Thermoresponsive Water-in-Oil-in-Water Pickering Double Emulsions Stabilized with Biodegradable and Semicrystalline Poly(ethylene glycol)-b-poly(ε-caprolactone-co-δ-valerolactone) Diblock Copolymer Micelles for Controlled Release

Abstract

Water-in-oil-in-water (W/O/W) Pickering double emulsions are promising materials for the construction of carriers for water-soluble and oil-soluble molecules or drug delivery systems if the contradictive trade-off between their extreme stability and controlled release properties can be resolved. In this study, biodegradable and biocompatible poly(ethylene glycol)-b-poly(ε-caprolactone-co-δ-valerolactone) (PEG-b-PCVL) diblock copolymers with predesigned hydrophilic to hydrophobic block length ratios and nearly identical ε-caprolactone/δ-valerolactone molar ratio (8/2), were synthesized by ring-opening copolymerization. Then, they self-assembled to create semicrystalline micelles. The melting points of PEG-b-PCVL copolymers and their lyophilized micelles were within a physiological range of temperatures, as determined by differential scanning calorimetry. Water contact angle measurements provided evidence that the surface wettability of PEG-b-PCVL micelles could be tuned by the PCVL block mass fractions or temperature stimulus. Such PEG-b-PCVL micelles were employed as a single particulate stabilizer to develop Pickering double emulsions through a one-step emulsification technique. W/O/W Pickering double emulsions could be generated using relatively hydrophobic PEG-b-PCVL micelles with high mass fractions (exceeding about 89%) of PCVL blocks, and they displayed excellent long-term physical stabilities at room temperature. However, the Pickering double emulsions underwent a rapid microstructural transition into simple oil-in-water Pickering emulsions instead of complete demulsification at elevated temperature (37 °C), which was attributed to the hydrophilicity of micelles enhanced when the core-forming PCVL melted realized by temperature stimulus. Consequently, such W/O/W Pickering double emulsions stabilized solely with semicrystalline PEG-b-PCVL micelles exhibit thermal responsiveness, enabling them to release vitamin B12 encapsulated within the internal aqueous phase rapidly.

Preparation of Temperature-Sensitive SiO2–PSBMA for Reducing the Viscosity of Heavy Oil

“…Although the long chain of the PSBMA polymer is amphiphilic, its hydrophilicity is dominant at high temperatures. In addition, when the water proportion is 80%, these long chains are more easily soaked by the water phase, so the O/W interface can be formed during the emulsification process, thus forming a more stable O/W Pickering emulsion. This is different from other applications of amphiphilic ion nanoparticles. − As shown in Figure , the heavy oil was well dispersed in water to form a brown emulsion at 60 °C.…”

One-Step Formation of Pickering Double Emulsion Costabilized by Hydrophobic Silica Nanoparticles and Sodium Alginate

“…27 prepare Pickering double emulsions. 30 However, particle stabilizers discussed in these research studies usually require particular surface modifications or tailored design and synthesis, which complicates the double emulsion preparation and compromises the large-scale adoption of particle stabilizers. Microfluidic emulsification has also been developed that uses various flow focusing techniques to prepare double emulsions with high monodispersity in a one-step process, which is more appropriate for surfactant-based systems.…”

“…Due to its ease of use and effectiveness, one-step emulsification has recently attracted increasing attention for preparing Pickering double emulsions in situations near phase inversion . Typically, this emulsification uses a single particle stabilizer, mainly including inorganic particles and synthetic polymer particles (micelles, microgel, and latex), with either intermediate hydrophobicity or a distribution of wettability. − For example, Bai et al prepared O/W/O Pickering double emulsions using palmitoyl chloride to increase the hydrophobicity of diatomite particles . A W/O/W Pickering double emulsion with amphiphilic Janus particles that have a hydrophilic area rich in acrylic acid and a hydrophobic area rich in styrene was described by Lee et al Nonomura et al found that silicone particles shaped like a bowl with varying wettability caused by contact angle hysteresis due to solvent entrapment can stabilize Pickering double emulsions .…”

“…A W/O/W Pickering double emulsion with amphiphilic Janus particles that have a hydrophilic area rich in acrylic acid and a hydrophobic area rich in styrene was described by Lee et al Nonomura et al found that silicone particles shaped like a bowl with varying wettability caused by contact angle hysteresis due to solvent entrapment can stabilize Pickering double emulsions . Lin et al first synthesized block copolymer micelles with predesigned hydrophilic and hydrophobic block lengths and used them to prepare Pickering double emulsions . However, particle stabilizers discussed in these research studies usually require particular surface modifications or tailored design and synthesis, which complicates the double emulsion preparation and compromises the large-scale adoption of particle stabilizers.…”

“… 27 Lin et al first synthesized block copolymer micelles with predesigned hydrophilic and hydrophobic block lengths and used them to prepare Pickering double emulsions. 30 However, particle stabilizers discussed in these research studies usually require particular surface modifications or tailored design and synthesis, which complicates the double emulsion preparation and compromises the large-scale adoption of particle stabilizers.…”