Pickering Emulsifiers Based on Block Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly.

Saul J Hunter,Steven P Armes

doi:10.1021/acs.langmuir.0c02595

Abstract

Block copolymer nanoparticles prepared via polymerization-induced self-assembly (PISA) represent an emerging class of organic Pickering emulsifiers. Such nanoparticles are readily prepared by chain-extending a soluble homopolymer precursor using a carefully selected second monomer that forms an insoluble block in the chosen solvent. As the second block grows, it undergoes phase separation that drives in situ self-assembly to form sterically stabilized nanoparticles. Conducting such PISA syntheses in aqueous solution leads to hydrophilic nanoparticles that enable the formation of oil-in-water emulsions. Alternatively, hydrophobic nanoparticles can be prepared in non-polar media (e.g., n-alkanes), which enables water-in-oil emulsions to be produced. In this review, the specific advantages of using PISA to prepare such bespoke Pickering emulsifiers are highlighted, which include fine control over particle size, copolymer morphology, and surface wettability. This has enabled various fundamental scientific questions regarding Pickering emulsions to be addressed. Moreover, block copolymer nanoparticles can be used to prepare Pickering emulsions over various length scales, with mean droplet diameters ranging from millimeters to less than 200 nm.

Highlights

At the turn of the last century, Ramsden[1] and Pickering[2] independently discovered that various types of particles can stabilize emulsions
The particle size, copolymer morphology, and surface chemistry can be predicted by selecting appropriate steric stabilizer and structure-directing blocks and targeting the desired DPs
Many of these nano-objects can be used as model polymer-based Pickering emulsifiers to examine the effect of varying the particle size, morphology, surface roughness, and surface charge

Summary

■ INTRODUCTION

At the turn of the last century, Ramsden[1] and Pickering[2] independently discovered that various types of particles can stabilize emulsions. Rymaruk and co-workers reported that a range of poly(3-[tris(trimethylsiloxy)silyl]propyl methacrylate)-poly(benzyl methacrylate) (PSiMA-PBzMA) spheres could be prepared directly in a low-viscosity silicone oil (DM5).[213] Such sterically stabilized nanoparticles were evaluated as Pickering emulsifiers for ten biosourced oils For three of these oils, using a copolymer concentration of 2.0% w/w and a DM5 volume fraction of 0.50 led to the formation of oil-in-oil Pickering emulsions, with DM5 forming the continuous phase in each case (Figure 12a). In contrast to the PGMA-PHPMA-PBzMA worms, droplet diameters for emulsions prepared using PGMAPHPMA worms remained relatively constant with increasing copolymer concentration This indicates that such worms dissociate even during low-shear emulsification, generating individual amphiphilic diblock copolymer chains that adsorb at the oil/water interface, rather than nanoparticles. This study highlights the versatility and potential offered by PISA for the rational design of bespoke Pickering emulsifiers of tunable size and surface chemistry

■ CONCLUSIONS AND PROSPECT

■ ACKNOWLEDGMENTS

Findings

■ REFERENCES