Efficient preparation of polystyrene/silica colloidal nanocomposite particles by emulsion polymerization using a glycerol-functionalized silica sol

Unraveling the Complexities of Silica Nanoparticle Adsorption onto Polymer Latexes in Pickering Emulsion Polymerization

Incorporating unmodified silica nanoparticles onto polymer latexes to fabricate aqueous polymer dispersions without relying on electrostatic attraction during the Pickering emulsion polymerization process still faces challenges. For negatively charged silica nanoparticles to successfully adsorb onto polymer latexes, particularly in an anionic initiator emulsion polymerization system, they have remained elusive without the use of auxiliary monomers and cationic initiators. This study investigates various experimental parameters, such as emulsion polymerization temperature, monomer solubility, salt concentration, and cation type, to elucidate the factors influencing the adsorption of unmodified silica nanoparticles in Pickering emulsion polymerization. While poly(methyl methacrylate) (PMMA)/SiO2 hybrid latexes can be obtained under pH conditions of 5-6 and at temperatures of 65 °C or below, the loading rate of silica nanoparticles decreases as the reaction temperature increases, resulting in bare PMMA latexes without silica nanoparticle adsorption at temperatures exceeding 70 °C. Introducing styrene (St) into the monomer mixture with methyl methacrylate in a ratio of up to 10 wt % leads to a gradual decrease in silica nanoparticle loading rate, from 27.3 to 8.2 wt %, attributed to the low solubility of St in water. Furthermore, the presence of sodium ions (Na+) is found to be crucial for silica nanoparticle adsorption onto PMMA latexes, as the sodium ions have a stabilizing effect on both the silica nanoparticles and the silica nanoparticle-armored latexes. These findings highlight the complex nature of Pickering emulsion polymerization in the presence of unmodified silica nanoparticles, demonstrating that the loading rate of silica nanoparticles onto polymer latexes is influenced by various factors. These insights pave the way for developing aqueous polymer dispersions with high silica nanoparticle loading rates onto polymer latexes, which is a desirable trait in the coating industry.

Preparation of Surface-Wrinkled Silica-Polystyrene Colloidal Composite Particles

In this work, we report a facile emulsion swelling route to prepare surface-wrinkled silica-polystyrene (SiO2-PS) composite particles. Submicrometer-sized, near-spherical SiO2-PS composite particles were first synthesized by dispersion polymerization of styrene in an ethanol/water mixture, and then, surface-wrinkled SiO2-PS particles were obtained by swelling the SiO2-PS particles with a toluene/water emulsion and subsequent drying. It is emphasized that no surface pretreatment on the SiO2-PS composite particles is required for the formation of the wrinkled surface, and the most striking feature is that the surface-wrinkled particle was not deformed from a single near-spherical SiO2-PS composite particle but from many ones. The influence of various swelling parameters including toluene/particle mass ratio, surfactant concentration, stirring rate, swelling temperature, swelling time, and silica size on the morphology of the composite particles was studied. This method represents a new paradigm for the preparation of concave polymer colloids.

Synthesis of dimpled polymer-silica nanocomposite particles by interfacial swelling-based seeded polymerization

Dimpled polymer-silica nanocomposite particles have the combined advantages of dimpled particles and polymer-silica nanocomposite particles. This study presents a novel approach to prepare these particles by interfacial swelling-based seeded polymerization. Polystyrene-silica (PS-SiO2) nanocomposite particles are first prepared by emulsion polymerization of styrene in the presence of glycerol-functionalized silica sols and then dimpled polymer-SiO2 particles are fabricated by interfacial swelling of butyl acrylate (BA)/toluene and subsequent seeded polymerization of BA with the PS-SiO2 particles as seeds. The effects of different parameters, such as the amount of surfactant used in the PS-SiO2/H2O dispersion, BA/toluene mass ratio, PS-SiO2/H2O mass ratio and stirring rate, on the formation of the dimpled particles are investigated. Optimization of the seeded polymerization conditions allows a relatively high percentage of dimpled particles to be achieved.

