Highly efficient photothermal conversion capric acid phase change microcapsule: Silicon carbide modified melamine urea formaldehyde

Enhancing solar photothermal conversion and energy storage with titanium carbide (Ti3C2) MXene nanosheets in phase-change microcapsules

We propose to enhance photothermal conversion via doping titanium carbide (Ti3C2) MXene nanosheets on the surfaces of phase-change microcapsules consisted of the n-Octadecane core and styrene divinylbenzene copolymer shell. Detected by scanning electron microscopy, the microcapsules showed a usually circular form with an appropriate dispersion. The thermal properties of the microcapsules were characterized using the differential scanning calorimetry and thermal conductivity instruments, realizing an excellent phase-change enthalpy of around 140 J/g, high encapsulation ratio of over 64 %, good heat transfer of 0.294 ± 0.003 W/(m·K), and great thermal reliability. More importantly, the microcapsules doped with Ti3C2 MXene nanosheets reach a solar-to-heat conversion efficiency of 85 ± 7 %, a substantial enhancement by 240 % in comparison with non-doping sample. The Ti3C2 MXene-doped microcapsules with excellent heat storage and solar-to-heat conversion capabilities offer great potential for high-efficiency solar energy utilization and can be applied to thermal energy storage systems and direct absorption solar collectors.

Preparation, thermal storage properties and application of sodium acetate trihydrate/expanded graphite composite phase change materials

The development of energy storage technology is beneficial for the efficient use of energy and sustainable development. As an effectual approach for storing and transporting thermal energy, latent heat storage using phase change materials (PCMs) has attracted tremendous attention. However, low thermal conductivity, poor stability, and leakages are considerable challenges to the widespread application of solid-liquid PCMs. Composite phase change materials (CPCMs) were prepared by combining expanded graphite (EG) and sodium acetate trihydrate (CH3COONa·3H2O, SAT). EG as a supporting material plays a crucial part in both enhancing the thermal conductivity and preventing the melted PCMs from leakage. The chemical structure, micromorphology, thermal stability, thermal conductivity, phase change behavior and heat storage performance of SAT/EG CPCMs have been extensively investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal conductivity analysis, differential scanning calorimetry (DSC), and cycling stability measurement. The results of SEM indicate that EG with a loose and porous layered structure has a good molding effect and can adsorb SAT well. XRD and FTIR results show that only a simple physical combination between EG and SAT exists, and no new substances have been produced. Compared with pure SAT, thermal conductivity and supercooling tests show that the supercooling degree of the CPCMs was decreased and the thermal conductivity was increased by 205.1%. In addition, the addition of 2 wt% of disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O, DHPD) as a nucleating agent and 0.5 wt% of gelatin as a thickening agent to SAT could reduce the supercooling degree and inhibit the phase separation well. Based on SAT/EG-8% CPCMs, an oven with phase change energy storage was designed and the heat storage/release performance of the oven was investigated under different operating conditions.

Thermally Conductive Molten Salt for Thermal Energy Storage: Synergistic Effect of a Hybrid Graphite-Graphene Nanoplatelet Filler

Renewable energy technologies depend, to a large extent, on the efficiency of thermal energy storage (TES) devices. In such storage applications, molten salts constitute an attractive platform due to their thermal and environmentally friendly properties. However, the low thermal conductivity (TC) of these salts (<1 W m-1 K-1) downgrades the storage kinetics. A commonly used method to enhance TC is the addition of highly conductive carbon-based fillers that form a composite material with molten salt. However, even that enhancement is rather limited (<9 W m-1 K-1). In this study, the partial exfoliation of graphite to graphene nanoplatelets (GnP) in a molten salt matrix is explored as a means to address this problem. A novel approach of hybrid filler formation directly in the molten salt is used to produce graphite-GnP-salt hybrid composite material. The good dispersion quality of the fillers in the salt matrix facilitates bridging between large graphite particles by the smaller GnP particles, resulting in the formation of a thermally conductive network. The thermal conductivity of the hybrid composite (up to 44 W m-1 K-1) is thus enhanced by two orders of magnitude versus that of the pristine salt (0.64 W m-1 K-1).

A Novel One-Step Reactive Extrusion Process for High-Performance Rigid Crosslinked PVC Composite Fabrication Using Triazine Crosslinking Agent@Melamine-Formaldehyde Microcapsules

In this work, we propose, for the first time, a simple, fast, and efficient strategy to fabricate high-performance rigid crosslinked PVC composites by continuous extrusion. This strategy improves the poor processing fluidity of composites and solves the impossibility of conducting extrusion in one step via using microcapsule-type crosslinking agents prepared by in situ polymerization to co-extrude with PVC blends. The results demonstrate that the PVC/microcapsule composites were successfully prepared. Within the studied parameters, the properties of crosslinked PVC gradually increased with the addition of microcapsules, and its Vicat softening temperature increased from 79.3 °C to 86.2 °C compared with pure PVC. This study shows the possibility for the industrial scale-up of the extrusion process for rigid crosslinked PVC.

