A pH switchable Pickering emulsion stabilised by controlled non-conventional lanthanum sulfide nanoparticles, in situ hydrophobized with a cationic surfactant

Abstract

Herein, microemulsion mediated controlled lanthanide metal based nanoparticles are employed in the preparation of a pH responsive Pickering emulsion. Lanthanum sulfide (LaS) nanoparticles are synthesised in the core of a water-in-oil microemulsion, prepared by Tween 80/1-butanol/water/toluene. The TEM images obtained, were used to evaluate the stages of the progress of nanosphere preparation. Novel oil-in-water (O/W) Pickering emulsions have been produced with the assistance of negatively charged, size and shape regulated lanthanum sulfide nanoparticles (0.05 wt%) and an adequate amount of a cationic CTAB surfactant. Adsorption of an ionic surfactant onto the surface of oppositely charged nanoparticles typically occurs in slightly acidic or neutral environments (pH 5.33 to 6.16), converting hydrophilic nanoparticles to hydrophobic ones through in situ hydrophobization. Because the emulsions are sensitive to pH alterations, an effective demulsification can be accomplished by pH changes. Demulsification occurs at two distinct pH ranges: a lower pH (3.50) and a higher pH (10.50). Surfactant molecules are desorbed from the surfaces of nanoparticles at these two pH ranges, causing the particles to revert to their hydrophilic form. Desorption of hydrophilic nanoparticles from the water–oil interface caused the Pickering emulsion to become unstable. Remulsification is achieved by just adjusting the pH with the addition KOH or HCl. It is feasible to produce eight consecutive cycles of emulsification and demulsification by just changing the pH. Thus, by using size- and shape-controlled nanoparticles, this study introduces an entirely new scientific perspective on the synthesis of distinct characteristics (likewise to pH responsiveness) of the Pickering emulsion.