Pickering Miniemulsion Research Articles

Durable and rechargeable antimicrobial cotton driven by enhanced UV stability and real-time detection of biocidal factors

In this study, graphene oxide/N-halamine nanocomposite was synthesized through Pickering miniemulsion polymerization, which was then coated on cotton surface. The modified cotton exhibited excellent superhydrophobicity, which could effectively prevent microbial infestation and reduce the probability of hydrolysis of active chlorine, with virtually no active chlorine released in water after 72 h. Deposition of reduced graphene oxide nanosheets endowed cotton with ultraviolet-blocking properties, attributing to enhanced UV adsorption and long UV paths. Moreover, encapsulation of polymeric N-halamine resulted in improved UV stability, thus extending the life of N-halamine-based agents. After 24 h of irradiation, 85 % of original biocidal component (active chlorine content) was retained, and approximately 97 % of initial chlorine could be regenerated. Modified cotton has been proven to be an effective oxidizing material against organic pollutants and a potential antimicrobial substance. Inoculated bacteria were completely killed after 1 and 10 min of contact time, respectively. An innovative and simple scheme for determination of active chlorine content was also devised, and real-time inspection of bactericidal activity could be achieved to assure antimicrobial sustainability. Moreover, this method could be utilized to evaluate hazard classification of microbial contamination in different locations, thus broadening the application scope of N-halamine-based cotton fabrics.

Synthesis of electrically conducting nanocomposites via Pickering miniemulsion polymerization: Effect of graphene oxide functionalized with different capping agents

Modification of graphene oxide (GO) sheets with various capping agents has been explored within the context of miniemulsion polymerization as a synthetic route towards ambient temperature film forming latexes for fabrication of electrically conducting films after thermal reduction to generate reduced GO. Miniemulsion polymerizations of styrene/n-butyl acrylate were conducted in the presence of non-modified GO as well as GO functionalized with poly(methyl methacrylate) (GO-PMMA), poly(di(ethylene glycol) ethyl ether acrylate) (GO-PDEGA), and carboxylic acid groups (GO-COOH). Colloidal instability was encountered for GO-PMMA and GO-PDEGA, but stable latexes and nanocomposite films were successfully obtained using GO and GO-COOH. Electrical conductivities in the approximate range of 0.1–4 S m−1 were obtained, with GO-COOH giving slightly lower values than GO, and the presence of sodium dodecyl sulfate (SDS) resulting in increasing conductivity values for both GO and GO-COOH.

Starch nanoparticles as Pickering emulsifiers in miniemulsion polymerization of styrene

AbstractPickering miniemulsion polymerizations of styrene using octenyl succinic anhydride (OSA) and dodecenyl succinic anhydride (DSA) modified starch nanoparticles (SNP) (~20–25 nm) were conducted. The effect of different degrees of substitution (DS), alkyl chain length, concentration of Pickering emulsifier (PE), and pH was correlated to the shelf‐life stability of the styrene Pickering miniemulsions and the particle size distribution (PSD). Interfacial tension values of aqueous dispersions of SNP‐OSA (DS = 0.11) and SNP‐DSA (DS = 0.14) against toluene as low as 14.7 and 11.0 mN/m, respectively, were observed. Average styrene droplet diameters in the miniemulsions (DV(sty)) ranged between 100–600 nm. 2,2′‐Azobisisobutyronitrile (AIBN) and lauroyl peroxide (LPO) were employed as initiators and the effect of the water solubility on the resulting PSD and latex stability was investigated. The resulting polystyrene (PS) latex particles ranged between 70 and 550 nm in diameter. When AIBN was used as initiator, secondary nucleation was observed. The rate of polymerization and conversion of SNP‐OSA and SNP‐DSA stabilized Pickering miniemulsion polymerizations were compared. The SNP‐armoured PS particles were visualized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At low conversions (<40%), the resulting latexes were relatively uniform when modified SNP were used as PE along with small amounts of hexadecane as a hydrophobe. At higher conversion, however, coagulation occurred which was correlated to a side reaction in which the PS particles grafted together to form large coagulates.

