Hollow porous poly(lactic acid) microspheres

On the basis of the water solubility of poly(N‐vinyl‐2‐pyrrolidinone), hollow porous poly(lactic acid) microspheres (HPPLAs) were prepared by a water‐in‐oil‐in‐water multiple‐emulsion solvent evaporation method. The influence of the concentration of the stabilizer Span80 in the oil phase on the morphology was investigated. It was found that when the content of Span80 solutions was 3.5 wt %, most HPPLAs were about 2 μm in diameter. Field scanning electron microscopy results show that the HPPLAs were porous and hollow. The structure and crystal form of the HPPLAs were characterized by Fourier transform infrared spectroscopy and X‐ray diffraction analysis. Using these HPPLAs as degradable templates, we successfully synthesized Litchi‐like polystyrene (PS) microspheres about 2 μm in diameter by the emulsion method. When used as drug carriers, these HPPLAs would be convenient in which to embed drugs, whereas the Litchi‐like PS microspheres may have potential as new materials for polymer modification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Preparation of novel hybrid inorganic–organic hollow microspheres via a self‐template approach

BACKGROUND: Hollow microspheres, especially biodegradable polymeric microspheres, have attracted considerable attention due to their particular characteristics. Up to now, microspheres have been prepared via various strategies, for instance the template synthesis method and the self‐assembly process. However, economic, novel and simple methods to prepare hollow microspheres are still being sought. RESULTS: Phosphazene‐containing microspheres, which contain self‐assembled core‐shell structures, were prepared at high colloid contents using an ultrasonic bath via a self‐template approach. Along with the controlled self‐degradation of the internal core, the corresponding hybrid inorganic–organic hollow microspheres appeared. The mechanism was evidenced by means of transmission and scanning electron microscopy, cross‐polarization with magic angle spinning NMR, Fourier transform infrared spectroscopy, X‐ray diffraction and thermogravimetric analysis. CONCLUSION: It was clarified that the phosphazene‐containing microspheres could be formed and stably dispersed without aggregation even at high colloid contents using the ultrasonic bath method and the microspheres contain self‐assembled core–shell structures. Along with the controlled self‐degradation of the internal core, the corresponding hollow microspheres appeared. The mechanism of this preparation is of great significance because it is completely different from the conventional template synthesis method and the self‐assembly process. The absence of any stabilizing agent and special templates might inspire creative imagination in the design of new morphologies of micro‐ and nanostructures. Copyright © 2007 Society of Chemical Industry     

Effect of Core Materials on the Formation of Hollow Alumina Microspheres by Mechanofusion Process

Core/shell structures have been prepared via a mechanofusion system by employing several kinds of spherical polymers as a core material and Al₂O₃ powder or a mixture of Al₂O₃ and SiO₂ powders as a shell material. The effect of the kind of core polymers on the quality of the resulting hollow alumina microspheres has been discussed on the basis of the thermal decomposition behavior of spherical polymers used as a core material. A large fraction of hollow alumina microspheres reflecting the shape and the particle size distribution of the core polymer could be fabricated after sintering at 1600°3C for 3 h, when highly cross-linked poly(methyl methacrylate) (PMMA) microspheres with a gel fraction of 99.03% were used as a core polymer, and abrupt firing at temperatures higher than 500°3C was adopted to remove the PMMA microspheres. The addition of 5 mass% SiO₂ to the Al₂O₃ shell layer was found to be useful for maintaining the spherical shell structure during the firing process and for fabricating a large fraction of hollow alumina microspheres after the sintering.     

Self‐assembly of pH‐responsive acrylate latex particles at emulsion droplets interface

The self‐assembly of pH‐responsive poly (methyl methacrylate‐co‐acrylic acid) latex particles at emulsion droplet interfaces was achieved. Raising pH increases the hydrophilicity of the latex particles in situ and the latex particle acts as an efficient particulate emulsifier self‐assembling at emulsion droplet interface at around pH 10–11 but exhibits no emulsifier activity at higher pH. This effect can be reversibly induced simply by varying the aqueous phase pH and thus the latex emulsifier can be reassembled. The effect factors, including the aqueous phase pH, the surface carboxyl content, ζ‐Potential of the latex particles and oil phase solvent have been investigated. Using monomer as oil phase, the latex particles could stabilize emulsion droplets during polymerization and cage‐like polymer microspheres with hollow core/porous shell structure were obtained after polymerization. The mechanism of the latex particles self‐assembly was discussed. The morphologies of emulsion and microspheres were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Syntheses of PAM microgel surfacely covered with alkyl quaternary ammonium surfactant/Keggin‐type polyoxometalate complexes

