbon nanotubes (MWCNTs-OH), used as thermo-conductive fillers, were covalently connected by newly formed urethane bonds to the in-situ-generated silica matrix. The study's main aim was to investigate the optimal amount of PEG₆₀₀₀ that can be added to the fixed sol-gel reaction mixture so that no leakage of PEG occurs after repeated heating-cooling cycles. The findings show that the optimum PEG₆₀₀₀/NCOTEOS molar ratio was 2/1 (~91.5% PEG₆₀₀₀), because both the connected and free PEG chains interacted strongly with the in-situ-generated silica matrix to form a shape-stabilized material while preserving high phase-transition enthalpies (~153 J/G). Morphological and structural findings obtained by SEM, X-ray and Raman techniques indicated a distribution of the silica component in the amorphous phase (~27% for the optimum composition) located among the crystalline lamellae built by the folded chains of the PEG component. This composite maintained good chemical stability after a 450-cycle thermal test and had a good storage efficiency (~84%).

Mesoporous carbon hollow spheres encapsulated phase change material for efficient emulsification of high-viscosity oil

Low fluidity of high-viscosity oil usually hinders its emulsification. Facing this dilemma, we proposed a novel functional composite phase change material (PCM) with in situ heating feature coupled with emulsification capability. This composite PCM consisting of mesoporous carbon hollow spheres (MCHS) and polyethylene glycol (PEG) shows excellent photothermal conversion ability, thermal conductivity and Pickering emulsification. Compared with the currently reported composite PCMs, the unique hollow cavity structure of MCHS not only enables excellent encapsulation of PCM, but also protects the PCM from leaking and direct contact with oil phase. Importantly, the thermal conductivity of 80% PEG@MCHS-4 was determined to be 1.372 W/m·K, which was 2.887 times superior to that of pure PEG. MCHS endows the composite PCM with excellent light absorption capacity and photothermal conversion efficiency. The viscosity of high-viscosity oil can be facilely reduced in situ once it comes into contact with the heat-storing PEG@MCHS, thus the emulsification is greatly enhanced. In view of the in situ heating feature and emulsification capability of PEG@MCHS, this work puts forward a novel solution to address the problem of emulsification of high-viscosity oil through the integration of MCHS and PCM.

Lipophilic Modified Hierarchical Multiporous rGO Aerogel-Based Organic Phase Change Materials for Effective Thermal Energy Storage

In the field of thermal energy storage, organic phase change materials (PCMs) are widely used as functional materials to boost thermal applications. However, there is often a tradeoff between constructing shape-stable composite PCMs with high enthalpy value and those with low leakage rates. Here, we proposed a promising scheme to address this issue. A novel hydrogel consisting of reduced graphene oxide (rGO) and covalent organic framework (COF) was prepared via hydrothermal methods, and the rGO-COF ultralight aerogel with a hierarchical porous structure was formed after freeze-drying. The rGO-COF aerogel shows excellent absorption ability and affinity for organic solvents. It can sufficiently adsorb the molten organic PCMs, such as polyethylene glycol (PEG), and synthesize shape-stable composite PCMs with excellent leak resistance. The COF grown on the surface of rGO has a superior affinity for PEG, so rGO-COF aerogel shows an outstanding PEG loading rate of up to 96.1 wt %, which is 1.7 wt % higher than that of rGO aerogel. In addition, the COF effectively reduces the subcooling of PEG/rGO-COF with 20.3%, compared to PEG/rGO. Meanwhile, the prepared PEG/rGO-COF exhibits extremely high enthalpy and relative enthalpy efficiency (164.6 J/g, 97.4%). This demonstrates that a promising direction was highlighte for the preparation of high-enthalpy shape-stable composite organic PCMs in this work.

Energy Conversion Efficiency Enhancement of Polyethylene Glycol and a SiO2 Composite Doped with Ni, Co, Zn, and Sc Oxides

Doping the SiO₂ support with Co, Ni, Zn, and Sc improves the thermal conductivity of a hybrid PEG/SiO₂ form-stable phase change material (PCM). Doping also improves the energy utilization efficiency and speeds up the charging and discharging rates. The thermal, chemical, and hydrothermal stability of the PEG/Zn-SiO₂ and PEG/Sc-SiO₂ hybrid materials is better than that of the other doped materials. The phase change enthalpy of PEG/Zn-SiO₂ is 147.6 J/g lower than that of PEG/Sc-SiO₂, while the thermal conductivity is 40% higher. The phase change enthalpy of 155.8 J/g of PEG/Sc-SiO₂ PCM is very close to that of the parent PEG. PEG/Sc-SiO₂ also demonstrates excellent thermal stability when subjected to 200 consecutive heating-cooling cycles and outstanding hydrothermal stability when examined under a stream at 120 °C for 2 h. The supercooling of the PEG/Sc-SiO₂ system is the lowest among the tested materials. In addition, the developed PCM composite has a high energy storage capacity and high thermal energy storage/release rates.

Enhanced Thermal Energy Storage of n-Octadecane-Impregnated Mesoporous Silica as a Novel Shape-Stabilized Phase Change Material

A series of n-octadecane/mesoporous silica (C₁₈/MS) shape-stabilized phase change materials (SSPCMs) with varying C₁₈ content were prepared, and the effects of adsorbed C₁₈ distributed within porous MS on the thermal properties were analyzed. As characterized, C₁₈ was first infiltrated into the mesoporous space, resulting in a SSPCM with a maximum of ∼52 wt % C₁₈. Additional adsorption of C₁₈ occurred on the external surface of MS. Consequently, the optimum 70 wt % C₁₈ SSPCM had no C₁₈ leakage and exhibited a heat storage capacity of 135.6 J/g and crystallinity of 83.5%, which were much larger than those of 52 wt % C₁₈ SSPCM (60.2 J/g and 68.2%, respectively). The prepared C₁₈/MS SSPCMs showed excellent thermal stability and thermal reliability up to 1000 accelerated thermal cycle tests. Moreover, the C₁₈/MS SSPCM incorporated in gypsum effectively reduced the temperature changes compared with the original gypsum, suggesting the promising application of the prepared C₁₈/MS SSPCM for energy-saving building applications.

