Double-shell Microcapsules Research Articles

Fabrication of double-shell microcapsule encapsulated with wormwood essential oil and its application in regenerated cellulose fiber

Fabrication of double-shell microcapsule encapsulated with wormwood essential oil and its application in regenerated cellulose fiber

Preparation and characterization of double-shell phase change material microcapsules with flame retardancy and temperature regulation capability as low-emission building fillers

The building application of phase change materials (PCMs) has attracted widespread attention due to energy conservation and emission reduction. In this study, designed and prepared by two-step polymerization poly melamine tetramethylene phosphonium sulfate (PMTMPS) coating the raw phase change materials microcapsules (MPCMs), which were novel double-shell microcapsules (D-MPCMs). D-MPCMs further achieved low smoke and low toxicity in the fire based on enhancing the temperature regulation performance of MPCMs. The chemical structure of D-MPCMs was characterized by Fourier transform infrared (FTIR) spectroscopy, and 13C solid-state nuclear magnetic resonance (NMR). Transmission electron microscope (TEM) confirmed that D-MPCMs were successfully prepared, whose shapes were regular spherical. The results of differential scanning calorimetry (DSC) showed that D-MPCMs revealed excellent phase transition enthalpy (80.51 J/g). Then, the resultant D-MPCMs had good thermal reliability and stability from the thermogravimetric analysis (TGA), characterized by a residual mass of D-MPCMs was 17 % more than that of MPCMs. In the cone calorimeter test (CCT), we confirmed that the coated PMTMPS significantly reduced the fire risk parameters of the rigid polyurethane foam (RPUF) containing D-MPCMs (D-MPCM/RPUF) referring to the heat release rate (HRR), total heat release (THR), and total smoke production (TSP). D-MPCM/RPUF exhibited the lowest peak values of HRR and TSP, which were 400.115 kW/m2 and 10.512 m2, respectively. In addition, the PMTMPS shell significantly enhanced the solar photo-thermal conversion performance of the D-MPCMs. To sum up, D-MPCMs have great potential to improve flame retardancy, environmental protection, and temperature regulation capability for building thermal insulation materials.

Tuning the thermal conductivity of organic-inorganic double-shell thermal storage microcapsules triggered by atomic layer deposition

The regulation of the thermal conductivity of thermal energy storage materials has become a primary challenge to expand the range of utilization for different application scenarios. In this study, organic-shell microcapsule (paraffin@melamine formaldehyde) was initially prepared by in situ polymerization, followed by the deposition of anatase TiO2 on the organic-shell microcapsule using atomic layer deposition (ALD) to form organic-inorganic double-shell microcapsule. The effect of the thickness of the TiO2 shell on the equivalent thermal conductivity of the microcapsules was investigated by utilizing ALD's precise and controllable characteristics for the coating thickness. The obtained double-shell microcapsules indicated a drop in thermal storage capacity, but a substantial boost in thermal stability. Moreover, the thermal conductivity of microcapsules can be tuned in the range between 0.1837 and 0.7529 W m−1 K−1 within 1500 ALD cycle treatment. Furthermore, the parameters of ALD, such as reaction temperature and exposure time, were varied to obtain an amorphous TiO2 shell, and the impacts of different crystal form of TiO2 on the heat transfer properties of microcapsules were concluded by comparison. Double-shell microcapsules exhibited superior mechanical properties compared to single-shell structure. The findings can stimulate significant research interest in broadening the applications of thermal storage microcapsules.

Phase change composites with ultra-high through-plane thermal conductivity achieved by vertically-aligned graphite film and double-shelled microcapsules

The heat dissipation in electronic devices has become bottleneck problem. One of the best solutions is to develop high performance materials which can not only dissipate the heat away, but also absorb heat energy. This kind of double function materials can be obtained by simultaneously using high thermal conductivity (TC) materials and phase change materials. The formation of continuous network of thermally conductive fillers is demonstrated as one of the most effective methods for fabricating highly thermally conductive composites. Here, graphite films (GF) are stacked and vertically cut to endow the composites with high through-plane TC. The obtained composites exhibit a through-plane TC of 51.55 W m−1 K−1 and a low thermal resistance of 0.398 °C cm2 W−1. Besides, double-shelled PDA@SiO2@paraffin (Pa) microcapsules are embedded into the composite to give its good heat-absorption capacity. Via a CPU thermal stress test, the composites demonstrate satisfactory temperature controlling performance.