The composite microspheres of poly(lacrylamide) microgels (PAM) surfacely covered with [2‐(methacryloyloxy)ethyl]dodecyldimethylammonium (MEDDAB)‐tungstophosphate (HPW) complexes (MEDDAB‐HPW) were synthesized by using ion‐exchange reaction between MEDDAB located within the porous PAM microgels and HPW in aqueous solution. The morphology and component of the composite microspheres were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, respectively. The results indicated that PAM/MEDDAB‐HPW composite microsphere with different hierarchical surface structures could be obtained by controlling the weight ratio of MEDDAB to HPW in the microgels and cross‐linking degree of PAM microgels. Although the surface morphologies of the composite microspheres prepared in different conditions were different, a general feature was that the composite microspheres have the core‐shell structure and the wrinkly surface covered with the particles of MEDDAB‐HPW complexes. The formation of the wrinkly surface is attributed to the difference in shrinkage between inside and outside of PAM microgel frameworks due to deposition of MEDDAB‐HPW on the surface, and the formation of MEDDAB‐HPW small particles originates from the reaction between MEDDAB aggregation and HPW. For this composite microsphere, PAM hydrogel core is suitable to store water‐soluble substances, and the shell composed of the surfactant/Keggin‐type polyoxometalate complexes is not only amphiphilic but also catalytic. Additionally, PAM/MEDDAB‐HPW composite microspheres with big size and MEDDAB‐HPW particles with small size make the composite microspheres not only easy for separation but also beneficial for catalysis. This material provides an example to construct microreactors with new structure used in diphase catalytic reaction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Design Strategy for the Multilayer Core–Shell Bioceramics with Controlled Chemistry

New strategies for fabricating multiphase bioceramic porous scaffolds with time‐dependent biodegradation and pore network enlargement are of fundamental importance in the advancement of bioceramics. Here, we developed a one‐step preparation of core–shell bioceramic microspheres (~2 mm in diameter) with single‐ or double‐shell structure through a coaxially aligned multilayer capillary system. The Ca‐phosphate (CaP) and Ca‐silicate (CaSi) ceramic phase distribution could be also adjusted by extruding through different capillaries, and thus the biodegradation rate would be readily tailored over time. When the polystyrene (PS) microbeads of ~15 μm in diameter were premixed into the CaP‐ or CaSi‐containing alginate slurry, the tailorable porous structures could be introduced into the core or different shell layers of the microspheres. These micropores may potentially maximize the permeability for rapid exchange of guest molecules or inorganic ions from the bioceramics. Totally, such strategy is promising because the ceramic phases with different biological properties can be assembled into the core–shell bioceramic microspheres, and thus the macropore structure evolution may be readily manipulated in the closely packed microsphere systems. We believe our gradient hybrid methodology will have potential in various categories of advanced biomaterials of organic–inorganic composites.     

Preparation of monodispersed porous polyacrylamide microspheres via phase separation in microchannels

We report on the formation of polyacrylamide (PAM)/polyethylene glycol (PEG) core/shell droplets in a microchannel via the polymerization-induced phase separation of an acrylamide (AM)/PEG aqueous system. Monodispersed porous PAM microspheres were prepared from the PAM/PEG core/shell droplets, and we examined the effects of experimental parameters on the phase separation process and on the particle size and pore structure of the resulting PAM microspheres. PAM microspheres could be readily obtained with adjustable particle sizes and porosities by altering the PEG and crosslinker contents and by using PEG with different molecular weights. The relation between the swelling value and porosity is correlated.     

Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes for pervaporation separation of ethanol/water solution

Polysulfone (PSF) hollow fiber membranes were spun by phase‐inversion method from 29 wt % solids of 29 : 65 : 6 PSF/NMP/glycerol and 29 : 64 : 7 PSF/DMAc/glycol using 93.5 : 6.5 NMP/water and 94.5 : 5.5 DMAc/water as bore fluids, respectively, while the external coagulant was water. Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes were prepared after PSF hollow fiber membranes were coated using different PVA aqueous solutions, which were composed of PVA, fatty alcohol polyoxyethylene ether (AEO₉), maleic acid (MAC), and water. Two coating methods (dip coating and vacuum coating) and different heat treatments were discussed. The effects of hollow fiber membrane treatment methods, membrane structures, ethanol solution temperatures, and MAC/PVA ratios on the pervaporation performance of 95 wt % ethanol/water solution were studied. Using the vacuum‐coating method, the suitable MAC/PVA ratio was 0.3 for the preparation of PVA/PSF hollow fiber composite membrane with the sponge‐like membrane structure. Its pervaporation performance was as follows: separation factor (α) was 185 while permeation flux (J) was 30g/m²·h at 50°C. Based on the experimental results, it was found that separation factor (α) of PVA/PSF composite membrane with single finger‐void membrane structure was higher than that with the sponge‐like membrane structure. Therefore, single finger‐void membrane structure as the supported membrane was more suitable than sponge‐like membrane structure for the preparation of PVA/PSF hollow fiber composite membrane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 247–254, 2005     

