Pickering Emulsion Polymerization Research Articles

Pickering emulsion fabrication and enhanced supercapacity of graphene oxide-covered polyaniline nanoparticles

Polyaniline/graphene oxide (PANI/GO) composites in a novel structure consisting of PANI nanoparticles covered by GO nanosheets are synthesized by means of Pickering emulsion polymerization for the first time. The Fourier transform infrared (FTIR) spectra indicate the main combination mode of the PANI/GO composite includes hydrogen bonding and π–π interactions between PANI and GO. The TGA and SEM results indicate the PANI/GO composite has better morphology stability than that of pure PANI. And thus the specific capacitance and cycling stability of the PANI/GO composite have been remarkably enhanced. The improved electrochemical performance may be attributed to the GO sheets not only improve the stability of the PANI nanoparticles, but also increase electronic conductivity and reduce electrical charge transfer resistance of the PANI/GO electrode.

Pickering emulsion polymerization of core–shell-structured polyaniline@SiO2 nanoparticles and their electrorheological response

We synthesized semiconducting polyaniline (PANI) nanoparticles through a solid-stabilized Pickering emulsion route using silica nanoparticles. Specific morphologies of the silica nanoparticle wrapped PANI particles were observed using both scanning electron microscope and transmission electron microscope, which showed the emulsifiability of silica nanoparticles in the emulsion system. Electrorheological (ER) behavior of this novel particle-based ER fluid dispersed in silicone oil was measured by a controlled shear stress rheometer and analyzed with a flow curve equation of Cho-Choi-Jhon model, which fitted well the flow curves measured in the exposed electric field.

Conductive composite particles synthesized via pickering emulsion polymerization using conductive latex of poly(3,4-ethylenedioxythiophene) (PEDOT) as stabilizer

In this research, poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles less than 100 nm were synthesized first and applied as the solid stabilizer for producing PEDOT-polystyrene (PEDOT-PSt) composite latex by Pickering emulsion polymerization. The results showed that most PEDOT nanoparticles adhered to the PSt core particles having the size from 100 to 250 nm. By casting the latex, the obtained PEDOT-PSt film had a surface resistance of 4–5 kΩ/□, almost the same as the pure PEDOT film, though its PEDOT content was only 6.2 wt%. Those PEDOT nanoparticles in the outer layer could contact with one another, forming a continuous network as the conductive passageway. Furthermore, soft latex particles of poly(styrene-co-butyl acrylate), P(St-BA), were synthesized and mixed with the conducting rigid PEDOT-PSt latex for improving the toughness and transparency of the casting film. A critical point at about 2 wt% of PEDOT content in the PEDOT-PSt/P(St-BA) film was observed in the surface resistance measurement.

Polystyrene/nano-SiO2 composite microspheres fabricated by Pickering emulsion polymerization: Preparation, mechanisms and thermal properties

We report the preparation, mechanisms and thermal properties of core-shell structured polymer/inorganic nanoparticle composite microspheres prepared by Pickering emulsion polymerization. Stable Pickering emulsion was firstly fabricated by using surface-modified nano-SiO2 particles as stabilizer. And then, two kinds of polystyrene/nano-SiO2 (PS/SiO2) composite microspheres with different sizes and morphologies were synthesized using hydrophobic azobisisobu- tyronitrile (AIBN) and hydrophilic ammonium persulfate (APS) as initiator, respectively. The possible mechanisms of Pickering emulsion polymerization initiated by different initiators were proposed according to the results of transmission electron microscope (TEM) and scanning electron microscope (SEM). The chemical structure and molecular weight of the composite microspheres were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and gel permeation chromatography coupled with a multi-angle laser light scattering photometer (GPC-MALLS). Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) were used to comparatively analyze the thermal properties of nanocomposites and corresponding pure polymer. The results indicated that the decomposition tem- perature and glass transition temperature (Tg) of nanocomposites were elevated to a certain degree due to the existence of nano-SiO2.

Molecular imprinting of protein in Pickering emulsion

A new strategy of molecular imprinting to prepare spherical hydrogels via water-in-oil Pickering emulsion polymerization was developed. The imprinted hydrogels exhibited fast adsorption kinetics and significant selectivity for the target protein.