Flexible and Mechanically Enhanced Polyurethane Composite for γ-ray Shielding and Thermal Regulation

Microencapsulation of paraffin with lead tungstate shell (Pn@PWO) shows the drawbacks of low wettability and poor leakage-proof property and thermal reliability, restricting the application of phase change microcapsules. Herein, a novel paraffin@lead tungstate@silicon dioxide double-shelled microcapsule (Pn@PWO@SiO₂) has been successfully constructed by the emulsion-templated interfacial polycondensation and applied in the waterborne polyurethane (WPU). The results indicated that a SiO₂ layer with controlled thickness was formed on the PbWO₄ shell. The Pn@PWO@SiO₂ microcapsules have exhibited superior leakage-proof properties and thermal reliability through double-shelled protection, and the leakage rate decreased by at least 54.11% compared to that of Pn@PWO microcapsules. The SiO₂ layer with abundant polar groups ameliorated the wettability of microcapsules and the interfacial compatibility between microcapsules and the WPU matrix. The tensile strength of WPU/Pn@PWO@SiO₂-2 composites reached 10.98 MPa, which was over 7 times greater than that of WPU/Pn@PWO composites. In addition, WPU/Pn@PWO@SiO₂-2 composites with a latent heat capacity of over 41 J/g exhibited efficient phase change stability and γ-ray shielding properties. Also, the mass attenuation coefficients reached 1.38 cm²/g at 105.3 keV and 1.12 cm²/g at 86.5 keV, respectively. These properties will greatly promote the application of WPU/Pn@PWO@SiO₂ composites into γ-ray-shielding devices with thermal regulation.

Cadmium Sulfide-Reinforced Double-Shell Microencapsulated Phase Change Materials for Advanced Thermal Energy Storage

Phase change materials (PCMs) are widely used to improve energy utilization efficiency due to their high energy storage capacity. In this study, double-shell microencapsulated PCMs were constructed to resolve the liquid leakage issue and low thermal conductivity of organic PCMs, which also possess high thermal stability and multifunctionality. We used assembly to construct an inorganic-organic double shell for microencapsulate PCMs, which possessed the unprecedented synergetic properties of a cadmium sulfide (CdS) shell and melamine-formaldehyde polymeric shell. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirmed the well-designed double-shell structure of the microcapsules, and the CdS was successfully assembled as the second shell on the surface of the polymer shell. The differential scanning calorimeter (DSC) showed that the double-shell microcapsules had a high enthalpy of 114.58 J/g, which indicated almost no changes after experiencing 100 thermal cycles, indicating good thermal reliability. The microcapsules also showed good shape stability and antileakage performance, which displayed no shape change and leakage after heating at 60 °C for 30 min. In addition, the photothermal conversion efficiency of the double-shell microcapsules reached 91.3%. Thus, this study may promote the development of microencapsulated PCMs with multifunctionality, offering considerable application prospects in intelligent temperature management for smart textiles and wearable electronic devices in combination with their solar thermal energy conversion and storage performance.

Superhydrophilic Modified Elastomeric RGO Aerogel Based Hydrated Salt Phase Change Materials for Effective Solar Thermal Conversion and Storage

As a typical phase-change material (PCM) with high heat storage capacity and wide distribution, hydrated salts play broad and critical roles in solar energy utilization in recent years. However, the leakage and supercooling problems of hydrated salts have been a constraint to their further practical applications. In the current work, the super-hydrophilic reduced graphene oxide (RGO) aerogels modified by konjac glucomannan (KGM) as supporting structural materials are prepared by the hydrothermal reaction-freeze-drying, which can effectively absorb and convert visible sunlight energy into thermal energy. In addition, the super-hydrophilic aerogels compounded with PCMs can ameliorate the shortcoming of leakage and suppress the supercooling temperature as low about 0.2-1.5 °C in the freezing process. Under 1 sun irradiation, the prepared sodium acetate trihydrate/KGM-modified graphene oxide aerogel (SAT/KRGO) composite PCM achieves a high photothermal conversion efficiency (86.3%) due to its good light absorption property. The number of cycles has no apparent effect on the supercooling of the composite materials, suggesting their stable thermal cycles and thermal storage.

