Physicochemical properties and mechanical characters of methanol-modified melamine-formaldehyde (MMF) shell microPCMs containing paraffin

Microcapsules containing phase change materials (microPCMs) with melamine-formaldehyde (MF) shells have been applied in many thermo-regulation or thermo-saving fields. However, it is still essential to decrease the residual formaldehyde and enhance the mechanical properties of MF shells. The objective of this work was to fabricate a series of microPCMs containing paraffin by an in situ polymerization method using methanol-modified melamine-formaldehyde (MMF) prepolymer as shell material and investigate the physicochemical properties and mechanical characters of these microPCMs. FT-IR analysis indicates that the methanol-modified method can reduce the free formaldehyde in shell material through increasing the cross-linking structure. Optical microphotographs and SEM morphologies show that the microPCMs have regular globe shape with smooth surface. With the increasing of emulsion stirring rates from 1,000 to 5,000 rpm, the average diameters decreased sharply from 27 to 2.5 μm. The phase change temperature (T _m) of microPCMs samples with the core/shell ratios of 3/1, 2/1, 1/1, and 2/1 are 22.6, 23.0, 23.4, and 23.9 °C, which are nearly equaled to the T _m of pure paraffin (22.5 °C). Mechanical properties test data show that the MMF shells have larger yield point value than that of MF shell for microPCMs with the same core/shell ratio, which means that the methanol-modified method shell can greatly enhanced the resistance of deformation for MF shells. Moreover, MMF shells can resist the interface extrusion force in epoxy resin owing to their higher yield point of enhanced MMF shell.     

Effects of ammonium chloride and heat treatment on residual formaldehyde contents of melamine-formaldehyde microcapsules

Microencapsulated n-octadecane with melamine–formaldehyde resin (MF) shell was synthesized by in situ polymerization. Ammonium chloride was used to reduce the residual formaldehyde content of microencapsulated phase change materials (microPCMs) caused by the inherent characteristics of MF. Moreover, microPCMs were heat-treated at 160 °C for 30 min. The surface morphology of the microPCMs fabricated at various microencapsulation periods was examined, and the shell thickness was measured. The effects of heat treatment on the surface morphology, residual formaldehyde content, phase change properties, and thermal stability of the microcapsules were systematically investigated. The globular surface of microcapsules fabricated at microencapsulation period of 120 min was smooth and compact with an average diameter about 2.2 μm, and the shell thickness was ranged from 30 to 70 nm. The thermal stability of heat-treated microcapsules enhanced significantly as microencapsulation period increased; in addition, the residual formaldehyde content of microcapsules decreased from 125 ± 1 mg/kg to 19 ± 1 mg/kg.     

Fabrication and interfacial morphologies of methanol–melamine–formaldehyde (MMF) shell microPCMs/epoxy composites

Microcapsules containing phase change materials (microPCMs) have many potential applications because of their thermoregulation or thermosaving abilities. At the same time, it is still essential to understand the interface stability of microPCMs/polymer composites during a thermal transmission. The aim of this work was to fabricate novel microPCMs containing dodecanol by an in situ polymerization using methanol-modified melamine–formaldehyde (MMF) prepolymer as shell material and investigate the interface morphologies of microPCMs/epoxy composites treated by a simulant thermal process with a ten times repeated temperature variation. A series of microPCMs were fabricated by 1,000–3,000 r·min⁻¹ emulsion speed with the PCM contents of 40–70%. The average diameter, melting temperature, and encapsulation efficiency of microPCMs were 1–16 μm, 19.5 °C, and 97.4%, respectively. Tests results indicated that the properties of the microPCMs were greatly affected by core/shell ratios and emulsification stirring rates of preparation conditions. With the increasing of stirring rates, the average diameters of microPCMs were sharply decreased. The encapsulation efficiency (E _e) values of microPCMs increased with the increasing of stirring rates. The contents of PCM in microcapsules (C _t) and the average diameter of microPCMs both affected the interface morphologies of microPCMs/epoxy composites after the repeated thermal treatments. Microcracks and gaps occurred after a thermal treatment in the interface of microPCMs and epoxy matrix obviously. The internal stress generated by the expansion or shrinking of the microPCMs was the main factor leading to the interface morphology changes and damaged of composites.     

