Formation of Pickering Emulsions Stabilized via Interaction between Nanoparticles Dispersed in Aqueous Phase and Polymer End Groups Dissolved in Oil Phase

Abstract

The influence of end groups of a polymer dissolved in an oil phase on the formation of a Pickering-type hydroxyapatite (HAp) nanoparticle-stabilized emulsion and on the morphology of HAp nanoparticle-coated microspheres prepared by evaporating solvent from the emulsion was investigated. Polystyrene (PS) molecules with varying end groups and molecular weights were used as model polymers. Although HAp nanoparticles alone could not function as a particulate emulsifier for stabilizing dichloromethane (oil) droplets, oil droplets could be stabilized with the aid of carboxyl end groups of the polymers dissolved in the oil phase. Lower-molecular-weight PS molecules containing carboxyl end groups formed small droplets and deflated microspheres, due to the higher concentration of carboxyl groups on the droplet/microsphere surface and hence stronger adsorption of the nanoparticles at the water/oil interface. In addition, Pickering-type suspension polymerization of styrene droplets stabilized by PS molecules containing carboxyl end groups successfully led to the formation of spherical HAp-coated microspheres.

An Overview of Pickering Emulsions: Solid-Particle Materials, Classification, Morphology, and Applications

“…A latter study further confirmed that the interactions between end groups of polymers and Hap nanoparticles at the oil–water interface were crucial in stabilizing Pickering emulsions as well as regulating the size of droplets and the morphology of products; the researchers chose polystyrene (PS) molecules with diverse end groups (like carboxyl groups, ester groups) and molecular weights to investigate their influence on the formation of Hap nanoparticle-stabilized droplets and MSs (Okada et al, 2012). Another work also utilized the interaction between the Hap nanoparticles and carbonyl/carboxylic acid groups, while the creative part was to add poly(ε-caprolactone) (PCL) which could dissolve in a wider range of organic solvents compared with another two polyesters, poly( L -lactic acid) (PLLA) and poly( L -lactide-co-glycolide) (PLGA); this means that non-halogenated solvents can be used (Fujii et al, 2012).…”

Hydroxylapatite nanoparticles: fabrication methods and medical applications

“…Although no stable emulsion was obtained using oils without an ester group (e.g. dichloromethane), dichloromethane droplets could be stabilized by dissolving polymers having ester groups (or carboxyl terminal group) via the interaction between polymer and HAp nanoparticles at the oil/water interfaces [285,286]. It was also demonstrated that emulsification-demulsification cycles could be repeatedly achieved by pH adjustment, because the HAp-adsorbed emulsion droplets became unstable at lower pH (< 4) and the emulsion stability was recovered by raising pH.…”

Effect of Pickering emulsion on the mechanical performances and fracture toughness of epoxy composites

“…Polystyrene/nano‐SiO 2 composite microspheres with core/shell structure were synthesized in a Pickering emulsion route using nano‐SiO 2 particles as stabilizers . Okada et al supposed a method for the synthesis of Pickering emulsion stabilized via interaction between nanoparticles and polymer end groups. Gao et al constructed a Pickering emulsion stabilized by glucose oxidase and catalase‐containing silica particles.…”