Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization

Nanocomposite of Graphene Oxide Encapsulated in Polymethylmethacrylate (PMMA): Pre-Modification, Synthesis, and Latex Stability

The compatibility of graphene oxide with its dispersion medium (polymer) plays a critical role in the formation of nanocomposite materials with significant property improvements. Environmentally friendly miniemulsion polymerization, which allows a formation of nanoencapsulation in an aqueous phase and high molecular weight polymer/composite production is one promising method. In this study, we screened a series of amphiphilic modifiers and found that the quaternary ammonium (ar-vinyl benzyl) trimethyl ammonium chloride (VBTAC) pending carbon double bonds could effectively modify the graphene oxide (GO) to be compatible with the organophilic monomer. After that, free radical miniemulsion polymerization successfully synthesized stable latex of exfoliated poly (methyl methacrylate) (PMMA)/ GO nanocomposite. The final latex had an extended storage life and a relatively uniform particle size distribution. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) analysis of this latex and its films indicated successful encapsulation of exfoliated nano-dimensional graphene oxide inside a polymer matrix.

Emulsion and miniemulsion techniques in preparation of polymer nanoparticles with versatile characteristics

In recent years, polymer nanoparticles (PNPs) have found their ways into numerous applications extending from electronics to photonics, conducting materials to sensors and medicine to biotechnology. Physical properties and surface morphology of PNPs are the most important parameters that significantly affect on their exploitations and can be controlled through the synthesis process. Emulsion and miniemulsion techniques are among the most efficient and wide-spread methods for preparation of PNPs. The objective of this review is to present and highlight the recent developments in the advanced PNPs with specific properties that are produced through emulsion and miniemulsion processes.

Polymer Nanocomposites-A Comparison between Carbon Nanotubes, Graphene, and Clay as Nanofillers

Nanofilled polymeric matrices have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review the processing of carbon nanotube, graphene, and clay montmorillonite platelet as potential nanofillers to form nanocomposites. The various functionalization techniques of modifying the nanofillers to enable interaction with polymers are summarized. The importance of filler dispersion in the polymeric matrix is highlighted. Finally, the challenges and future outlook for nanofilled polymeric composites are presented.

Synthesis of multi-hollow clay-armored latexes by surfactant-free emulsion polymerization of styrene mediated by poly(ethylene oxide)-based macroRAFT/Laponite complexes

We report the RAFT-mediated synthesis of Laponite-armored latexes by surfactant-free emulsion polymerization.

Encapsulation of clay by ad-miniemulsion polymerization: the influence of clay size and modifier reactivity on latex morphology and physical properties

The influence of clay platelet size and type of organic modifier (reactive or nonreactive) on highly filled hybrid latex morphology and physical properties of the resultant polymer/clay nanocomposites (PCNs) were investigated. The hybrid latexes, containing clay loadings between 30 and 50 wt % clay, were prepared using ad-miniemulsion polymerization. These materials have potential use in the packaging and coating industry since clay platelets are well-known for barrier property improvements. Comparative studies on the use of montmorillonite (MMT), a large clay platelet (average size: 50-500 nm), and Laponite (Lap), small-sized clay platelets (average size: 25-40 nm), were conducted. Two different clay modifiers were used to modify the clays, i.e., a conventional nonreactive modifier (cetyltrimethylammonium bromide (CTAB)) and a reactive modifier (vinylbenzyldodecyldimethylammonium chloride (VBDAC)). Transmission electron microscopy (TEM) imaging of the hybrid latexes clearly showed strong morphological dependency on both the type of modifier and the clay platelet size. Furthermore, TEM together with small-angle X-ray scattering (SAXS) showed that the extent of clay exfoliation was strongly dependent on the reactivity of the clay modifier, irrespective of the clay platelet size. Both the type of modifier and clay platelets size were found to have an influence on different physical properties of the resultant PCNs. The influence of clay size was clearly indicated by storage modulus and thermal stability behaviors, while that of the clay modifier was indicated by the T(g). Lap-based PCNs exhibited constant or increasing storage modulus and no change in thermal stability with increasing clay content, while MMT-based PCNs showed a decreasing trend in both storage modulus and thermal stability. PCNs based on clay modified with CTAB showed a decreasing T(g) with increasing clay content, while those based on clay modified with VBDAC showed an increasing trend. It was concluded that the clay platelet size and the type of modifier play a crucial part of both the latex morphology and the physical properties of the resultant PCNs.

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.

Polymer Nanocomposites in Emulsion and Suspension: an Overview

Polymer nanocomposites have been a subject of intense research in the recent yeas. By nanoscale dispersion of inorganic fillers in the polymer matrices, significant enhancements in the properties of the materials have been achieved at very low filler volume fractions. Different modes of nanocomposite synthesis have been developed in the recent years which include template synthesis, in-situ polymerization, melt intercalation and polymer or prepolymer adsorption from solution. The last methodology also covers emulsion and suspension polymerization techniques for the synthesis of nanocomposites. These emulsion and suspension modes of polymer nanocomposite synthesis have the advantage that the polymerization is carried out in the presence of water which does not allow buildup of viscosity and the heat dissipation from the system is also easily achieved. The potential thermal damage to the polymer and the organic modification usually encountered in the melt intercalation is also avoided in the case of emulsion and suspension polymerization. Different polymer systems have been reported like polystyrene, polyurethanes, epoxy, poly(methyl methacrylate), poly(N-isopropylacrylamide), poly(butyl acrylate) etc. Specific synthetic methodologies like surfactant free polymerization, controlled living polymerization etc. have also been reported to successfully achieve nanocomposites with superior properties than the pure polymers. Majority of the studies bring home the conclusion that the amount of clay as well as surface modification present on clay surface significantly affect the microstructure and properties of the nanocomposite particles. Apart from clay as filler, many studies also have used the spherical inorganic particles as reinforcements.

Polymer encapsulated gibbsite nanoparticles: efficient preparation of anisotropic composite latex particles by RAFT-based starved feed emulsion polymerization

Anisotropic polymer-inorganic composite latex particles were synthesized by using a RAFT-based encapsulation approach on cationic gibbsite platelets. By using the RAFT agent dibenzyl trithiocarbonate, a series of amphipatic living random RAFT copolymers with different combinations of acrylic acid and butyl acrylate units were synthesized. These RAFT copolymers were used as living stabilizers for the gibbsite platelets and chain extended to form a polymeric shell by starved feed emulsion polymerization. Cryo-TEM characterization of the resulting composite latexes demonstrates the formation of anisotropic composite latex particles with mostly one platelet per particle. Monomer feed composition, chain length, and hydrophilic-lipophilic balance of the RAFT copolymer were found to be important factors for the overall efficiency of the encapsulation. Good control over platelet orientation and high encapsulation efficiency were achieved via this route.