Design and application of polyurethane-polydopamine/Ag double-shell microcapsules for enhanced photothermal conversion and incremental energy storage

Solar energy is a clean and renewable source of energy. However, its intermittent nature hampers its utilization efficiency. Although phase change microcapsules store and release energy using latent heat, they rely on temperature differences, which limits their effectiveness in absorbing and utilizing solar energy as heat. This study employed a two-step method to synthesize a novel double-shell phase change microcapsule to enhance the conversion and step-by-step storage of solar energy. The double shell was constructed using polyurethane (PU) and polydopamine/silver (PDA/Ag), while octadecane and paraffin (P/O) served as the core materials. The synthesized microcapsules displayed a unique double-shell structure, and a consistent spherical shape, and demonstrated a remarkable latent heat storage capacity surpassing 150 J/g. The coating exhibited outstanding photothermal conversion performance, attributed to the synergistic photothermal conversion effect of PDA and Ag in the first shell. The gradual energy transfer within microcapsules was achieved by integrating polyethylene glycol into the PU layer and utilizing two different PCMs as the core materials. Furthermore, the antimicrobial of the treated textiles against S. aureus and E. coli were 99.99% and 99.56%, respectively. The double-layer design of the P/O@PU@PDA/AgNPs provides leakproofness and shape stability, making them ideal for photothermal energy storage applications.

Ultrafast Self-Healing Fiber/Matrix Composite with Single-Component Microcapsules Loaded with Cationic Catalyst

In this study, ultrafast self-healing of different damage modes in resin and fiber/matrix composites was achieved by incorporating single-component double-shell microcapsules loaded with a cationic catalyst. The formation of stable and size-controllable inner microcapsules was achieved using hydrophilic metal–organic frameworks (MOFs) as stabilizers for the Pickering emulsion. With adjustable nanospaces, MOFs served as a good platform for host–guest interactions, providing an ideal environment for capturing and storing the cationic catalyst. Unlike traditional two-component microcapsule systems, the cationic catalyst could be loaded relatively easily into the double-shell microcapsules. More importantly, a single-component microcapsule system could achieve immediate repair of microcracks in situ as the agents could immediately react with the cationic catalyst upon the rupturing of microcapsules. A satisfactory healing efficiency was achieved along with outstanding mechanical properties of the composite. For example, epoxy resin with 15 wt % microcapsules loading showed 95% healing efficiency within 10 min at room temperature, and the interlaminar shear strength of the composite reached 92% in 5 min.

One-pot preparation of inorganic-organic double-shell microcapsule with good barrier and mechanical property via photopolymerization

Microcapsule has been widely used for fabricating functional coatings. For practical application in coatings, an ideal microcapsule should possess outstanding barrier, thermal and mechanical properties simultaneously. In this paper, a series of double-shell hybrid microcapsule loaded with self-healing agent (linseed oil, LO) with outer inorganic SiO2 shell and inner UV-cured polymeric shell were successfully synthesized via photopolymerization. The obtained double-shell hybrid microcapsule was characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The barrier properties, thermal stability and mechanical property of the microcapsules were investigated in detail. Via the adjustment of chemical structure of photo-curable resin and the crosslinking density, the core release of the microcapsule could be reduced to only 2.5 wt% after immersing in organic solvent for 48 h, suggesting the outstanding barrier properties of the double-shell microsphere. The double-shell hybrid microcapsules also possessed outstanding thermal stability, and its initial decomposition temperature increased by about 32 ℃ and 14 ℃ compared with that of mono-shell organic and inorganic microcapsules. Moreover, the Young's modulus and hardness of the double-shell hybrid microcapsules were thirty-fold and forty-fold that of mono-shell organic microcapsules, which proved their excellent mechanical property. And the prepared double-shell hybrid microcapsule could encapsulate LO stably for a long time to avoid its failure, which was successfully employed to the construction of self-healing coatings.

