A simple route to prepare pomegranate‐like polystyrene‐based microspheres with high porosity

Pomegranate‐like polystyrene‐based microspheres with high porosity were successfully prepared via a simple route involving two steps. The first step was the preparation of polystyrene‐based microspheres with multi‐cores and a non‐porous shell via suspension polymerization of divinylbenzene and vinylbenzyl chloride. Nitrogen sorption failed to characterize the pore structure of the microspheres because of the non‐porous shell, but the results of Hg intrusion indicated that the pore volume of the microspheres was 0.36 cm³ g^?1. The second step was post crosslinking of the microspheres derived from the first step. Extensive porosity was generated in the shell and the pomegranate‐like structure of the microspheres remained almost unchanged. The results showed that the pore volumes of the final products derived from N₂ sorption and Hg intrusion were 0.54 cm³ g^?1 and 0.66 cm³ g^?1, respectively. Overall, this provides a simple and feasible route to biomimetic preparation of pomegranate‐like polystyrene‐based microspheres with high porosity. Copyright © 2011 Society of Chemical Industry     

Study of the preparation and mechanism of formation of hollow monodisperse polystyrene microspheres by SPG (Shirasu Porous Glass) emulsification technique

In a previous study, it was found that monodisperse polystyrene (PSt) hollow particles can be prepared under special conditions by combining a Shirasu Porous Glass (SPG) emulsification technique and subsequent suspension polymerization process. That is, a mixture of styrene (St), N,N‐dimethylamino ethyl methacrylate (DMAEMA), hexadecane (HD), and initiator N, N′‐azobis(2,4‐dimethylvaleronitrile) (ADVN) was used as the dispersed phase in an aqueous phase containing poly(vinyl pyrrolidone) (PVP), sodium lauryl sulfate (SLS), and water‐soluble inhibitor. The dispersed phase was created by pushing the oil phase through the uniform pores of an SPG membrane into the continuous phase to form uniform droplets. Then, the droplets were polymerized at 70°C. It has been puzzling that hollow microspheres were obtained only when sodium nitrite (NaNO₂) was used as a water‐soluble inhibitor, while one‐hole particles were formed when hydroquinone (HQ) or diaminophenylene (DAP) was used. In this study, the mechanism of formation of the hollow microspheres was verified by measuring the variation of diameter, molecular weight distribution, and monomer conversion, and by observing morphological changes during the polymerization, as well as by changing the type and amount of hydrophilic monomer, and initiator. It was found that the diameter of the oil droplets decreased, and a large amount of secondary new particles formed immediately after polymerization started in the case of NaNO₂. However, there was no such apparent behavior to be observed when HQ or DAP was used. It was determined that the hollow particles formed due to the rapid phase separation between PSt and HD, and as a consequence, a large amount of monomer diffused into the aqueous phase to form the secondary particles. Rapid phase separation confined the HD inside the droplets, a nonequilibrium morphology. On the other hand, one‐hole particles, representing an equilibrium morphology, formed when the phase separation occurred slowly because a lot of monomer existed inside of the droplets to allow mobility of the PSt. The addition of DMAEMA allowed the hollow particles to be formed more easily by decreasing the interfacial tension between the copolymer and aqueous phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1530–1543, 2002     

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     

Preparation of polystyrene/zirconia core-shell microspheres and zirconia hollow shells

Zirconia/polystyrene core-shell microspheres were prepared through room-temperature aging process and a solvothermal process with ethanol as solvent. Through the hydrolysis of zirconium propoxide, ZrO₂ was coated on PS cores to form the core-shell microspheres. And hollow ZrO₂ shells were formed by calcining the core-shell particles in a muffle oven under static air at 600 °C.     