Advances in Organic-Inorganic Hybrid Latex Particles via In Situ Emulsion Polymerization

Hybrid latex particles combine the unique properties of inorganic nano/micro particles with the inherent properties of polymers, exhibiting tremendous potential for a variety of applications. Recent years have witnessed an increased interest in the design and preparation of hybrid latex particles with well-defined size, structure and morphology. Due to its simplicity, versatility and environmental friendliness, the in situ (Pickering) emulsion polymerization has been demonstrated to be a powerful approach for the large-scale preparation of hybrid latex particles. In this review, the strategies and applications of in situ (Pickering) emulsion polymerization for the preparation of hybrid latex particles are systematically summarized. A particular focus is placed on the strategies for the preparation of hybrid latex particles with enhanced properties and well-defined core-shell, yolk-shell, multinuclear, raspberry-like, dumbbell-shaped, multipod-like or armored morphologies. We hope that the considerable advances, examples and principles presented in this review can motivate future contributions to provide a deeper understanding of current preparation technologies, develop new processes, and enable further exploitation of hybrid latex particles with outstanding characteristics and properties.

Nanocomposite Polymer Colloids Prepared via Emulsion Polymerization and Stabilized Using Polydopamine-Coated Silica Particles

Polymer/inorganic colloidal nanocomposites can be prepared via Pickering emulsion polymerization (PEP); however, this process usually requires the use of surfactants, auxiliary comonomers, and volatile organic compounds. Herein, we report a versatile and efficient method for synthesizing stable monodisperse polymer/silica colloidal nanocomposite particles via PEP. First, silica nanoparticles were modified by depositing a multifunctional polydopamine (PDA) film. The outermost PDA film could enhance the precipitation of oligomeric polymer radicals on the silica surface, which is crucial for the preparation of stable polymer/inorganic colloidal nanocomposites via PEP. Notably, this PDA modification approach can employ different initiator systems, such as cationic initiators and redox initiator couples, and can be applied to various monomers and monomer pairs (St, St/nBA, MMA, MMA/nBA, Vac, Vac/nBA). The influence of the concentration and size of polydopamine-coated silica (SiO₂@PDA) on the colloidal nanocomposite was investigated. Increasing the diameter of SiO₂@PDA and decreasing the concentration of SiO₂@PDA both lead to the formation of larger nanocomposite particles. Considering its wide applicability, the proposed PDA modification approach can be applied to other functional inorganic particles to prepare multifunctional polymer/inorganic nanocomposite particles.

In situ small-angle X-ray scattering studies during the formation of polymer/silica nanocomposite particles in aqueous solution

This study is focused on the formation of polymer/silica nanocomposite particles prepared by the surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) in the presence of 19 nm glycerol-functionalized aqueous silica nanoparticles using a cationic azo initiator at 60 °C. The TFEMA polymerization kinetics are monitored using 1H NMR spectroscopy, while postmortem TEM analysis confirms that the final nanocomposite particles possess a well-defined core-shell morphology. Time-resolved small-angle X-ray scattering (SAXS) is used in conjunction with a stirrable reaction cell to monitor the evolution of the nanocomposite particle diameter, mean silica shell thickness, mean number of silica nanoparticles within the shell, silica aggregation efficiency and packing density during the TFEMA polymerization. Nucleation occurs after 10-15 min and the nascent particles quickly become swollen with TFEMA monomer, which leads to a relatively fast rate of polymerization. Additional surface area is created as these initial particles grow and anionic silica nanoparticles adsorb at the particle surface to maintain a relatively high surface coverage and hence ensure colloidal stability. At high TFEMA conversion, a contiguous silica shell is formed and essentially no further adsorption of silica nanoparticles occurs. A population balance model is introduced into the SAXS model to account for the gradual incorporation of the silica nanoparticles within the nanocomposite particles. The final PTFEMA/silica nanocomposite particles are obtained at 96% TFEMA conversion after 140 min, have a volume-average diameter of 216 ± 9 nm and contain approximately 274 silica nanoparticles within their outer shells; a silica aggregation efficiency of 75% can be achieved for such formulations.

