Hollow Polymer Microspheres Research Articles

Carboxyl-functionalized hollow polymer microspheres for detection of trace metal elements in complex food matrixes by ICP-MS assisted with solid-phase extraction

In this work, carboxyl-functionalized hollow polymer microspheres (CHPMs) was successfully fabricated using poly (styrene-itaconic anhydride) particles as the core template and itaconic anhydride and trans-anethole cross-linked with divinylbenzene as the shell. The desirable microspheres and hollow structure of CHPMs were demonstrated by scanning and transmission electron microscopies, respectively. The characterized CHPMs as an adsorbent was packed into a solid phase extraction column to simultaneously detect the V(V), Cr(III), Cu(II), Cd(II), and Pb(II) in digested food samples by inductively coupled plasma-mass spectrometry (ICP-MS). A series of experimental parameters of solid-phase extraction (SPE) were investigated through vast experiments to improve sensitivity of the proposed method in metal ions detection. The detection limits of the method reached 0.8–3.2 ng L−1 for the target elements, and the relative standard deviations (RSDs) ranging from 1.2% to 3.5% were obtained from eleven parallel experiments using a 1.0 μg L−1 sample solution. The stability allowed the material to withstand more than 15 cycling while the recoveries remained above 88%. In food samples, the detection limits were at 0.20–0.80 μg kg−1, and satisfactory recoveries of 85–104% were obtained in spike tests of laver, fish as well as chicken.

Recent developments on epoxy-based syntactic foams for deep sea exploration

Epoxy syntactic foam (ESF) materials are widely used in marine detection systems, deep sea diving equipment, offshore oil exploration and other deep sea development and exploration equipment due to their superior properties such as low density, high compressive strength and low water absorption. The composition and preparation process of the ESF material determine the structure of the ESF material, the structure determines the performance, and the performance determines the application of the ESF material. The review describes the epoxy-based syntactic foams from the following aspects: definition and classification, preparation methods, properties and influencing factors, application, problems and development trend. The forming methods of hollow glass microspheres (solid-state powder processing method and liquid atomization method), hollow polymer microspheres (spray drying method) and centimeter-sized hollow spheres (rolling ball method and electrostatic fiber flocking method) are introduced in detail, as well as the casting molding method, vacuum molding method and pressure molding method of the syntactic foams. The main objective of this paper is focusing on the influence of various factors including filler content, graded structure, clay material, carbon material, fiber-reinforced material, molding process, material structure (sandwich structure) on the compressive strength and the density of the syntactic foam in detail. The paper may also provide some guidance to the preparation of ESF used in deep sea development and exploration equipment.

Compression properties of polymeric syntactic foam composites under cyclic loading

In the present work, polymer-based syntactic foams were studied under cyclic compression in order to investigate their compressibility, recoverability, energy dissipation and damage tolerance. These syntactic foams were manufactured by adding hollow polymer microspheres of various sizes and wall thicknesses into a polyurethane matrix. The associated loading and unloading curves during cyclic testing were recorded, revealing the viscoelastic nature of the materials. SEM images of the samples were obtained in order to study potential damage mechanisms during compression. It was observed that these syntactic foams exhibit high elastic recovery and energy dissipation over a wide range of compressional strains and the addition of polymer microspheres mitigates the damage under compressional loading.

Porous Reaction-Bonded Silicon Nitride Ceramics: Fabrication Using Hollow Polymer Microspheres and Properties

A process has been proposed for the preparation of porous reaction-bonded silicon nitride (RBSN) via the addition of a pore former, uniaxial pressing, and subsequent reaction sintering in a vacuum furnace. As a pore former, we used a commercially available powder consisting of hollow polymer microspheres (Akzonobel) with an average diameter of 9 μm. We have studied the effect of pore former content in green compacts on the mechanical, dielectric, and thermophysical properties of the ceramics. The proposed process allows one to prepare porous RBSN with the following properties: σb = 48 MPa, e = 3.2, tan δ = 35 × 10–4 at a frequency of 10 GHz, and λ = 0.96 W/(m K) at 1100°C. The ceramic obtained in this study is potentially attractive for industrial application as a radar-transparent structural material with reduced thermal conductivity.

