Dynamic Covalent Nanoparticles for Acid-Responsive Nonaqueous Pickering Emulsions

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 oil-wetted 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.