Facile preparation of PLGA microspheres with diverse internal structures by modified double‐emulsion method for controlled release

Poly(l ‐lactide‐co‐glycolide) (PLGA) microspheres with diverse internal structures and different release behaviors were prepared via a modified double‐emulsion method by introduction of heparin or carboxymethyl chitosan in the inner aqueous phase and calcium chloride in the outer aqueous phase, respectively. The main factors affecting the microsphere morphology were systematically studied, including compositions in the inner aqueous phase, the oily phase, and the outer aqueous phase. The transmission electron microscope images demonstrated that the microspheres are featured with single core, hollow, and multicore structures when their sizes were less than 200 nm, in the range of 200–700 nm, and greater than 700 nm, respectively. In comparison with hollow PLGA microspheres, the PLGA microspheres with heparin and carboxymethyl chitosan in the inner aqueous phase also showed multicore and single core structures, respectively, and exhibited higher loading efficiencies and slower release rates by using bovine serum albumin as a model for bioactive substances. It was concluded that this study provided a facile method to prepare microspheres with single core, multicore, or hollow feature, and the tunability of the different internal structures and related release profiles enables these systems cater to specific requirements for potential applications in controlled biomolecule delivery for tissue regeneration. POLYM. ENG. SCI., 55:896–906, 2015. © 2014 Society of Plastics Engineers     

Preparation and characterization of porous titanium dioxide sulfonated polystyrene composite microspheres with amphiphilicity

Porous particles with amphiphilicity were prepared by a nonpolymeric pore‐formation process with the sulfonation of polystyrene microspheres. Nano titanium dioxide (TiO₂) particles were then grafted onto the surface via a sol–gel method to finally form the composite particles. The effects of the mass ratio of ethanol (EtOH) to water, temperature, and solubility parameter on the pore‐formation process is discussed in detail. The morphology, porous structure, and wetting properties of the particles were studied by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and contact angle measurement. The results show that porous sulfonated polystyrene (SP) microspheres could be fabricated at 60°C with a 1 : 1 mass ratio of EtOH–water and a solubility parameter of 29.69 MPa^1/2. The TiO₂ particles were determined to be grafted onto the SP microspheres by physical‐bond interaction on the basis of FTIR analysis. The contact angles for both water (aqueous‐phase) and various organic solvent (oil‐phase) droplets with different polarities on the surface of compressed tablets of TiO₂–SP powder were all lower than 30°; this indicated excellent amphiphilicity in the composite particles. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

PS/TiO2核壳型微球和空心TiO2微球有序排列的制备

利用纳米级二氧化钛（TiO₂）溶胶微粒与聚苯乙烯（PS）胶体颗粒的混合悬浮液,以垂直共沉积的方法制备了核壳型PS/TiO₂微球的有序排列。当利用煅烧的方法去除PS胶粒晶体模板后,可以形成空心TiO₂微球的三维有序排列。考察了混合悬浮液中两种胶体颗粒的体积比（PS∶TiO₂=R）对空心TiO₂微球有序排列形成的影响。实验结果表明,合适的R值（6∶1）对于空心微球有序排列的形成至关重要。与此同时,浸渍填充法对照实验的结果表明,煅烧过程中TiO₂纳米颗粒晶型转化引起的收缩是造成TiO₂空心球产生的主要原因。     

Fabrication of Hydroxyapatite Hollow Microspheres by the Composite‐Hydroxide Approach

Hydroxyapatite (HAp) hollow microspheres with hierarchically porous structure and nanorice‐like architecture units were synthesized by the composite‐hydroxide approach. NH₄H₂PO₄ was first reacted with hydroxides to form a hydroxide‐insoluble M₃PO₄ (the term M represents either Na or K). The diffusing M₃PO₄ at the liquid–solid interface then reacted with the Ca(OH)₂, forming insoluble HAp hollow spheres by Kirkendall process. Results show that when reaction time is increased from 3 to 12 h, the average diameter of the microspheres increased from 2.64 to 4.16 μm. In addition, the size homogeneity of the hollow microspheres was improved gradually due to Ostwald ripening. The prepared hollow microspheres were treated by ultrasound, and nanorice‐like component units with a large mass of mesopores (<10 nm) were displayed. These prepared HAp hollow microspheres might be expected to apply to ion adsorption and drug delivery.     