Janus membrane emulsification for facile preparation of hollow microspheres

Hollow microspheres have aroused considerable interests in the materials community owing to their numerous potential applications; however, scalable, facile, low-cost production of hollow microspheres has not yet been demonstrated. Here, inspired by the idea that a hydrophilic surface allows the rapid detachment of gas bubbles to reduce the bubble size significantly, a novel and feasible approach to preparing gas-in-oil-in-water (G/O/W) emulsions on a large scale using Janus membrane emulsification is presented. A Janus membrane with asymmetric wettability, rather than a fully hydrophilic or a fully hydrophobic membrane, is employed in the emulsification system, in which the hydrophobic side allows gas/oil permeation and the hydrophilic side achieves fast release of oily bubbles. The wetting and chemical properties of each side of the membrane were investigated by contact angle and spectroscopy measurement. It was observed that the stability of the emulsions increased with increasing solution pH values. The variation of droplet size and distribution with the gas flow rate was also studied. The outer diameters of double emulsion drops are in the order of 100–300 μm. These droplets are further exposed to UV light to obtain hollow polymeric microspheres through solidification of the oil layers. Hollow structures of the microspheres were verified by HIM observations. This simple strategy opens a new avenue for generating double emulsions and hollow microspheres at scale with relatively narrow polydispersity.

Co-electrospraying of tumour cell mimicking hollow polymeric microspheres for diffusion magnetic resonance imaging

Diffusion magnetic resonance imaging (dMRI) is considered as a useful tool to study solid tumours. However, the interpretation of dMRI signal and validation of quantitative measurements of is challenging. One way to address these challenges is by using a standard reference material that can mimic tumour cell microstructure. There is a growing interest in using hollow polymeric microspheres, mainly prepared by multiple steps, as mimics of cells in healthy and diseased tissue. The present work reports on tumour cell-mimicking materials composed of hollow microspheres for application as a standard material in dMRI. These microspheres were prepared via one-step co-electrospraying process. The shell material was poly(d,l-lactic-co-glycolic acid) (PLGA) polymers with different molecule weights and/or ratios of glycolic acid-to-lactic, while the core was polyethylene glycol (PEG) or ethylene glycol. The resultant co-electrosprayed products were characterised by optical microscopy, scanning electron microscopy (SEM) and synchrotron X-ray micro-CT. These products were found to have variable structures and morphologies, e.g. from spherical particles with/without surface hole, through beaded fibres to smooth fibres, which mainly depend on PLGA composition and core materials. Only the shell material of PLGA polymer with ester terminated, Mw 50,000–75,000 g mol−1, and lactide:glycolide 85:15 formed hollow microspheres via the co-electrospraying process using the core material of 8 wt% PEG/chloroform as the core. A water-filled test object (or phantom) was designed and constructed from samples of the material generated from co-electrosprayed PLGA microspheres and tested on a 7 T MRI scanner. The preliminary MRI results provide evidence that hollow PLGA microspheres can restrict/hinder water diffusion as cells do in tumour tissue, implying that the phantom may be suitable for use as a quantitative validation and calibration tool for dMRI.

Molecularly imprinted polymers based on zeolite imidazolate framework-8 for selective removal of 2,4-dichlorophenoxyacetic acid

Novel molecularly imprinted polymers (MIPs) based on zeolite imidazolate framework-8 (ZIF-8) stabilized Pickering emulsions polymerization were successfully prepared for the selective identification and separation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solutions. Experimentally, ZIF-8 of particle size of about 100 nm was successfully synthesized, which can be used as a stabilizer in Pickering emulsion. And then, with 2,4-D as the template monomer, 4-vinylpyridine (4-VP) as the functional monomer, the hollow spherical polymer microspheres were formed via Pickering emulsions polymerization. At last, after the removal of ZIF-8 and template, MIPs were obtained, which were characterized by Fourier transmission infrared (FT-IR) spectrometry and scanning electron microscopy (SEM). Through experiments, the results showed that the adsorption capacity of MIPs and NIPs had a good correlation with Langmuir isothermal model and the kinetic adsorption of MIPs was well suitable for the pseudo-second order kinetic model. The maximum adsorption capacity of MIPs was 108.10 mg/g, while that of NIPs was 28.22 mg/g. The imprinting factor (IF) was about 3.83. And the optimal adsorption equilibrium time was 60 min. The selective and regeneration adsorption experiments showed that MIPs had a high specific selectivity and stability. Also, MIPs revealed good selectivity for 2,4-D in complex water samples. On the basis, it could be proved that ZIF-8 is an excellent alternate for the traditional stabilizers and sacrificial materials, providing a new idea for separation and analysis of harmful substances in water environment.

