Synthesis and Characterization of Microencapsulated Phase Change Materials with Poly(urea-urethane) Shells Containing Cellulose Nanocrystals

Polyurethane/n-Octadecane Phase-Change Microcapsules via Emulsion Interfacial Polymerization: The Effect of Paraffin Loading on Capsule Shell Formation and Latent Heat Storage Properties

Organic phase-change materials (PCMs) hold promise in developing advanced thermoregulation and responsive energy systems owing to their high latent heat capacity and thermal reliability. However, organic PCMs are prone to leakages in the liquid state and, thus, are hardly applicable in their pristine form. Herein, we encapsulated organic PCM n-Octadecane into polyurethane capsules via polymerization of commercially available polymethylene polyphenylene isocyanate and polyethylene glycol at the interface oil-in-water emulsion and studied how various n-Octadecane feeding affected the shell formation, capsule structure, and latent heat storage properties. The successful shell polymerization and encapsulation of n-Octadecane dissolved in the oil core was verified by confocal microscopy and Fourier-transform infrared spectroscopy. The mean capsule size varied from 9.4 to 16.7 µm while the shell was found to reduce in thickness from 460 to 220 nm as the n-Octadecane feeding increased. Conversely, the latent heat storage capacity increased from 50 to 132 J/g corresponding to the growth in actual n-Octadecane content from 25% to 67% as revealed by differential scanning calorimetry. The actual n-Octadecane content increased non-linearly along with the n-Octadecane feeding and reached a plateau at 66-67% corresponded to 3.44-3.69 core-to-monomer ratio. Finally, the capsules with the reasonable combination of structural and thermal properties were evaluated as a thermoregulating additive to a commercially available paint.

Phase-Change-Material-Impregnated Wood for Potential Energy-Saving Building Materials

PCMs (phase change materials) are ideal for thermal management solutions in buildings. This is because they release and store thermal energy during melting and freezing. When this material freezes, it releases a lot of energy in the form of latent heat of fusion or crystallization energy. Conversely, when the material melts, it absorbs the same amount of energy from its surroundings as it changes from a solid to a liquid state. In this study, Oriental spruce (Picea orientalis L.) sapwood was impregnated with three different commercial PCMs. The biological properties and the hygroscopic and thermal performance of the PCM-impregnated wood were studied. The morphology of PCM-impregnated wood was characterized through the use of scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). PCM-impregnated wood demonstrated low performance in terms of storing and releasing heat during phase change processes, as confirmed by DSC. The results show that PCMs possess excellent thermal stability at working temperatures, and the most satisfying sample is PCM1W, with a phase change enthalpy of 40.34 J/g and a phase change temperature of 21.49 °C. This study revealed that PCMs are resistant to wood-destroying fungi. After the 96 h water absorption test, the water absorption of the wood samples decreased by 28%, and the tangential swelling decreased by 75%. In addition, it has been proven on a laboratory scale that the PCM material used is highly resistant to biological attacks. However, large-scale pilot studies are still needed.

Phase-Change Microcapsules with a Stable Polyurethane Shell through the Direct Crosslinking of Cellulose Nanocrystals with Polyisocyanate at the Oil/Water Interface of Pickering Emulsion

Phase-change materials (PCMs) attract much attention with regard to their capability of mitigating fossil fuel-based heating in in-building applications, due to the responsive accumulation and release of thermal energy as a latent heat of reversible phase transitions. Organic PCMs possess high latent heat storage capacity and thermal reliability. However, bare PCMs suffer from leakages in the liquid form. Here, we demonstrate a reliable approach to improve the shape stability of organic PCM n-octadecane by encapsulation via interfacial polymerization at an oil/water interface of Pickering emulsion. Cellulose nanocrystals are employed as emulsion stabilizers and branched oligo-polyol with high functionality to crosslink the polyurethane shell in reaction with polyisocyanate dissolved in the oil core. This gives rise to a rigid polyurethane structure with a high density of urethane groups. The formation of a polyurethane shell and successful encapsulation of n-octadecane is confirmed by FTIR spectroscopy, XRD analysis, and fluorescent confocal microscopy. Electron microscopy reveals the formation of non-aggregated capsules with an average size of 18.6 µm and a smooth uniform shell with the thickness of 450 nm. The capsules demonstrate a latent heat storage capacity of 79 J/g, while the encapsulation of n-octadecane greatly improves its shape and thermal stability compared with bulk paraffin.