Preparation of Porous Hollow SiO2 Spheres by a Modified St?ber Process Using MF Microspheres as Templates

Using the surface charged and acid dissolvable melamine formaldehyde (MF) microspheres as sacrificial hard templates, silica coated MF core?Cshell composite microspheres, denoted as MF@SiO₂, were synthesized via a surfactant-assisted sol?Cgel process by using tetraethyl orthosilicate (TEOS) as silica source. Hollow SiO₂ spheres with mesoporous shells were then obtained after selective removal of the MF cores and the pore directing surfactant by hydrochloric acid etching or calcinations in air. Interesting shrinkage phenomena were observed in both the hollow products derived from hydrochloric acid etching and calcinations. The influence of the ratio of MF sphere to TEOS and the removal method of the MF core on the size of the hollow spheres, the shell thickness and the shell surface roughness have been studied. The composition, the thermal stability, the morphology, the surface area and pore size distribution, the wall thickness and adsorption properties of the hollow spheres derived from hydrochloric acid etching and calcinations were also investigated and compared based on the FTIR, SEM, TEM, TGA, Nitrogen adsorption?Cdesorption and spectrophotometer techniques or measurements.     

Preparation,characterization, and thermal properties of microPCMs containing <Emphasis Type="Italic">n</Emphasis>-dodecanol by using different types of styrene-maleic anhydride as emulsifier

Microcapsules containing polar phase change material (PCM) n-dodecanol were synthesized by in situ polymerization using melamine-formaldehyde resin as shell and styrene-maleic anhydride copolymer (SMA) as emulsifier. The effects of polarity of PCM and types and amounts of SMA emulsifier on the properties of microencapsulated PCMs (microPCMs) were studied and characterized by using Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and laser particle diameter analyzer. The results show that thermal properties of microPCMs are affected greatly by the types and amounts of SMA. Anionic SMA emulsifier is suitable for the encapsulation of n-dodecanol. The polarity of PCM leads to the higher adding amount of SMA emulsifier. When mass ratio of emulsifier to n-dodecanol is 4.8%, the phase change latent heat and encapsulation efficiency reach to the maximum value of 187.5 J/g and 93.1%, respectively. Irregular spherical microPCMs with mean diameter of 30.6 μm and phase change temperature of 21.5 °C are obtained and can be used for energy storage.     

电子墨水微胶囊及电泳显示原型器件的制备

TiO2 particles coated with polystyrene which were prepared via in situ polymerization and oil green dye were dispersed in tetrachloroethylene and xylene, the mixture came to be electrophoretic ink and was encapsulated in to microcapsules by complex coacervation from gelatin and a hydrolyzed copolymer of styrene and maleic anhydride(SMA). It was demonstrated that the membranes of the microcapsules were formed from nano sized coacervate droplets resulting from gelation and hydrolyzed SMA, which leads to a compact membrane structure. Microcapsules were characterized in terms of microstructure, morphologies by scanning electron microscopy(SEM). Electrophoretic display prototype was prepared by coating electrophoretic ink microcapsules slurry on ITO glass with nearly single layer and sealed by UV curable adhesires. The characters “Zheda” in Chinese was firstly displayed at a low volt 9 V D. C..     

