Poly(methyl methacrylate)‐coated carbonyl iron particles and their magnetorheological characteristics

Magnetorheological fluids (MRFs) are types of suspensions that contain magnetic particles and a carrier fluid, and are considered as semi‐active smart materials. By tuning the strength of an external magnetic field, like other traditional MRFs, a carbonyl iron (CI)–poly(methyl methacrylate) (PMMA) particle‐based MRF can change reversibly from a fluid‐like state to a solid‐like state within milliseconds. In the research reported, CI particles were encapsulated with PMMA via emulsion polymerization. After the polymerization, the fabricated CI–PMMA composite particles were dispersed in a suspension medium to prepare MRF. The synthesized CI–PMMA composite particle‐based MRF showed a shear stress of 60 kPa at the magnetic field strength of 0.6 T, and a greatly enhanced anti‐sedimentation stability. Copyright © 2010 Society of Chemical Industry     

Microcapsules prepared from a polycondensate‐based cement dispersant via layer‐by‐layer self‐assembly on melamine‐formaldehyde core templates

Novel microcapsules were prepared from colloidal core–shell particles by acid dissolution of the organic core. Weakly crosslinked, monodisperse and spherical melamine‐formaldehyde polycondensate particles (diameter ～ 1 μm) were synthesized as core template and coated with multilayers of an anionic polyelectrolyte via layer‐by‐layer deposition technique. As polyelectrolytes, an anionic naphthalenesulfonate formaldehyde polycondensate that is a common concrete superplasticizer and thus industrially available, and cationic poly(allylamine hydrochloride) were used. Core removal was achieved by soaking the core–shell particles in aqueous hydrochloric acid at pH 1.6, resulting in hollow microcapsules consisting of the polyelectrolytes. Characterization of the template, the core–shell particles, and the microcapsules plus tracking of the layer‐by‐layer polyelectrolyte deposition was performed by means of zeta potential measurement and scanning electron microscopy. The microcapsules might be useful as microcontainers for cement additives. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of polystyrene/poly(methyl methacrylate) core‐shell composite particles by suspension‐emulsion combined polymerization

Suspension‐emulsion combined polymerization process, in which methyl methacrylate (MMA) emulsion polymerization constituents (EPC) were drop wise added to styrene (St) suspension polymerization system, was applied to prepare polystyrene/poly(methyl methacrylate) (PS/PMMA) composite particles. The influences of the feeding condition and the composition of EPC on the particle feature of the resulting composite polymer particles were investigated. It was found that PS/PMMA core‐shell composite particles with a narrow particle size distribution and a great size would be formed when the EPC was added at the viscous energy dominated particle formation stage of St suspension polymerization with a suitable feeding rate, whereas St‐MMA copolymer particles or PS/PMMA composite particles with imperfect core‐shell structure would be formed when the EPC was added at the earlier or later stage of St suspension polymerization, respectively. It was also showed that the EPC composition affected the composite particles formation process. The individual latex particles would exist in the final product when the concentrations of MMA monomer, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator were great in the EPC. Considering the feature of St suspension polymerization and the morphology of PS/PMMA composite particles, the formation mechanism of PS/PMMA particles with core‐shell structure was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Formation of transparent conducting films based on core‐shell latices: Influence of the polypyrrole shell thickness

Transparent conducting latex films have been prepared from core‐shell latices. The latex particles have a poly(butyl methacrylate) (PBMA) core of about 700 nm and a very thin polypyrrole (PPy) shell. We have studied the film formation of latices with 1, 2, and 4 wt % PPy and compared this with the film formation of the pure PBMA latex. The film formation process was studied by transparency measurements, atomic force microscopy surface flattening, and transmission electron microscopy on ultrathin sections of films after various annealing times at 120°C. It is demonstrated that highly transparent (>90%) and antistatic films can be produced using these latices. The presence of a polypyrrole shell around the PBMA latex particle seriously hinders the deformation of the particles. The amount of polypyrrole, and thus the shell thickness, is the determining factor for the speed of film formation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 900–909, 2001     

Effects of hydrophobic interaction on rheological behavior and microstructure of carboxylated core‐shell latex suspension