Preparation and characterization of attapulgite-supported phase change energy storage materials

Phase change materials (PCMs) for the charge and discharge of thermal energy at a nearly constant temperature are of interest for thermal energy storage and management, and porous materials are usually used to support PCMs for preventing the liquid leakage and shape instability during the phase change process. Compared with commonly used polymer matrices and porous carbons, mineral materials with naturally occurring porous structures have obvious advantages such as cost-saving and abundant resources. Attapulgite (ATP) is a clay mineral with natural porous structures, which can be used to contain PCMs for thermal energy storage. However, the poor compatibility between ATP and PCMs is a significant defect that has rarely been studied. Herein, a facile one-step organic modification method of ATP was developed and the chlorosilane-modified ATP (Si-ATP) possesses great hydrophobic and lipophilic properties. Three types of ATP with different compatibility and pore volumes were used as the supports and paraffin as the energy storage units to fabricate a series of form-stable PCMs (FSPCMs). The results showed that the shape-stabilized ability of Si-ATP for paraffin was significantly enhanced, and the Si-ATP supported FSPCM yielded an optimal latent heat of 83.7 J g⁻¹, which was 64.4% higher than that of the pristine ATP based composite. Meanwhile, the thermal energy storage densities of the resulting FSPCMs were gradually increased with an increase in the pore volumes of the three supporting materials. These results may provide a strategy for preparing porous materials as containers to realize the shape stabilization of PCMs and improve the thermal energy storage densities of the resulting FSPCMs.

A facile organic modification method of attapulgite was developedand it's supporting capacity for organic PCMs was significantly enhanced.

Large-Scale Fabrication of Form-Stable Phase Change Nanotube Composite for Photothermal/Electrothermal Energy Conversion and Storage

Photothermal/electrothermal advanced functional form-stable phase change materials (FSPCMs) can efficiently make use of solar energy and electrical energy by using supporting materials to encapsulate phase change materials. Herein, a novel low-cost integrated supporting material, denoted PDVB-12/PPy NTs, is quickly constructed via wrapping the polypyrrole (PPy) on the mesoporous polydivinylbenzene nanotubes (PDVB-12 NTs) through a fast oxidative initiation method. PDVB-12/PPy NTs exhibits good loading capacity (72.9 wt %) for industrial paraffin wax (IPW) due to the large specific surface area, and the resulting FSPCM composite (IPW@PDVB-12/PPy) exhibits a large latent heat of fusion (145.7 J/g), high thermal stability, and excellent shape stability. In addition, PPy imparts the IPW@PDVB-12/PPy composite with high electrical conductivity (55.6 S m^-1) and high photoabsorption ability (whole visible light band). The energy stored in the IPW@PDVB-12/PPy composite could be triggered and released under relatively low voltages (2.5 V) with electrothermal energy conversion efficiency (89.6%) or solar radiation (100 mW cm^-2) with photothermal energy conversion efficiency (85.2%). This study provides a low-cost and fast method for large-scale fabrication of supporting materials, which can be a good candidate in energy storage applications.

Design and Construction of Photochromic and Antileakage Reinforced Wood-Based Cellulose Microframework/Hexadecanol-Coconut Oil Composite Phase Change Material

The development of high-performance shape-stable phase change material composites (SPCMs) with high phase change enthalpy and high conversion efficiency, especially with good photochromic properties, is essential for thermal energy storage. Here, we report that one type of SPCMs with both photochromic and phase change energy storage is obtained by incorporating organic binary composite PCMs (hexadecanol/coconut oil, H/C) and photochromic phosphotungstic acid (PA) into Ochroma pyramidale wood-based cellulose microframe (DOW) through simple vacuum impregnation. When the ratio of hexadecanol to coconut oil is 3:7 and the ratio of phosphotungstic acid to N,N-dimethylacetamide is 4:13.6, the SPCM composite material (DOW-H3C7-4PA) represents a high phase transition enthalpy of 163.7 J/g and an appropriate phase transition temperature of 42.55 °C that can be applied to the environmental temperature adjustment of high-temperature areas (>40 °C) mentioned in this paper, in addition to the excellent thermal stability and photochromic stability; for example, even after 100 thermal cycles and UV radiation cycles, its phase transition enthalpy remains almost unchanged. The DOW-H3C7-4PA composite material also shows good shape stability and leakage resistance. In addition, the high photothermal conversion efficiency (65.71%) of DOW-H3C7-4PA is considered to be a promising candidate for photothermal energy storage applications. Therefore, the manufactured SPCMs (DOW-H3C7-4PA) have high latent heat, good melting/freezing cycle reliability, high photochromic stability, and remarkable light-to-heat energy conversion ability, making them show broad application prospects in energy conversion and storage devices.

