Dye-hybrid Polyphosphazene Particle Prepared by Acid-base Interaction and Its Emulsifying Performance

The surface modification of colloidal particles using intermolecular weak interactions, such as electrostatic interaction, pi-pi interaction, and acid-base interaction, could endow the particles with environmental stimulus responsiveness, and it is more convenient and mild compared with chemical approach. In this study, dyehybrid polyphosphazene particles (PZS@RhB) was facilely prepared by surface modification of poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) particles with Rhodamine B (RhB), an acidic organic dye, by acid-base interaction. The chemical structure, morphology, surface wettability and pH-responsiveness of PZS@RhB particles were characterized by Fourier transform infrared spectroscopy, UV-Vis absorption spectroscopy, scanning electron microscopy, water contact angle test, and conductivity measurement, respectively. The emulsifying performance of PZS@RhB particles as Pickering stabilizer was further investigated, and the demulsification conditions and mechanism were also discussed. The results showed that the hydrophobicity of PZS particles was enhanced after RhB was adsorbed. Meanwhile, PZS@RhB particles exhibited pH-responsiveness due to the introduction of carboxyl groups from RhB. PZS@RhB particles could well stabilize toluene-water system (1:1, by volume) to form fine water-in-oil Pickering emulsion, when the concentration of particles in aqueous phase increased to 14 mg/mL. The obtained emulsion showed remarkable pH-responsiveness, derived from PZS@RhB particles. The stability and type of emulsion could be changed by adjusting pH of aqueous phase. When pH increased to 10.11, the surface of PZS@RhB particles was changed from hydrophobic to hydrophilic because of the continuous ionization of carboxyl groups, and thus the transition from W/0 to 0/W emulsion (phase inversion) took place. In addition, it was found that the demulsification of the emulsion was easily realized by adding a low amount of triethylamine, a stronger Lewis base compared to PZS, probably because the acid-base interaction established between PZS particles and RhB was disturbed, resulting in the desorption of RhB from the surface of PZS particles. Therefore, the surface wettability of the particles was changed, and the stability of the emulsion was destroyed. Considering above features, including pH-responsiveness, phase inversion behavior, and controllable emulsification, the emulsion stabilized by PZS@RhB particles has a great potential to be applied in various fields, such as biphasic catalysis and oil-water separation.