Preparation of Polyacrylate Hollow Microspheres via Facile Spray Drying

Polyacrylate microspheres with a hollow structure were prepared by a facile spray drying method. The effects of spray drying process parameters, including inlet temperature, atomizer rotational speed, and feed speed, on the particle size, bulk density, and morphology of the resultant polyacrylate hollow microspheres were investigated and discussed. The mechanism for the formation of the polyacrylate hollow microspheres was proposed. This facile and scalable method for preparing hollow polymer microspheres is expected to be valuable to prepare various polymer hollow structures for widespread application.

Heterophase polymer dispersion: A green approach to the synthesis of functional hollow polymer microparticles

Hollow nanostructured polymer microspheres have various potential applications; however, the development of a facile method to synthesize such particles has proved challenging. In the current work, an easy-to-use, green and low-cost method adopting a heterophase polymer dispersion strategy was developed to produce monodisperse hollow microparticles with well-defined nanostructures. When polystyrene (PS) seed microparticles prepared using modified dispersion polymerization were dispersed in an ethanol-water mixture at 70 °C, they transformed into hollow PS microparticles as a result of uptake of the continuous phase by the particles. Via consecutive heterophase polymer dispersion processes involving the addition of metal precursors, hollow PS microparticles covered with bimetallic nanocrystals were obtained. That is, metal nanocrystals were produced in situ from metal precursors on the polymer particles. Based on our results and observations, we propose plausible mechanisms for the formation of these hollow microparticles. The hollow PS microparticles covered with bimetallic nanocrystals exhibited high catalytic activity at a low concentration and excellent reusability when used as catalysts for the reduction of 4-nitrophenol to 4-aminophenol using sodium borohydride as the reducing agent.

Effects of shell composition, dosage and alkali type on the morphology of polymer hollow microspheres

Polymer hollow microspheres were prepared by performing alkali treatment on the multilayer core/shell polymer latex particles containing carboxyl groups. Effects of the shell composition and dosage as well as alkali type on the morphology of the microspheres were investigated. Results showed that in comparison with acrylonitrile (AN) and methacrylic acid (MAA), using butyl acrylate (BA) as the shell co-monomer decreased the glass transition temperature (T g) of shell effectively and was beneficial to the formation of uniform and big hollow structure. Along with the increase of the shell dosage, the alkali-treated microspheres sequentially presented porous and hollow morphology, and the size of microspheres increased, while the hollow diameter increased first and then decreased, and the maximum hollow ratio reached 39.5%. Furthermore, the multilayer core/shell microspheres had better tolerance to NH3·H2O than to NaOH. When the molar ratio of alkali to methacrylic acid (MRalkali/acid) for NaOH ranged from 1.15 to 1.30 or MRalkali/acid for NH3·H2O ranged from 1.30 to 2.00, the regular polymer hollow microspheres could be obtained.

Microstructure Evolution of Copper-Doped Tungsten Coatings for Inertial Confinement Fusion Application

High-Z (Z is an atomic number) metals are often deposited on hollow glass or polymer microspheres to improve the implosion efficiency of targets in inertial confinement fusion experiments. Smooth and crack-free thick tungsten coatings on glow discharge polymer shells have been deposited via copper doping by direct-current magnetron sputtering. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and a white light interferometer were used to characterize the microstructure, composition, phase evolution, and surface roughness of tungsten coatings. The copper atoms with appropriate amounts were found to form a supersaturated solid solution with tungsten, which can serve to refine the grains of these coatings and to smooth their surface. Copper atoms in tungsten coatings were also found to stabilize the metastable β-phase W. This β-phase W is believed to play a key role in the evolution of the size and morphology of the grains of tungsten coatings. This may become a probable method to fabricate high-Z coated targets via doping.