Preparation and Properties of a Composite Phase Change Energy Storage Gypsum Board Based on Capric Acid-Paraffin/Expanded Graphite

Energy has become the key material basis of social development. In this work, liquid capric acid-paraffin was evenly adsorbed in the pore structure of expanded graphite (EG) by a physical adsorption method, and the new composite phase change material of capric acid-paraffin/expanded graphite (CA-P/EG) was prepared. The Fourier transform infrared (FT-IR) curves of CA-P/EG composites did not change after 1000 cycles, and there was no new characteristic absorption peak, indicating that CA-P/EG composites have good chemical stability. The results showed that the optimum content of CA-P/EG in a phase change energy storage gypsum board was 20%, and the wet bending strength and compressive strength were 2.42 and 6.45 MPa, respectively. The water absorption was 16.37%, and the apparent density was 1.410 g/cm³. In addition, the melting and freezing temperatures were 26.40 and 23.10 °C, and the latent heats of melting and freezing were 27.20 and 25.69 J/g, respectively. It was found that the gypsum board has excellent thermal stability after 400 times of melting-freezing cycling and that the heat storage capacity increases with the increase of the CA-P/EG content and the thickness of the gypsum board.

Cellulose Nanofibrils Endow Phase-Change Polyethylene Glycol with Form Control and Solid-to-gel Transition for Thermal Energy Storage

Green energy-storage materials enable the sustainable use of renewable energy and waste heat. As such, a form-stable phase-change nanohybrid (PCN) is demonstrated to solve the fluidity and leakage issues typical of phase-change materials (PCMs). Here, we introduce the advantage of solid-to-gel transition to overcome the drawbacks of typical solid-to-liquid counterparts in applications related to thermal energy storage and regulation. Polyethylene glycol (PEG) is form-stabilized with cellulose nanofibrils (CNFs) through surface interactions. The cellulosic nanofibrillar matrix is shown to act as an organogelator of highly loaded PEG melt (85 wt %) while ensuring the absence of leakage. CNFs also preserve the physical structure of the PCM and facilitate handling above its fusion temperature. The porous CNF scaffold, its crystalline structure, and the ability to hold PEG in the PCN are characterized by optical and scanning electron imaging, infrared spectroscopy, and X-ray diffraction. By the selection of the PEG molecular mass, the lightweight PCN provides a tailorable fusion temperature in the range between 18 and 65 °C for a latent heat storage of up to 146 J/g. The proposed PCN shows remarkable repeatability in latent heat storage after 100 heating/cooling cycles as assessed by differential scanning calorimetry. The thermal regulation and light-to-heat conversion of the PCN are confirmed via infrared thermal imaging under simulated sunlight and in a thermal chamber, outperforming those of a reference, commercial insulation material. Our PCN is easily processed as a structurally stable design, including three-dimensional, two-dimensional (films), and one-dimensional (filaments) materials; they are, respectively, synthesized by direct ink writing, casting/molding, and wet spinning. We demonstrate the prospects of the lightweight, green nanohybrid for smart-energy buildings and waste heat-generating electronics for thermal energy storage and management.

Large-Scale Fabrication of a Robust Superhydrophobic Thermal Energy Storage Sprayable Coating Based on Polymer Nanotubes

We propose a facile and effective route for large-scale fabrication of a superhydrophobic thermal energy storage (STES) sprayable coating with heat storage capacity and superhydrophobicity based on polydivinylbenzene (PDVB) nanotubes (NTs). Herein, the STES coating was applied on wood by convenient spraying, and the PDVB NTs played an integral role in the STES coating. On the one hand, PDVB NTs act as a support material to adsorb and prevent the leakage of industrial paraffin wax (IPW) because of the lipophilicity of PDVB NTs and the capillary forces between the PDVB NTs and the melted IPW. By improving the specific surface area of PDVB NTs, the PDVB NTs show a great loading capacity for IPW (78.29 wt %), which contributes to the large latent heat of fusion (119.6 J/g) of the STES coating. Moreover, the STES coating possesses good thermal reliability and thermal energy conversion ability. On the other hand, PDVB NTs as a framework combine with fluorine-containing SiO₂ nanoparticles to form a hierarchical structure of the STES coating, which endows the STES coating satisfactory water-repellent properties with a water contact angle of 157.7° and a sliding angle of 1.3°. In addition, the coating possesses outstanding resistance against corrosive liquids and UV irradiation as well as has self-cleaning properties. Surprisingly, the knife scratch test confirms that even if the surface of the STES coating is destroyed, the revealed surface will also present superhydrophobicity. Simultaneously, the STES coating has good adhesion strength that maintains excellent superhydrophobicity under ultrasonic treatment, finger rubbing, and severe friction due to the contribution of ethyl α-cyanoacrylate. Therefore, the STES coating has both great phase change behaviors and remarkable superhydrophobic properties to resist the erosion of the natural environment, which will pave the way for its application in practice.

Toward Tailoring Chemistry of Silica-Based Phase Change Materials for Thermal Energy Storage

Efficient thermal energy harvesting using phase change materials (PCMs) has great potential for thermal energy storage and thermal management applications. Benefiting from these merits of pore structure diversity, convenient controllability, and excellent thermophysical stability, SiO2-based composite PCMs have comparatively shown more promising prospect. In this regard, the microstructure-thermal property correlation of SiO2-based composite PCMs is still unclear despite the significant achievements in structural design. To enrich the fundamental understanding on the correlations between the microstructure and the thermal properties, we systematically summarize the state-of-the-art advances in SiO2-based composite PCMs for tuning thermal energy storage from the perspective of tailoring chemistry strategies. In this review, the tailoring chemistry influences of surface functional groups, pore sizes, dopants, single shell, and hybrid shells on the thermal properties of SiO2-based composite PCMs are systematically summarized and discussed. This review aims to provide in-depth insights into the correlation between structural designs and thermal properties, thus showing better guides on the tailor-made construction of high-performance SiO2-based composite PCMs. Finally, the current challenges and future recommendations for the tailoring chemistry are also highlighted.