Polyureas Versatile Polymers for New Academic and Technological Applications

Polyureas (PURs) are a competitive polymer to their analogs, polyurethanes (PUs). Whereas PUs' main functional group is carbamate (urethane), PURs contain urea. In this revision, a comprehensive overview of PUR properties, from synthesis to technical applications, is displayed. Preparative routes that can be used to obtain PURs using diisocianates or harmless reagents such as CO₂ and NH₃ are explained, and aterials, urea monomers and PURs are discussed; PUR copolymers are included in this discussion as well. Bulk to soft components of PUR, as well as porous materials and meso, micro or nanomaterials are evaluated. Topics of this paper include the general properties of aliphatic and aromatic PUR, followed by practical synthetic pathways, catalyst uses, aggregation, sol-gel formation and mechanical aspects.

Pretilachlor Releasable Polyurea Microcapsules Suspension Optimization and Its Paddy Field Weeding Investigation

In this study, pretilachlor was encapsulated into polyurea microcapsules prepared by water-initiated polymerization of polyaryl polymethylene isocyanate and eventually made into pretilachlor microcapsules suspension (PMS). We used response surface methodology (RSM) combined with the Box–Behnken design (BBD) model to optimize the formulation of PMS. The encapsulation efficiency (EE) of PMS was investigated with respect to three independent variables including wall material dosage (X₁), emulsifier dosage (X₂), and polymerization stirring speed (X₃). The results showed that the regression equation model had a satisfactory accuracy in predicting the EE of PMS. To achieve an optimal condition for PMS preparation, the dose of wall material was set to 5%, the dose of emulsifier was set to 3.5% and the polymerization stirring speed was set to 200 rpm. The EE of PMS was up to 95.68% under the optimized condition, and the spherical shape with smooth surface morphology was observed. PMS was also proven to have delayed release capability and in vivo herbicidal activity against barnyard grass [Echinochloa crusgalli (L.) Beauv.] with an LC₅₀ value of 274 mg/L. Furthermore, PMS had efficient weed management compared to commercially available 30% pretilachlor emulsifier (PE), showing a promising potential application for weeding paddy fields.

Leakage-proof microencapsulation of phase change materials by emulsification with acetylated cellulose nanofibrils

We use acetylated cellulose nanofibrils (AcCNF) to stabilize transient emulsions with paraffin that becomes shape-stable and encapsulated phase change material (PCM) upon cooling. Rheology measurements confirm the gel behavior and colloidal stability of the solid suspensions. We study the effect of nanofiber content on PCM leakage upon melting and compare the results to those from unmodified CNF. The nanostructured cellulose promotes paraffin phase transition, which improves the efficiency of thermal energy exchange. The leakage-proof microcapsules display high energy absorption capacity (ΔH_m = 173 J/g) at high PCM loading (up to 80 wt%), while effectively controlling the extent of supercooling. An excellent thermal stability is observed during at least 100 heating/cooling cycles. Degradation takes place at 291 °C, indicating good thermal stability. The high energy density and the effective shape and thermal stabilization of the AcCNF-encapsulated paraffin points to a sustainable solution for thermal energy storage and conversion.