Polyimide‐based porous hollow carbon nanofibers for supercapacitor electrode

Porous hollow carbon nanofibers (PHCNFs) using styrene‐acrylonitrile copolymer (SAN) solution as core and polyacrylic acid (PAA) as shell were manufactured by co‐axial electrospinning technique, taking polyvinyl pyrrolidone (PVP) as a pore inducer additive in the shell. The shell thickness of PHCNFs could be adjusted by controlling flow rates of core and shell fluids. The prepared PHCNFs showed excellent electrochemical properties with the high specific capacitance of 221 F g^?1 and superior cycling stability, remaining a capacitance retention of 95% after 5000 cycles under a scan rate of 0.1 V s^?1. In this system, hollow structures bring a 20% capacitance improvement, while the porous morphology brings a 47% capacitance improvement. The attractive performances exhibited by these sponge supercapacitors make them potentially promising candidates for future energy storage systems. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43397.     

A facile route to poly(divinylbenzene) hollow microspheres with pyridyl group on the interior surface

Poly(divinylbenzene) (PDVB) hollow microspheres with pyridyl group located on their interior surface were prepared by a facile route with the aid of the vinyl groups on the surface of poly(methacrylic acid) (PMAA) microspheres, which were incorporated through the hydrogen-bonding interaction between the carboxylic acid group and pyridyl group of 4-vinylpyridine (VPy). Poly(methacrylic acid)@polydivinylbenzene (PMAA@PDVB) core-shell structure microspheres with PMAA as core and PDVB as shell were synthesized by a two-stage distillation-precipitation polymerization technique through the capture of the DVB monomer from solution of the reactive vinyl groups on pyridyl-functionalized PMAA microspheres based on a seeded-nucleation mechanism during the second-stage polymerization. The PDVB hollow microspheres with different shell thicknesses were developed after the PMAA core particles were removed by selective dissolution under basic condition in ethanol, during which the pyridyl group was left on the interior surface of the shell layer in PDVB hollow microspheres. The resultant core-shell and hollow microspheres were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier transform infrared spectra (FT-IR) and elemental analysis.     

Aqueous core polystyrene microspheres fabricated via suspension polymerization basing on a multiple pickering emulsion

Multi‐hollow or hollow polymer particles are of great interest in many fields. Here we successfully fabricate polystyrene microspheres with aqueous cores through w/o/w Pickering emulsion stabilized by modified SiO₂ nanoparticles. The final structure and constituents of the microspheres is investigated via SEM, X‐ray photoelectron spectra, and thermo‐gravimetric analysis. The results demonstrate that the size and amount of aqueous cores in the microspheres can be tuned by the original structure of the multiple emulsions: when the volume fraction of inner water is 0.2, the inner structure of the microspheres obtained is porous and each pore is not interconnected; when the volume fraction of inner water is increased to 0.7, the resulting products are hollow microspheres and when 0.3% wt/vol of salt is added to the inner aqueous phase, the inner pores of the resulting microspheres enlarge or even coalesce. The multi‐hollow or hollow polystyrene microspheres with aqueous cores are expected to be candidates for encapsulation in biotechnology. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39761.     

Preparation magnetite core/coated with polystyrene shell hybrid materials via redox interfacial‐initiated emulsion polymerization