Nanoflake-Constructed Supramolecular Hierarchical Porous Microspheres for Fire-Safety and Highly Efficient Thermal Energy Storage

The leakage and fire hazard of organic solid-liquid phase change material (PCM) tremendously limit its long-term and safe application in thermal energy storage and regulation. In this work, novel nanoflake-fabricated organic-inorganic supramolecular hierarchical microspheres denoted as BPL were synthesized through the electrostatically driven assembly of poly(ethylene ammonium phenylphosphamide) (BP) decorated layered double hydroxides using sodium dodecyl sulfate as a template. Then the BPL was simultaneously utilized as a porous supporting material and flame retardant for polyethylene glycol to fabricate shape-stabilized PCM (BS-PCM). Benefiting from the structural uniqueness of the BPL microsphere, the BS-PCM possessed a high latent heat capacity of 116.7 J g^-1 and excellent thermoregulatory capability. Moreover, the BS-PCM had no apparent leakage after a 200-cycle heating/cooling process and showed excellent thermal reversibility, superior to similar solid-liquid PCMs reported in recent literature. More interestingly, unlike flammable PEG, BS-PCM showed excellent fire resistance when exposed to a fire source. The unique BPL porous microsphere provided not only a microcontainer with high storage capacity for solid-liquid PCM, but also a fire resistant barrier to PEG, supplying a promising solution for highly efficient and fire-safe thermal energy storage.

Phase-Change Materials for Controlled Release and Related Applications

Phase-change materials (PCMs) have emerged as a novel class of thermo-responsive materials for controlled release, where the payloads encapsulated in a solid matrix are released only upon melting the PCM to trigger a solid-to-liquid phase transition. Herein, the advances over the past 10 years in utilizing PCMs as a versatile platform for the encapsulation and release of various types of therapeutic agents and biological effectors are highlighted. A brief introduction to PCMs in the context of desired properties for controlled release and related applications is provided. Among the various types of PCMs, a specific focus is placed on fatty acids and fatty alcohols for their natural availability, low toxicity, biodegradability, diversity, high abundance, and low cost. Then, various methods capable of processing PCMs, and their mixtures with payloads, into stable suspensions of colloidal particles, and the different means for triggering the solid-to-liquid phase transition are discussed. Finally, a range of applications enabled by the controlled release system based on PCMs are presented together with some perspectives on future directions.

Shape-stabilization of polyethylene glycol phase change materials with chitin nanofibers for applications in "smart" windows

Polyethylene glycol (PEG) based shape-stabilized phase change materials (PCMs) were successfully prepared using chitin nanofibers (CNFs). CNFs were isolated from crab shells and, resulted CNFs were several tenth of nanometers in diameter and had lengths ranging from several hundreds of nanometers to few micrometers. Introduction of CNFs in to PEG resulted shape-stabilized composites. Various PEG-CNF composites were fabricated and the resulted materials were encapsulated in to an optical device to obtain temperature dependent transparency. In the optimized formulation, the device remained opaque (∼3.5 %) below the melting point of the PEG-CNF composite and became gradually transparent as the temperature of the device increased ultimately stabilizing at a transmittance value of ∼88 %. CNF phase was seen to have an effect on the thermal properties of the PEG-CNF material. The work introduces a novel strategy for the shape stabilization of liquid-solid phase change materials unlocking potential for new PCM based devices.

Shape-Stabilized Phase Change Materials for Solar Energy Storage: MgO and Mg(OH)2 Mixed with Polyethylene Glycol

Heat energy storage systems were fabricated with the impregnation method using MgO and Mg(OH)₂ as supporting materials and polyethylene glycol (PEG-6000) as the functional phase. MgO and Mg(OH)₂ were synthesized from the salt Mg(NO₃)·6H₂O by performing hydrothermal reactions with various precipitating agents. The precipitating agents were NaOH, KOH, NH₃, NH₃ with pamoic acid (PA), or (NH₄)₂CO₃. The result shows that the selection of the precipitating agent has a significant impact on the crystallite structure, size, and shape of the final products. Of the precipitating agents tested, only NaOH and NH₃ with PA produce single-phase Mg(OH)₂ as the as-synthesized product. Pore size distribution analyses revealed that the surfaces of the as-synthesized MgO have a slit-like pore structure with a broad-type pore size distribution, whereas the as-synthesized Mg(OH)₂ has a mesoporous structure with a narrow pore size distribution. This structure enhances the latent heat of the phase change material (PCM) as well as super cooling mitigation. The PEG/Mg(OH)₂ PCM also exhibits reproducible behavior over a large number of thermal cycles. Both MgO and Mg(OH)₂ matrices prevent the leakage of liquid PEG during the phase transition in phase change materials (PCMs). However, MgO/PEG has a low impregnation ratio and efficiency, with a low thermal storage capability. This is due to the large pore diameter, which does not allow MgO to retain a larger amount of PEG. The latent heat values of PEG-1000/PEG-6000 blends with MgO and Mg(OH)₂ were also determined with a view to extending the application of the PCMs to energy storage over wider temperature ranges.

