One-Step and Solvent-Free Synthesis of Polyethylene Glycol-Based Polyurethane As Solid–Solid Phase Change Materials for Solar Thermal Energy Storage

Multi-Scale Study of a Phase Change Material on a Tropical Island for Evaluating Its Impact on Human Comfort in the Building Sector

Our study explores the utilization of a phase change material (PCM) to optimize energy efficiency and thermal comfort in buildings in tropical climates. Employing a comprehensive multi-scale approach, this research encompasses both microscopic and macroscopic analyses to rigorously evaluate the PCM's performance under various environmental conditions. It evaluates the effect of PCMs on ambient conditions in the face of temperature variations and high humidity, utilizing experimental methods at different scales (microscopic and macroscopic). Microscopic analyses reveal the composite structure of the PCM, consisting of microencapsulated paraffin within a cellulose fiber matrix. At a macroscopic scale, experiments using two real-scale test cells evaluated thermal performance and its influence on thermal comfort. Temperature and humidity data were meticulously collected over an extended period to assess the PCM's impact on indoor regulation. We employed type T thermocouples and flux meters to monitor thermal dynamics and energy flux across the building walls. This setup facilitated a detailed comparison of temperature variations and thermal comfort metrics between the PCM-equipped test cell and a control cell. The results indicate a seasonal duality of the PCM: beneficial in winter for thermal regulation but problematic in summer due to excessive heat retention. The conclusions highlight the importance of carefully selecting and adapting PCMs for tropical climates, thus providing valuable insights for designing sustainable buildings in regions facing similar climatic challenges.

Effects of Ammonium Polyphosphate and Organic Modified Montmorillonite on Flame Retardancy of Polyethylene Glycol/Wood-Flour-Based Phase Change Composites

With the depletion of fossil fuel energy and both the slow development and low utilization rate of new eco-friendly energy, finding new ways to efficiently store energy has become a research hotspot. Presently, polyethylene glycol (PEG) is an excellent heat storage material, but it is a typical solid-liquid phase change material (PCM) with a risk of leakage during phase transition. A combination of wood flour (WF) and PEG can effectively eliminate the risk of leakage after the melting of PEG. However, WF and PEG are both flammable materials, which impedes their application. Therefore, it is of great significance to expand their application by forming composites from among PEG, supporting mediums, and flame-retardant additives. This will improve both their flame retardancy and phase change energy storage performance, and will also lead to the preparation of excellent flame-retardant phase change composite materials with solid-solid phase change characteristics. To address this issue, ammonium polyphosphate (APP), organic modified montmorillonite (OMMT), and WF were blended into PEG in specific proportions to prepare a series of PEG/WF-based composites. Both thermal cycling tests and thermogravimetric analysis results demonstrated that the as-prepared composites had good thermal reliability and chemical stability. In addition, during differential scanning calorimetry tests, the PEG/WF/8.0APP@2.0OMMT composite presented the highest melting latent heat (176.6 J/g), and its enthalpy efficiency reached more than 98.3%. The PEG/WF/8.0APP@2.0OMMT composite also exhibited superior thermal insulation performance when compared to the pure PEG/WF composite. Furthermore, the PEG/WF/8.0APP@2.0OMMT composite exhibited a significant 50% reduction in peak heat release rate as a result of the synergistic effect between OMMT and APP in the gas and condensed phases. This work offers a useful strategy for the fabrication of multifunctional phase-change material, which is expected to broaden its industrial applications.

Single pot organic solvent-free thermocycling technology for siRNA-ionizable LNPs: a proof-of-concept approach for alternative to microfluidics

Ionizable LNPs are the latest trend in nucleic acid delivery. Microfluidics technology has recently gained interest owing to its rapid mixing, production of nucleic acid-ionizable LNPs, and stability of nucleic acid inside the body. Industrial scale-up, nucleic acid-lipid long-term storage instability, and high production costs prompted scientists to seek alternate solutions to replace microfluidic technology. We proposed a single-pot, organic solvent-free thermocycling technology to efficiently and economically overcome most of the limitations of microfluidic technology. New thermocycling technology needs optimization of process parameters such as sonication duration, cooling–heating cycle, number of thermal cycles, and lipid:aqueous phase ratio to formulate precisely sized particles, effective nucleic acid encapsulation, and better shelf-life stability. Our research led to the formulation of siRNA-ionizable LNPs with particle sizes of 104.2 ± 34.7 nm and PDI 0.111 ± 0.109, with 83.3 ± 4.1% siRNA encapsulation. Thermocycling siRNA-ionizable LNPs had comparable morphological structures with commercialized microfluidics ionizable LNPs imaged by TEM and cryo-TEM. When compared to microfluidics ionizable LNPs, thermocycling siRNA-ionizable LNPs had a longer shelf life at 4°C. Our thermocycling technology showed an effective alternative to microfluidics technology in the production of nucleic acid–ionizable LNPs to meet global demand.

Thermocycling technology is a low-energy, low-temperature, self-assembling cooling–heating process in which lipid droplets spontaneously break apart into much smaller droplets to form siRNA-ionizable LNPs.