We have investigated the effects of hydrophobic interactions on the rheological behavior and microstructure of suspension of carboxylated core‐shell latex particles with changing hydrophobicity of shell polymer and suspending medium. The carboxylated core‐shell latex particles formed lattice‐like microstructures in aqueous suspension with dissociation of carboxyl groups. With increasing hydrophobicity of the shell polymer, the interparticle distance ξ in the microstructure decreased. However, ξ increased with increasing hydrophobicity of the suspending medium. The effect of hydrophobic interaction on ξ was explained by the steric stabilization theory for particles with grafted polymer on the surface. As the carboxylated core‐shell latex particles overlapped each other in the microstructure, an attractive force was generated between the particles in aqueous suspension. With increasing hydrophobicity of the shell, the attractive force increased, but with increasing hydrophobicity of the suspending medium, the attractive force decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4153–4158, 2006     

Effect of the core‐shell impact modifier shell thickness on toughening PVC

The shell thickness of a core/shell impact modifier is found to be the single most important factor in the toughening of rigid polyvinyl chloride (PVC). When the shell thickness is greater than a critical value of 15.8 nm, these core‐shell elastomeric particles are able to remain structurally intact and well dispersed within the PVC matrix after melt blending. However, too thick a shell thickness results in a hard core (high modulus) of these core/shell particles and loss of the rubbery nature required of an efficient impact modifier. Therefore, these over‐thick particles can act only as rigid fillers, not as efficient rubbery modifiers. On the other hand, when the shell thickness is less than the critical value of 4.9 nm, too thin a shell layer is simply unable to fully protect and cover the inner rubbery core during vigorous processing conditions, and these core‐shell particles tend to connect with one another through the partially exposed core to form a cellular‐like structure, thus resulting in poor toughening efficiency. Regardless of the particle size, as long as the shell thickness of these core/shell elastomers is between these two critical values (15.8 nm and 4.9 nm), they all display high efficiency in toughening rigid PVC. Polym. Eng. Sci. 44:1885–1889, 2004. © 2004 Society of Plastics Engineers.     

Formation mechanism of polyaniline self‐assembled needles and urchin‐like structures assisted by magnesium oxide

The polyaniline (PANI) morphological structure is strongly correlated with the preparation procedure, yielding diverse geometries such as nano‐tubes, belts, rods, fibres and particles. In this study, the synthesis of a novel PANI morphology of consisting of hollow needles and urchin‐like structures is presented and its formation mechanism is explained. The polymer was synthesized by chemical oxidative polymerization of aniline in the presence of magnesium oxide as a structural directing agent. The morphological study of the urchin‐like PANI was conducted using scanning electron microscopy and in situ monitoring of needle growth was done using optical microscopy. The structure and functional groups of these novel structures were characterized using Fourier transform infrared spectroscopy. Additionally, the formation mechanism is modelled based on the multi‐layer theory where a core–shell structure exists between the polymer (shell) and the magnesium oxide particles (core). © 2014 Society of Chemical Industry     

Preparation and characterization core‐shell particles and application for E‐Ink

the core‐shell particles were prepared by dispersion copolymerization. The core‐shell particles were characterized with Fourier‐transform infrared spectroscopy, Transmission electron microscope and scanning electron microscope. The dispersion stability and electrophoretic performance of core‐shell particles were studied in the mixed medium of tetrachloroethylene and cyclohexance. Microcapsules containing the core‐shell particles were prepared by coacervation. Results showed that the core‐shell particles had good dispersion stability and it had no electric response, which could be used as grounding particles for E‐Ink. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1195–1199, 2007     

Emulsifier‐free emulsion polymerization of acrylonitrile in the presence of poly(methyl methacrylate) seed particles: Influence of the addition mode on the surface morphology

Acrylonitrile (AN) was polymerized in the presence of poly(methyl methacrylate) (PMMA) seed latex by both the batch and dropwise addition modes. The two addition modes both led to PMMA/polyacrylonitrile (PAN) composite particles with a core/shell structure with PMMA as the core and PAN as the shell. The shell thickness could be adjusted by a change in the amount of the second‐stage AN monomer relative to the PMMA seed polymer. However, the surface morphologies of the composite polymers were quite different, which showed a rambutan‐like batch mode and an urchinlike dropwise mode. The reason was considered as the different precipitation mechanisms of PAN small‐particle precipitation for the batch mode and linear PAN segment growth for the dropwise mode. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polyurethane‐incorporated chitosan/alginate core–shell nano‐particles for controlled oral insulin delivery

