Preparation of Pickering emulsions through interfacial adsorption by soft cyclodextrin nanogels.

Shintaro Kawano,Hirofumi Sato,Motohiro Shizuma,Mitsuru Akashi,Toshiyuki Kida,Daisuke Ono

doi:10.3762/bjoc.11.257

Abstract

Background: Emulsions stabilized by colloidal particles are known as Pickering emulsions. To date, soft microgel particles as well as inorganic and organic particles have been utilized as Pickering emulsifiers. Although cyclodextrin (CD) works as an attractive emulsion stabilizer through the formation of a CD–oil complex at the oil–water interface, a high concentration of CD is normally required. Our research focuses on an effective Pickering emulsifier based on a soft colloidal CD polymer (CD nanogel) with a unique surface-active property.Results: CD nanogels were prepared by crosslinking heptakis(2,6-di-O-methyl)-β-cyclodextrin with phenyl diisocyanate and subsequent immersion of the resulting polymer in water. A dynamic light scattering study shows that primary CD nanogels with 30–50 nm diameter assemble into larger CD nanogels with 120 nm diameter by an increase in the concentration of CD nanogel from 0.01 to 0.1 wt %. The CD nanogel has a surface-active property at the air–water interface, which reduces the surface tension of water. The CD nanogel works as an effective Pickering emulsion stabilizer even at a low concentration (0.1 wt %), forming stable oil-in-water emulsions through interfacial adsorption by the CD nanogels.Conclusion: Soft CD nanogel particles adsorb at the oil–water interface with an effective coverage by forming a strong interconnected network and form a stable Pickering emulsion. The adsorption property of CD nanogels on the droplet surface has great potential to become new microcapsule building blocks with porous surfaces. These microcapsules may act as stimuli-responsive nanocarriers and nanocontainers.

Highlights

Pickering emulsions, which are emulsions stabilized by colloidal particles instead of conventional low-molecularweight surfactants [1], are formed through the adsorption of colloidal particles at an oil–water interface to give stable emulsion droplets
We have previously reported urethane-crosslinked CD polymers, which were prepared by reacting heptakis(2,6-di-Omethyl)-β-cyclodextrins (DM-β-CDs) with aromatic diisocyanates such as 4,4’-methylenebis(phenyl isocyanate) (MDI) and 1,4-phenylene diisocyanate (PDI) [18]
Nanometer-sized CD nanogels were prepared by crosslinking DM-β-CD with PDI and subsequent immersion of the resulting polymers in water (Figure 1)

Summary

Results

CD nanogels were prepared by crosslinking heptakis(2,6-di-O-methyl)-β-cyclodextrin with phenyl diisocyanate and subsequent immersion of the resulting polymer in water. A dynamic light scattering study shows that primary CD nanogels with 30–50 nm diameter assemble into larger CD nanogels with 120 nm diameter by an increase in the concentration of CD nanogel from 0.01 to 0.1 wt %. The CD nanogel has a surface-active property at the air–water interface, which reduces the surface tension of water. The CD nanogel works as an effective Pickering emulsion stabilizer even at a low concentration (0.1 wt %), forming stable oil-in-water emulsions through interfacial adsorption by the CD nanogels

Conclusion

Introduction

Results and Discussion