In this article, we describe a novel redox interfacial‐initiated micro‐emulsion polymerization (RIEP) to prepare hollow polystyrene microspheres with magnetite nanoparticles (MPs) core and polystyrene (PS) shell (MPs‐PS) under ambient pressure. The emulsion was constituted water‐based magnetic ferro‐fluid as dispersing phase and organic solvent and styrene (St) as continuous phase. Cumene hydroperoxide (CHPO)/iron (II) sulfates (FS) as the redox initiation system, the water‐soluble FS acted as the reducing component and the oil‐soluble CHPO as the oxidant component of the redox initiation system. Therefore, the primary radicals are produced mainly at the oil/water interface to initiate the polymerization of styrene to form polymer shell. The final products thoroughly characterized by X‐ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, field‐emission scanning electron microscopy, thermogravimetric analysis, dynamic light scattering, and X‐ray photoelectron spectroscopy, which showed the formation of hollow magnetite/polystyrene nanocomposite microspheres. Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer. The saturation magnetization (M_s), remanent magnetization (M_r) and coercivity (H_c) is 30 emu/g, 15 emu/g and 370 Oe, respectively. The results revealed that the hybrid materials microspheres were super‐paramagnetic. POLYM. COMPOS., 31:1846–1852, 2010. © 2010 Society of Plastics Engineers     

A physical route to porous ethyl cellulose microspheres loaded with TiO2 nanoparticles

Porous ethyl cellulose (EC) microspheres were prepared via a physical method in oil‐in‐water (O/W) emulsions. The morphologies and pore structures of the resulting porous microspheres were investigated by scanning electron microscopy (SEM), mercury porosimeter and spectrometer equipped with an integrating sphere. The increase of EC amount in oil phase will increase the size of the microspheres. All the microspheres possess open macropores in the shell and interconnected pores inside the microspheres by means of phase separation. The saturation of the Ethyl acetate (EA) in external phase has an effect on the morphology of the EC particles obtained. Using EA unsaturated aqueous solution as the external water phase in the emulsion process results in the formation of porous EC particles with irregular shape. The loaded TiO₂ nanoparticles uniformly disperse in EC matrix, and slightly deceases the size and volume of interconnected pores inside the microspheres. The addition of TiO₂ nanoparticles is also proved to increase the light‐scattering power of the porous EC microspheres. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40822.     

Influence of unsaturated acid monomer on the morphology of latex particles in the preparation of hollow latex via the alkali post‐treatment

Multistage hydrophilic core/hydrophobic shell latexes containing carboxyl groups were prepared via multistep seeded emulsion copolymerization, and particles with different morphologies were obtained after alkali post‐treatment. Influences of the type and content of unsaturated acid monomer on the polymerization and the particle morphology were investigated based on conductometric titration and TEM observation. Results showed that the hydrophilic core/hydrophobic shell particles could be easily formed using methacrylic acid (MAA) instead of acrylic acid. When MAA was 12.2 wt % in the core latex preparation, only fine pores existed inside the alkali‐treated particles. With MAA increased from 20.0 to 30.0 wt %, the alkali‐treated particle morphology evolved from porous, hollow to collapse structure. When MAA further increased to 40.0 wt %, it was difficult to prepare uniform multistage particles and distinct morphologies including solid, deficient swelling, hollow and collapse structure were coexistent in the alkali‐treated particles. Moreover, the forming mechanism of different morphologies was proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of Magnetic Porous Microspheres and Their Ability to Remove Oils

Magnetic, porous poly (tripropylene glycol diacrylate) (PTPGDA) microspheres are successfully prepared using a combination of microfluidic emulsification and free‐radical polymerization. The porous structure can be precisely controlled by controlling the amount of the oil‐phase emulsifier polyglycerol polyricinoleate (PGPR). The effects of PGPR content and pH on the contact angle of the microspheres is investigated. The contact angle of the microspheres increases with the raise of PGPR content, and the hydrophobicity of the microspheres remains stable at different pHs. The microstructure, magnetic properties, and oil adsorption abilities of the microspheres are also studied. The as‐prepared microspheres perform adsorption well, the higher the PGPR content, the more pore structures and larger contact angle occurres on the microspheres, which improves the adsorption capacity. In addition, the adsorption capacity of the microspheres for diesel can reach 3.38 g·g^?1 when the mass fraction of PGPR in oil phase is 50% w/v. After adsorbing oil, the microspheres can be separated, recovered, and reused by applying an external magnetic field. The magnetic microspheres have good oil adsorption abilities and recyclability, which shows their potential for use in oil removal.     