Thermal conductivity of microPCMs-filled epoxy matrix composites

Microencapsulated phase change materials (microPCMs) have been widely applied in solid matrix as thermal-storage or temperature-controlling functional composites. The thermal conductivity of these microPCMs/matrix composites is an important property need to be considered. In this study, a series of microPCMs have been fabricated using the in situ polymerization with various core/shell ratio and average diameter; the thermal conductivity of microPCMs/epoxy composites were investigated in details. The results show that the microPCMs have smooth surface and regular global shape with compact methanol–melamine–formaldehyde shell. The shell thickness does not greatly influence the phase change behaviors of PCM. Moreover, smaller microPCMs embedded in epoxy can improve the thermal transmission ability of composites. The effect of thermal conductivity of composites can be improved with higher volume fraction (10–30%) of microPCMs; and smaller size microPCMs with the same content of PCM may also enhance the thermal transmission area in matrix. Modeling analysis of relative thermal conductivity indicates that mixing higher thermal conductivity additive in PCM or matrix is an appropriate method to improve the thermal conductivity of microPCMs/matrix composites.     

Synthesis and Photoluminescence Properties of Uniform Y2O3:Eu3+ Hollow Spheres with Tunable Shell Thickness

Y2O3:Eu3+ hollow spheres were successfully prepared with melamine formaldehyde(MF) spheres as template. The MF spheres played a significant role in directing the formation of the hollow shells which are composed of numerous primary nanoparticles. Furthermore, the shell thickness of these hollow spheres could be readily tailored by adjusting the dosage of MF template. Based on the photoluminescence(PL) investigation, the red emission intensities(613 nm) of these Y2O3:Eu3+ hollow spheres are greatly influenced by their shell thickness and it was found that hollow spheres with thin shell thickness and intact hollow structures permit a better PL performance.     

空心玻璃微珠/TiO2复合微球的制备及其性能研究

本文以脲为沉淀剂,通过化学沉淀法成功实现了锐钛矿型二氧化钛壳层在空心玻璃微珠表面的可控组装,从而制备出玻璃/二氧化钛核壳空心微球,并通过XRD、SEM、EDX和拉曼光谱对其结构、形貌、粒径、壳厚和化学组成进行了表征.提出了二氧化钛在空心玻璃微珠表面的定向生长的可能机制和形成过程.     

Fabrication of spindle Fe(2)O(3)@polypyrrole core/shell particles by surface-modified hematite templating and conversion to spindle polypyrrole capsules and carbon capsules

By using a surface-modified templating method, Fe(2)O(3)@polypyrrole (PPy) core/shell spindles have been successfully prepared in this paper. The Fe(2)O(3) particles with spindle morphology were initially fabricated as core materials. After the PVP modification, the Fe(2)O(3) spindles were subsequently coated with a tunable thickness layer of PPy by in situ deposition of the conducting polymer from aqueous solution. Hollow PPy spindles were produced by dissolution of the Fe(2)O(3) core from the core/shell particles. High-temperature treatment under vacuum condition covert the hollow PPy spindles into carbon capsules by carbonization of the PPy shell. Transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) confirmed the formation of the Fe(2)O(3)@PPy core/shell particles, PPy and carbon capsules with spindle morphology.     

Fabrication and characterization of micro-encapsulated sodium phosphate dodecahydrate with different crosslinked polymer shells

Microencapsulations of sodium phosphate dodecahydrate with different crosslinked polymer as shells were carried out by in situ polymerization and solvent evaporation method. Methyl methacrylate (MMA), urea were employed to crosslink with ethyl acrylate (EA) and formaldehyde, respectively. The influences of the type of crosslinking agent on the performance of as-prepared microencapsulated phase change materials (microPCMs) have been studied. The microPCMs were investigated using Fourier transformed infrared spectroscopy, scanning electron microscopy, and transmission electron microscope. Thermal properties and thermal stability of microPCMs were characterized by differential scanning calorimetry and thermalgravimetric analysis. Conclusion points out that thermal properties and thermal resistant temperatures of microPCMs vary from the type of crosslinkable functional moieties of the crosslinking agents. The temperature range of melting enlarged and the melting temperature increased according to the prepared microPCMs, which is suitable for thermal energy storage.     