Design and application of polyurea microcapsules containing herbicide (oxyfluorfen)

Polyurea, a controlled release material, has been widely applied in agricultural fields due to high thermal stability and low cost. In this article oxyfluorfen polyurea microcapsules suspension was successfully prepared by interfacial polymerization using diisocyanate and polyamines such as Ethylenediamine, Hexamethylenediamine, Diethylenetriamine in presence of green solvent, i.e., N,N-dimethyldecanamide. The microcapsule suspension of oxyfluorfen has not been researched yet by using solvent N,N-dimethyldecanamide and polyamines. The effect and the type of diamines on the morphology and properties of the microcapsules have been investigated. The synthesized microcapsules were characterized by scanning electron microscope, ultraviolet spectrometry, Fourier transform iInfrared spectrometer, thermogravimetric analysis and particle size analyser. The effect of the core to shell ratio on encapsulation efficiency and release kinetics were also studied. The oxyfluorfen microcapsules had an excellent encapsulation efficiency (98.2%) using EDA as the monomer and Release kinetics depended upon the type of monomers used and also on core to shell ratio used (6.5:1, 5:1, 4:1). As core to shell ratio was increased the encapsulation efficiency was found to decrease. Prepared Microcapsules when sprayed on paddy crop was found to be safe in comparison with Emulsifiable concentrate sample.

Temperature-humidity dual regulation of a single-core-double-shell microcapsule fabricated by electrostatic-assembly and chemical precipitation

Humidity and temperature control materials have attracted increasing attention due to their energy saving and intelligent regulation of human comfort in the field of interior building and clothing. Phase change microcapsules have been widely used, however, most of which focus on temperature regulation without humidity control. In this work, we report a novel temperature–humidity dual regulation microcapsule with single-core–double-shell structure. FT-IR and XRD measurements confirmed that the shell materials were successfully fabricated on the paraffin core via electrostatic-assembly and the subsequent chemical precipitation method. SEM, TEM and optical microscope photos showed that the microcapsules were spherical morphology with layer-by-layer shells at a diameter around 2–5 μm. The SiO₂ shell was aggregated from nano-sized particles and formed a loose and porous micro-structure, supported by the result of N₂ adsorption–desorption isotherms. In addition, the synergistic effect of hydrophilic and porous loose (chitosan/GO/chitosan)–SiO₂ double shells endowed the microcapsules with humidity regulation. The constructed microcapsules showed temperature regulation behavior due to its phase change performance of paraffin and good thermal durability after 10 thermal cycles. They also showed stable humidity regulation performance after repeated adsorption/desorption. The simulation experiments of temperature and humidity regulation indicated that the microcapsule could keep the temperature and humidity in a stable range. The as-prepared microcapsules have outstanding temperature and humidity regulation properties, showing an application prospects in energy-saving fields.

A single-core–double-shell microcapsule with temperature–humidity dual regulation was achieved by artfully designing of core and shell to realize the multi-functional and multi-factors regulation.

Bio-Based Phase Change Materials Incorporated in Lignocellulose Matrix for Energy Storage in Buildings—A Review

Due to growing consciousness regarding the environmental impact of fossil-based and non-sustainable materials in construction and building applications, there have been an increasing interest in bio-based and degradable materials in this industry. Due to their excellent chemical and thermo-physical properties for thermal energy storage, bio-based phase change materials (BPCMs) have started to attract attention worldwide for low to medium temperature applications. The ready availability, renewability, and low carbon footprint of BPCMs make them suitable for a large spectrum of applications. Up to now, most of the BPCMs have been incorporated into inorganic matrices with only a few attempts to set the BPCMs into bio-matrices. The current paper is the first comprehensive review on BPCMs incorporation in wood and wood-based materials, as renewable and sustainable materials in buildings, to enhance the thermal mass in the environmentally-friendly buildings. In the paper, the aspects of choosing BPCMs, bio-based matrices, phase change mechanisms and their combination, interpretation of life cycle analyses, and the eventual challenges of using these materials are presented and discussed.