Chitosan (CS) and polyurethane‐chitosan (PU‐CS) nano‐particles (NPs) were prepared for the core formation by complex coacervation method whereas alginate (ALG) and PU‐ALG were crosslinked by ionic gelation method to form the protective shell‐layer over the core. Effects of PU incorporation either within the core or shell or both were investigated by different in vitro and in vivo parameters. Fourier transform infrared (FTIR) spectroscopy of different compositions of nano‐particles showed distinct characteristic peaks for CS, PU, and ALG, indicating their presence in variable ratios. Significance of polyurethane‐incorporated systems towards insulin encapsulation efficiency, swelling parameters, insulin release, and in vivo pharmacological effect were also studied. Particle sizes, zeta potential, morphological analysis, mucoadhesion study, and in vivo acute toxicity studies of these core–shell nano‐particles were also performed. Bioavailability of insulin ranged from 9.04% to 11.6% for polyurethane‐incorporated chitosan‐alginate core–shell nano‐particle formulations which was significantly higher than the insulin bioavailability of basic CS/ALG core–shell nano‐particle system. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46365.     

Design of gas‐phase synthesis of core‐shell particles by computational fluid–aerosol dynamics

Core‐shell particles preserve the bulk properties (e.g., magnetic and optical) of the core while its surface is modified by a shell material. Continuous aerosol coating of core TiO₂ nanoparticles with nanothin silicon dioxide shells by jet injection of hexamethyldisiloxane precursor vapor downstream of titania particle formation is elucidated by combining computational fluid and aerosol dynamics. The effect of inlet coating vapor concentration and mixing intensity on product shell thickness distribution is presented. Rapid mixing of the core aerosol with the shell precursor vapor facilitates efficient synthesis of hermetically coated core‐shell nanoparticles. The predicted extent of hermetic coating shells is compared with the measured photocatalytic oxidation of isopropanol by such particles as hermetic SiO₂ shells prevent the photocatalytic activity of titania. Finally, the performance of a simpler, plug‐flow coating model is assessed by comparisons with the present detailed computational fluid dynamics (CFD) model in terms of coating efficiency and silica average shell thickness and texture. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Preparation and characterization of core‐shell nanoparticles containing poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core

Core shell latex particles with a glassy core and a low T_g polymeric shell are usually preferred. More so, the glassy core happens to be a fluoropolymer with a shell polymer that helps in processability. We describe here the preparation and characterization of core shell nanoparticles consisting of poly(chlorotrifluoroethylene‐co‐ethylvinylether) as core encapsulated in poly(styrene‐acrylate) copolymer shell using seeded emulsion polymerization method under kinetically controlled monomer starved conditions. Properties of the emulsion using surfactants (fluoro/conventional) and surfactant free conditions were investigated. Average size (100 nm), spherical shape and core–shell morphology of the latex particles was confirmed by dynamic light scattering and transmission electron microscopy. Absence of C? F and C? Cl peaks in X‐ray photoelectron spectroscopy proves that cores are completely covered. Polymerization in the presence of fluorocarbon surfactant was found to give optimum features like narrow size distribution, good shell deposition and no traces of agglomeration. Films of core shell latex particles exhibited improved transparency and enhanced water contact angles thus making them suitable for applications in various fields including coatings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Particle size and morphology of poly[styrene‐co‐(butyl acrylate)]/nano‐silica composite latex

Nanocomposite latex with nano‐silica of varying particle sizes was prepared via in situ polymerization and investigated by submicron particle size analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier‐transform infrared spectrometry (FTIR) and Raman spectrometry. It was found that nanocomposite latex exhibited a core–shell structure with nano‐silica particles enwrapped, resulting in an increase in the latex particle size. The smaller the nano‐silica particles, the more were embedded in each latex particle. The increase in the particle size of latex depended not only on the particle size of nano‐silica, but also on the number of nano‐silica particles in each latex particle. Copyright © 2004 Society of Chemical Industry     

