Pickering emulsions stabilized by palygorskite particles grafted with pH-responsive polymer brushes

Poly(2-(diethylamino)ethyl methacrylate (PDEAEMA) was grafted from the surface of palygorskite (PAL) particulates via Cu(0) radical polymerization to form PAL–PDEAEMA nanocomposites. The successful grafting was confirmed by Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), and elemental analysis (EA). Water (pH 9)/toluene (W/O) Pickering emulsions stabilized by PAL–PDEAEMA particles were prepared. Spherical emulsion droplets with absorbed small PAL–PDEAEMA aggregates on the interface were observed via scanning electron microscopy (SEM), polarizing optical microscopy (POM) and optical microscopy (OM). The size of the emulsion droplets was decreased with the increase of PAL–PDEAEMA particle concentrations, and reached a limited value at 2 wt%. By changing the pH of water (pH < 3), O/W Pickering emulsions were formed by the same PAL–PDEAEMA particles. Moreover, W/O emulsion–de-emulsion–O/W emulsion transitions can be realized simply by adding HCl/NaOH, which can last at least 7 successive cycles. Therefore, a reversible Pickering emulsion system switched by pH can result on the basis of PAL–PDEAEMA particles.