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 and characterization of poly(vinyl chloride)/polystyrene/poly(ethylene glycol) hollow‐fiber ultrafiltration membranes

Hollow‐fiber ultrafiltration (UF) membranes were prepared from blends of poly(vinyl chloride) (PVC) and polystyrene (PS) with a dry/wet phase inversion method. Poly(ethylene glycol) (PEG) and N,N‐dimethylacetamide were used as the additive and solvent, respectively. The effects of the PEG concentration in the dope solution as an additive on the cross sections and inner and outer surface morphologies, permeability, and separation performance of the hollow fibers were examined. The mean pore size, pore size distribution, and mean roughness of both the inner and outer surfaces of the produced hollow fibers were determined by atomic force microscopy. Also, the mechanical properties of the hollow‐fiber membranes were investigated. UF experiments were conducted with aqueous solutions of poly(vinyl pyrrolidone) (PVP; K‐90, M_w = 360 kDa). From the results, we found that the PVC/PS hollow‐fiber membranes had two layers with a fingerlike structure. These two layers were changed from a wide and long to a thin and short morphology with increasing PEG concentration. A novel and until now undescribed shape of the nodules in the outer surfaces, which was denoted as a sea‐waves shape, was observed. The outer and inner pore sizes both increased with increasing PEG concentration. The water permeation flux of the hollow fibers increased from 104 to 367 L m^?2 h^?1 bar^?1) at higher PEG concentrations. The PVP rejection reached the highest value at a PEG concentration of 4 wt %, whereas at higher values (from 4 to 9 wt %), the rejection decreased. The same trend was found also for the tensile stress at break, Young's modulus, and elongation at break of the hollow fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 989‐1004, 2013     

Synthesis and characterization of air‐stable magnetic Fe composites microspheres of narrow size distribution

Air‐stable Fe magnetic nanoparticles entrapped within carbon and porous crosslinked polystyrene microspheres of narrow size distribution were prepared by the following sequential steps: (1) Polystyrene/poly(divinyl benzene) and polystyrene/poly(styrene‐divinyl benzene) uniform micrometer‐sized composite particles were prepared by a single‐step swelling of uniform polystyrene template microspheres dispersed in an aqueous continuous phase with emulsion droplets of dibutyl phthalate containing the monomers divinyl benzene and styrene and the initiator benzoyl peroxide. The monomers within the swollen polystyrene template microspheres were then polymerized by raising the temperature to 73°C; (2) Porous poly (divinyl benzene) and poly(styrene‐divinyl benzene) uniform crosslinked microspheres were prepared by dissolution of the polystyrene template part of the former composite particles; (3) Uniform magnetic poly(divinyl benzene)/Fe and poly(styrene‐divinyl benzene)/Fe composite microspheres were prepared by entrapping Fe(CO)₅ within the porous crosslinked microspheres, by suction of the Fe complex into the dried porous particles, followed by decomposition of the encapsulated Fe(CO)₅ at 200°C in Ar atmosphere; (4) Uniform magnetic air‐stable C/Fe composite microspheres were prepared similarly, apart from changing the decomposition temperature from 200 to 600°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly(vinyl chloride) hollow‐fiber membranes for ultrafiltration applications: Effects of the internal coagulant composition

Poly(vinyl chloride) (PVC) hollow‐fiber membranes were spun by a dry/wet phase‐inversion technique from dopes containing 15 wt % PVC to achieve membranes with different pore sizes for ultrafiltration (UF) applications. The effects of the N,N‐dimethylacetamide (DMAc) concentration in the internal coagulant on the structural morphology, separation performance, and mechanical properties of the produced PVC hollow fibers were investigated. The PVC membranes were characterized by scanning electron microscopy, average pore size, pore size distribution, void volume fraction measurements, and solubility parameter difference. Moreover, the UF experiments were conducted with pure water and aqueous solutions of poly(vinyl pyrrolidone) as feeds. The mechanical properties of the PVC hollow‐fiber membranes were discussed in terms of the tensile strength and Young's modulus. It was found that the PVC membrane morphology changed from thin, fingerlike macrovoids at the inner edge to fully spongelike structure with DMAc concentration in the internal coagulant. The effective pores showed a wide distribution, between 0.2 and 1.1 μm, for the membranes prepared with H₂O as the internal coagulant and a narrow distribution, between 0.114 and 0.135 μm, with 50 wt % DMAc. The results illustrate that the difference in the membrane performances was dependent on the DMAc concentration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