Boron Carbide Hollow Microspheres Prepared by Polymer Derived Method

Polycarborane, as a kind of boron carbide polymeric precursor, was synthesized by hydroboration reaction with styrene, divinylbenzene as the carbon resource and borane as the boron resource in this work. The polymer precursor which had good solubility and film-forming ability was soluble in most organic solvents. Furthermore, polycarborane was used to fabricate hollow polymer microspheres by emulsion technique. The compact boron carbide ceramic hollow microspheres were prepared by ceramization of the polymer microspheres. Ceramic microspheres with diameters ranging from 1 to 1.5 mm and shell thicknesses from 15 to 30 μm were easily prepared by changing emulsion composition and curing conditions. Micrographs of SEM showed that the hollow microspheres had smooth surface and good sphericity. These boron carbide ceramic hollow microspheres are of significant importance for application in the field of neutron moderator in nuclear reactors, power generation in deep space flight, etc.

Heteroatom–doped hollow carbon microspheres based on amphiphilic supramolecular vesicles and highly crosslinked polyphosphazene for high performance supercapacitor electrode materials

Hybrid hollow polymeric microspheres (HPMSs) are synthesized by encapsulating the supramolecular vesicles with polyphosphazene through a rapid one-step polycondensation reaction. Subsequent carbonization treatments of the HPMSs lead to corresponding hollow carbon microspheres (HCMSs) with well-preserved geometry. The sizes of HPMSs and HCMSs are controlled by the vesicles, which is directly determined by the feeding ratio of the assembly units. Electrodes based on HCMSs showed a specific capacitance of 314.6F/g at a current density of 0.2A/g in 6M KOH electrolyte, 180.0F/g at a current density of 30A/g, and high stability of 98.2% of capacity retention after 2000 cycles. Both the high surface area and high heteroatoms level of HCMSs contribute to the excellent capacitive performance. Meanwhile, the hollow carbon structure ensured the satisfactory capacitive performance by increasing utilization efficiency of the surface area as well as achieving short diffusion paths for electrolyte ions.

Fabrication of polymeric–Laponite composite hollow microspheres via LBL assembly

Hollow structure microspheres with composite polymeric–Laponite shells were prepared by electrostatic self-assembly of Laponite on the polymeric hollow microspheres in this work. The multilayer hydrophilic core/hydrophobic shell polymer latex particles containing carboxyl groups inside were first synthesized via seeded emulsion polymerization, followed by alkali treatment, generating polymeric hollow microspheres. Then, polyethyleneimine (PEI) and Laponite were alternately electrostatic adsorbed on the prepared polymeric hollow microspheres to form polymeric–Laponite composite hollow microspheres. It was indicated that the morphology of alkali-treated microspheres could be tuned through simply altering the dosage of alkali used in the post-treatment process. Along with the increasing of the coating layers, the zeta potential of microspheres absorbed PEI or Laponite approximately tended to be constant respectively, and the thickness of Laponite layer around the hollow microspheres increased clearly, getting more uniform and homogenous. Furthermore, the corresponding polymeric–Laponite hollow microspheres showed high pressure resistance ability compared to the polymeric hollow microspheres.

Enhancing the properties of Candida antarctica lipase B by immobilization on precipitated silica modified with 3-aminopropyltriethoxysilane (APTES)

Hybrid hollow polymeric microspheres (HPMSs) are synthesized by encapsulating the supramolecular vesicles with polyphosphazene through a rapid one-step polycondensation reaction. Subsequent carbonization treatments of the HPMSs lead to corresponding hollow carbon microspheres (HCMSs) with well-preserved geometry. The sizes of HPMSs and HCMSs are controlled by the vesicles, which is directly determined by the feeding ratio of the assembly units. Electrodes based on HCMSs showed a specific capacitance of 314.6 F/g at a current density of 0.2 A/g in 6 M KOH electrolyte, 180.0 F/g at a current density of 30 A/g, and high stability of 98.2% of capacity retention after 2000 cycles. Both the high surface area and high heteroatoms level of HCMSs contribute to the excellent capacitive performance. Meanwhile, the hollow carbon structure ensured the satisfactory capacitive performance by increasing utilization efficiency of the surface area as well as achieving short diffusion paths for electrolyte ions.