Applications of Sustainable Polymer-Based Phase Change Materials in Mortars Composed by Different Binders

Eco-sustainable, low toxic and low flammable poly-ethylene glycol (PEG) was forced into flakes of the porous Lecce stone (LS), collected as stone cutting wastes, employing a very simple cheap method, to produce a “form-stable” phase change material (PCM). The experimental PCM was included in mortars based on different binders (hydraulic lime, gypsum and cement) in two compositions. The main thermal and mechanical characteristics of the produced mortars were evaluated in order to assess the effects due to the incorporation of the PEG-based PCM. The mortars containing the PEG-based PCM were found to be suitable as thermal energy storage systems, still displaying the characteristics melting and crystallization peaks of PEG polymer, even if the related enthalpies measured on the mortars were appreciably reduced respect to pure PEG. The general reduction in mechanical properties (in flexural and compressive mode) measured on all the mortars, brought about by the presence of PEG-based PCM, was overcome by producing mortars possessing a greater amount of binder. The proposed LS/PEG composite can be considered, therefore, as a promising PCM system for the different mortars analyzed, provided that an optimal composition is identified for each binder.

A Facile and Simple Method for Preparation of Novel High-Efficient Form-Stable Phase Change Materials Using Biomimetic-Synthetic Polydopamine Microspheres as a Matrix for Thermal Energy Storage

Polydopamine microspheres (PDAMs), synthesized using a biomimetic method, were used as a matrix for polyethylene glycol (PEG) to develop a novel high-efficient form-stable phase change material (PEG/PDAM) using a simple vacuum impregnation strategy. The PDAMs were first used as a support for the organic phase change materials, and the biomimetic synthesis of the PDAMs had the advantages of easy operation, mild conditions, and environmental friendliness. The characteristics and thermal properties of the PEG/PDAMs were investigated using SEM, FTIR, XRD, TGA, DSC, and XPS, and the results demonstrated that the PEG/PDAMs possessed favourable heat storage capacity, excellent thermal stability, and reliability, and the melting and freezing latent heats of PEG/PDAM-3 reached 133.20 ± 2.50 J/g and 107.55 ± 4.45 J/g, respectively. Therefore, the PEG/PDAMs possess great potential in real-world applications for thermal energy storage. Additionally, the study on the interaction mechanism between the PEG and PDAMs indicated that PEG was immobilized on the surface of PDAMs through hydrogen bonds between the PEG molecules and the PDAMs. Moreover, the PDAMs can also be used as a matrix for other organic materials for the preparation of form-stable phase change materials.

Comparative Study of Carbon Nanoparticles and Single-Walled Carbon Nanotube for Light-Heat Conversion and Thermal Conductivity Enhancement of the Multifunctional PEG/Diatomite Composite Phase Change Material

We report two novel 3-dimension hierarchical diatomite struts by filling the diatomite pores with a small amount of single-walled carbon nanotubes (SWCNs) and carbon nanoparticles (CNPs). The emerging supporting scaffolds are then applied to a prepare polyethylene glycol (PEG)-infiltrated composite phase change material to seek an efficient but easy way to improve the thermal conductivity and synchronously accomplish the light-thermal conversion on the one hand. On the other hand, the mechanism of the microstructure-performance relationship of these composites has also been briefly presented and compared. In addition, the involved differences and synergistic effects between the diatomite and carbon filler have been quantified and visualized for the first time. Compared with CNPs, the SWCNs with the same content inside diatomite pores enable a much more packed architecture and faster thermal conductive route, light harvesting ability, form stability, and comparable energy storage density. Obviously, the superior comprehensive performance of PEG/DCNs can be attributed to the filler dimension discrepancy trend of 0D < 1D. Compared to PEG/Dt, the thermal conductivity of the PEG/diatomite/SWCNs (1.52 W/m K) increases by nearly 5.2-fold (∼424% increase) upon ∼3.2 wt % SWCN addition along with an unexpected rise in the energy storage density of ∼12.1%. To the best of our knowledge, this is the first study on the light-thermal conversion behavior of mineral-based composites, let alone using diatomite, which provides critical insights to design the high performance energy storage composites for domestic solar hot water supply systems.

Nanostructured polymers with embedded self-assembled networks: reversibly tunable phase behaviors and physical properties

1,3:2,4-Dibenzylidene sorbitol (DBS) can self-assemble into nanofibrillar networks to form organogels in a variety of organic solvents and liquid polymers. In this study, we induced the formation of organogels in solid poly(ethylene glycol) (PEG) polymers. The DBS gels appeared at temperatures above the melting point of PEG. When the DBS/PEG systems were heated at higher temperatures, they exhibited transparent, clear solution states due to the collapse of the DBS networks. Upon cooling to room temperature, the DBS self-assembled nanostructures appeared again, followed by the solidification (crystallization) of PEG. These DBS/PEG systems possess three different phases (solid, gel and liquid) and can be tuned by changes in the composition and temperature. Using polarized optical microscopy, all the gel systems were found to exhibit spherulite-like morphologies. Small-angle X-ray scattering results revealed lamellar packing in these spherulite-like morphologies. Transmission electron microscopy verified that these features were formed due to the presence of DBS nanofibrillar networks consisting of fibrils that were approximately 10-20 nm in diameter. In addition, the crystallization of PEG was strongly templated by the existing DBS nanofibrils. Moreover, there were no significant distortions in the PEG crystal structures due to the confinement of PEG between the DBS nanofibrils.