含锰铁氧化物磁性中空微球的制备与性能表征

用沉积表面反应法制备了以聚苯乙烯为核、Mn-Fe氧化物为壳的磁性核-壳微球. 考察了锰含量对核-壳球磁性的影响,分别采用烧结法和溶剂萃取法去除核-壳球内的聚苯乙烯以制取中空微球. 讨论了烧结温度与所形成的中空微球比表面积的关系,考察了溶剂萃取法去除聚苯乙烯的效果,比较了两者所形成的中空微球的性能. 结果表明,烧结法所得微球性能优于溶剂萃取法所得微球. 探讨了烧结法形成中空磁性球的最佳条件,在400℃下煅烧核-壳微球可以得到饱和磁化强度为68.66 emu/g、比表面积为27.8438 m2/g的含锰铁氧化物磁性中空微球.     

Facile synthesis of hollow microspheres of polyaniline using poly(sodium 4‐styrenesulfonate) as dopant

In a conventional chemical oxidative polymerization of aniline in poly(sodium 4‐styrenesulfonate) aqueous solution, hollow microspheres of polyaniline were easily prepared, instead of common particles. The morphology of the hollow microspheres was studied and confirmed using scanning electron microscopy and transmission electron microscopy. The molecular structure, room temperature conductivities and thermal stability of the resulting polyaniline were characterized using Fourier transform infrared spectroscopy, the standard DC four‐probe method, thermogravimetric analysis and differential thermal analysis. The influence of poly(sodium 4‐styrenesulfonate) and aniline on the morphology and physical properties of the resulting polymer were investigated. The results showed that the proper ratio of poly(sodium 4‐styrenesulfonate) and aniline was a critical factor in the synthesis of hollow microspheres, which may be related to the chemical structure of poly(sodium 4‐styrenesulfonate) as polyanion and of polyaniline as polycation and the electrostatic interaction between them in the doping process. A possible formation mechanism is proposed in this work. © 2013 Society of Chemical Industry     

Study on preparation of monodispersed poly(styrene‐co‐N‐dimethylaminoethyl methacrylate) composite microspheres by SPG (Shirasu Porous Glass) emulsification technique

Monodispersed poly(styrene‐co‐N‐dimethylaminoethyl methacrylate) [P(St‐DMAEMA)] composite microspheres were prepared by employing a Shirasu Porous Glass (SPG) emulsification technique. A mixture of monomer, hexadecane (HD), and initiator N,N′‐azobis(2,4‐dimethylvaleronitrile) (ADVN) was used as a dispersed phase and an aqueous phase containing stabilizer [poly(vinyl pyrrolidone) (PVP) or poly(vinyl alcohol) (PVA)], sodium lauryl sulfate (SLS), and water‐soluble inhibitor [hydroquinone (HQ), diaminophenylene (DAP), or sodium nitrite (NaNO₂)], was used as a continuous phase. The dispersed phase was permeated through the uniform pores of SPG membrane into the continuous phase by a gas pressure to form the uniform droplets. Then, the droplets were polymerized at 70°C. The effects of inhibitor, stabilizer, ADVN, and DMAEMA on the secondary nucleation, DMAEMA fraction in the polymer, conversion, and morphologies of the particles were investigated. It was found that the secondary nucleation was prevented effectively in the presence of HQ or DAP when PVP was used as the stabilizer. The secondary particle was observed when ADVN amount was raised to 0.3 g (/18 g monomer); however, no secondary nucleation occurred even by increasing DMAEMA fraction to 10 wt %. This result implied that the diffusion of ADVN into the aqueous phase was a main factor responsible to the secondary nucleation more than that of DMAEMA. The hollow particles were obtained when NaNO₂ was used, while one‐hole particles formed in the other cases. By adding crosslinking agent, the hole disappeared and the monomer conversion was improved. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2408–2424, 2001     

