Triple Phase Inversion of Emulsions Stabilized by Amphiphilic Graphene Oxide and Cationic Surfactants

Amphiphilic graphene oxide (A-GO) with grafted octylamine was prepared via a one-step method of N,N'-dicyclohexylcarbodiimide coupling and epoxide ring opening at a mild temperature of 40 °C. The phase of oil-water emulsion stabilized by the complexes of A-GO and the cetyltrimethyl ammonium bromide (CTAB) surfactant could invert three times by adding CTAB or A-GO. This process was called triple phase inversion, which was a function of the concentration of A-GO or CTAB surfactants. The conductivity and zeta potential measurements confirmed that CTAB could influence the carboxyl ionization of A-GO. In addition, the turbidity of the A-GO and CTAB mixed dispersion system revealed that the appearance and disappearance of precipitation occurred when CTAB or A-GO concentration was increased. Meanwhile, the emulsion prepared by mixing the dispersion with an equal volume of xylene at a fixed CTAB concentration also showed triple phase inversion as the A-GO concentration varied. Results indicated that the stability of the emulsion and the size of the emulsion droplets had a certain correlation during the phase inversion process, which varied with the concentration of CTAB or A-GO.