Transparent Wood for Thermal Energy Storage and Reversible Optical Transmittance

Functional load-bearing materials based on phase-change materials (PCMs) are under rapid development for thermal energy storage (TES) applications. Mesoporous structures are ideal carriers for PCMs and guarantee shape stability during the thermal cycle. In this study, we introduce transparent wood (TW) as a TES system. A shape-stabilized PCM based on polyethylene glycol is encapsulated into a delignified wood substrate, and the TW obtained is fully characterized, also in terms of nano- and mesoscale structures. Transparent wood for thermal energy storage (TW-TES) combines large latent heat (∼76 J g^-1) with switchable optical transparency. During the heating process, optical transmittance increases by 6% and reaches 68% for 1.5 mm thick TW-TES. Characterization of the thermal energy regulation performance shows that the prepared TW-TES composite is superior to normal glass because of the combination of good heat-storage and thermal insulation properties. This makes TW-TES composites interesting candidates for applications in energy-saving buildings.

Protein Shell-Encapsulated Pt Clusters as Continuous O2-Supplied Biocoats for Photodynamic Therapy in Hypoxic Cancer Cells

As a highly oxygen-dependent process, the effect of photodynamic therapy is often obstructed by the premature leakage of photosensitizers and the lack of oxygen in hypoxic cancer cells. To overcome these limitations, this study designs bovine serum albumin protein (BSA)-encapsulated Pt nanoclusters (PtBSA) as O₂-supplied biocoats and further incorporates them with mesoporous silica nanospheres to develop intelligent nanoaggregates for achieving improved therapeutic outcomes against hypoxic tumors. The large number of amino groups on BSA can provide sufficient functional groups to anchor tumor targeting agents and thus enhance the selective cellular uptake efficiency. Owing to the outstanding biocompatibility features of BSA and the state-of-the-art catalytic activity of Pt nanoclusters, the nanocomposites have lower dark cytotoxicity, and O₂ continuously evolves via the decomposition of H₂O₂ in a tumor microenvironment. Both in vivo and in vitro experiments indicate that the resulting nanocomposites can effectively relieve hypoxic conditions, specifically induce necrotic cell apoptosis, and remarkably hinder tumor growth. Our results illuminate the great potential of BSA-encapsulated Pt nanoclusters as versatile biocoats in designing intelligent nanocarriers for hypoxic-resistant photodynamic therapy.

Mullite Stabilized Palmitic Acid as Phase Change Materials for Thermal Energy Storage

In this paper, mullite was adopted in order to absorb Palmitic Acid (PA) via a direct impregnation method. The prepared PA/mullite form-stable phase change materials (FSPCM) were systematically characterized by the Leakage Test (LT), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimeter (DSC), Thermogravimetry (TG) and Cooling Curve Method (CCM). The results indicated that, among these composites with different mass fractions of PA, the sample with the 32 wt % Palmitic Acid has the best properties without any leakage. The enthalpy of 32%PA/68%mullite FSPCM is 50.8 J/g for melting process, and 58.3 J/g for solidifying process. The phase change point of 32%PA/68%mullite FSPCM is 64.1 °C for melting and 58.7 °C for solidifying. The heat storage efficiency of the PA/mullite FSPCM was enhanced considerably by adding mullite. The leakage and thermal properties of PA/mullite FSPCM were discussed and the performance of the FSPCM has been apparently improved.

Secondary-Structure-Mediated Hierarchy and Mechanics in Polyurea-Peptide Hybrids

Peptide-polymer hybrids combine the hierarchy of biological species with synthetic concepts to achieve control over molecular design and material properties. By further incorporating covalent cross-links, the enhancement of molecular complexity is achieved, allowing for both a physical and covalent network. In this work, the structure and function of poly(ethylene glycol) (PEG)-network hybrids are tuned by varying peptide block length and overall peptide content. Here the impact of poly(ε-carbobenzyloxy-l-lysine) (PZLY) units on block interactions and mechanics is explored by probing secondary structure, PEG crystallinity, and hierarchical organization. The incorporation of PZLY reveals a mixture of α-helices and β-sheets at smaller repeat lengths ( n = 5) and selective α-helix formation at a higher peptide molecular weight ( n = 20). Secondary structure variations tailored the solid-state film hierarchy, whereby nanoscale fibers and microscale spherulites varied in size depending on the amount of α-helices and β-sheets. This long-range ordering influenced mechanical properties, resulting in a decrease in elongation-at-break (from 400 to 20%) with increasing spherulite diameter. Furthermore, the reduction in soft segment crystallinity with the addition of PZLY resulted in a decrease in moduli. It was determined that, by controlling PZLY content, a balance of physical associations and self-assembly is obtained, leading to tunable PEG crystallinity, spherulite formation, and mechanics.

High Performance Shape-Stabilized Phase Change Material with Nanoflower-Like Wrinkled Mesoporous Silica Encapsulating Polyethylene Glycol: Preparation and Thermal Properties

Nanoflower-like wrinkled mesoporous silica (NFMS) was prepared for further application as the carrier of polyethylene glycol (PEG) to fabricate the new, shape-stabilized phase change composites (PEG/NFMS); NFMS could improve the loading content of PEG in the PEG/NFMS. To investigate the properties of PEG/NFMS, characterization approaches, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) analysis, and differential scanning calorimetry (DSC), were carried out. The characterization results illustrated that the PEG was completely adsorbed in the NFMS by physical adsorption, and the nanoflower-like wrinkled silica did not affect the crystal structure of PEG. As reported by the DSC test, although NFMS had a restriction influence on the activity of the PEG molecules, the melting and binding enthalpies of the PEG/NFMS could reach 136.6 J/g and 132.6 J/g, respectively. In addition, the TGA curves demonstrated that no evident weight loss was observed from 20 °C to 190 °C for the PEG/NFMS, and the results revealed that the PEG/NFMS had remarkable thermal stability. These results indicated that the NFMS is a potential carrier of organic phase change material for the preparation of shape-stabilized phase change composites.