The preparation of composite microsphere with hollow core/porous shell structure by self-assembling of latex particles at emulsion droplet interface

A submicrometer-scaled polystyrene/melamine-formaldehyde hollow microsphere composite was prepared by self-assembling of sulfonated polystyrene (SPS) latex particles at the interface of emulsion droplets and then being fixed in place using a hard melamine-formaldehyde (MF) composite layer. For control-released purposes, the influential factors that control the size and uniformity of the packed-droplets and the permeability of the composite shell, including the initial particle location, the hydrophilicity and the size of colloidal templates, the oil phase solvent and reserving time of emulsions after the addition of MF prepolymer, were further studied. Relatively uniform sized particle packed-droplets with an average diameter of 10 microm were obtained. The assembled SPS particles kept ordering and minimal conglutination after the preparation of composite microspheres, which allows of controlling the permeability from the interstices between the particles. Porous-mesh-structured MF composite layer was formed to further control the permeability. The morphology of emulsions and composite microspheres were characterized by optical microscopy, scanning and transmission electron microscopy.     

帽状铝纳米粒子的制备及表面等离子共振特性

金属纳米材料具有许多独特的物理和化学性质,其中一个重要的光学性质就是表面等离子共振,然而在大多数情况下,金属纳米粒子表面等离子共振所产生的吸收峰被限制在相对狭小的范围内,很难进行调谐。近年来,以电介质为核金属为壳的核壳结构复合纳米材料成功的解决了这一问题,通过设计和剪裁内核的直径与外壳层厚度的比值,可以实现光学性质可调的特性[1～5]。此类复合材料可被广泛应用于光催化、传感器、光信息存储、生物光子学、生物医学等领域[6～11]。美国莱斯大学及德州的研究人员利用这类核壳结构纳米材料成功地实现了对体外乳腺肿瘤的杀灭实验[12]。在这种类型的材料中,对称性降低的即不完全包裹的纳米粒子如杯状[13]、帽状[13,14]、半球壳状[15]、月牙状[16]等核壳结构复合粒子由     

A facile pathway to prepare enzymatically degradable microcapsules with tunable capsule shell properties

Dextran sulfate (DS)/poly-l-lysine (PLL) microcapsules are fabricated by an in situ coacervation method using DS-doped CaCO₃ microparticles as templates. Twinned superstructures or spherical CaCO₃ microparticles are produced depending on DS concentration in the starting solution. DS/PLL microcapsules with ellipsoidal or spherical outline are obtained after removal of templates in disodium ethylene diamine tetraacetate dehydrate (EDTA) without PLL. Their shell thickness and negative surface charges increase with the DS weight percentage in the templates. The surface potential of DS/PLL microcapsules, fabricated by core removal in an EDTA/PLL solution, can be easily tuned by altering PLL concentration in template removal solution. DS/PLL microcapsules fabricated by template removal in solution with or without PLL are both degraded by α-chymotrypsin, and different degradation profiles are observed because of shell thickness differences. DS/PLL may be used as transport vehicles for various compounds regardless of their charge sign in biomedical fields.     

Preparation, structure, and magnetic properties of polystyrene coated by Fe3O4 nanoparticles

A novel method of fabricating core-shell structure particles, comprising nearly monodisperse polystyrene (PS) spheres as cores and Fe3O4 as shells, is submitted. In this research, the magnetite (Fe3O4) shell was prepared by seeded growth from the reaction of FeCl2 with diethylene glycol (DEG) in aqueous solutions. The thickness of the shell were controlled in the range of 0-60 nm by using slow injection. The composition and the structure of the shell were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and vibrating-sample magnetometry (VSM). It is found that there are some differences between the magnetic composite spheres shelled with Fe3O4 and pure Fe3O4 particles, such as the size of the magnetites and the ferromagnetic property. Furthermore, the spheres exhibited the superparamagnetic characterization when the thickness of the Fe3O4 shell was less than 15 nm.     

