pH-Responsive Non-Pickering Emulsion Stabilized by Dynamic Covalent Bond Surfactants and Nano-SiO₂ Particles

Abstract

A novel stimulus-responsive non-Pickering emulsion stabilized by nano-SiO2 particles was prepared in our recent study. 4-formylbenzoic acid and hexylamine through a dynamic covalent bond form a surface-active substance, which was confirmed by Fourier transform infrared (FTIR) and 1H NMR. Through optimization experiments, it was proved that a stable emulsion can be formed by low surfactant concentration (below cmc) and low nano-SiO2 particle concentration (0.5 wt %). In this emulsion, nano-SiO2 particles are not located at the interface of oil–water but dispersed in the continuous phase of the emulsion, which is different from the Pickering emulsion. The negatively charged nano-SiO2 particles and anionic surfactants repel each other, thereby synergistically stabilizing the emulsion so that the concentrations of surfactants and nanoparticles required to stabilize the emulsion are reduced. In addition, the system can also control the formation and fracture of dynamic covalent bonds by changing pH, thereby controlling the stability and demulsification of the emulsion. At the same time, this non-Pickering emulsion could be used as a microreactor for chemical synthesis and still had a high yield after three cycles. This study provides a new application direction for this environmentally friendly emulsion.

Titanium Dioxide Nanoparticle-Decorated Polymer Microcapsules Enclosing Phase Change Material for Thermal Energy Storage and Photocatalysis

“…36 The amount of nanoparticle and surfactant concentration required to stabilize emulsion is extremely low, i.e., nanoparticle loading can be as low as 0.001 wt %, and surfactant concentration can be well below its critical micelle concentration (CMC). 33 Here, a small quantity (critical micelle concentration, CMC/ 5) of tetradecyltrimethylammonium bromide (TTAB, a cationic surfactant, CMC = 1.16 mM) was used, assuming whole of the TTAB molecules get adhered to the surface of TiO 2 particles. The weight percent of TiO 2 was varied as 0.8, 1.7, 2.6, and 3.5% along with TTAB, keeping the TTAB/TiO 2 weight ratio constant at 0.15.…”

“…Therefore, it is mandatory to incorporate the “amphiphilic” character by altering the wettability of nanoparticles. In the non-Pickering emulsion technique, the hydrophilic TiO 2 nanoparticles are made partially hydrophobic by adsorbing a trace amount of cationic surfactant. , Cationic headgroups irreversibly adsorb at the nanoparticle surface because of electrostatic attraction, whereas the long C-14 hydrocarbon chain forms a hydrophobic monolayer, which renders amphiphilic nature to the nanoparticles. The amphiphilicity promotes the anchoring ability of nanoparticles at the oil–water interface and stabilization of the emulsion .…”

“…The key factor for non-Pickering emulsion stabilization is repulsive entropic forces and steric hindrance applied by nanoparticles in the water phase between dispersed oil droplets . The amount of nanoparticle and surfactant concentration required to stabilize emulsion is extremely low, i.e., nanoparticle loading can be as low as 0.001 wt %, and surfactant concentration can be well below its critical micelle concentration (CMC) . Here, a small quantity (critical micelle concentration, CMC/5) of tetradecyltrimethylammonium bromide (TTAB, a cationic surfactant, CMC = 1.16 mM) was used, assuming whole of the TTAB molecules get adhered to the surface of TiO 2 particles.…”

Fabrication and In Vitro/Vivo Evaluation of Drug Nanocrystals Self-Stabilized Pickering Emulsion for Oral Delivery of Quercetin

“…Among these solid particles, silica has been the most frequently used in the drug delivery systems of Pickering emulsions. Nevertheless, massive use of silica might take some adverse effects, such as neurotoxic damage, cytotoxicity, and renal damage [ 33 , 34 , 35 , 36 ]. Furthermore, Pickering emulsions usually have low drug loading capacity owing to the limitation of drug solubility in the oil phase.…”

Gelator-Enhanced Organohydrogels with Switchable Mechanics and High-Strain Shape-Memory Capacity

“…The hydrophilic PDMA and hydrophobic PLMA polymer chain segments are chemically connected at the oil–water interface during emulsion polymerization, producing an integrated amphiphilic network on the molecular dimension. The nanoclay plays an important role in this work. , On the one hand, it acts as a Pickering emulsifier that adsorbs on the oil/water interface to prevent the aggregation of oil droplets. − Owing to the high adsorption energy of these solid emulsifiers, Pickering emulsions generally show high stability compared to normal emulsions, even at high temperature . In this work, stable emulsions at high temperature are an indispensable condition due to the need for oil-phase fluidity and successful polymerization above T gel .…”