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.

Preparation and Characterization of Cyclodextrin Coated Red Phosphorus Double-Shell Microcapsules and Its Application in Flame Retardant Polyamide6.

Using the melamine borate and crosslinked β−cyclodextrin as shell materials, the double−shell microcapsules (Mic−DP) of red phosphorus (RP) was prepared, and its flame−retardant effect on polyamide 6 (PA6) was investigated. Compared with RP, Mic−DP showed lower hygroscopic and better inoxidizability. The limiting oxygen index (LOI) of PA6/13%Mic−DP was 27.8%, and PA6/13%Mic−DP reached V−0 rating. After the addition of 13% Mic−DP, the total exothermic (THR), peak exothermic (PK−HRR), and average effective thermal combustion (AV−EHC) rates of PA6 decreased. In addition, in order to investigate its flame−retardant mechanism, the pyrolysis gas chromatography−mass spectrometry (Py−GC−MS), scanning electron microscopy (SEM), and Fourier transform infrared (FT−IR) methods were used, and the results showed that mic DP acted as a flame retardant in the gas and condensed phases. The Mic−DP exhibited good compatibility and dispersibility in PA6.

Phase change composites based on double-shell microcapsules with high latent heat and low leakage rate for thermal energy storage and temperature regulation

A series of novel paraffin (Pn)@polymethyl methacrylate (PMMA)@silicon dioxide (SiO2) double-shell phase change microcapsules (Pn@PMMA@SiO2) were designed by interfacial polycondensation and radical polymerization, and then Pn@PMMA@SiO2 were embedded in high density polyethylene (HDPE) to fabricate HDPE/Pn@PMMA@SiO2 phase change composites (PCCs) by melt blending. The effect of PMMA contents on Pn@PMMA@SiO2 and Pn@PMMA@SiO2 contents on PCCs were investigated, respectively. Thermal and anti-permeable properties of Pn@PMMA@SiO2 and PCCs were characterized by differential scanning calorimetry (DSC) and leakage rate tests. The results showed that the enthalpy and leakage rate of Pn@PMMA@SiO2 with 10 wt% PMMA were 156.6 J/g and 1.85 %, which displayed outstanding latent heat storage/release capability and good anti-permeable property. And the PCCs with 40 wt% Pn@PMMA@SiO2 displayed dependable thermal energy storage capability as well, which could reach to 52.7 J/g. In addition, the tensile strength of PCCs-40 could be up to 19.9 MPa, and the density of PCCs was decreased with introduction of Pn@PMMA@SiO2. Hence, the new kind of PCCs can be used for thermal management and temperature regulation for lightweight building materials.

Phase-Change Composites Composed of Silicone Rubber and Pa@SiO2@PDA Double-Shelled Microcapsules with Low Leakage Rate and Improved Mechanical Strength.

A kind of silicone rubber (SR)/paraffin (Pa)@silicon dioxide (SiO2)@polydopamine (PDA) phase-change composite was prepared in this work. The double-shelled Pa@SiO2@PDA phase-change microcapsules were constructed by oxidative self-polymerization of dopamine (DA) in Tris-HCl buffer solution. The effect of the DA content on the properties of Pa@SiO2@PDA microcapsules and SR/Pa@SiO2@PDA composites was researched. Due to the protective effect of SiO2, PDA layer, and SR matrix, the SR/Pa@SiO2@PDA composites have good leak-proofing performance, and the leakage rate of SR/Pa@SiO2@PDA-2 is as low as 0.45%. Phase-change enthalpies of the Pa@SiO2@PDA microcapsules and SR/Pa@SiO2@PDA composites are reduced slightly with increasing DA content. Meanwhile, the composites displayed improved mechanical strength. The tensile strength of SR/Pa@SiO2@PDA-2 can be up to 0.560 MPa, which is 1.85 times higher than the tensile strength of pure SR/Pa@SiO2 because the interface compatibility between Pa@SiO2 microcapsules and SR is improved through hydrogen bonding between the abundant groups on the PDA surface and the matrix. Moreover, the rough surface of the PDA-modified microcapsules also enhances the interface interaction through physical "interlocking". The new kind of SR/Pa@SiO2@PDA composite can be used for thermal management.