Polyvinyl alcohol-montmorillonite composites for water purification: Analysis of clay mineral cation exchange and composite particle synthesis

Municipal and residential water purification rely heavily on activated carbon (AC), but regeneration of AC is costly and cannot be performed at the point-of-use. Clay minerals (CMs) comprise a class of naturally abundant materials with known capacities for analyte adsorbance. However, the gel-forming properties of CMs in aqueous suspension pose problems for these materials being used in water-purification. In this study, we have taken three main steps to optimize the use of CMs in these applications. First, we produced several variants of montmorillonite CMs to evaluate the effect of interstitial cation hydrophobicity on the ability of the CM to uptake chargecarrying organic pollutants. These variants include CMs with the following cations: sodium, hexyl(triphenyl) phosphonium, hexyadecyl(triphenyl)phosphonium, and hexyl(tributyl)phosphonium. Second, we synthesized polymer-clay mineral composite films composed of polyvinyl alcohol (PVA), crosslinked in the presence of a CM variant. These films were evaluated for their ability to uptake malachite green (MG). Finally, we developed a one-pot synthetic method for the generation of polymer-clay particles for use in a continuous column process. We synthesized polymer-clay mineral particles using the highest performing CM (based on the film experiments) and evaluated the equilibrium capacity and kinetics of MG uptake from solution.

Double in Situ Preparation of Raspberry-like Polymer Particles

Well-defined raspberry-like poly(styrene- co-4-vinylpyridine)-SiO₂ nanocomposite particles with a diameter of around 200 nm were easily prepared by a double in situ process in nanoemulsion with the water-soluble dye Eosin Y as the stabilizer. During radical polymerization of the nanodroplets comprising styrene, 4-vinylpyridine (4-VP), and tetraethoxysilane (TEOS), the silane phase is expelled from the polymer phase to the oil/water (o/w) interface. In the later polymerization stage, SiO₂ nanoparticles with a size of around 25 nm were produced via the in situ sol-gel reaction of TEOS at the o/w interface promoted by the negatively charged dye. The pyridine moieties in the copolymer fix the SiO₂ nanoparticles on the surface of the polymer particles by electrostatic interactions without any sign of free unbound silica particles as proven by transmission electron microscopy.

Recent advances in colloidal nanocomposite designviaheterogeneous polymerization techniques

Recent advances in colloidal nanocomposite design by heterogeneous polymerization are reviewed, with a specific focus on encapsulation and particle-based stabilization for specific materials applications.

Entrapped Styrene Butadiene Polymer Chains by Sol-Gel-Derived Silica Nanoparticles with Hierarchical Raspberry Structures

A sol-gel transformation of liquid silica precursor to solid silica particles was carried out in a one-pot synthesis way, where a solution of styrene butadiene elastomer was present. The composites, thus produced, offered remarkable improvements of mechanical and dynamic mechanical performances compared to precipitated silica. The morphological analysis reveals that the alkoxy-based silica particles resemble a raspberry structure when the synthesis of the silica was carried out in the presence of polymer molecules and represent a much more open silica-network structure. However, in the absence of the polymer, the morphology of the silica particles is found to be different. It is envisaged that the special morphology of the in situ synthesized silica particles contributes to the superior reinforcement effects, which are associated with a strong silica-rubber interaction by rubber chains trapped inside the raspberry-like silica aggregates. Therefore, the interfaces are characterized in detail by low-field solid-state ¹H NMR spectroscopy, ²⁹Si solid-state NMR spectroscopy, and energy-dispersive X-ray spectroscopy. Low-field ¹H NMR-based double-quantum experiments provide a quantitative information about the cross-link density of the silica-filled rubber composites and about the influence of silane coupling agent on the chemical cross-link density of the network and correlates well with equilibrium swelling measurements. The special microstructure of the alkoxy-based silica was found to be associated with the interaction between alkoxy-based silica and rubber chains as a consequence of particle growth in the presence of rubber chains.

Adsorption of Silica Nanoparticles onto Poly(N-vinylpyrrolidone)-Functionalized Polystyrene Latex

This paper presents a more general method to prepare silica-coated polystyrene (PS) particles with minimal excess silica by adsorption, highlighting the role of poly(N-vinylpyrrolidone) (PVP). The method is based on the addition of small silica nanoparticles onto submicrometer-sized near-monodisperse polymer latex particles under the conditions of monolayer silica coverage of the latex surface. Either a cationic or an anionic initiator could be used in the PVP-involved emulsion polymerization to prepare PS particles, and the adsorption was conducted successfully either under acidic or basic conditions. Neither a cationic initiator nor a basic condition is a prerequisite for the adsorption process, which should be related to the much stronger interaction between PVP and the silica surface. This method is expected to substantially extend the adsorption conditions of polymer-silica colloidal nanocomposite syntheses.

Photocatalytic Surface-Initiated Polymerization on TiO2 toward Well-Defined Composite Nanostructures

We demonstrate the use of TiO2 nanospheres as the photoinitiator for photocatalytic surface-initiated polymerization for the synthesis of various inorganic/polymer nanocomposites with well-defined structures. The excitation of TiO2 by UV-light irradiation produces electrons and holes which drive the free radical polymerization near its surface, producing core/shell composite nanospheres with eccentric or concentric structures that can be tuned by controlling the surface compatibility between the polymer and the TiO2. When highly porous TiO2 nanospheres were employed as the photoinitiator, polymerization could disintegrate the mesoporous framework and give rise to nanocomposites with multiple TiO2 nanoparticles evenly distributed in the polymer spheres. Thanks to the well-developed sol-gel chemistry of titania, this synthesis is well-extendable to the coating of the polymers on many other substrates of interest such as silica and ZnS by simply premodifying their surface with a thin layer of titania. In addition, this strategy could be easily applied to coating of different types of polymers such as polystyrene, poly(methyl methacrylate), and poly(N-isopropylacrylamide). We expect this photocatalytic surface-initiated polymerization process could provide a platform for the synthesis of various inorganic/polymer hybrid nanocomposites for many interesting applications.

Pickering polymerization of styrene stabilized by starch-based nanospheres

Pickering polymerization of styrene stabilized by starch-based nanospheres to synthesize composite particles with different morphologies is reported.

One-step fabrication of 3-methacryloxypropyltrimethoxysilane modified silica and investigation of fluorinated polyacrylate/silica nanocomposite films

One-step synthesis of MPS-functionalized silica and preparation of film forming fluorinated polyacrylate/silica nanocomposite particles.

Synthesis of core-shell bioaffinity chitosan-TiO₂ composite and its environmental applications

Based on the coupling of molecular imprinting, chitosan biosorption, and nano TiO2 photocatalysis technologies, a novel core-shell organic-inorganic hybrid material of surface imprinted chitosan-TiO2 composite (SICT) was prepared with methyl orange as the template. SEM, EDS, AFM, pore size analysis, and FTIR characterization results illustrated that TiO2 nano powder was successfully coated on the surface of chitosan microparticles via intermolecular hydrogen bonds to form the core-shell organic-inorganic composites with rough and porous surface morphology. SICT showed enhanced photocatalytic selectivity for methyl orange (M.O.) compared with the non-imprinted chitosan-TiO2 composites because of the existing of more suitable sites generated by surface molecular imprinting. The removal of M.O. by SICT was mainly from the photocatalytic degradation rather than simple adsorption. SICT could be reused directly without further desorption and regeneration for 10 cycles with preserving 60% of its photocatalytic efficiency. The reusability of SICT would be beneficial for the simplification of the operating steps and the cost reduction which facilitated its practical applications in wastewater treatment concerning environmental organic pollutants.

Physical adsorption of anisotropic titania nanoparticles onto poly(2-vinylpyridine) latex and characterisation of the resulting nanocomposite particles

Four poly(2-vinylpyridine) latexes with intensity-average mean diameters ranging between 246 and 955nm were prepared by aqueous emulsion polymerisation. These latexes were characterised by transmission electron microscopy, field emission scanning electron microscopy, dynamic light scattering, aqueous electrophoresis, disc centrifuge photosedimentometry and thermogravimetry. The adsorption of rice grain-shaped nano-sized titania particles onto the surface of these latex particles from aqueous solution was investigated. It was found that the titania particles adsorb strongly at pH 10 and the optimal loading and packing density of titania was investigated for each latex. The resulting core-shell P2VP-titania nanocomposite particles were characterised in terms of their titania contents, surface coverages and colloidal stabilities. UV-Vis spectra were recorded for the titania nanoparticles, the original P2VP latexes and the poly(2-vinylpyridine)-titania nanocomposite particles. It was found that, for the larger nanocomposite particles, UV-Vis absorption was dominated by the latex core, whereas the smaller P2VP-titania nanocomposite particles exhibited UV attenuation to longer wavelengths compared to both the bare latex and the titania particles. The poly(2-vinylpyridine) cores were selectively removed by calcination of the nanocomposite particles and the resulting hollow titania structures were investigated by transmission electron microscopy.

Synthesis and properties of hybrid core–shell poly(alkyltrialkoxysiloxane) latex

We discuss the nucleation mechanism and process of hybrid core–shell poly(alkyltrialkoxysiloxane) latex particles’ formation.

Synthesis of polystyrene/polysilsesquioxane core/shell composite particles via emulsion polymerization in the existence of poly(γ-methacryloxypropyl trimethoxysilane) sol

Here, we synthesized the polystyrene/polysilsesquioxane (PS/PSQ) core/shell latex particles via emulsion polymerization, which behave as an amusing morphology. First, the nanosized PSQ particles were prepared by the hydrolysis-condensation reaction of γ-methacryloxypropyl trimethoxysilane (MPTS) in ethanol medium. Subsequently, the as-obtained methacryloxypropylene functionalized PSQ (PMPTS) sol was directly added into the emulsion system of styrene (St) monomer, and PS/PSQ composite particles with core/shell structure were obtained through emulsion polymerization. We found that the structure of the composite particles can be affected by the synthesis parameters such as reaction time, content of PMPTS added in the reaction, amount of coemulsifier, and the pH value of emulsion system, which were systemically explored by transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), and thermogravimetric analysis (TGA) in this work. These results indicate that the PMPTS particles in the size of about 5 nm could first absorb onto the surface of PS latex particles so as to assemble in a strawberry-like morphology. The further coalescence among the PMPTS particles would result in a continuous PMPTS shell around the PS core. Moreover, the hollow PSQ capsules were prepared after extraction of the PS core by organic solvent, further confirming the core/shell structure of the as-synthesized PS/PMPTS particles. Meanwhile, we also explored the application of the PS/PSQ core/shell particles as a new kind of Pickering emulsifier in the emulsion polymerization of St, and composite particles with complex patchy morphologies have been obtained finally under different ratios of styrene monomer to PS/PMPTS colloidal emulsifier.

Correcting for a density distribution: particle size analysis of core-shell nanocomposite particles using disk centrifuge photosedimentometry

Many types of colloidal particles possess a core-shell morphology. In this Article, we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle X-ray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction, and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.

Efficient synthesis of poly(2-hydroxypropyl methacrylate)-silica colloidal nanocomposite particles via aqueous dispersion polymerization

Colloidally stable poly(2-hydroxypropyl methacrylate)-silica nanocomposite particles can be efficiently prepared by aqueous dispersion polymerization at 60 °C using a binary mixture of an ultrafine aqueous silica sol and poly(N-vinylpyrrolidone) [PVP] as the stabilizer system.

A miniemulsion polymerization technique for encapsulation of silicon quantum dots in polymer nanoparticles

Miniemulsion polymerization techniques were used to encapsulate luminescent alkylated silicon quantum dots (Si-QDs) within polymer nanoparticles composed of styrene and 4-vinylbenzaldehyde monomers. The polymer nanoparticles had mean diameters in the range 90-150 nm depending on the reaction conditions, however all samples showed narrow particle size distributions, as determined by dynamic light scattering and atomic force microscopy. The Si-QDs were found to have a small, but beneficial effect on the polymerization process by reducing the polydispersity of the final polymer particles, which we attribute to co-surfactant action of the undecene used to form the alkyl capping layer on the Si-QDs. Confocal microspectroscopy was used to confirm that the luminescent alkylated Si-QDs were encapsulated within the polymer nanoparticles and also provided luminescence and Raman spectra which show peaks corresponding to both alkylated Si-QDs and the polymer nanoparticles. Treatment of the polymer nanoparticles with dilute aqueous sodium hydroxide solution, which is known to corrode Si and extinguish the luminescence of alkylated Si-QDs, results in only a partial reduction in luminescence suggesting that the majority of the alkylated Si-QDs are encapsulated sufficiently deep within the polymer matrix to protect them from alkaline attack. Miniemulsion polymerization of the monomers styrene and 4-vinylbenzaldehyde affords polymer nanoparticles displaying reactive aldehyde groups upon their surfaces, which could then be decorated with a selection of molecules through imine, oxime or hydrazone condensation reactions. We speculate that polymer-SiQD composite nanoparticles whose surfaces can be further decorated will increase the utility of luminescent Si-QDs in applications such as anti-counterfeiting and as probes of biological processes.