Novel Magnetic-to-Thermal Conversion and Thermal Energy Management Composite Phase Change Material

Superparamagnetic materials have elicited increasing interest due to their high-efficiency magnetothermal conversion. However, it is difficult to effectively manage the magnetothermal energy due to the continuous magnetothermal effect at present. In this study, we designed and synthesized a novel Fe₃O₄/PEG/SiO₂ composite phase change material (PCM) that can simultaneously realize magnetic-to-thermal conversion and thermal energy management because of outstanding thermal energy storage ability of PCM. The composite was fabricated by in situ doping of superparamagnetic Fe₃O₄ nanoclusters through a simple sol–gel method. The synthesized Fe₃O₄/PEG/SiO₂ PCM exhibited good thermal stability, high phase change enthalpy, and excellent shape-stabilized property. This study provides an additional promising route for application of the magnetothermal effect.

Mesoporous silica nanoparticles with wrinkled structure as the matrix of myristic acid for the preparation of a promising new shape-stabilized phase change material via simple method

Wrinkled mesoporous silica nanoparticle (WMSN), with a special and highly uniform morphology, large specific surface area and pore volume, high porosity and radial-like wrinkled channels, was successfully prepared by a simple and easy synthetic method. WMSN was used as the matrix of myristic acid (MA) to prepare a new attractive shape-stabilized PCM (MA/WMSN), and the wrinkled channels of WMSN are useful to prevent the leakage of PCM, and increase the thermal stability and phase change enthalpy of shape-stabilized PCM. Characterizations of MA/WMSN, such as structure, crystallization properties, chemical properties and thermal properties were studied, and the interaction mechanism between the WMSN and MA molecules was elucidated. TGA results suggested that MA/WMSN had excellent thermal stability. When the loading of MA in MA/WMSN was 65%, the melting and crystallizing enthalpies of MA/WSSN were 92.0 J g⁻¹ and 86.0 J g⁻¹, respectively. Additionally, the thermal conductivity of MA/WMSN was 0.37 W mK⁻¹, which was about 1.37 times higher than that of the pure MA. All of the study results demonstrated that MA/WMSN possessed of favourable thermal conductivity, high latent heats and excellent thermal stability, and therefore it could be a suitable thermal energy storage material for practical applications.

Mesoporous silica nanoparticle with wrinkled structure as the matrix of myristic acid for the preparation of a promising new shape-stabilized phase change material via simple method.

PEG 400-Based Phase Change Materials Nano-Enhanced with Functionalized Graphene Nanoplatelets

This study presents new Nano-enhanced Phase Change Materials, NePCMs, formulated as dispersions of functionalized graphene nanoplatelets in a poly(ethylene glycol) with a mass-average molecular mass of 400 g·mol⁻¹ for possible use in Thermal Energy Storage. Morphology, functionalization, purity, molecular mass and thermal stability of the graphene nanomaterial and/or the poly(ethylene glycol) were characterized. Design parameters of NePCMs were defined on the basis of a temporal stability study of nanoplatelet dispersions using dynamic light scattering. Influence of graphene loading on solid-liquid phase change transition temperature, latent heat of fusion, isobaric heat capacity, thermal conductivity, density, isobaric thermal expansivity, thermal diffusivity and dynamic viscosity were also investigated for designed dispersions. Graphene nanoplatelet loading leads to thermal conductivity enhancements up to 23% while the crystallization temperature reduces up to in 4 K. Finally, the heat storage capacities of base fluid and new designed NePCMs were examined by means of the thermophysical properties through Stefan and Rayleigh numbers. Functionalized graphene nanoplatelets leads to a slight increase in the Stefan number.

Self-assembly behaviors of dibenzylidene sorbitol hybrid organogels with inorganic silica

Molecular interactions, rheological behaviors and microstructures of 1,3:2,4-dibenzylidene-d-sorbitol (DBS)/poly(ethylene glycol) (PEG) organogel-inorganic silica hybrid materials are discussed in this study. DBS can dissolve in low-molecular-weight PEG to form organogels. The self-assembly behavior of these organogels was significantly influenced by the addition of the inorganic silica. The π interactions between the phenyl rings of DBS were not influenced by silica addition; however, the addition of silica affected the intermolecular hydrogen bonding of DBS, which interacts with PEG. The silica more likely interacted with PEG and decreased the intermolecular interactions between DBS and PEG, which resulted in an increase in the self-assembly of DBS. Therefore, the gel formation time and gel dissolution temperature increased as the amount of silica increased, as determined by dynamic rheological instruments. In addition, these organogel systems were all found to exhibit spherulite-like textures under polarized optical microscopy. The addition of silica and the increased DBS self-assembly in PEG resulted in a higher self-assembly temperature of the organogels. The higher temperature resulted in the presence of fewer nucleation sites and larger spherulite sizes in these systems. Small-angle X-ray scattering results demonstrated lamellar packing in these spherulite-like morphologies. Furthermore, the organogels with silica affected the intermolecular hydrogen bonding between DBS and PEG to facilitate the self-assembly of DBS, which resulted in increased diameter sizes of the DBS nanofibrils, as observed using scanning electron microscopy. It was observed that the silica was entrapped within these nanofibrillar networks.