Nanospheres self-assembled by hybrid oxide nanocrystal and their photoelectric properties

The hybrid nanocrystals of zinc oxide (ZnO), cadmium oxide (CdO) and copper oxide (CuO) were self-assembled to the nanospheres with special structure in the process of inverse Pickering miniemulsion. The 3-(methacryloxy) propyltrimethoxysilane (MPS) was used to modify the crystalline nanoparticles to obtain the partial hydrophobicity on their surfaces. The influences of the dosage ratio of MPS to the crystalline nanoparticles on the size distribution and surface hydrophobicity of modified nanoparticles were discussed. The modified ZnO, CdO and CuO nanocrystals as solid emulsifiers were self-assembled into four kind structure of nanospheres by inverse Pickering miniemulsion. The dosage usage, the three-phase contact angle and their initial dispersion positions of the modified nanocrystals codetermined the structure of hybrid oxide nanocrystals. The nanospheres of hybrid oxide nanocrystal will be successfully prepared by inverse Pickering miniemulsion; they provide the distinctively photoelectric properties.

ZnO@PNIPAM nanospheres synthesis from inverse Pickering miniemulsion polymerization

Zinc oxide (ZnO) @ poly (N-isopropyl acrylamide (NIPAM)) (PNIPAM) nanospheres, which the modified ZnO nanoparticles had attached on the interface-layer of PNIPAM, were a special structure material prepared by inverse Pickering miniemulsion polymerization. The original ZnO nanoparticles were synthesized by the sol-gel method and then their surfaces were modified to be partly hydrophobic. The NIPAM inverse Pickering miniemulsion was polymerized to form ZnO@PNIPAM nanospheres, using the modified ZnO nanoparticles as a solid surfactant. The influences of the dosage ratios of modifier to original ZnO nanoparticles on size, distribution and surface hydrophobicity of the modified ZnO nanoparticles were discussed. The self-assembly mechanism of the modified ZnO nanoparticles on the oil/water interface was suggested. The effect of dosage and size of the modified ZnO nanoparticles on miniemulsion stability and polymerization was researched. The nanospheres with the specific ZnO@PNIPAM structure and good dispersibility could be successfully prepared by the inverse Pickering miniemulsion method. The extracted ZnO@PNIPAM nanospheres simultaneously exhibited strong ultraviolet-visible absorption characteristics and luminescence intensity.

Preparation of superparamagnetic γ-Fe2O3@LS@PS composite latex particles through pickering miniemulsion polymerization

Based on the electrostatic interaction, prepared γ-Fe2O3 nanoparticles with high positive charges (+ 45 mv) were modified by negative charged ligninsulfonate (LS, - 34 mv) to synthensize LS/γ-Fe2O3 composite. LS is low-price, environmentally friendly and renewable biomacromolecule. The LS/γ-Fe2O3 composite were applied in a Pickering miniemulsion polymerization as the only stabilizer, without any auxiliary comonomers and surfactants. The surface anchored γ-Fe2O3 induced the formation of strawberry-like hybrid latex particles who were endowed with superparamagnetic functional properties. Furthermore, the effect of the ratios of LS to γ-Fe2O3 on the stability of the LS/γ-Fe2O3 composites was investigated. The content of γ-Fe2O3 in the LS/γ-Fe2O3 composites should be lower than 66.7 wt%, or the stability of the Pickering miniemulsion polymerization would be destroyed, owing to the charge neutralization behavior of the LS and γ-Fe2O3. Within this range, the latex particle size increased with the increasing of γ-Fe2O3 content.

