Abstract Nanocellulose-stabilized Pickering emulsions typically utilize oils that display high interfacial tension with water. For the first time, this work describes the stabilization of aniline (12 wt.%)-in-water emulsions, where the interfacial tension lies below 6 mN/m. The stabilizing agent consisted of oxidized cellulose nanofibrils (CNFs). While the density of aniline, alike to that of water, granted high kinetic stability with 0.18 wt.% CNFs (3 days), phase separation was avoided for at least 30 days if CNF concentration was 0.28 wt.% or higher. Easily dispersible polyaniline was attained by adding orthophosphoric acid (doping), sodium dihydrogen orthophosphate (pH adjusting), and ammonium persulfate (initiator) to a previously prepared aniline-in-water emulsion (dispersion polymerization). The resulting dispersions did not suffer from creaming or sedimentation. Polyaniline samples exhibited average molecular weights below 100 kDa. They were hardly electroconductive and possessed relatively low thermal stability, but they were chromogenic. Owing to the latter feature and to the suitable rheological behavior of the suspensions, packaging paper was coated on one side with those samples to produce visually responsive sheets. When their uncoated side was exposed to gaseous ammonia, volatile amines, or spoiled fish (cod, hake, and salmon), their green-colored surface (emeraldine salt) turned blue (emeraldine base). Electron microscopy assays ruled out diffusion of polyaniline from the coated side to the exposed side. Overall, the strategy presented here implies several innovative advantages: allowing for the high-concentration polymerization of aniline, keeping the polymer dispersed, and producing suspensions that can be readily applied to the manufacture of smart food packaging.
Aguado et al. (Tue,) studied this question.