Preparation and properties of core [poly(styrene‐n‐butyl acrylate)]–shell [poly(styrene–methyl methacrylate–vinyl triethoxide silane)] structured latex particles with self‐crosslinking characteristics

Structured latex particles with a slightly crosslinked poly(styrene‐n‐butyl acrylate) (PSB) core and a poly(styrene–methacrylate–vinyl triethoxide silane) (PSMV) shell were prepared by seed emulsion polymerization, and the latex particle structures were investigated with Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, transmission electron microscopy, and dynamic light scattering. The films that were formed from the structured core (PSB)–shell (PSMV) particles under ambient conditions had good water repellency and good tensile strength in comparison with films from structured core (PSB)–shell [poly(styrene–methyl methyacrylate)] latex particles; this was attributed to the self‐crosslinking of CH₂?CH? Si(OCH₂CH₃)₃ in the outer shell structure. The relationship between the particle structure and the film properties was also investigated in this work. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1824–1830, 2006     

Simultaneously improved toughness and dielectric properties of epoxy/core‐shell particle blends

Epoxy/core‐shell particle blends were prepared using a diglycidylether of bisphenol A epoxy and acrylics‐type core‐shell particles. The impact strength of the blends was tested, and the result showed that the epoxy was greatly toughened with optimum core‐shell particle content. Meanwhile, the dielectric properties of both epoxy and its blends were investigated using a broadband dielectric analyzer. It was found that the dielectric constant of the epoxy blends with lower core‐shell particle content were less than that of the epoxy in the investigated frequency range, while the dielectric loss was less than that of the neat epoxy over a low frequency range, even for the epoxy blends with the optimum core‐shell particle content. The dielectric breakdown strength of the epoxy blends at room and cryogenic temperature were also investigated. To identify the primary relationship of the above properties and structure of the epoxy blends, the microstructure of the core‐shell particle and the morphology of the samples were observed by transmission electron microscopy and scanning electron microscopy. It was considered that these epoxy/core‐shell particle blends with improved toughness and desirable dielectric properties could have a potential application in the insulation of electronic packaging system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Preparation and properties of porous L‐tryptophan imprinted latex membrane from core‐shell emulsion

Molecularly imprinted latex membrane (MILM) is prepared by core‐shell emulsion technique in the presence of a template molecule (L ‐Tryptophan). A hard inward and soft outward microstructure latex particle is designed to obtain MILM with both flexibility and impact strength. Molecularly imprinted layer with high crosslinking degree is grafted on the surface of core‐shell latex particles. NaCl, glucose, urea, polyethylene glycol, M_w 300, etc., are added during the film‐forming process to produce porous microstructure in MILM. Fourier transform infrared spectroscopy (FTIR) and Scatchard analysis are used to investigate the interaction between L ‐Tryptophan and MILM and the binding ability of the resultant MILM, respectively. The functional binding and separation performances in aqueous medium towards template are carried out. The results reveal that the content and type of porogen and the shell composition have significant effects on adsorption capacity and separation ability. MILM with glucose as porogen shows high recognition towards the template with adsorption separation factor reaching 9.06. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of sub‐micrometer core–shell rubber particles with 1,2‐azobisisobutyronitrile as initiator and deformation mechanisms of modified polystyrene under various conditions

BACKGROUND: Sub‐micrometer core‐shell polybutadiene‐graft‐polystyrene (PB‐g‐PS) copolymers with various ratios of polybutadiene (PB) core to polystyrene (PS) shell were synthesized by emulsion grafting polymerization with 1,2‐azobisisobutyronitrile (AIBN) as initiator. These graft copolymers were blended with PS to prepare PS/PB‐g‐PS with a rubber content of 20 wt%. The mechanical properties, morphologies of the core‐shell rubber particles and deformation mechanisms under various conditions were investigated. RESULTS: Infrared spectroscopic analysis confirmed that PS could be grafted onto the PB rubber particles. The experimental results showed that a specimen with a ‘cluster’ dispersion state of rubber particles in the PS matrix displayed better mechanical properties. Transmission electron micrographs suggested that crazing only occurred from rubber particles and extended in a bridge‐like manner to neighboring rubber particles parallel to the equatorial plane at a high speed for failure specimens, while the interaction between crazing and shear yielding stabilized the growing crazes at a low speed in tensile tests. CONCLUSION: AIBN can be used as an initiator in the graft polymerization of styrene onto PB. The dispersion of rubber particles in a ‘cluster’ state leads to better impact resistance. The deformation mechanism in impact tests was multi‐crazing, and crazing and shear yielding absorbed the energy in tensile experiments. Copyright © 2009 Society of Chemical Industry     