Highly Durable and Thermally Conductive Shell-Coated Phase-Change Capsule as a Thermal Energy Battery

Robust and thermally conductive phase-change capsules (PCCs) can be effectively used as dispersoids for heat transfer fluids (HTFs) to utilize waste heat. Here, we demonstrate PCCs encapsulated with a cross-linked poly(2-hydroxyethyl methacrylate) shell that showed high durability and low thermal hysteresis for effective heat uptake and release. The circulation system was manufactured by mimicking the 4th Generation District Heating (4GDH) system to confirm the heat delivery efficiencies of PCC-dispersed slurries (PCSs) as the HTFs. The enthalpy change of water after it received heat from the PCS improved by up to 41.1% on increasing the amount of PCCs in the PCS. Furthermore, a high PCC recovery of 92 wt % was achieved after 1500 cycles, which accompanied a phase transition. The PCC developed by us can thus enable effective storage/delivery of waste heat-driven energy for zero-energy buildings and a 4GDH system, as well as thermal management of electronics.

Crystallization and thermal performance of poly(acrylonitrile-co-alkyl acrylate) comb-like polymeric phase change materials with various side-chain lengths

With an enhanced shape-stabilized performance, PANAn PCMs tuned by varying the alkyl side-chain lengths demonstrate a prospective TES application.

In Situ Fabrication of Polymeric Microcapsules by Ink-Jet Printing of Emulsions

Phase separation driven by solvent evaporation of emulsions can be used to create polymeric microcapsules. The combination of emulsion solvent evaporation with ink-jet printing allows the rapid fabrication of polymeric microcapsules at a target location on a surface. The ink is an oil-in-water emulsion containing in the dispersed phase a shell-forming polymer, a core-forming fluid that is a poor solvent for the polymer, and a low-boiling good solvent. After the emulsion is printed onto the substrate, the good solvent evaporates by diffusion through the aqueous phase, and the polymer and the poor solvent phase separate to form microcapsules. The continuous aqueous phase contains polyvinyl alcohol that serves as an emulsifier and a binder of the capsules to the substrate. This method is demonstrated for microcapsules with various shell-forming polymers (polystyrene, poly(methylmethacrylate) and poly(l-lactide)) and core-forming poor solvents (hexadecane and a 4-heptanone/sunflower oil mixture). Cargoes such as fluorescent dyes (Nile Red and tetracyanoquinodimethane) or active ingredients (e.g., the fungicide tebuconazole) can be encapsulated. Uniform microcapsules are obtained by printing emulsions containing monodisperse oil droplets produced in a microfluidic device. We discuss the physical parameters that need to be controlled for the successful fabrication of microcapsules in inkjet printing. The method for rapid, in situ encapsulation could be useful for controlled-release applications such as in agrochemical sprays, fragrances, functional coatings, and topical medicines.

Ultralight and Flexible Carbon Foam-Based Phase Change Composites with High Latent-Heat Capacity and Photothermal Conversion Capability

It is important to explore and develop multifunctional phase change composites with high latent-heat capacity and photothermal conversion capability. A novel ultralight and flexible carbon foam (CF)-based phase change composite was fabricated by encapsulating n-eicosane into a CF skeleton that had been precoated with titanium(III) oxide (Ti₂O₃) nanoparticles (NPs). Morphological structures, as well as the properties of leakage-proof, thermal energy storage, temperature regulation, and photothermal conversion, of the fabricated phase change composites were investigated. The results indicated that the flexible CF skeleton derived from melamine foam (MF) through stabilization in air followed by carbonization in nitrogen was highly porous, which ensured excellent mechanical support and large mass ratio of n-eicosane for the composites. The loading percentage of n-eicosane as high as 84% which acted as thermal storage unit guaranteed high latent-heat capacity and good temperature regulation property of the composite; the melting/crystallization temperatures and enthalpies of the corresponding composite was 36.4/33.7 °C and 200.1/200.6 kJ·kg^-1, respectively. The CF skeleton modified with Ti₂O₃ NPs endowed the fabricated phase change composites with enhanced leakage-proof property, photothermal conversion capability, superior thermal reliability, and temperature regulation ability. Therefore, the resultant phase change composites are believed to have promising and potential applications in solar thermal-energy storage, waste-heat recovery, and infrared stealth of military targets, and so forth.

