Robust pH-switchable pickering emulsions stabilized solely by organic Rosin-based particles with adjustable wettability

Pickering emulsions that are stabilized by organic particles that are issued from renewable sources have attracted considerable attention. However, developing green and robust Pickering emulsions of various types via simple methods has always been an important challenge. Herein, a rosin derivative, namely, maleopimaric acid (MPA), which has three carboxylic acid groups, is used to stabilize Pickering emulsions. Various types of gel-like Pickering emulsions can be obtained by adjusting the wettability of rigid MPA by changing the pH, such as water (W) in oil (O), O/W, double, and multiple emulsions. With increasing MPA concentration and volume fraction of the oil phase, phase inversion occurs from W/O to O/W and from O/W to W/O, respectively. The formed gel-like Pickering emulsions have excellent external stimulus and mechanical stabilities and can withstand high temperature (70 °C), freeze-thaw treatment and high centrifugal forces. These outstanding properties are due to the stable interfacial film and the network structure that are formed by the self-assembly of MPA with heterogeneous ionization degrees. This study provides a natural rosin-based solid stabilizer with adjustable wettability and further advances the design of stable Pickering emulsions with various structural features based on practical application needs.