Scalable preparation of hollow polymer and carbon microspheres by spray drying and their application in low-density syntactic foam

Monodispersed hollow polymer microspheres (HPMs) and hollow carbon microspheres (HCMs) are prepared by a low-cost and rapid spray-drying technique using resorcinol-formaldehyde as precursors. By spraying the precursor solution into a high-temperature chamber, micrometer-scale hollow structure can be immediately obtained. To achieve the required morphology, the factors of influencing the products morphology and purity are systematically optimized. The as-obtained HPMs have a low bulk density of 0.089 g/cm3, narrow particle size distribution of 15–80 μm with a mean size of 37 μm, a high floatation ratio of 96.3% and high mechanical strength. Followed by a simple carbonization, HCMs with a bulk density of ca. 0.1 g/cm3 and a mean size of 23 μm are achieved. This spray-drying strategy could drastically reduce their production times and costs, enabling continuous and scalable synthesis of hollow microspheres for practical use. As a proof-of-concept application, a series of syntactic foam consisting of HPMs and HCMs as fillers and phenolic resin as matrix are prepared via a hot-press molding. The resulting composite materials have low bulk densities but improved mechanical properties, which highlights the possibility for the manufacturing of light-weight materials using these kinds of hollow microspheres.

Surface modification of light hollow polymer microspheres and its application in external wall thermal insulation coatings

Purpose – The purpose of this paper is to modify light hollow polymer microsphere (LHPM) with titanium dioxide nanoparticles (nano-TiO2) to improve its compatibility with latex and apply the obtained nano-TiO2/LHPM composite particles in external wall thermal insulation coatings. Design/methodology/approach – The nano-TiO2/LHPM composite particles were prepared via vigorous stirring. The morphology and chemical composition of the produced nano-TiO2/LHPM composite particles were characterized using scanning electron microscopy, energy dispersion spectrum, thermo-gravimetric analyzer and Fourier transform infrared. The performance of this new composite coating was evaluated by checking its stability, density, radiation reflectivity, thermal conductivity and the resulting insulation temperature difference when forming coating film. Findings – It was found that a 9:1 mass ratio of nano-TiO2/LHPM with total 10 weight per cent composite particles in the thermal insulation paint showed low density, good stability, low thermal conductivity (0.1687 W/m·K) and high insulation temperature difference (5.8°C). Research limitations/implications – The LHPM can be modified by other nanoparticles to improve its insulation performance in thermal insulation coatings. Practical implications – This work provides a simple, robust, but effective approach to produce new thermal insulation coatings with nano-TiO2/LHPM composite particles. Originality/value – This method for surface modification of LHPMs is novel and the modified hollow polymer microspheres could be applied to external wall insulation coatings.

Hollow cobalt coordination polymer microspheres: A promising anode material for lithium-ion batteries with high performance

A simple and versatile method for preparation of hollow cobalt furandicarboxylate microspheres is developed via a solvothermal approach, which are tested as a new high-capacity anode material for lithium-ion batteries. It shows better cycling performance than non-hollow microspheres. A reversible capacity of 549.8mAhg−1 yielded after 95 cycles at a current density of 100mAg−1. While a reversible capacity of 513.4mAhg−1 was remained after 499 cycles at a current density of 1250mAg−1. Research on this topic mainly sheds some light on the discovery of new high energy density organic–inorganic hybrid materials prepared with a bio-based platform chemical.

Hollow Microspheres Fabricated from Aqueous Bubbles Stabilized with Latex Particles

Abstract Aqueous bubbles stabilized solely by micrometer-sized, near-monodisperse, sterically stabilized polystyrene (PS) latex particles can be transformed into polymeric hollow microspheres containing air by exposure to a solvent: the PS particles adsorbed at the air–water interface are plasticized with the solvent to form a polymer film on the surface of the aqueous bubbles.

Synthesis and characterization of B–C polymer hollow microspheres from a new organodecaborane preceramic polymer

A new poly(norbornenyldecaborane-co-hexadiene) (P(NB-co-DE)) copolymer as a kind of boron carbide preceramic polymer was synthesized by the ROMP reaction. And it was used to fabricate B–C polymer hollow microspheres by microencapsulation.