The new technology is an alternative to multistep, costly, and complex microfluidics technology for the formulation and bulk up of siRNA-ionizable LNPs economically.

Thermocycling siRNA-ionizable LNPs formulation focused on optimizing process parameters such as thermal cycle rate, number of thermal cycles, and lipid:aqueous phase ratio.

The thermocycling technology is able to overcome the limitations of the storage stability limitations of commercialized ionizable LNPs.

Effect of Different Soft Segment Contents on the Energy Storage Capacity and Photo-Thermal Performance of Polyurethane-Based/Graphene Oxide Composite Solid-Solid Phase Change Materials

A series of polyurethane/graphene oxide (PU/GO) solid-solid phase change materials (SSPCMs) were synthesized by using GO as a light-absorbing filler and polyethylene glycol (PEG) as a phase change matrix. The effects of PEG content on the energy storage capacity, thermal stability and photo-thermal conversion performance of PU were investigated. The results show that the form-stability of PU/GO decreases while the phase change enthalpy and photo-thermal conversion efficiency of PU/GO increases with the increasing PEG content. The introduction of a very low content of GO can maintain comparable energy storage density and greatly improve light absorption by reasonably modulating the soft segment contents. The PU/GO composite with 92 wt% PEG has a phase change enthalpy of 138.12 J/g and a high photo-thermal conversion efficiency (87.6%). The composite solid-solid PCMs have great potential for effective energy storage and solar energy utilization.

Emerging Solid-to-Solid Phase-Change Materials for Thermal-Energy Harvesting, Storage, and Utilization

Phase-change materials (PCMs) offer tremendous potential to store thermal energy during reversible phase transitions for state-of-the-art applications. The practicality of these materials is adversely restricted by volume expansion, phase segregation, and leakage problems associated with conventional solid-liquid PCMs. Solid-solid PCMs, as promising alternatives to solid-liquid PCMs, are gaining much attention toward practical thermal-energy storage (TES) owing to their inimitable advantages such as solid-state processing, negligible volume change during phase transition, no contamination, and long cyclic life. Herein, the aim is to provide a holistic analysis of solid-solid PCMs suitable for thermal-energy harvesting, storage, and utilization. The developing strategies of solid-solid PCMs are presented and then the structure-property relationship is discussed, followed by potential applications. Finally, an outlook discussion with momentous challenges and future directions is presented. Hopefully, this review will provide a guideline to the scientific community to develop high-performance solid-solid PCMs for advanced TES applications.

Flexible engineering of advanced phase change materials

Liquid phase leakage, intrinsic rigidity, and easy brittle failure are the longstanding bottlenecks of phase change materials (PCMs) for thermal energy storage, which seriously hinder their widespread applications in advanced energy-efficient systems. Emerging flexible composite PCMs that are capable of enduring certain deformation and guaranteeing superior mutual contact with integrated devices are considered as a cutting-edge effective solution. Flexible PCMs-based thermal regulation technology can reallocate thermal energy and regulate the temperature within an optimal range. Currently, tireless efforts are devoted to the development of versatile flexible PCMs-based thermal regulation devices, and a big step forward has been taken. Herein, we systematically outline fabrication techniques, flexibility evaluation strategies, advanced functions and advances of flexible composite PCMs. Furthermore, existing challenges and future perspectives are provided in terms of flexible PCMs-based thermal regulation techniques. This insightful review aims to provide an in-depth understanding and constructive guidance of engineering advanced flexible multifunctional PCMs.

Functional Unit Construction for Heat Storage by Using Biomass-Based Composite

How to construct a functional unit for heat storage by using biomass materials is significant for the exploration of phase change materials (PCMs). In this work, we try to design and construct a functional unit for heat storage by employing a vacuum impregnation method to prepare sugarcane-based shape stabilized phase change materials (SSPCMs) for improving the thermal conductivity of phase change materials (PCMs) and preventing the liquid state leakage of PCMs. The morphologies of the prepared materials are characterized by Scanning electron microscope (SEM) as containing a unique channel structure which is viewed as the key factor for heat storage. X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to characterize the prepared materials. The results indicated that no chemical reaction occurred between PEG and sugarcane-based biomass during the preparation process and SSPCMs showed great thermal stability. Their thermal properties are measured by using the differential scanning calorimetry (DSC) characterization and show a high melting enthalpy of 140.04 J/g and 94.84% of the relative enthalpy efficiency, illustrating the excellent shape stabilized phase change behavior. Moreover, the highest thermal conductivity of SSPCMs is up to 0.297 W/(mK), which is 28.02% higher than that of the pristine PEG. The excellent capability for thermal energy storage is attributed to the directional thermal conduction skeletons and perfect open channels and the unique anisotropic three-dimensional structure of the SSPCMs. Hence, the unique structure with PEG is testified as the functional unit for heat storage. Comprehensively considering the excellent properties of sugarcane-based materials—providing cheap raw materials via green preparation—it is conceived that sugarcane-based materials could be applied in many energy-related devices with reasonable function unit design.