Enhanced thermal conductivity of form-stable phase change composite with single-walled carbon nanotubes for thermal energy storage

A striking contrast in the thermal conductivities of polyethylene glycol (PEG)/diatomite form-stable phase change composite (fs-PCC) with single-walled carbon nanotubes (SWCNs) as nano-additive has been reported in our present study. Compared to the pure PEG, the thermal conductivity of the prepared fs-PCC has increased from 0.24 W/mK to 0.87 W/Mk with a small SWCNs loading of 2 wt%. SWCNs are decorated on the inner surface of diatomite pores whilst retaining its porous structure. Compared to PEG/diatomite fs-PCC, the melting and solidification time of the PEG/diatomite/SWCNs fs-PCC are respectively decreased by 54.7% and 51.1%, and its thermal conductivity is 2.8 times higher. The composite can contain PEG as high as 60 wt% and maintain its original shape perfectly without any PEG leakage after subjected to 200 melt-freeze cycles. DSC results indicates that the melting point of the PEG/diatomite/SWCNs fs-PCC shifts to a lower temperature while the solidification point shifts to a higher temperature due to the presence of SWCNs. Importantly, the use of SWCNs is found to have clear beneficial effects for enhancing the thermal conductivity and thermal storage/release rates, without affecting thermal properties, chemical compatibility and thermal stability. The prepared PEG/diatomite/SWCNs fs-PCC exhibits excellent chemical and thermal durability and has potential application in solar thermal energy storage and solar heating.

Fabrication and characterization of dual-functional ultrafine composite fibers with phase-change energy storage and luminescence properties

Ultrafine composite fibers consisting of a thermoplastic polyurethane solid-solid phase-change material and organic lanthanide luminescent materials were prepared through a parallel electrospinning technique as an innovative type of ultrafine, dual-functional fibers containing phase-change and luminescent properties. The morphology and structure, thermal energy storage, and luminescent properties of parallel electrospun ultrafine fibers were investigated. Scanning electron microscopy (SEM) images showed that the parallel electrospun ultrafine fibers possessed the desired morphologies with smaller average fiber diameters than those of traditional mixed electrospun ultrafine fibers. Transmission electron microscopy (TEM) images revealed that the parallel electrospun ultrafine fibers were composed of two parts. Polymeric phase-change materials, which can be directly produced and spun, were used to provide temperature stability, while a mixture of polymethyl methacrylate and an organic lanthanide complex acted as the luminescent unit. Differential scanning calorimetry (DSC) and luminescence measurements indicated that the unique structure of the parallel electrospun ultrafine fibers provides the products with good thermal energy storage and luminescence properties. The fluorescence intensity and the phase-change enthalpy values of the ultrafine fibers prepared by parallel electrospinning were respectively 1.6 and 2.1 times those of ultrafine fibers prepared by mixed electrospinning.

Graphene-decorated silica stabilized stearic acid as a thermal energy storage material

Graphene-decorated silica stabilized stearic acid composites with interesting thermal energy storage behaviors.

Fabrication and characterization of novel shape-stabilized stearic acid composite phase change materials with tannic-acid-templated mesoporous silica nanoparticles for thermal energy storage

A novel shape-stabilized phase change material, prepared by immobilizing stearic acid onto tannic-acid-templated mesoporous silica nanoparticles.

Core-shell microstructured nanocomposites for synergistic adjustment of environmental temperature and humidity

The adjustment of temperature and humidity is of great importance in a variety of fields. Composites that can perform both functions are prepared by mixing phase change materials (PCMs) with hygroscopic materials. However, the contact area between the adsorbent and humid air is inevitably decreased in such structures, which reduces the number of mass transfer channels for water vapor. An approach entailing the increase in the mass ratio of the adsorbent is presented here to improve the adsorption capacity. A core-shell CuSO₄/polyethylene glycol (PEG) nanomaterial was developed to satisfy the conflicting requirements of temperature control and dehumidification. The results show that the equilibrium adsorption capacity of the PEG coating layer was enhanced by a factor of 188 compared with that of the pure PEG powder. The coating layer easily concentrates vapor, providing better adsorption properties for the composite. Furthermore, the volume modification of the CuSO₄ matrix was reduced by 80% by the PEG coated layer, a factor that increases the stability of the composite. For the phase change process, the crystallization temperature of the coating layer was adjusted between 37.2 and 46.3 °C by interfacial tension. The core-shell CuSO₄/PEG composite reported here provides a new general approach for the simultaneous control of temperature and humidity.

Pore structure modified diatomite-supported PEG composites for thermal energy storage

A series of novel composite phase change materials (PCMs) were tailored by blending PEG and five kinds of diatomite via a vacuum impregnation method. To enlarge its pore size and specific surface area, different modification approaches including calcination, acid treatment, alkali leaching and nano-silica decoration on the microstructure of diatomite were outlined. Among them, 8 min of 5 wt% NaOH dissolution at 70 °C has been proven to be the most effective and facile. While PEG melted during phase transformation, the maximum load of PEG could reach 70 wt.%, which was 46% higher than that of the raw diatomite. The apparent activation energy of PEG in the composite was 1031.85 kJ·mol(-1), which was twice higher than that of the pristine PEG. Moreover, using the nano-silica decorated diatomite as carrier, the maximum PEG load was 66 wt%. The composite PCM was stable in terms of thermal and chemical manners even after 200 cycles of melting and freezing. All results indicated that the obtained composite PCMs were promising candidate materials for building applications due to its large latent heat, suitable phase change temperature, excellent chemical compatibility, improved supercooling extent, high thermal stability and long-term reliability.

Polyethylene glycol/Cu/SiO2 form stable composite phase change materials: preparation, characterization, and thermal conductivity enhancement

Novel form-stable composite phase change materials (FS-CPCMs) of polyethylene glycol (PEG)/Cu/SiO₂ were prepared by adding Cu powder to PEG and SiO₂via the ultrasound-assisted sol–gel method.