Multihollow nanocomposite microspheres with tunable pore structures by templating Pickering double emulsions

Micrometer-sized dual nanocomposite polymer microspheres with tunable pore structures were fabricated using a simple and straightforward method based on Pickering double emulsions. First, a primary water-in-styrene (oil) emulsion (w₁/o) was prepared using the hydrophobic silica nanoparticles as a particulate emulsifier without any molecular surfactants. Then, a water-in-styrene-in-water (w₁/o/w₂) Pickering emulsion was produced by the emulsification of the primary w₁/o emulsion into water using Fe₃O₄ nanoparticles as external emulsifier. The big styrene droplets containing small water droplets were polymerized after the formation of the double emulsions. Nanocomposite polystyrene microspheres with a multihollow structure were obtained and their morphological structures were studied by scanning electron microscopy (SEM). The pore structure of the microspheres could be tuned by the volume ratio of the internal water phase to the medium oil phase (w₁:o) of the primary emulsions. With increasing w₁:o from 1:8 to 4:1, the amount of the pores in one microsphere increased gradually and the pore structures changed from close to interconnected. The resulting multihollow microspheres had a responsive ability to magnetic stimulus due to the existence of Fe₃O₄ nanoparticles. This kind of multihollow hybrid polymer microspheres is expected to have a wide potential application in materials science and biotechnology.     

Optical properties of colloidal crystalline arrays composed of hollow polystyrene spheres

We have evaluated the optical properties of close‐packed and non close‐packed colloidal crystalline arrays made of hollow polystyrene spheres. Close‐packed colloidal crystalline arrays were fabricated by simple evaporation of dispersions, whereas nonclose‐packed colloidal crystalline arrays were fabricated by exploiting electrostatic interactions between the spheres in aqueous dispersion. Optical properties of the arrays were estimated from angle‐resolved reflection spectra. The Bragg diffraction peak of the colloidal crystalline array made of hollow spheres was of shorter wavelength than in the case of solid spheres, not only for the close‐packed array but also for the nonclose‐packed array. These shifts were caused by a decrease in the effective refractive index n_eff with decreasing particle refractive index. We have found that this relationship could be explained by the simple equation n_eff = n_particle?+ n_solvent (1 ? ?), where ? is the volume fraction of the particles, for both close‐packed and non close‐packed arrays. The current work suggests new possibilities for the creation of advanced colloidal crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2364–2368, 2007     

Facile fabrication of polystyrene/halloysite nanotube microspheres with core–shell structure via Pickering suspension polymerization

In this article, a facile method for fabrication of core–shell nanocomposite microspheres with polystyrene (PS) as the core and halloysite nanotubes (HNTs) as the shell via Pickering suspension polymerization was introduced. Stable Pickering emulsions of styrene in water were prepared using HNTs without any modification as a particulate emulsifier. The size of the Pickering emulsions varied from 195.7 to 26.7?μm with the water phase volume fraction increasing from 33.3 to 90.9?%. The resulting Pickering emulsions with the water phase volume fraction of above 66.7?% were easily polymerized in situ at 70?°C without stirring. HNTs played an important role during polymerization and effectively acted as building blocks for creating organic–inorganic nanocomposite microspheres after polymerization. The sizes of PS/HNTs microspheres were roughly in accord with that of the corresponding emulsion droplets before polymerization. The effect of the water phase volume fraction on the stability of Pickering emulsions and the morphologies of nanocomposite microspheres was investigated by optical microscopy, confocal laser scanning microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and so on.