Dynamic Covalent Nanoparticles for Acid-Responsive Nonaqueous Pickering Emulsions

Abstract

Acid-responsive nonaqueous (glycerol in n-decane) Pickering emulsions were prepared using preferentially oil-wetted dynamic covalent silica (SiO 2 −pDB) nanoparticles as the Pickering emulsifiers. The acid-responsive Pickering emulsifier SiO 2 −pDB was prepared based on a Schiff base reaction between amino silica (SiO 2 −NH 2 ) and p-decanoxybenzaldehyde (pDBA). The formation of SiO 2 −pDB was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and elemental analysis. The preferentially oil-wetted character of SiO 2 −pDB was indicated by contact angle measurement. Stable nonaqueous Pickering emulsions were prepared using preferentially oilwetted SiO 2 −pDB as the Pickering emulsifier. However, after adjusting the nonaqueous Pickering emulsions to an acidic environment, complete phase separation occurred. In the acidic environment, preferentially oil-wetted SiO 2 − pDB decomposed into hydrophilic SiO 2 −NH 2 and hydrophobic pDBA due to the decomposition of the dynamic imine bond in the SiO 2 −pDB. Then, the hydrophilic SiO 2 −NH 2 and hydrophobic pDBA desorbed from the two-phase interface, resulting in complete phase separation of the initially stable nonaqueous Pickering emulsions. The acid-responsive nonaqueous Pickering emulsions show great potential in application in water sensitive systems, such as oil-based drilling fluids.

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

“…Recently, stimuli-responsive Pickering emulsions have received much attention [ 13 , 14 , 15 , 16 , 17 ]. So far, the stimuli of the Pickering emulsions include pH [ 18 , 19 , 20 ], magnetism [ 21 , 22 , 23 ], CO 2 [ 24 ], temperature [ 25 ], light irradiation [ 26 ], redox state [ 27 ], specific ion concentration [ 28 ], and so on.…”