Effect on the characterization of metolachlor polyurea microcapsules with urea instead of polyamines

In this paper, a novel metolachlor microcapsules suspension (CS) was prepared by interfacial polymerization. Metolachlor polyurea microcapsules suspension was successfully prepared by urea instead of polyamines which could reduce the use of organic solvents and production costs. The synthesized microcapsules were characterized by Fourier Transform Infrared Spectrometer, Scanning Electron Microscope, Ultraviolet Spectrometry, Thermogravimetric analyses and particle size analyzer. In conclusion, the diameter of the urea microcapsules were the smallest (11.52 μm) and excellent encapsulation efficiency (81.45%). In addition, Urea microcapsules had compact microstructures and global shapes, which had a good thermal stability and metolachlor could be preserved better in the polyurea microcapsules. These results indicated that the prepared microcapsules by urea had better thermal storage properties and physicochemical property. The microcapsule suspension of metolachlor hasn’t been researched yet. Therefore, it is significant to prepare microcapsule suspension. More importantly, there is no use of organic solvents in the preparation of microcapsules suspension, which avoided the pollution of solvents to the ecological environment. It is hoped that this polyurea material will be applied in the field of pesticide synthesis and polymers.

Natural Microtubule-Encapsulated Phase-Change Material with Simultaneously High Latent Heat Capacity and Enhanced Thermal Conductivity

It is of critical importance to exploit high-performance phase-change materials (PCM) for thermal energy storage. Present form-stable PCM suffer from the defects in low PCM loading, poor form stability, low thermal conductivity, and complicated approaches. We prepared a novel microtubule-encapsulated phase-change material (MTPCM) by encapsulating lauric acid (LA) into kapok fiber (KF) microtubules that had been precoated with silver nanoparticles. The measured melting and freezing temperatures were 43.9 and 41.3 °C for the LA/KF MTPCM and 44.1 and 42.1 °C for the LA/KF@Ag MTPCM, respectively. After being heated, the MTPCM can retain its original solid state without leaking, even under a pressure of 500 times the gravity of MTPCM itself, which shows that the encapsulated phase-change material can undergo a solid-liquid transition microscopically while retaining its macroscopic solid state. The latent heats of fusion were found to be 153.5 J/g for the LA/KF MTPCM and 146.8 J/g for the LA/KF@Ag MTPCM, which is up to 86.5% and 82.7% that of pristine LA, respectively. This thermal energy storage capacity is much higher than reported values in recent literature, which tend to be ≤60%. In contrast with the penalty of a 3.8% decrease in latent heat capacity, the remarkable 92.3% increase in thermal conductivity caused by the introduction of silver nanoparticles is more pronounced. The thermoregulatory capacity analysis results show that the thermal transfer efficiency of LA/KF@Ag MTPCM has been enhanced significantly by 15.8% and 23.5% in terms of thermal energy storage and release compared to that of the LA/KF MTPCM. Moreover, the LA/KF@Ag MTPCM exhibits a robust thermal, chemical, and morphological reliability after 2000 thermal cycles, which makes it favorable for repetitive thermal energy storage/retrieval applications. The high latent heat, suitable phase-change temperature, outstanding form stability, robust thermal reliability, enhanced thermal transfer efficiency, and the inherited advantages of KF and nanosilver provide potential for the novel application of MTPCM in solar thermal energy storage, waste heat recovery, intelligent thermoregulated textiles, and infrared stealth of important military targets.