One-Pot Facile Synthesis of Double-Shelled Mesoporous Silica Microcapsules with an Improved Soft-Template Method for Sustainable Pest Management.

A controlled release formulation based on silica microcapsules is an ideal selection to improve both the effective utilization and duration of pesticides to decrease ecological damage. Herein, a simple and green method for preparing double-shelled microcapsules was developed using a newly prepared quaternary ammonium ionic liquid (IL) as the functional additive to entrap avermectin (Ave) in mesoporous silica nanospheres (MSNs) and tannic acid-Cu (TA-Cu) complex as the sealing agent to form the core-shell structure (Ave-IL@MSN@TA-Cu). The obtained microcapsules with an average size of 538 nm had pH-responsive release property and good stability in soil. The half-life of microcapsules (34.66 days) was 3 times that of Ave emulsifiable concentrate (EC) (11.55 days) in a test soil, which illustrated that microcapsules could protect Ave from rapid degradation by microorganisms by releasing TA, copper, and quaternary ammonium in the soil. Ave-IL@MSN@TA-Cu microcapsules had better nematicidal activity and antibacterial activity than Ave EC due to the synergistic effect of Ave, IL, and copper incorporated in the microcapsules. Pot experiments showed that the control efficacy of microcapsules was 87.10% against Meloidogyne incognita, which is better than that of Ave EC (41.94%) at the concentration of 1.0 mg/plant by the root-irrigation method after 60 days of treatment owing to the extended duration of Ave in microcapsules. The simple and green method for the preparation of double-shelled microcapsules based on natural quaternary ammonium IL would have tremendous potential for the extensive development of controlled release pesticide formulations.

Temperature control and low infrared emissivity double-shell phase change microcapsules and their application in infrared stealth fabric

With the rapid development of infrared detection technology, the development of infrared stealth products has become an urgent requirement. Infrared stealth effect is affected by both temperature and infrared emissivity, but most of the previous studies focus on a single factor, which limits the effectiveness of the products. Herein, we prepared double-shell microcapsules (DSMs) with both temperature control and low infrared emissivity. It firstly uses eicosane as the phase change material (PCM) and melamine, urea and formaldehyde (MUF) as the shell material to form microcapsules. Then, polyaniline (PANI) is deposited on the surface of these microcapsules to form DSMs. The DSMs were measured to have a particle size concentrated at 1.484 μm, a latent heat of 155.1 J/g, a core content of 63.25% and an infrared emissivity as low as 0.722. After coating the DSMs onto polyester fabrics, the infrared emissivity of the coating has a little increase to 0.794, but impressively, the as prepared fabric can be cooled down by a maximum of 11.2 °C compared to the untreated fabric, and the temperature control process can last for 27 min, which is superior to similar products. Featured with temperature control by PCM and low emissivity by PANI, the infrared camera image shows that the fabric has an obvious infrared stealth effect, proving it is a great potential candidate in infrared stealth materials.

Double-shell microcapsules with spatially arranged Au nanoparticles and single Zn atoms for tandem synthesis of cyclic carbonates.

