A Highly Anisotropic and Hydrolytically Degradable Pickering Emulsifier for Oil-in-Water Emulsions

Highly anisotropic poly(l-lactide)-based block copolymer nanoparticles are prepared by the judicious combination of reverse sequence polymerization-induced self-assembly with crystallization-driven self-assembly (CDSA). Such nanoparticles can be efficiently prepared as a 30% w/w aqueous dispersion and possess a distinctive diamond platelet morphology as judged by transmission electron microscopy. X-ray diffraction studies confirm the semicrystalline nature of the poly(l-lactide) block, while atomic force microscopy analysis suggests a mean thickness of approximately 6 nm for the dried platelets. Small-angle X-ray scattering studies suggest that these platelets form localized tactoids at copolymer concentrations as low as 1.0% w/w. Herein we evaluate these platelets as a new hydrolytically degradable Pickering emulsifier for the preparation of oil-in-water emulsions using various oils. In the case of squalane, systematic variation of the copolymer concentration and the high-shear homogenization conditions enabled the mean oil droplet diameter to be varied from approximately 40 to 125 μm. Fluorescein-labeled platelets were imaged on the surface of oil droplets using confocal microscopy. Such studies indicate submonolayer surface coverage of the droplets even under optimized conditions, which may account for the unexpected long-term instability observed for such Pickering emulsions.