Short-Chain Modified SiO2 with High Absorption of Organic PCM for Thermal Protection

Organic phase change materials (PCMs) have great potential in thermal protection applications but they suffer from high volumetric change and easy leakage, which require "leak-proof" packaging materials with low thermal conductivity. Herein, we successfully modify SiO2 through a simple 2-step method consisting of n-hexane activation followed by short-chain alkane silanization. The modified SiO2 (M-SiO2) exhibits superior hydrophobic property while maintaining the intrinsic high porosity of SiO2. The surface modification significantly improves the absorption rate of RT60 in SiO2 by 38%. The M-SiO2/RT60 composite shows high latent heat of 180 J·g-1, low thermal conductivity of 0.178 W·m-1·K-1, and great heat capacity behavior in a high-power thermal circuit with low penetrated heating flow. Our results provide a simple approach for preparing hydrophobic SiO2 with high absorption of organic PCM for thermal protection applications.

Hollow particles templated from Pickering emulsion with high thermal stability and solvent resistance: Young investigator perspective

HYPOTHESIS

Hollow particles have been used in a variety of applications and many methods have been developed. Hollow particles templated from Pickering emulsions due to nanoparticle adsorption at the oil-water interface usually suffer from the collapsed morphologies and low thermal and solvent stability and enhancement of the shell can significantly improve the hollow particle performance.

EXPERIMENTS

This paper reports hollow particles templated from Pickering emulsion droplets in combination with UV photopolymerization. The Pickering emulsions were stabilized by functional silica nanoparticles at the O/W interface and the oil phase contains photosensitive reactants, initiator, catalyst and volatile solvents. The effects of nanoparticles concentration, O/W volume ratio, pH, dispersion speed and time on the stabilization of Pickering emulsion were firstly carried out and the properties of hollow particles formed by traditional interfacial crosslinking and UV photopolymerization were systematically investigated.

FINDINGS

Compared with previous interfacial crosslinking method, the UV photopolymerization method gives much more robust shells and we show in the paper that the hollow particles have much higher solvent resistance and thermal stability. The enhancement of thermal stability and solvent resistance of the hollow particle could extend its applications to more harsh fields such as self-healing coatings used in deep sea conditions.

Converting Capsules to Sensors for Nondestructive Analysis: From Cargo-Responsive Self-Sensing to Functional Characterization

A general concept of converting capsules into sensors is reported. Such simple conversion enables instantaneous nondestructive analysis for applications such as controlled release and energy storage among others. Converted capsule sensors are responsive in emission colors to varying core cargos via the incorporation of a solvatochromic fluorophore under excitation. Such cargo-responsive self-sensing abilities facilitate their application in capsule-level analysis such as cargo retention-leakage detection and release implications, as well as defect identification. The versatile concept is shown as an auxiliary tool in thermal energy storage to visualize phase transition, exhibiting promising potentials in application-level characterization.

Aerogel-Directed Energy-Storage Films with Thermally Stimulant Multiresponsiveness

Phase change materials offer enormous potential for thermal energy storage due to their high latent heat and chemical stability. Researchers have developed numerous innovative strategies to overcome the leakage of organic phase change materials and enhance thermal performance. However, the manufacture of form-stable, free-standing energy storage films based on phase change materials with high latent heat remains difficult. Therefore, the present study focused on the production of free-standing, form-stable energy storage films with high phase-change enthalpy and thermally stimulant multiresponsiveness from the simple composite of paraffin with a polytetrafluoroethylene/silica (PTFE/SiO₂) aerogel framework, where paraffin was effectively confined in PTFE/SiO₂. The resulting paraffin/PTFE/SiO₂ films exhibited a large phase change enthalpy (128 J/g) at a paraffin content of 62.8 wt %. The temperature-dependent wettability, transmittance, and mechanical properties of this composite film have also been investigated.

Encapsulating an organic phase change material within emulsion-templated poly(urethane urea)s

Interfacial step growth polymerization within oil-in-water high internal phase emulsions was used to synthesize poly(urethane urea) monoliths, consisting of 90% organic phase change material encapsulated within micrometer-scale capsules, for thermal energy storage and release applications.