Toughening modification of PS with n‐BA/MMA/styrene core–shell structured copolymer from emulsifier‐free emulsion polymerization

Core–shell structured particles, which comprise the rubbery core and glassy layers, were prepared by emulsifier‐free emulsion polymerization of poly(n‐butyl acrylate/methyl methacrylate)/polystyrene [P(n‐BA/MMA)/PS]. The particle diameter was about 0.22 μm, and the rubbery core was uncrosslinked and lightly crosslinked, respectively. The smaller core–shell structured particle–toughened PS blends were investigated in detail. The dynamic mechanical behavior and observation by scanning electron microscopy of the modified blend system with core–shell structured particles indicated good compatibility between PS and the particles, which is the necessary qualification for an effective toughening modifier. Notched‐impact strength and related mechanical properties were measured for further evaluation of the toughening efficiency. The notched‐impact strength of the toughened PS blends with uncrosslinked particles reached almost sixfold higher than that of the untoughened PS when 15 phr of the core–shell structured particles was added. For the crosslinked particles the toughening effect for PS was not obvious. The toughening mechanism for these smaller particles also is discussed in this article. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1290–1297, 2003     

Preparation and surface properties of core‐shell polyacrylate latex containing fluorine and silicon in the shell

The core‐shell polyacrylate latex particles containing fluorine and silicon in the shell were successfully synthesized by a seed emulsion polymerization, using methyl methacrylate (MMA) and butyl acrylate (BA) as main monomers, dodecafluoroheptyl methacrylate (DFMA), and γ‐(methacryloxy) propyltrimethoxy silane (KH‐570) as functional monomers. The influence of the amount of fluorine and silicon monomers on the emulsion polymerization process and the surface properties of the latex films were discussed, and the surface free energy of latex films were estimated using two different theoretical models. The emulsion and its films were characterized by particle size distribution (PSD) analysis, transmission electron microscopy (TEM), Fourier transform infrared spectrum (FTIR), nuclear magnetic resonance (¹H‐NMR and ¹⁹F‐NMR) spectrometry, contact angle (CA) and X‐ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and thermogravimetry (TG) analysis. The results indicate that the average particle size of the latex particles is about 160 nm and the PSD is narrow, the synthesized latex particles exist with core‐shell structure, and a gradient distribution of fluorine and silicon exist in the latex films. In addition, both the hydrophobicity and thermal stability of the latex films are greatly improved because of the enrichment of fluorine and silicon at the film‐air interface, and the surface free energy is as low as 15.4 mN/m, which is comparable to that of polytetrafluoroethylene (PTFE). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ultrasonication‐assisted synthesis of molecularly imprinted polymer‐encapsulated magnetic nanoparticles for rapid and selective removal of 17β‐estradiol from aqueous environment

Molecularly imprinting technique was combined with magnetic nanoparticles to synthesize molecularly imprinted polymer‐encapsulated particles for selective removal and efficient separation of estrogenic compounds from water. The core‐shell‐structured particles were successfully prepared by a novel 2‐h ultrasonication‐assisted synthesis in a mixture of water and organic solvent using dual‐layer surfactant‐modified magnetic particles as core, the most physiologically active estrogenic compound (17β‐estradiol) as template, and widely adapted methacrylic acid as functional monomer. Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and magnetic separation were used to characterize the particles. High‐performance liquid chromatography–tandem mass spectrometry was used for quantitative binding performance analysis at low‐nanogram per milliliter levels. The particles exhibited satisfactory recognition of 17β‐estradiol in water. They possessed great potential for rapid, cost‐effective, and efficient separation of estrogenic compounds from aqueous environment with specificity. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers