Facile fabrication of nanocomposite microspheres with polymer cores and magnetic shells by Pickering suspension polymerization

Preparation of Colored Polymer Microspheres

Colored polymer microspheres have attracted significant attention in both academia and industry due to their unique optical properties and extensive application potential. However, achieving a uniform distribution of dyes within these microspheres remains a challenge, particularly when heavy concentrations of dye are used, as this can lead to aggregation or delamination, adversely affecting their application. Additionally, many dyes are prone to degradation or fading when exposed to light, heat, or chemicals, which compromises the long-term color stability of the microspheres. Consequently, the preparation of colored polymer microspheres with high stability continues to be a significant challenge. This review offers a comprehensive overview of the preparation techniques for colored polymer microspheres and their dyeing mechanisms, introducing the fundamental concepts of these microspheres and their applications in various fields, such as biomedicine, optical devices, and electronic display technologies. It further presents a detailed discussion of the different preparation methods, including physical adsorption, chemical bonding, and copolymerization. The advantages, limitations, and potential improvements of each method are explored, along with an analysis of the interactions between dyes and the polymer matrix, and how these interactions influence the properties of the microspheres, including their color uniformity, stability, and durability. Finally, the review discusses future perspectives on the development of colored polymer microspheres, highlighting the advancement of novel materials, innovations in preparation technology, and the exploration of potential new application areas.

Silica-Supported Styrene-Co-Divinylbenzene Pickering Emulsion Polymerization: Tuning Surface Charge and Hydrophobicity by pH and Co-Aid Adsorption

In this work, polymerizations of styrene (St) in the presence of divinylbenzene (DVB) as a crosslinking agent and sodium 4-vinylbenzenesulfonate (VBS) have been performed in Pickering emulsions, using silica nanoparticles (SNps) as stabilizing agents and ammonium persulfate as a hydrophilic initiator. In oil-in-water Pickering emulsions with alkaline continuous phase (pH = 9) at 1, 2, and 3 wt% DVB (relative to St), polydisperse spheroid copolymer submicronic nanoparticles were obtained. Comparatively, polymerizations performed in Pickering emulsions with acidic continuous phase (pH = 5) allowed preparing St-co-DVB microspheres with core–shell structures at 1 wt% DVB and St-co-DVB hybrid monoliths with bi-continuous morphologies at 2 and 3 wt% DVB. It is noteworthy that this work reports Pickering emulsion polymerization as a new strategy for preparing hybrid percolated scaffolds with bi-continuous porosity. The proposed mechanisms originated by pH, DVB, and VBS and the drastic impact caused on the final morphology obtained, either hybrid particles or monoliths, are discussed herein.

Layer-by-Layer Assembly of Polystyrene/Ag for a Highly Reproducible SERS Substrate and Its Use for the Detection of Food Contaminants

Polystyrene (PS) spheres were prepared through an emulsifier-free emulsion polymerization method, in which the reaction time, ionic strength, concentrations of copolymer were studied in detail. The resulting PS microspheres and Ag nanoparticles were used to construct a surface enhanced Raman scattering (SERS) substrate by a layer-by-layer assembly method. A relatively uniform distribution of PS/Ag in the films was obtained, and the multilayer substrate presented excellent SERS reproducibility and a tunable enhancement effect. The SERS substrate was used for detecting harmful pesticides (malachite green and dimetridazole) in food samples, with a limit of detection as low as 3.5 ppb. The obtained plasmonic composite has a promising future in the field of SERS sensing.

Effect of pH and zeta potential of Pickering stabilizing magnetite nanoparticles on the features of magnetized polystyrene microspheres

Styrene as a monomer was emulsified in water using several magnetite nanoparticles concentration and pH values. Emulsified styrene drops were used as templates for polymerization, in presence of water soluble free radical initiator, and formation of composite particles. Styrene template drops stabilization was verified by light as well as scanning electron microscopy imaging, which ensured the participation of the particles in building up a mechanical barrier to stop oil drops coalescence. Furthermore, the produced polystyrene composites were strongly attracted to an external magnet. The difference in particles size as a function of pH was elucidated using zeta potential measurements, which indicated dominance of pH on the hydrophilicity of the particles and consequently the extent of emulsification, which in turn affected the size of the obtained microspheres. Under some circumstances, capsules were formed instead of particles. Thereby, it can be concluded that the magnetic microspheres are optimally formed at pH 2.3 independently of the magnetite content used.

Nanohybrid carriers: the yin–yang equilibrium between natural and synthetic in biomedicine

Nanocarriers are key players in biomedicine applications. The development of hybrid nanoparticles stems from the need to enhance their quality by lowering disadvantages and fusing the positive qualities of both natural and synthetic materials.

Cellulose Nanocrystals to Improve Stability and Functional Properties of Emulsified Film Based on Chitosan Nanoparticles and Beeswax

The framework of this work was to develop an emulsion-based edible film based on a chitosan nanoparticle matrix with cellulose nanocrystals (CNCs) as a stabilizer and reinforcement filler. The chitosan nanoparticles were synthesized based on ionic cross-linking with sodium tripolyphosphate and glycerol as a plasticizer. The emulsified film was prepared through a combination system of Pickering emulsification and water evaporation. The oil-in-water emulsion was prepared by dispersing beeswax into an aqueous colloidal suspension of chitosan nanoparticles using high-speed homogenizer at room temperature. Various properties were characterized, including surface morphology, stability, water vapor barrier, mechanical properties, compatibility, and thermal behaviour. Experimental results established that CNCs and glycerol improve the homogeneity and stability of the beeswax dispersed droplets in the emulsion system which promotes the water-resistant properties but deteriorates the film strength at the same time. When incorporating 2.5% w/w CNCs, the tensile strength of the composite film reached the maximum value, 74.9 MPa, which was 32.5% higher than that of the pure chitosan film, while the optimum one was at 62.5 MPa, and was obtained by the addition of 25% w/w beeswax. All film characterizations demonstrated that the interaction between CNCs and chitosan molecules improved their physical and thermal properties.

Emulsions stabilized with mixed SiO2 and Fe3O4 nanoparticles: mechanisms of stabilization and long-term stability

Using SiO₂ and Fe₃O₄ nanoparticles as stabilizers makes it possible to obtain Pickering emulsions with long-term stability to coalescence and creaming.

Polymer Capsules for Enzymatic Catalysis in Confined Environments

Catalysis is at the base of a series of biological and technological application processes. In recent years, the tendency has developed to carry out catalyzed reactions within confined structures, thus forming systems called micro or nanoreactors. Compartmentalized structures are cavities delimited by a wall where specific functions are introduced with a defined concentration and in the desired sites. These containers are generally referred to as nano or microcapsules, assuming the function of reactors in the presence of chemical reactions. Among the various types of existing structures, one of the most interesting is represented by systems made with polymers. This review aims to highlight some of the current advances in the use of functionalized structures that are useful for catalysis reactions, paying particular attention to polymer capsules and enzymes. The built-up methods used for the production of polymer capsules, as well as the aspects that influence membrane permeability and reactivity to environmental conditions, are discussed. Recent advances on biocatalysis confined in polymeric capsules are illustrated, and the strengths and weaknesses of the principal nanoreactors are considered.

Design of polymer particle dispersions (latexes) in the course of radical heterophase polymerization for biomedical applications

Dispersions of polymer particle (DPPs) are increasingly being exploited both as biomolecule carriers, and as markers in various DPP biomedical applications related to cell and molecular biology, enzymology, immunology, diagnostics, in vitro and in vivo visualization, bioseparation, etc. Their potential to reduce reaction scales, lower costs, improve the rate, sensitivity, selectivity, stability and reproducibility of assays governs the diversity of their bioapplications. This review focuses on the design of DPPs with innovative special properties in the course of free radical heterophase polymerization that provides careful control of both macromolecular and colloidal properties. We demonstrate approaches that, according to the polymerization technique, regulate the particle size, shape, particle size distribution, morphology, surface chemistry and functionality, as well as the formation of organic-inorganic hybrid DPPs. The production of bioreagents based on DPPs and their use in bioassay are also reviewed.

Polymerizable Microsphere-Induced High Mechanical Strength of Hydrogel Composed of Acrylamide

Polymerizable microspheres are introduced into acrylamide to prepare the high mechanical strength hydrogels with a novel three-dimensional pore structure. Rheological properties, compressive stress–strain, tensile property, and compression strength of three different types of hydrogels were investigated. Moreover, a scanning electron microscope (SEM) was adopted to observe the three-dimension network structure of three different types of hydrogels. The test results illustrated that viscous moduli (G″) and elastic moduli (G′) of a hydrogel containing polymerizable microspheres (P) reached maximum values, compared to the normal hydrogel (N) and the composite hydrogel containing ordinary microspheres (O). When the hydrogels were squeezed, the N was easily fractured under high strain (99%), whereas the P was not broken, and quickly recovered its initial morphology after the release of load. The P showed excellent tensile properties, with an elongation at break up to 90% and a tensile strength greater than 220 g. The compression strength of the N was 100.44 kPa·m⁻¹, while the resulting strength of P was enhanced to be 248.00 kPa·m⁻¹. Therefore, the various performances of N were improved by adding polymerizable microspheres. In addition, the SEM images indicated that N has a general three-dimensional network structure; the conventional network structure did not exist in the P, which has a novel three-dimensional pore structure in the spherical projection and very dense channels, which led to the compaction of the space between the three-dimensional pore network layers and reduced the flowing of free water wrapped in the network. Therefore, the mechanical strength of hydrogel was enhanced.

A new strategy to elaborate polymer composites via Pickering emulsion polymerization of a wide range of monomers

We report a novel strategy to prepare polymer composites reinforced with cellulose nanocrystals (CNCs) via Pickering emulsion polymerization.

Polymeric Nanoparticle-Coated Pickering Emulsion-Synthesized Conducting Polyaniline Hybrid Particles and Their Electrorheological Study

To produce an electric stimuli-responsive electrorheological (ER) material, semiconducting core/shell-type polyaniline (PANI) hybrid particles were fabricated through Pickering emulsion-type polymerization, using poly(divinylbenzene-alt-maleic anhydride) (PDVMA) particles as a solid surfactant. The PDVMA nanoparticles were initially polymerized using a self-stable precipitation method. The fabricated PANI/PDVMA composite particles were subjected to various chemical characterizations; further, they were suspended in silicone oil at 10 vol % to prepare an ER fluid, and their viscoelastic behaviors were scrutinized using a rheometer under various input electric fields. We also adopted an LCR meter to evaluate its dielectric characteristics. Our results showed that the PANI/PDVMA composite particles display typical ER performance, such that both dynamic and elastic yield stresses follow a polarization mechanism with a slope of 2.0.

Preparation and characterization of core-shell oil absorption materials stabilized by modified fumed silica

The core-shell oil absorption material (OAM) with fumed silica shell was achieved from Pickering polymerization. The modified fumed silica wall could well stabilize both Pickering emulsion and Pickering polymerization. The particle size of encapsulated OAMs decreased with the increasing concentration of fumed silica and remained unchanged when the concentration was more than 1 wt.%. This fumed silica shell had little effect on the oil absorption rate of OAM. The importance was that the shell reversed the surface property and improved the alkali resistance of OAM. We believe that our core-shell OAMs could reach the self-healing ability of the oil well cement.

Synthesis of surfactant-free micro- and nanolatexes from Pickering emulsions stabilized by acetylated cellulose nanocrystals

Surfactant-free micro- and nanolatexes from Pickering emulsions stabilized by acetylated cellulose nanocrystals (CNCs).

Nanoparticles change drop breakup mechanism to obtain icecream-like microparticles in inverse suspension polymerization

Nanoparticle modify particle shaped in suspension polymerization by changing drop breakup. (a) 0.4% initiator, (b) 0.05% initiator.

Polymer/graphene oxide composite microcapsules with greatly improved barrier properties

Microcapsules with excellent barrier property are fabricated by Pickering emulsion templating stabilized using relatively lipophilic GO nanosheets to achieve good dispersion of GO in polymer shells.

Synthesis of magnetic Fe3O4/polyamine hybrid microsphere using O/W/O Pickering emulsion droplet as the polymerization micro-reactor

An O/W/O emulsion containing Fe₃O₄NPs and PEI was obtained using SM-CaCO₃NPs as the stabilizer. In a droplet-to-droplet reaction mode, a magnetic polyamine microsphere was achieved by crosslinking PEI in the emulsion droplet with glutaraldehyde.

Pickering emulsion polymerized smart magnetic poly(methyl methacrylate)/Fe2O3 composite particles and their stimulus-response

Smart polymer/inorganic composite magnetic particles were synthesized by Pickering emulsion polymerization using magnetic iron oxide (Fe₂O₃) particles as a solid stabilizer.

Microbeads and hollow microcapsules obtained by self-assembly of pickering magneto-responsive cellulose nanocrystals

Cellulose microbeads can be used as immobilization supports. We report on the design and preparation of magneto-responsive cellulose microbeads and microcapsules by self-assembled shells of cellulose nanocrystals (CNC) carrying magnetic CoFe2O4 nanoparticles, that is, a mixture of isotropic and anisotropic nanomaterials. The magnetic CNCs formed a structured layer, a mesh, consisting of CNCs and magnetic particles bound together on the surface of distinct droplets of hexadecane and styrene dispersed in water. Because of the presence of CNCs the highly crystalline mesh was targeted to provide an improved barrier property of the microbead shell compared to neat polymer shells, while the magnetic particles provided the magnetic response. In situ polymerization of the styrene phase led to the formation of solid microbeads (∼8 μm diameter) consisting of polystyrene (PS) cores encapsulated in the magnetic CNC shells (shell-to-core mass ratio of 4:96). The obtained solid microbeads were ferromagnetic (saturation magnetization of ∼60 emu per gram of the magnetic phase). The magnetic functionality enables easy separation of substances immobilized on the beads. Such a functionality was tested in removal of a dye from water. The microbeads were further utilized to synthesize hollow microcapsules by solubilization of the PS core. The CNC-based, magneto-responsive solid microbeads and hollow microcapsules were characterized by electron microscopy (morphology), X-ray diffraction (phase composition), and magnetometry (magnetic properties). Such hybrid systems can be used in the design of materials and devices for application in colloidal stabilization, concentration, separation, and delivery, among others.

Templated globules--applications and perspectives

Polyelectrolyte capsules represent a class of particles composed of an internal core and an external polymer matrix shell. In recent years, it has become clear that the manufacture of polyelectrolyte capsule is likely to have a significant role in several areas including medicine and biology. Many distinct methodologies for the fabrications of templated globules have been reported. Despite the huge availability of knowledge used to obtain such globules, the choice of the appropriate technology for the desired applications demands a deeper appreciation of this issue. Furthermore, the extent to which the applications of polyelectrolyte capsule may be actively involved in the practical biomedical field is still a fascinating challenge. Here, we review the recipes for the globule assembly with their own benefits and limitations and how different templates could affect the final globule features, with a particular focus on the Layer by Layer (LbL) procedure. The latest applications in biological, therapeutical and diagnostic areas are also discussed and some outlooks for the strategic development of polymer globule are highlighted.