Scalable Flexible Phase Change Materials with a Swollen Polymer Network Structure for Thermal Energy Storage

3D porous structural materials are proved to be enticing candidates for the fabrication of high-performance organic phase change materials (PCMs), but the stringent fabrication process and poor processability greatly hampered their commercialization. Herein, flexible leakage-proof composite PCMs with pronounced comprehensive performance are fabricated by a scalable polymer swelling strategy without using any solvent, in which the paraffin wax (PW) segment is confined in a robust flexible 3D polymer network, giving rise to the composite PCMs with excellent form stability even at 160 °C, a high latent heat energy storage density of 133.6 J/g, and an outstanding thermal conductivity of up to ∼5.11 W/mK. More importantly, the mass production of the flexible composite phase change fiber, film, and bulk products can be achieved by adopting mature processing technologies. These resultant composite PCMs exhibit promising thermal management ability to solve the overheating problem of electronics and high-efficiency solar-thermal energy conversion capacity.

Recyclable, Self-Healing, and Flame-Retardant Solid-Solid Phase Change Materials Based on Thermally Reversible Cross-Links for Sustainable Thermal Energy Storage

Conventional polymeric phase change materials (PCMs) exhibit good shape stability, large energy storage density, and satisfactory chemical stability, but they cannot be recycled and self-healed due to their permanent cross-linking structure. Additionally, the high flammability of organic PCMs seriously restricts their applications for thermal energy storage (TES). Therefore, it is urgently required to explore PCM composites exhibiting superior recyclability, good self-healing capability, and excellent flame retardancy simultaneously. Herein, tri-maleimide end-capped cyclotriphosphazene flame retardant (TMCTP) was synthesized via the nucleophilic substitution between 1,3,5,2,4,6-triazatriphosphorine-2,2,4,4,6,6-hexachloride and N-(2-hydroxyethyl)maleimide. Then, novel dynamically cross-linked PCM composites (FPCMs) with superior recyclability, good self-healing capability, and excellent flame retardancy were fabricated by bonding PEG and TMCTP to polymeric skeleton via reversible furan/maleimide Diels-Alder (DA) reaction. TMCTP, which covalently and dynamically binding in the polymeric FPCMs, acted not only as an efficient flame retardant for reducing the flammability of PCM composites but also as dynamic cross-linking skeletons for thermally induced self-healing and recycling. Differential scanning calorimetry (DSC) analysis confirmed the reversible energy storage and release ability of FPCMs. Due to its reversible DA covalent bonds, the introduction of TMCTP endowed the FPCMs with considerably increased self-healing efficiency (up to 93.1%) and recyclability efficiency (94.6%). Moreover, with the introduction of TMCTP into FPCMs, the heat release rate (HRR) and total heat release (THR) significantly decreased, while the char residue and limiting oxygen index (LOI) value increased, confirming that the flame retardancy of FPCMs greatly improved. Hence, the synthesized FPCMs show enormous potential in TES applications.

Infiltration properties of n-alkanes in mesoporous biochar: The capacity of smokeless support for stability and energy storage

Biochar, also named biocarbon, is a solid particulate material produced from the thermal decomposition of biomass at moderate temperatures. It has progressively become the topic of scientific interest in energy storage and conversion applications due to its affordability, environment friendliness, and structural tunability. In this study, biochar (obtained 600 °C pyrolysis) was introduced as phase change materials (PCMs) support. Three different n-alkanes (such as dodecane, tetradecane, and octadecane) are used as PCMs. The PCMs were infiltrated in the biochar network via the vacuum impregnation method. Among the biochar/n-alkane composites, one from octadecane exhibited a high latent heat storage capacity of 91.5 kJ/kg, 15.7 % and 25.9 % higher than that of dodecane and tetradecane-based composites, respectively. The molecular length of the PCMs and intermolecular interaction between the functional groups play an imperative role. The infiltration ratio of PCM in the biochar reached 50.1 % with improved thermal stability and chemical compatibility. This is attributed to the favorable morphological and structural properties (e.g., large BET surface area and mesopore structure) of the biochar that resides the n-alkanes found in the nanosized chain length. Hence, this report will lay a foundation for the application of biochars in thermal energy management systems.

Novel Bio-Based Pomelo Peel Flour/Polyethylene Glycol Composite Phase Change Material for Thermal Energy Storage

Abstract: A series of novel bio-based form stable composite phase-change materials (fs-CPCMs) for solar thermal energy storage and management applications were prepared, using the pomelo peel flour (PPF) as the supporting matrix and poly (ethylene glycol) (PEG) or isocyanate-terminated PEG to induce a phase change. The microscopic structure, crystalline structures and morphologies, phase change properties, thermal stability, light-to-thermal conversion behavior, and thermal management characteristics of the obtained fs-CPCMs were studied. The results indicate that the obtained fs-CPCM-2 presented remarkable phase-change performance and high thermal stability. The melting latent heat and crystallization heat for fs-CPCM-2 are 143.2 J/g and 141.8 J/g, respectively, and its relative enthalpy efficiency (λ) is 87.4%, which are higher than most reported values in the related literature. The obtained novel bio-based fs-CPCM-2 demonstrated good potential for applications in solar thermal energy storage and waste heat recovery.