Encapsulation of montmorillonite in nanoparticles by miniemulsion polymerization

Synthesis of a paraffin phase change material microencapsulated in a siloxane polymer

The coemulsification method suitable for the formulation of microcapsules of n-eicosane coated with a polysiloxane is developed. This method allows to synthesize core–shell microcapsules of paraffin which have the shape of spheres or distorted spheres and are designed for the use as phase change materials. The microcapsules are formed in aqueous phase by the precipitation of n-eicosane together with modified polyhydromethylsiloxane from a common solvent which is miscible with aqueous media. The polysiloxane is modified by the attachment of silylvinyl and alkoxy functions before coemulsification with the paraffin. It also contains the Pt(0) Karstedt catalyst. The microcapsules formed by coemulsification are stabilized by the in situ cross-linking of the polysiloxane shell. The shell is additionally modified by the in situ generation of silanol groups which provide colloidal stabilization of microspheres in aqueous phase. Microcapsules were studied by DSC, SEM, optical polarized microscope, and by thermooptical analysis (TOA).

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.

Miniemulsion polymerization and the structure of polymer and hybrid nanoparticles

The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.