Quantum dot encapsulated nanocolloidal bioconjugates function as bioprobes for in vitro intracellular imaging

Bioimaging probes incorporating quantum dots (QDs) are important for identifying organelles and monitoring their movement/location in living cells. Organelle specificity can be accomplished by functionalizing probe surfaces with chemical groups that can react with antibodies capable of targeting specific organelle-protein epitopes. Here, such a bioprobe is generated by encapsulating ZnS-capped CdSe QDs within polystyrene (PS) nanocolloids via Pickering miniemulsion using laponite nanoclay platelets as solid-stabilizers. The surfaces of these platelets are modified with aminopropyltriethoxysilane (APTES), and biotinylated by reacting sulfo-NHS-Biotin via the APTES amine group. Surface functionalization and bioconjugation are confirmed using X-ray photoelectron spectroscopy. The number of sites available on Streptavidin for Biotin binding is determined using a competitive HABA assay to optimize the bioconjugation protocol. The PS-encapsulated QDs (PS-QDs) nanocolloids are 50–200 nm in diameter and colloidally stable, as evidenced by transmission electron microscopy and ζ-potential measurements, respectively. Spherical particle shape is confirmed by scanning electron microscopy. Transmission electron microscopy also showed the nanoclay platelets on the surface of QD-encapsulating latex particles. The PS-QDs particles are easily dispersed in water and exhibit long-term photostability over various conditions. Cell viability of >95% is observed for NIH-3T3 cells after 72-h exposure to PS-QDs nanocolloids, with no cytotoxicity to living cells, even at 0.1 mg mL−1. NIH-3T3 cellular uptake and internalization are confirmed by confocal microscopy, with PS-QDs fluorescence within cells remaining high even after 24-h exposure, demonstrating the applicability of PS-QDs nanocolloids as long-lived fluorescent bioprobes for in vitro intracellular imaging.

Nanoclay stabilized Pickering miniemulsion of fluorinated copolymer with improved hydrophobicity via RAFT polymerization

Fluoropolymer/clay nanocomposite with improved polymer–clay interaction via electrostatic attraction was prepared by Pickering miniemulsion polymerization.

Tailor-Made Fluorinated Copolymer/Clay Nanocomposite by Cationic RAFT Assisted Pickering Miniemulsion Polymerization

Fluorinated polymers in emulsion find enormous applications in hydrophobic surface coating. Currently, lots of efforts are being made to develop specialty polymer emulsions which are free from surfactants. This investigation reports the preparation of a fluorinated copolymer via Pickering miniemulsion polymerization. In this case, 2,2,3,3,3-pentafluoropropyl acrylate (PFPA), methyl methacrylate (MMA), and n-butyl acrylate (nBA) were copolymerized in miniemulsion using Laponite-RDS as the stabilizer. The copolymerization was carried out via reversible addition-fragmentation chain transfer (RAFT) process. Here, a cationic RAFT agent, S-1-dodecyl-S'-(methylbenzyltriethylammonium bromide) trithiocarbonate (DMTTC), was used to promote polymer-Laponite interaction by means of ionic attraction. The polymerization was much faster when Laponite content was 30 wt % or above with 1.2 wt % RAFT agent. The stability of the miniemulsion in terms of zeta potential was found to be dependent on the amount of both Laponite and RAFT agent. The miniemulsion had particle sizes in the range of 200-300 nm. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses showed the formation of Laponite armored spherical copolymer particles. The fluorinated copolymer films had improved surface properties because of polymer-Laponite interaction.

Photoactive self-cleaning polymer coatings by TiO2 nanoparticle Pickering miniemulsion polymerization

Titanium dioxide Pickering stabilized methyl methacrylate/n-butyl acrylate (MMA/BA) copolymer latexes were synthesized by miniemulsion polymerization. The particle size of the hybrid latexes was controlled by the concentration of TiO2 used as stabilizer; the larger the concentration, the smaller the particle size. The hybrid latexes formed coherent films with honey comb structures, the opacity of the films increased with the amount of TiO2. The photocatalytic activity of the hybrid films was assessed by coating concrete specimens and analyzing the capabilities to degrade Rhodamine B under UV-light exposure. The films showed excellent self-cleaning activity and it was found that the photocatalytic activity index was little affected by the concentration of TiO2 and the roughness of the film. The kinetic of the photocatalytic reaction was controlled by the diffusion of the Rhodamine B from the inner of the film to the interface.