Preparation of Polymer Microspheres Using Silane Coupling Agent Modified Nano-SiO<sub>2</sub> as Single Stabilizer

This paper demonstrates that silica nanoparticles were modified by the four silane coupling agents (KH-151, KH-550, KH-560, KH-570) firstly, then polystyrene/silica (PS/SiO2) composite microsphere with PS core and silica nanoparticles shell were prepared by Pickering emulsion polymerization. The characterization of optical microscope (OM), scanning electron microscope (SEM), and thermogravimetic analysis ( TGA) illustrates that these microsphere are composed of PS and silica nanoparticles. Silica nanoparticles modified by the different silane coupling agents could form the stable PS/SiO2 microsphere over 70 °C, while the unmodified silica nanoparticles are difficult to form stable PS/SiO2 microspheres at the same temperature. The PS/KH-151-SiO2 microsphere exhibits the least average particle size, while the PS/KH-570-SiO2 microsphere produces the largest. Both SEM and TGA confirm that microsphere surface exists solid nanoparticles.

Pickering Emulsion Polymerization Using Laponite Clay as Stabilizer To Prepare Armored “Soft” Polymer Latexes

The fabrication of “soft” nanocomposite clay armored polymer latexes is described. Laponite clay XLS is used as stabilizer in the Pickering emulsion polymerization of a variety of monomer mixtures, that is, methyl methacrylate and n-butyl acrylate, styrene and n-butyl acrylate, and styrene and 2-ethylhexyl acrylate. Overall solids contents of the hybrid latexes in complete absence of coagulation of up to 24 wt % are reported under batch conditions. Key mechanistic aspects of the Pickering emulsion polymerization process are discussed. The use of monomers that have high water solubility and are prone to hydrolyze under basic conditions, for example methyl methacrylate, should be restricted. The use of small amounts of methacrylic acid as auxiliary monomer promotes clay adhesion to the surface of the particles in the Pickering emulsion (co)polymerization of hydrophobic monomers. Detailed kinetic studies at both 60 and 80 °C of the Pickering emulsion copolymerization of styrene and n-butyl acrylate (Sty:BA = 0.67 w/w) are reported, with varying amounts of Pickering stabilizer. The Laponite clay discs play a crucial role in the particle formation (nucleation) stage of the Pickering emulsion polymerization process. Use of increasing amounts leads to smaller average particle sizes but inflicts longer nucleation periods, thereby broadening the particle size distributions. We report the occurrence of a catastrophic coagulation phenomenon for Pickering emulsion polymerizations carried out at a low initiator (ammonium persulfate) flux at 60 °C, for a small window of concentrations of Laponite clay discs.

Interfacial Molecular Imprinting in Nanoparticle-Stabilized Emulsions

A new interfacial nano and molecular imprinting approach is developed to prepare spherical molecularly imprinted polymers with well-controlled hierarchical structures. This method is based on Pickering emulsion polymerization using template-modified colloidal particles. The interfacial imprinting is carried out in particle-stabilized oil-in-water emulsions, where the molecular template is presented on the surface of silica nanoparticles during the polymerization of the monomer phase. After polymerization, the template-modified silica nanoparticles are removed from the new spherical particles to leave tiny indentations decorated with molecularly imprinted sites. The imprinted microspheres prepared using the new interfacial nano and molecular imprinting have very interesting features: a well-controlled hierarchical structure composed of large pores decorated with easily accessible molecular binding sites, group selectivity toward a series of chemicals having a common structural moiety (epitopes), and a hydrophilic surface that enables the MIPs to be used under aqueous conditions.

Preparation of novel suspensions of ZnO/living block copolymer latex nanoparticles via pickering emulsion polymerization and their long term stability

In this work, we present the first Pickering emulsion polymerization with a controlled/living character. Pickering emulsion polymerization in the presence of a novel suspension of zinc oxide/poly(sodium 4-styrenesulfonate) (ZnO/PSS−) nanocomposite particles was applied to prepare ZnO/living block copolymer latexes. In the emulsion system, 1,1-diphenylethene (DPE)-controlled radical polymerization of poly(methyl methacrylate)-b-poly(butyl acrylate) (PMMA-b-PBA) was proceeded in oil phase. The nanocomposite particles of ZnO/PSS− with an average diameter of 20 nm and negatively charged zeta potential around −30 mV were synthesized via hydrothermal method then served as an effective emulsion stabilizer at the oil/water interface. Living polymerization was carried out using DPE-capped PMMA as the macroinitiator and PMMA-b-PBA block copolymer latex was successfully prepared with coverage of ZnO/PSS− nanoparticles. Narrow size distributions of the droplets as well as latex particles were obtained, and the livingness of block copolymers was comparable to that of emulsions stabilized by conventional surfactants. The controlled/living character in Pickering emulsion polymerization was slightly influenced by the amount of PSS− immobilized into the ZnO/PSS− nanoparticles, whereas it was significantly influenced by the weight ratios between ZnO/PSS− and oil phase. The Pickering latexes showed excellent long term stability against either coalescence or sedimentation over several months. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Slightly surface-functionalized polystyrene microspheres prepared via Pickering emulsion polymerization using for electrophoretic displays

