Pickering emulsions synergistic-stabilized by amphoteric lignin and SiO2 nanoparticles: Stability and pH-responsive mechanism

The pH-responsive O/W Pickering emulsions were stabilized by amphoteric lignin (AML) absorbed with SiO 2 nanoparticles via electrostatic interaction. AML was gained by quaternary ammonium modification of alkali lignin, and its structure was characterized by 1 H NMR. Fourier transform infrared spectroscopies and Zeta potential measurements were performed to investigate the interaction between AML and SiO 2 . The formed AML@SiO 2 compounds were utilized to prepare Pickering emulsions. The influences of AML concentration and pH on emulsions were studied by rheological measurements and Turbiscan Lab Expert stability index system. The pH-responsive mechanism of Pickering emulsions was investigated by Zeta potential, quartz crystal microbalance with dissipation, atomic force microscopy and three-phase contact angle. The results indicated that at the pH range of 3-4, AML was absorbed on SiO 2 to realize the in-situ hydrophobization of SiO 2 , forming stable Pickering emulsions. When pH was above 4, only a little amount of AML was absorbed on SiO 2 due to the strong electrostatic repulsion between them, resulting in unstable emulsions. The emulsions could be cycled at least 5 times between emulsification and demulsification as well as exhibited excellent salt tolerance.