Anion effect on the tunable stability of a thermoresponsive pickering emulsion based on SiO₂-PNIPAM

Thermoresponsive hybrid particles of SiO₂-PNIPAM (PNIPAM: poly(N-isopropyl acrylamide) were synthesized by surface initiated atom transfer radical polymerization (SI-ATRP). The structure of hybrid particles was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The grafting ratio of PNIPAM on the silica surface was about 103.7%as measured by thermogravimetric analysis (TGA). The thermoresponsive behavior of monodisperse hybrid particles was analyzed by dynamic light scattering (DLS), and its lower critical solution temperature (LCST) is 30 °C. The influence of anions on the wettability of hybrid particles was studied by measuring the surface contact angle. A large stability difference of the emulsion based on SiO₂-PNIPAM exists between 40 and 10 °C. The degree of flocculation of hybrid particles shows a significant influence on the stability of the emulsion. The emulsion stability is dependent on the electrostatic interaction and salting out caused by the solvation effect. This stability is tunable by introducing different anions at different concentrations.