Tandem catalysts with multifunctional sites can achieve high-efficiency catalytic transformations for quickly converting simple raw materials into complex value-added products. The integration of highly active species of metal nanoparticles (NPs) and single-atom catalytic sites (SACs) into one tandem system promises to synthesize an ideal bifunctional catalyst on account of the synergistic effect between NPs and SACs. However, such ideas face some challenges as deactivation or loss of active species, and low efficiency or side reactions caused by the disorder of different active species. Herein, a double-shell microencapsulated nanoreactor was fabricated as a bifunctional catalyst for the one-pot synthesis of cyclic carbonates from olefins. The microcapsules consist of an inner shell of nitrogen-doped porous carbon rich in Zn SACs, an outer shell of mesoporous SiO2, and Au NPs confined between the outer and inner shells, noted as Zn-N-C/Au@mSiO2. Particularly, two active species are spatially compartmented within microcapsules. Furthermore, the catalyst was applied in the one-pot synthesis of styrene carbonate from styrene with CO2 under normal pressure and showed admirable performance. The yield of cyclic carbonate reached 92.9% at 93.2% olefins conversion. Furthermore, the catalyst shows good reusability with little loss of catalytic performance (4.0%) even after using it 15 consecutive times. The unique structure used in this work can rationally integrate diverse catalytic species into one system and offering adequate protection, which provides an effective strategy for the development of multi-site catalysts.

Al–Si @ Al2O3 @ mullite microcapsules for thermal energy storage: Preparation and thermal properties

Encapsulation is an effective method to prevent leakage of molten phase change materials (PCMs). However, it is difficult for microcapsules to acquire high latent heat capacity as well as good thermal cycling performance. In the present study, double shell microcapsules, using aluminum silicon alloy as the core, Al2O3 as the inner shell, and mullite as the outer shell, were prepared for heat storage by steam corrosion followed by silica sol immersion and high-temperature calcination. A cross-section of microcapsule showed that the total thickness of the double shell was approximately 1.5 μm. The latent heat storage and latent heat release of the microcapsules were 367.1 J g−1 and 298.4 J g−1 and still remained 90.4% and 80.0% after 3000 thermal cycles, respectively. The latent heat storage and release rate were 72.0 J g−1·min−1 and 20.3 J g−1·min−1, respectively. With an increase of temperature from 40 to 950 °C, the calculated total heat absorption of the microcapsules reached as high as 1850.3 J g−1, 22.7% greater than that without phase change. This double shell microcapsule has a high potential to be used in thermal energy storage systems.

Imidazole-loaded microcapsules as latent curing agent with superior solvent stability and shelf life

A novel microcapsule-type thermal latent curing agent with a double-shell structure was successfully fabricated. 1-Benzyl-2-methylimidazole (1B2MZ) was encapsulated by poly(methyl methacrylate-n-butyl acrylate) (PMMA/BA) using the solvent evaporation method, which served as the primary microcapsules (PMCs) to be deposited by polydopamine (PDA). Various glass transition temperatures (Tg, from 116.7 to 57.2 °C) and thermal properties of shell material PMMA/BA were obtained by tuning the mass ratio of BA to MMA monomer. PMMA/BA with 20 wt% of BA ratio was selected as the shell of PMCs for its appropriate Tg (92.33 °C) and relatively good thermal resistance. (Decomposition temperature was 222.83 °C.) The obtained PMCs and the double-shell microcapsules (DMCs) had good spherical shape, and the chemical structure of DMCs was confirmed by Fourier transform infrared spectra. Thermogravimetric analysis indicated that the core contents of PMCs and DMCs were 11.95 and 11.37%, respectively. After being coated by PDA, the solvent resistances of microcapsules in weak-polar (toluene) and high-polar (dichloromethane, DCM and acetone) solvents were significantly improved. When storing at room temperature for more than 4 months, the mixture of DMCs and the diluted epoxy could be cured at 120 °C for 1 h.