Microencapsulation of decabromodiphenyl ether by in situ polymerization: Preparation and characterization

Melamine-formaldehyde (MF) resin microcapsules containing decabromodiphenyl ether (DBDPO) with better thermal stability were successfully prepared by in situ polymerization, DBDPO being the core material and MF resins being the wall materials. Chemical structure of the prepared microcapsules was characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Morphologies and thermal properties were also investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), respectively. The results indicated that MF microcapsules with DBDPO particles prepared in this study showed better thermal stability, and could be used as effective flame retardant even for the resins which should be processed at temperatures higher than 350 °C.     

Hematite nanoparticles as polystyrene microsphere coatings and hollow spheres: preparation and characterization

A novel method of fabricating composite particles with core–shell structures is demonstrated. The particles comprised monodisperse submicrometer-sized copolymer latex spheres as cores and Fe₂O₃ crystallites as shells. The shell was formed by controlled hydrolysis of aqueous iron solutions, and the growth of hematite on the surface of the copolymer spheres was controlled by slow injection. Hollow spheres were obtained by calcinations of the so-coated copolymer lattices at 500°C in air. The void size of these hollow spheres was determined by the diameter of the copolymer template, and the wall thickness could be easily controlled in the range of 20–60 nm by using this coating process. The structure and the composition of the spheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). It can be seen that a crystallite change and a crystal phase transformation occurred during coating and calcination of the composite spheres. The formation of the composite particles is simply explained by the nucleation of iron oxide on the surface of the latex followed by growth of the iron compound shell.     

水相一步合成锐钛矿型二氧化钛空心球

报道了水相一步直接合成晶体TiO2空心球的方法. 以水溶性的过氧化钛配合物(peroxo-titanium complex, PTC)为前驱体、聚苯乙烯(polystyrene, PS)球为模板, 在水溶液体系中可直接制备得到锐钛矿型纳米TiO2空心球. 与传统的模板法相比, 模板的包覆、去除及TiO2壳层的晶化等步骤在水相中可一步完成. 利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)及热重分析仪(TGA)对所合成的纳米TiO2空心球进行了表征, 同时推断了可能的反应机理.     

Hollow microspheres with covalent‐bonded colloidal and polymeric shell by Pickering emulsion polymerization

Hollow microspheres with SiO₂/polymer binary shell were fabricated from Pickering emulsion stabilized solely by methacryloxypropyltrimethoxysilane‐modified SiO₂ particles, and were characterized by optical microscopy, scanning electron microscopy, Fourier transformation infrared spectrum, thermogravimetric analysis (TGA), and energy dispersive X‐ray spectroscopy. The microspheres were templated by the Pickering droplets and the inner structure was affect by the proportion of crosslinking reagent. TGA result indicated that 60.3% of polymer in the shell was connected with SiO₂ by covalent bond which was formed by copolymerization of styrene and the reactive C?C group on SiO₂ stabilizer. Copyright © 2011 John Wiley & Sons, Ltd.     

Deformable hollow hybrid silica/siloxane colloids by emulsion templating

A procedure to obtain hollow colloidal particles has been developed using an emulsion templating technique. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysilane monomer and incorporated in a solid shell using tetraethoxysilane. Hollow shells were obtained by exchange of the core. The formation of the oil droplets was investigated using static light scattering and 29Si solution NMR, and the hollow shells were characterized by electron microscopy and static light scattering. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis and 29Si solid state NMR, revealing that the shells consist of a hybrid cross-linked network of silica and siloxane units. Confocal microscopy was used to show that the shells are permeable to small dye molecules. The thickness of the coating can be easily varied from a few nanometers upward. Depending on the ratio of shell thickness to particle radius, three types of hollow shells can be distinguished depending on the way in which they buckle upon drying. We designate them as microspheres, microcapsules, and microballoons. As a result of their monodispersity, these particles can be used for making 3D-ordered materials.