A Mild Method for Encapsulation of Citral in Monodispersed Alginate Microcapsules

Citral is a typical UV-irritation and acid-sensitive active and here we develop a mild method for the encapsulation of citral in calcium alginate microcapsules, in which UV irritation or acetic acid is avoided. Monodispersed oil-in-water-in-oil (O/W/O) emulsions are generated in a capillary microfluidic device as precursors. The middle aqueous phase of O/W/O emulsions contains sodium alginate, calcium-ethylenediaminetetraacetic acid (EDTA-Ca) complex as the calcium source, and D-(+)-Gluconic acid δ-lactone (GDL) as the acidifier. Hydrolysis of GDL will decrease the pH value of the middle aqueous solution, which will trigger the calcium ions released from the EDTA-Ca complex to cross-link with alginate molecules. After the gelling process, the O/W/O emulsions will convert to alginate microcapsules with a uniform structure and monodispersed size. The preparation conditions for alginate microcapsules are optimized, including the constituent concentration in the middle aqueous phase of O/W/O emulsions and the mixing manner of GDL with the alginate-contained aqueous solution. Citral-containing alginate microcapsules are successfully prepared by this mild method and the sustained-release characteristic of citral from alginate microcapsules is analyzed. Furthermore, a typical application of citral-containing alginate microcapsules to delay the oxidation of oil is also demonstrated. The mild gelling method provides us a chance to encapsulate sensitive hydrophobic actives with alginate, which takes many potential applications in pharmaceutical, food, and cosmetic areas.

Effect of Coating Process on Mechanical, Optical, and Self-Healing Properties of Waterborne Coating on Basswood Surface with MF-Coated Shellac Core Microcapsule

Self-repairing microcapsules prepared with melamine formaldehyde (MF) resin as wall material and shellac and waterborne coating as core material were added to waterborne coating to prepare a self-repairing coating. In order to explore the effect of the coating process on the performance of the waterborne coating on the basswood surface with microcapsules, the number of coating layers of primer and finish and the addition mode of the microcapsules were tested as influencing factors. The effects of different coating processes on the optical, mechanical, and liquid resistance of the basswood surface coating were investigated. The results showed that different coating processes had little effect on the color difference of the coating. When the coating process was two layers of primer and three layers of finish, and microcapsules were added to the finish, the minimum gloss of the basswood surface coating at 60° incident angle was 10.2%, and the best mechanical properties, liquid resistance, and comprehensive properties were achieved. Finally, the aging resistance and self-healing performance of the waterborne coating on the basswood surface prepared by this coating process were explored. The results showed that the waterborne coating had a certain repair effect on scratch damage. This paper lays a theoretical foundation for the practical application of self-healing microcapsules in wood-surface waterborne coatings.

Efficient and economical approach for flexible photothermal icephobic copper mesh with robust superhydrophobicity and active deicing property

Facing various problems caused by icing in daily life, preparing photothermal deicing materials with wide applicability in high efficiency and low cost is not only a current research hotspot but also a great challenge. Herein, an economical spray-coating method is applied to prepare high-efficiency flexible photothermal icephobic copper mesh using micro silicon carbide (SiC) particles as photothermal conversion material and nano silica (SiO₂) particles as a surface superhydrophobic modifier. Owing to the excellent hierarchical micro-nanostructures, the SiC/SiO₂ coated copper mesh exhibits a water contact angle (CA) of 162 ± 2° and a sliding angle (SA) of 3 ± 2°. Interestingly, the coated copper mesh exhibits exceptional mechanical durability against water droplet and water flow impact, repeated bending-twisting and tape-peeling. Benefitting from the robust superhydrophobicity, the SiC/SiO₂ coating on the copper mesh can significantly delay the freezing time of the droplets and reduce the ice adhesion strength. Furthermore, the coated copper mesh well retains the good photothermal conversion and thermal conductivity properties of the micro SiC particles. Under NIR irradiation, the surface temperature of the coated copper mesh placed on the ice layer can increase by 35.3 °C in 220 s, so that it can rapidly melt the accumulated frost and ice layer on the inner wall of the refrigerator. The presented flexible photothermal icephobic copper mesh exhibits enormous potential when applied to remove ice from apparatus that is accessible, such as road, overhead transmission lines and power networks owing to its flexibility, economy, and high energy efficiency.

Form-stable phase change composites based on nanofibrillated cellulose/polydopamine hybrid aerogels with extremely high energy storage density and improved photothermal conversion efficiency

Novel form-stable composite phase change materials were fabricated by impregnating n-octacosane into nanofibrillated cellulose/polydopamine hybrid aerogels.