Factors influencing the preparation of hollow polymer-graphene oxide microcapsules via Pickering miniemulsion polymerization

The synthesis of hollow, cross-linked polymer particles (‘capsules’) via Pickering miniemulsion polymerization using graphene oxide (GO) nanosheets as sole surfactant is reported. The influence of monomer, cross-linker and initiator type was studied, in addition to hydrophobe loading and initiator concentration. The desired hollow capsule morphology was shown to be strongly dependent on the choice of cross-linker; an aromatic crosslinker (divinylbenzene) consistently yielded hollow structures as determined by transmission electron microscopy, whereas ethylene glycol dimethacrylate typically resulted in polymer particles with a solid core. The use of an aromatic monomer with high propagation rate coefficient (benzyl methacrylate) and a strongly oil-soluble initiator, lauroyl peroxide, resulted in capsule synthesis with very high conversion (>85%) after 6 h. Surface area and pore analysis of the capsules established that while the capsules possessed a hollow interior, the shell was essentially non-porous. The potential of these materials towards novel nanocarbon-based materials was demonstrated via the preservation of colloidal stability and particle morphology after chemical reduction of GO, in addition to successful encapsulation of hydrophobic nanoparticles within the capsule core.

Facile fabrication of poly(acrylic acid) hollow nanogels via in situ Pickering miniemulsion polymerization

We report herein a facile and large fabrication of PAA hollow nanogels via an in situ Pickering miniemulsion polymerization method by using a hydrophobic solvent as the liquid core.

Surface Modification of Clay and Use as Stabilizer in Miniemulsion Polymerization

AbstractPoly(styrene‐co‐butyl acrylate) latexes were successfully synthesized via Pickering miniemulsion polymerization, using modified Montmorillonite clay as the exclusive stabilizer. The latexes were stable to relatively high concentration of electrolyte due to the presence of the clay at the interface, providing both a physical barrier and electrostatic stabilization. Film formation could be done at room temperature, but the barrier properties to water and oil were poor. This was attributed to compartmentalization of the film, where the morphology of the latex particles was retained.

Synthesis and characterization of positively charged, alumina‐coated silica/polystyrene hybrid nanoparticles via pickering miniemulsion polymerization

AbstractPositively charged, raspberry‐like hybrid nanoparticles, consisting of a polystyrene core and an alumina‐coated silica shell were successfully prepared in a surfactant free system via the radical copolymerization of styrene (St) and different comonomers (acrylic acid, methacrylic acid, and acrylamide) by using a cationic silica sol as the sole emulsifier in Pickering miniemulsion polymerization. The influence of different parameters like pH of the dispersion, comonomer content, and the amount and size of silica nanoparticles on the colloidal stability of the systems, prepared with different comonomers, was examined. The particles' morphology was observed via high‐resolution scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The removal of free silica particles via centrifugation was proved by TEM and SEM, and the content of free and adsorbed silica was quantified via thermogravimetric analysis (TGA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis of raspberry‐like organic–inorganic hybrid nanocapsules via pickering miniemulsion polymerization: Colloidal stability and morphology

AbstractRaspberry‐like hybrid nanocapsules with a hydrophobic liquid core were successfully prepared via the copolymerization of styrene, divinylbenzene (DVB), and 4‐vinyl pyridine (4‐VP) in Pickering‐stabilized miniemulsions by using silica particles as the sole emulsifier and hexadecane (HD) as liquid template. When compared with conventional Pickering miniemulsions and Pickering suspensions, the colloidal stability of the current systems is much more sensitive to the variation of reaction parameters such as pH, size, amount of silica particles, and content of 4‐VP. The systems without coagulum were only obtained in a narrow pH range at around 9.5 and by using 12 nm silica particles as emulsifier. The formation of well‐defined raspberry‐like capsules was confirmed by transmission electron microscopy (TEM) and high‐resolution scanning electron microscopy (HRSEM). The stable attachment of silica particles on the surface of hybrid particles was verified by centrifugation and subsequent characterizations, such as Fourier transform infrared spectroscopy, TEM, and HRSEM. The influence of pH and weight content of HD, DVB, and 4‐VP on the particle morphology was extensively investigated. Interestingly, the particle morphology strongly depends on the particle size. When compared with the organic surface‐active surfactant, the formation of capsule morphology could be promoted by the application of silica particles taking advantage of their surface inactivity. The formation mechanisms of capsules/solid particles are discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Pickering Emulsion as a Template to Synthesize Janus Colloids with Anisotropy in the Surface Potential

