Fabrication and stabilization of nanoscale emulsions by formation of a thin polymer membrane at the oil–water interface

Abstract

This study introduces a robust approach for the fabrication of extremely stable oil-in-water nanoemulsions in which the interface is stabilized by assembly of amphiphilic poly(ethylene oxide)-block-poly(3caprolactone) (PEO-b-PCL) copolymers. Phase inversion emulsification, induced by variation of the water volume fraction, facilitated effective assembly of the block copolymers at the oil-water interface.Subsequent application of simple probe-type sonication reduced the droplet size of the precursor emulsions to approximately 200 nm. The prepared nanoemulsions were surprisingly stable against drop coalescence and aggregation, as confirmed by analysis of changes in the droplet size after repeated freeze-thaw cycling and by monitoring the creaming kinetics under conditions of high ionic strength and density mismatch. The results highlight that good structural assembly of the PEO-b-PCL block copolymers at the oil-water interface generated a mechanically flexible but tough polymer film, thereby remarkably improving the emulsion stability.

Methods for producing microstructured hydrogels for targeted applications in biology

“…Owing to the benefit of amphipathy for stabilizers to migrate to and assemble at the phase interface, block copolymers are commonly used due to the versatility of having both hydrophilic and hydrophobic polymer chains conjugated in the same molecule. The capability of these materials to form semisolid structures and crystals impart both yield stress to the phases involved and stability against mechanical stress in the interface, so the coalescence is delayed and there is inherent steric repulsion of the polymer-covered domains [197,198]. Hydrophobic polymers such as poly(caprolactone), poly(lactide), and poly(hydroxypropyl methacrylate) and hydrophilic polymers like poly(glycerol) and poly(ethylene oxide) are the most commonly used combination for producing the copolymer emulsifiers [198][199][200].…”

“…The capability of these materials to form semisolid structures and crystals impart both yield stress to the phases involved and stability against mechanical stress in the interface, so the coalescence is delayed and there is inherent steric repulsion of the polymer-covered domains [197,198]. Hydrophobic polymers such as poly(caprolactone), poly(lactide), and poly(hydroxypropyl methacrylate) and hydrophilic polymers like poly(glycerol) and poly(ethylene oxide) are the most commonly used combination for producing the copolymer emulsifiers [198][199][200]. Triblock copolymers involving two different hydrophobic polymers and one hydrophilic have also been used to take advantage of the crystallization of the lipophilic moieties, which reinforces both the steric and elastic effects in the stabilization process [76].…”

Confined Self-Assembly of Block Copolymers within Emulsion Droplets: A Perspective

“…As BCPs are confined inside the emulsion droplet, the oil/water interface provides a soft and deformable template for BCPs. Therefore, the interactions between the interface and each individual block play a critical role in the self-assembly of BCPs. ,− Take the AB diblock copolymer as an example; if the oil/water interface is attractive to A-type monomers, AB diblock copolymers normally aggregate into spherical particles with an A-type outmost shell. Otherwise, if the oil/water interface is nearly neutral for both A and B blocks, BCPs tend to form the ellipsoid particles with an A–B striped structure .…”

Stabilization of Dispersed Oil Droplets in Nanoemulsions by Synergistic Effects of the Gemini Surfactant, PHPA Polymer, and Silica Nanoparticle

“…Nanoemulsion droplet sizes fall in the range 20–500 nm, depending on the composition and structural arrangement constituting emulsifier particles responsible for stabilization. , Selection of emulsifier(s) is critical for the phenomena of simultaneous droplet breakdown and droplet coalescence, which is a function of the interfacial energy barrier per unit area between the dispersed oil droplet and continuous aqueous phase. Controlling emulsion droplet stability and behavior plays a primary role in the development of many interesting properties, such as robust stability, low interfacial tension (IFT), and high surface area. − Nanoemulsions essentially permit solubilization and transport of hydrophobic materials within a water-based medium. This ability is useful in pharmaceutical applications and drug delivery research as carriers of nutrients, contrast agents, and drugs to targeted organs and tissues for treatment/imaging purposes. , In addition, nanoemulsions aid in crystallization of active pharmaceutical ingredients to form drug nanocrystals. , Nanoemulsions are also suitable in manufacturing smart cosmetic products to target external tissues .…”