Development and characterisation of a continuous phase based on a fumed silica and a green surfactant with emulsion applications

Interfacial Cooperative Assembly of Surfactants and Opposite Wettability Nanoparticles Stabilizes Water-in-Oil Emulsions at High Temperature

Pickering emulsions have promising applications in the development of unconventional oil and gas resources. However, the high-temperature environment of the reservoir is not conducive to the stabilization of Pickering emulsions. In addition, the preparation of Pickering emulsions under low-energy emulsification and low-concentration emulsifier conditions is a difficult challenge. Here, we report a high-temperature resistant water-in-paraffin oil Pickering emulsion, which is synergistically stabilized by polyglycerol ester (PGE) and nanoparticles with opposite wettability (lipophilic silica and hydrophilic alumina). This emulsion can be prepared under mild stirring (500 rpm) conditions and can be stable at 140 °C for at least 30 days. The synergistic effects of surfactant, silicon nanoparticles (MSNPs) with different wettability, and alumina nanoparticles (AONPs) on the stability of both emulsions and water-oil interfacial membranes were investigated through bottle experiments, cryogenic scanning electron microscopy (cryo-SEM), optical microscopy, fluorescence microscopy, etc. The results showed that both hydrophobic MSNPs and hydrophilic AONPs are adsorbed together at the water-oil interface to stabilize the W/O emulsion, which can be prepared by 500 rpm stirring. The stability of emulsions strongly depends on the wettability of MSNPs, and the MSNP with moderate hydrophobicity (for example, aqueous phase contact angle of 136°) makes the emulsion exhibit the highest stability against aggregation and settling at elevated temperatures. The emulsion stabilization mechanism was revealed in terms of the adsorption capacity of the surfactant by MSNPs, the adsorption morphology and desorption energy of nanoparticles at the water-oil interface adsorption layer, and emulsion rheology. These findings demonstrate a novel and simple strategy to prepare Pickering W/O emulsions with high-temperature stability at low shear strength.

Development of Avocado and Lemon Oil Emulgels Based on Natural Products: Phycocyanin and Pectin

Phycocyanin (PC), a natural product obtained from algae, is attracting attention due to its health benefits, such as its antioxidant and anti-inflammatory properties. This work studies the use of PC as the main stabilizer in avocado and lemon oil emulgels, a format for drug delivery. The influence of PC concentration on droplet size distribution, rheological properties, and physical stability is studied using a laser diffraction technique, rheological measurements, and multiple light scattering. The 5 wt.% PC emulsions show the lowest droplet size and, consequently, the best stability against creaming and droplet growth. Emulsions formulated with PC as the only stabilizer show a slight pseudoplastic character with an apparent viscosity below 10 mPa·s at 2 Pa. This indicates that these emulsions undergo creaming with aging time. In order to reduce creaming, pectin is incorporated into the 5 wt.% PC emulsion at different concentrations. Interestingly, yield stress and an incipient gel character are observed due to the presence of pectin. This is why the creaming mechanism is reduced. In conclusion, PC forms a layer that protects the interface against coalescence and Ostwald ripening. And, pectin is incorporated to reduce creaming. This research has the potential to make valuable contributions to diverse fields, such as health, medicine, and encapsulation technology.

Strategies for reducing Ostwald ripening phenomenon in nanoemulsions based on thyme essential oil

BACKGROUND

White thyme essential oil, which can be incorporated in clean-label and food emulsion-based products, is a natural antimicrobial agent. However, emulsions containing essential oils commonly undergo Ostwald ripening as the main destabilization process. The main objective of this work was to evaluate various strategies for the inhibition of Ostwald ripening so as to develop stable nanoemulsions containing white thyme essential oil as food preservative and Kolliphor EL as surfactant.

RESULTS

In a first approach, the influence of the surfactant/dispersed phase ratio and the number of cycles through a microfluidizer on droplet size distribution was evaluated. Unfortunately, these emulsions underwent Ostwald ripening, which was demonstrated by the application of the Lifshitz-Slyozov-Wagner theory. In order to reduce this destabilization mechanism, two different techniques based on the modification of the formulation (addition of rosin gum or Aerosil COK84) were analysed using laser diffraction and multiple light scattering techniques. The addition of rosin gum inhibited the Ostwald ripening mechanism, but only partially. Conversely, the incorporation of Aerosil COK84 to the continuous phase led to a gel-like rheological behaviour which seemed to practically avoid Ostwald ripening.

CONCLUSIONS

Aerosil particles cover the droplets and form a three-dimensional network suggesting a Pickering stabilization, which was confirmed using transmission electronic microscopy. The results confirmed the role of Aerosil COK84, not only as a thickener or gelling agent, but also as an Ostwald ripening inhibitor. © 2019 Society of Chemical Industry.