A versatile new concept is presented for the synthesis of Janus colloids composed of Laponite nanoclay armored poly(divinylbenzene) with an anisotropic surface potential via a double Pickering emulsion template. First, polystyrene or poly(divinylbenzene) colloids stabilized with Laponite nanoclay are synthesized via a Pickering miniemulsion approach. These nanoparticle-stabilized colloids were then templated at a wax-water interface in a second Pickering emulsion in order to chemically modify one hemisphere of the colloids. Janus modification of the colloids was accomplished by cation exchange of sodium ions, originally present on the surface of the Laponite with various salts of modifying ions (Ca(2+), Fe(2+), and Fe(3+)) in the suspension. The zeta potential of the chemically modified and unmodified colloids was compared. The maximum change in the zeta potential was given by the calcium ions, Ca(2+)-adsorbed modified colloids as compared to unmodified sodium ions, Na(+)-adsorbed colloids. The distribution of charges on the Janus colloids results in a nonuniform zeta potential. XPS and optical microscopy were used to verify the successful chemical modification by the cation exchange of Na(+) for Ca(2+) ions on one hemisphere of the Janus colloids.

Soft polymer and nano-clay supracolloidal particles in adhesives: synergistic effects on mechanical properties

Numerous synthesis routes toward nanostructured polymer particles have emerged, but few examples demonstrate the essential need for such complex particle structures to achieve any added benefit in a target application. Here, polymer particles having Laponite clay armor were prepared by the Pickering miniemulsion polymerization of n-lauryl acrylate. The resulting “soft–hard” poly(lauryl acrylate) (PLA)–Laponite hybrid particles were blended at various low concentrations with a standard poly(butyl acrylate-co-acrylic acid) (PBA) latex for application as a waterborne pressure-sensitive adhesive (PSA). The tack adhesion properties of the resulting nanocomposite films were compared with the performance of the PBA when blended with either a conventional non-armored PLA latex, with Laponite RD nanosized clay discs, or a mixture of both. A true synergistic effect was discovered showing that the clay-armored supracolloidal structure of the hybrid particles was essential to achieve a superior balance of viscoelastic properties. The addition of small amounts, e.g. 2.7 wt%, of the “soft–hard” clay-armored PLA particles increased the tack adhesion energy considerably more than found for the two individual components or for the sum of their individual contributions. The soft PLA core ensures that the adhesives are not stiffened too much by the nanosized Laponite clay. Slippage at the interface between the nanoclay platelets and the PBA matrix introduces an additional energy dissipation mechanism during deformation. Through the synergistic effect of the clay and PLA in the supracolloidal armored latex structure, the tack adhesion energy is increased by 45 J m−2, which is about 70% greater than found for the PBA adhesive alone.

Pickering Miniemulsion Polymerization Using Laponite Clay as a Stabilizer

Solid-stabilized, or Pickering, miniemulsion polymerizations using Laponite clay discs as stabilizer are investigated. Free radical polymerizations are carried out using a variety of hydrophobic monomers (i.e., styrene, lauryl (meth)acrylate, butyl (meth)acrylate, octyl acrylate, and 2-ethyl hexyl acrylate). Armored latexes, of which the surfaces of the particles are covered with clay discs, are obtained, as confirmed by scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Overall polymerization kinetics of the Pickering miniemulsion polymerizations of styrene were investigated via gravimetry. Comparison with the bulk polymerization analogue clearly shows compartmentalization. Moreover, retardation effects up to intermediate monomer conversions are observed; they are more prominent for the smaller particles and are ascribed to the Laponite clay. A model is presented that allows for the prediction of the average particle size of the latexes produced as a function of the amounts of monomer and Pickering stabilizers used. It shows that under specific generic conditions the number of clay discs used correlates in a linear fashion with the total surface area of the latex particles. This is a direct result of the reversibility of the Laponite clay disc adhesion process under the emulsification conditions (i.e., sonication) used.