Slightly surface-functionalized polystyrene (PS) microspheres are prepared by photocatalytic Pickering emulsion polymerization using sodium styrene sulfonate (SSS)-modified titania hydrosol as a stabilizer. Aqueous electrophoresis measurements indicate the adsorption of bifunctional SSS anions on the surface of titania nanoparticles via electrostatic interaction. SSS molecules participate in the copolymerization with the monomers before the nucleation and thus have a great effect on the morphology and surface structure of the obtained PS microspheres. Appropriate SSS concentration leads to PS microspheres with small size, narrow distribution, and uniform surface chemistry. This kind of polymer particles can be used as a good candidate for the electrophoretic displays because of their high colloidal stability and electrophoretic mobility in the apolar solvent.

Synthesis of temperature-responsive hybrid capsules and their controlled release property

In this work, a temperature-responsive hybrid capsules (TRHCs) was prepared from inverse pickering emulsion polymerization route. The aqueous solution of N-isopropyl acrylamide and poly (N-isopropyl acrylamide) was emulsified into an oil phase containing divinyl benzene (DVB) by sonication to obtain a water-in-oil (W/O) pickering emulsion stabilized by modified silica nanoparticles. Then the emulsion was polymerized to obtain the hybrid capsules. The sizes of the capsules are about 5–10 μm and can be tuned by the modified silica nanoparticles concentration in continuous phase. The capsules wall consists of two layers: a solid particle layer and a polymer layer, whose thickness can be conveniently controlled by adjusting the DVB concentrations in the continuous phase before polymerization. The as-synthesized capsules exhibit good temperature-responsive property with a phase-transition temperature of 27 °C. The controlled release experiment shows that the release rate of a model drug (Rhodamine B) from the hybrid capsules can be controlled by adjusting the temperature of the release medium. When the medium temperatures were 25 °C and 45 °C, the released percents of Rhodamine B from TRHCs within 35 h were 25.7% and 70.9%, respectively.

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

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

Self assembly of graphene oxide at the liquid–liquid interface: A new route to the fabrication of graphene based composites

Dispersion of graphene in a polymer matrix as mono layers is an important step towards fabricating high performance polymer–graphene nanocomposites. In this paper, a novel method based on Pickering emulsion polymerization has been introduced that assures fine dispersion and enhances loading. The major idea is to use a high affinity of graphene oxide (GO) for assembly at the liquid–liquid interface for Pickering emulsion polymerization. A guideline for ensuring stable hybrid colloids of polymer–graphene oxide with an appropriate polymer particle size has been introduced. Then a system of poly (methyl methacrylate) (PMMA)–GO has been selected and the nanocomposites have been made by Pickering emulsion polymerization to examine the theory. TEM studies of the products show various interesting arrangements of PMMA and GO for a different size ratio of nanolayers to polymer particles. The new method paves the way for an environmentally benign process for the production of high quality polymer graphene nanocomposites as it is water-based (no organic solvent is employed) and soap free. Furthermore, resulting hybrid particles were melt mixed with PMMA as a master batch. The resulting nanocomposites with 0.3 wt% graphene showed improved thermal stability and stiffness.

Thermo-Responsive Core-Shell Composite Nanoparticles Synthesized via One-Step Pickering Emulsion Polymerization for Controlled Drug Delivery

Purpose: The focus of this work is to develop a unique drug delivery vehicle which can be taken up by cancer cells and can release the loaded drug. Methods: Core-shell composite nanoparticles have been prepared by one-step Pickering emulsion polymerization with a nonionic initiator, using silica as the sole stabilizer. More importantly, the Pickering emulsion polymerization is applied to synthesize polystyrene/poly(N-isopropylacrylamide) (PNIPAAm)-silica core-shell nanoparticles with N-isopropylacrylamide incorporated into the core as a co-monomer. Results: The composite nanoparticles are temperature sensitive and can be taken up by human prostate cancer (PC3 and PC3-PSMA) cells. An anticancer agent 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) has been loaded into the polymeric cores during formation of the nanoparticles and drug release has been successfully observed at elevated temperatures. The ability of the various nanoparticles for inducing death in human prostate cancer cells has been evaluated. Conclusion: The work has demonstrated the temperature sensitivity, controlled drug release properties of the synthesized core-shell nanoparticles, and their effectiveness for inducing death of human prostate cancer cells.

Molecular imprinting in Pickering emulsions: a new insight into molecular recognition in water

Molecularly imprinted polymer microspheres were synthesized by Pickering emulsion polymerization. Fluorescence spectroscopic investigations provided insights into the template recognition in water.