Highly stable spray dried tuna oil powders encapsulated in double shells of whey protein isolate-agar gum and gellan gum complex coacervates

This study was aimed at producing multi-core fish oil powders by developing a double-shelled microencapsulation system using complex coacervation. Whey protein isolate (WPI)-agar gum (WPI-AG) complex coacervates and WPI-gellan gum (WPI-GG) complex coacervates were used as the inner and outer shells, respectively. Tuna oil was used as a representative core material. The oil was first encapsulated in WPI-AG complex coacervates at pH 4.75 to produce the primary microcapsule. The second microcapsule shell was created by using WPI-GG complex coacervates at the same pH and mixed with the primary microcapsule, followed by the cooling to 15 °C in the presence of calcium ions. The WPI-GG outer shell was clearly visible under a light microscope. The outer shell significantly improved the oxidative stability of the entrapped tuna oil, compared with the microcapsule powder without the outer shell. These spray dried double-shell microcapsule powders had low surface oil (1.8%), high encapsulation efficiency (95.8%) and a high payload (42. 6%). These shells were glassy with glass transition temperature around 53 °C and they acted as effective barriers to transmission of oxygen at ambient temperature.

Water resistant reactive microcapsules for self-healing coatings in harsh environments

Double-shelled microcapsules containing liquid 4,4′-bis-methylene cyclohexane diisocyanate (HMDI) with outstanding water resistance are successfully synthesized via combination of interfacial and in-situ polymerization reactions in an oil-in-water emulsion. The diameter and shell thickness of microcapsules increased under lower agitation rate. The relative residue of core content of microcapsules remains more than 90% after 24 days in both ambient open air and water. Manually scratched polymer coatings with both fresh and conditioned microcapsules showed satisfactory anticorrosion performance in salt water via self-healing functionality. In addition, self-healing coatings with fresh microcapsules after immersion in ambient water for 30 days still possessed superior anticorrosion performance.

Independent control of water retention and acid–base pairing through double-shelled microcapsules to confer membranes with enhanced proton conduction under low humidity

Proton exchange membranes (PEM) with affordable and controllable proton conductivity under low humidity are crucial to the commercial application of PEM fuel cells. In this study, double-shelled polymer microcapsules bearing a carboxylic acid inner shell and imidazole outer shell (PMC-Ns) are synthesized via distillation–precipitation polymerization and then incorporated into a sulfonated poly(ether ether ketone) matrix to fabricate composite membranes. The inner shell renders the absorbed water of lower chemical potential and higher bound water content, yielding the composite membrane with enhanced water retention properties. The higher water uptake ensures composite membrane facilitated proton transfer via a vehicle mechanism and the lower water loss confers a reduced proton conductivity decline. The outer shell generates sulfonic acid–imidazole pairs within the membranes, which construct low-energy-barrier pathways to facilitate proton transfer via the Grotthuss mechanism. Under identical conditions, PMC-Ns endow much higher proton conductivity to composite membranes than the microcapsules with both carboxylic acid inner shell and outer shell, or both imidazole inner shell and outer shell. Particularly, incorporating 20 wt% PMC-Ns affords the composite membrane a 1.7 times increase in proton conductivity under 100% relative humidity (RH) and a 41.8 times increase in proton conductivity under 20% RH. Moreover, the methanol barrier property of the composite membranes is explored.

Fabrication and Mechanical Properties of Double-Shell Thermal Energy Storage Microcapsules Applied as Environmental Temperature-Controlling Materials in Building

The aim of the present work was to fabricate heat energy storage microcapsules, which could be used in indoor-wall materials as environmental temperature-controller. Melamine formaldehyde resin (MF) double-shell structure microcapsules were fabricated and the mechanical properties of shell were investigated. The average diameter of microcapsules was in the range of 5-10 μm, and the globular surface was smooth and compact. The mechanical properties of shell were evaluated through observing the surface morphological structure change after pressure by means of scanning electron microscopy (SEM). The results showed that a yield point was found both on single and double shell, and when the press was beyond the point the microcapsules showed plastic behavior. In addition, the mechanical intensity of double-shell microcapsules was better than that of single shell. Analysis of DSC indicated that the phase change temperature was not affected by the double –shell structure.