Preparation of polyaniline coated polystyrene‐poly(styrene‐co‐sodium 4‐styrenesulfonate) microparticles and the further fabrication of hollow polyaniline microspheres

In this article, the microparticles of polystyrene‐poly(styrene‐co‐sodium 4‐styrenesulfonate) (PS‐PSS) coated by polyaniline (PANI) were prepared and hollow PANI microspheres were further obtained by dissolving the core. First, surface‐sulfonated monodispersed PS was prepared by copolymerization of sodium 4‐styrenesulfonate (SSS) and styrene with dispersion polymerization method. Then aniline was polymerized on the surface of the surface‐sulfonated PS (PS‐PSS) by chemical oxidative polymerization. After purification, we prepared core‐shell (PS‐PSS)/PANI particles. Hollow PANI microspheres were prepared by dissolving the plastic PS core of the (PS‐PSS)/PANI particles in chloroform. The growth process of PANI on the surface of PS‐PSS particles was investigated and the hollow PANI microspheres were characterized. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Comparatively Thermal and Crystalline Study of Poly(methyl‐methacrylate)/Polyacrylonitrile Hybrids: Core–Shell Hollow Fibers,Porous Fibers,and Thin Films

The polyacrylonitrile/polymethyl‐methacrylate (PMMA/PAN) porous fibers, core–shell hollow fibers, and porous thin films are prepared by coaxial electrospinning, single electrospinning, and spin‐coating technologies, respectively. The different morphologies arising from different processes display great influences on their thermal and crystalline properties. The adding of PMMA causes porous structure due to the microphase‐separation structure of immiscible PMMA and PAN phases. The lower weight loss, higher degradation temperature, and glass‐transition temperatures of porous thin films than those of porous fibers and core–shell hollow fibers are obtained, evidencing that the polymer morphologies produced from the different process can efficiently influence their physical properties. The orthorhombic structure of PAN crystals are found in the PMMA/PAN porous thin films, but the rotational disorder PAN crystals due to intermolecular packing are observed in the PMMA/PAN porous fibers and core–shell hollow fibers, indicating that different processes cause different types of PAN crystals.

     

Vi‐PDMS incorporated with protein‐based coatings designed for permeability‐enhanced applications

Functional polydimethylsiloxanes containing vinyl groups (Vi‐PDMS) were used for silicone‐based organic polymers in composites and adhesive formulations. Poly(butyl acrylate/methyl methacrylate/vinyl silicone oil)/casein–caprolactam [P(BA‐MMA‐Vi‐PDMS)/CA‐CPL] nanoparticles were prepared via emulsifier‐free polymerization. The well‐defined core–shell structure of P(BA‐MMA‐Vi‐PDMS)/CA‐CPL nanoparticles was verified by transmission electron microscopy. The results of scanning electron microscopy and contact angle measurements proved that the as‐obtained coatings exhibited porous and hydrophobic properties, which were helpful for superior water vapor permeability. By comparing the appearance of the coatings before and after adhesion analysis, the excellent adhesion strength was proved to be dominated by Vi‐PDMS. The relationship between interface morphology and properties of the resultant coatings was investigated in detail. The nucleation mechanism for this soap‐free emulsion synthesis was also proposed accordingly. These results could help in designing coatings with better surface properties and wider application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46501.     

亚微米中空微球聚合物的制备及其形貌调控

采用乳液聚合协同碱渗透溶胀法，制备了亚微米中空微球聚合物。通过SEM、TEM、DLS分别对中空微球的形貌和粒径进行表征，并考察了中空微球聚合物的遮盖性能。研究了引发剂用量对核粒径的影响，中间层和壳层聚合物配比对微球形貌结构及其遮盖性能的影响。结果表明，在核制备过程中，核的粒径随引发剂用量的增加而减小；对于平均粒径为148 nm的核，当中间层甲基丙烯酸丁酯（BMA）用量为10 wt%、甲基丙烯酸（MAA）用量为3 wt%，甲基丙烯酸甲酯（MMA）用量为87 wt%，壳层苯乙烯（St）用量为97 wt%，交联剂用量为3 wt%时，可制备平均粒径414 nm，中空率为40.6 %的聚合物微球，且微球表面较为光滑，此时中空微球聚合物具有优异遮盖性能，遮盖度达到66 %。     

油页岩灰渣制备空心陶瓷微球及机理探讨

以油页岩灰渣为实验原料,利用火焰喷枪熔射法制备了空心陶瓷微球.采用TG-DSC对油页岩灰渣进行热分析,采用SEM和XRD分别对油页岩灰渣和空心陶瓷微球的微观形貌和物相组成进行分析.研究结果表明,利用火焰喷枪熔射法制备的微球绝大多数为球状,极少部分为不规则形状,微球破碎后可发现其为空心结构;空心微球的形成机理为:油页岩灰渣粉末受热熔化、发气物质形成气泡、气泡合并、降温凝固、最终形成空心微球;油页岩灰渣自身疏松的结构、所含充足的发气物质和适宜的熔射温度是形成微球空心结构的重要因素.