PS Colloidal Particles Stabilized by Graphene Oxide

Exfoliated graphene oxide (GO) sheets with hydrophilic functional groups on the surface were prepared by the oxidation of graphite. Because of the hydrophilic groups on the sheets and the hydrophobic carbon surface, GO sheets were located at the oil-water interface and could be used as a stabilizer in Pickering emulsions. After the Pickering emulsion polymerization of styrene, PS colloidal particles with GO sheets on the surface were prepared. The size of the GO sheets exerts an important influence on the preparation of PS colloidal particles. Small GO sheets located at the liquid-liquid interface and GO-stabilized PS colloidal particles were prepared; however, for large GO sheets, smaller PS colloidal particles prepared on the GO surface were observed. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the colloidal particles. TEM, SEM, and XPS results all suggest the successful preparation of GO-stabilized PS colloidal particles.

Fabrication of Two Kinds of Polymer Microspheres Stabilized by Modified Titania during Pickering Emulsion Polymerization

AbstractTwo kinds of PS microspheres with different structures are prepared in one reaction system via Pickering emulsion polymerization. As the stabilizer, titania nanoparticles are modified by oleic acid or sodium oleate and then investigated using aqueous electrophoresis measurements, DLS and oil/water partitioning experiments. The morphology of the resulting polymer microspheres is characterized using TEM and FE‐SEM. It is proven that the surface structure of the titania nanoparticles determines the polymerization routes it adopts and affects the morphology of the final polymer microspheres. magnified image

Synthesis of microcapsules with polystyrene/ZnO hybrid shell by Pickering emulsion polymerization

Polystyrene/zinc oxide (ZnO) hybrid microcapsules having polystyrene as inner shell and ZnO nanoparticles as outer shell were synthesized by Pickering emulsion polymerization method. ZnO nanoparticles were used to form the colloidosomes that worked as the polymerization vessels, where both styrene monomer and crosslink agent were polymerized together. Fourier transform infrared spectra and thermogravimetric thermograms showed the existence of ZnO and polystyrene in the shell of hybrid microcapsules. The hollow structure and the different morphology under various conditions were also observed by field emission scanning electron microscopy. In addition, the shell thickness of hybrid microcapsules increased as the monomer concentration increased. The photoluminescence property of PS/ZnO hybrid microcapsules could be maintained without any noticeable variation by comparing with the pure ZnO particles. It could be reasonably deduced that hybrid hollow microspheres with multifarious polymer as inner shell and ZnO nanoparticles as outer shell would be produced for many applications.

Effect of particle coverage on morphology of SiO 2-covered polymer microspheres by Pickering emulsion polymerization

Pickering emulsion polymerization is of particular interest as a simple one-step method to prepare inorganic-covered microspheres. In this article, droplets with different particle coverages of <100%, ≈100% and 100% were prepared by variety of particle amounts, and subsequently, were employed as templates to fabricate hybrid microspheres. Especially, effect of particle coverage on nuclei mechanism and morphology of products was investigated. The results showed that particle-formed film with high coverage suppressed the transport of monomers and radicals across the film, and subsequently, inhabited the polymerization in the continuous phase. Also the results indicated that this inhibiting effect was a crucial factor to the morphology of products. By increasing SiO 2 amount to prepare emulsion droplets with high coverage and/or employing inhibitor in continuous phase, dispersive microspheres can be prepared.

Investigation of internal microstructure and thermo-responsive properties of composite PNIPAM/silica microcapsules

Composite microcapsules consisting of a thermo-responsive hydrogel poly- N-isopropylacrylamide (PNIPAM) and coated by silica (SiO 2) nanoparticles have been synthesized by the inverse Pickering emulsion polymerization method. The composite capsules, whose mean diameter is in the 25–86 μm range in the expanded state, were characterized by static light scattering, atomic force microscopy (AFM), scanning electron microscopy (SEM), and laser scanning confocal microscopy (LSCM). It is reported that the hydrogel surface is uniformly covered by a monolayer of silica nanoparticles and that depending on the capsule size and degree of polymer cross-linking, either hollow-core or partially-filled hydrogel-core microcapsules can be created. Equilibrium thermo-responsive behavior of the composite microcapsules is investigated and it is found that after heating the particles above the lower critical solution temperature (LCST) of PNIPAM, the shrinkage ratio V/ V max varies from 0.8 to 0.4 for a cross-linking ratio from 0.6% to 9% on a mass basis. Dynamic temperature cycling studies reveal no hysteresis in the shrinking and recovery phases, but a small measurable dependence of the asymptotic shrinkage ratio V/ V max on the rate of temperature change exists. The composite capsules are stable under long-term storage in both dried and hydrated states and easily re-dispersible in water.