Polyurethane Microparticles for Stimuli Response and Reduced Oxidative Degradation in Highly Porous Shape Memory Polymers

Shape memory polymers (SMPs) have been found to be promising biomaterials for a variety of medical applications; however, the clinical translation of such technology is dependent on tailorable properties such as gravimetric changes in degradation environments. For SMPs synthesized from amino-alcohols, oxidation resulting in rapid mass loss may be problematic in terms of loss of material functionality as well as toxicity and cytocompatibility concerns. Control of gravimetric changes was achieved through the incorporation of small molecule antioxidants, either directly into the polymer matrix or included in microparticles to form a SMP composite material. With direct incorporation of small molecule phenolic antioxidant 2,2'-methylenebis(6- tert-butyl)-methylphenol (Methyl), SMPs displayed reduce strain recovery by more than 50% (Methyl) and increase elastic modulus from approximately 1.4 to 2.3 MPa, at the expense of the strain to failure being reduced from 45% to 32%. Importantly, such changes could not ensure retention of the antioxidants and therefore did not increase oxidative stability beyond 15 days in accelerated oxidative conditions (equivalent to approximately 800 days in porcine aneurysms) in all cases except for the inclusion of a hindered amine that capped network growth, which also resulted in shape memory reduction (only 80% recoverable strain achieved). However, the inclusion of antioxidants in microparticles was found to produce materials with similar thermomechanical ( T_g migration below 1.0 °C) and shape recovery of 100%, while increasing oxidative resistance compared to controls (oxidation onset was delayed by 3 days and material lifespan increased to approximately 20-22 days in accelerated oxidative solution or beyond 1000 days in the porcine aneurysm). The microparticle composite SMPs also act as a platform for environmental sensing, such as pH-dependent fluorescence shifts and payload release, as demonstrated by fluorescent dye studies using phloxine B and nile blue chloride and the release of antioxidants over a 3 week period. The use of polyurethane-urea microparticles in porous SMPs is demonstrated to increase biostability of the materials, by approximately 25%, and ultimately extend their lifespan for use in aneurysm occlusion as determined through calculated in vivo degradation rates corresponding to a porcine aneurysm environment.

Hierarchical 3D Reduced Graphene Porous-Carbon-Based PCMs for Superior Thermal Energy Storage Performance

Phase change enthalpy and thermal conductivity are the two essential parameters for practical applications of shape-stabilized phase change materials (ss-PCMs). Herein, hierarchical three-dimensional (3D) reduced graphene porous carbon support PCMs have been successfully synthesized by carbonizing a graphene oxide@metal-organic framework (GO@MOF) template, which simultaneously realizes large phase change enthalpy and high thermal conductivity. During the carbonization process, MOFs were converted into hierarchical porous carbons, whereas GO was reduced to high-thermal-performance reduced graphene (rGO). Thus, a hierarchical 3D porous carbon structure with high porosity and large specific surface area was obtained, which provided a suitable condition for encapsulating PCMs. Furthermore, the pores of carbon stabilized the PCMs by capillary force and surface tension. The interaction between the PCM molecule and rGO significantly decreased the interfacial thermal resistance and made the composites reveal high thermal conductivity. Furthermore, the 3D network structure promoted the stretching and crystallization characteristics of the stearic acid molecule in the confined pore space, which enhanced the heat release efficiency. Compared with the rGO/MOF-5-C support, the hierarchical 3D structure of rGO@MOF-5-C revealed a thermal conductivity of 0.60 ± 0.02 W m^-1 K^-1, which was 27.7% improvement, with large phase change latent heat of 168.7 J g^-1, which increased by 18.5%. Additionally, the obtained ss-PCMs showed transient thermal response and good durability, indicating its promising potential in thermal energy storage application.

Ultraviolet light-, temperature- and pH-responsive fluorescent sensors based on cellulose nanocrystals

Intelligent CNC-g-P(AzoC₆MA-co-DMAEMA) fluorescent nanosensors present ultraviolet light-, temperature- and pH-responsive properties.