Dual Stimuli-Responsive Pickering Emulsions from Novel Magnetic Hydroxyapatite Nanoparticles and Their Characterization Using a Microfluidic Platform

Abstract

Stimuli-responsive emulsifiers have emerged as a class of smart agents that can permit regulated stabilization and destabilization of emulsions, which is essential for food, cosmetic, pharmaceutical, and petroleum industries. Here, we report the synthesis of novel “smart” hydroxyapatite (HaP) magnetic nanoparticles and their corresponding stimuli-responsive Pickering emulsions and explore their movement under confined spaces using a microfluidic platform. Pickering emulsions prepared with our magnetic stearic acid-functionalized Fe2O3@HaP nanoparticles exhibited pronounced pH-responsive behavior. We observed that the diameter of emulsion droplets decreases with an increase in pH. Swift demulsification was achieved by lowering the pH, whereas the reformation of emulsions was achieved by increasing the pH; this emulsification-demulsification cycling was successful for at least ten cycles. We used a microfluidic platform to test the stability of the emulsions under flowing conditions and their response to a magnetic field. We observed that the emulsion stability was diminished and droplet coalescence was enhanced by the application of the magnetic field. The smart nanoparticles we developed and their HaP-based emulsions present promising materials for pharmaceutical and petroleum industries, where responsive emulsions with controlled stabilities are required.

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives

“…We think that the smart tunability of the Pickering emulsion opens a new avenue for integrating the in situ catalyst recovery and product separation with the chemical reaction. Analogy to the concept of the thermoregulated phase transfer catalysis developed by Jin et al., [143] where a thermal response triggers the water‐soluble catalysts migrating to the organic phase to catalyze a reaction, building the smart emulsion system which responses to the external controllable stimuli such as magnetic field, [120,144] pH, [92,115,144b,145] CO 2 , [117–118,120] heat, [122,146] and light [123,132] was demonstrated to effectively switch the type and the stability of the Pickering emulsion. The stimulus‐responsive Pickering emulsion was proven to be the promising strategy to boost the catalyst/product recovery and the construction of the corresponding functional emulsifiers is becoming a front‐burner issue in the field, requiring the in‐depth study.…”

Advanced Materials Based on Nanosized Hydroxyapatite

“…We also showed that cell migration was inversely proportional to HAP concentration [ 97 ]. Along the same lines, the bibliography offers original studies covering different objectives that are worth consulting [ 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 ].…”

pH and Magnetism Dual-Responsive Pickering Emulsion Stabilized by Dynamic Covalent Fe3O4 Nanoparticles

“…Pickering emulsions responding to dual triggers such as temperature–pH [ 29 ], CO 2 –temperature [ 16 ], CO 2 –magnetism [ 14 , 30 ], and redox–magnetism [ 9 ] have been investigated. For CO 2 -stimulated systems, a long time and high ventilation are needed [ 31 ]. Light-stimulated systems are difficult to achieve because of the cloudy appearance of the Pickering emulsions [ 32 ].…”

“…Light-stimulated systems are difficult to achieve because of the cloudy appearance of the Pickering emulsions [ 32 ]. Temperature-stimulated systems are energy-demanding [ 31 ]. Among these stimuli, pH is readily implementable and magnetism is non-invasive and reversible [ 2 , 7 , 10 , 32 , 33 ].…”