Nanohybrids from Direct Chemical Self-Assembly of Poly(styrene-alt-maleic anhydride) as pH-Responsive Particulate Emulsifiers

The nanohybrid particulate emulsifiers based on poly(styrene-alt-maleic anhydride) (SMA) were facilely prepared via the direct chemical self-assembly triggered by the aminolysis of SMA with 3-aminopropyltriethoxysilane (APTES) and the in situ polycondensation of APTES under refluxing in acetone. Transmission electron microscopy and scanning electron microscopy confirmed the spherical-like morphology of the nanohybrids. Dynamic light scattering and electrophoresis revealed the structure transition of the nanohybrids in response to pH change. The emulsification study showed that the nanohybrids were effective particulate emulsifiers when homogenized with various oils including toluene, paraffin oil, silicone oil, isooctyl palmitate, dicaprylyl carbonate, and propylheptyl caprylate. The nanohybrid particulate emulsifiers exhibited pH-sensitivity, and the diameter of paraffin oil droplets remarkably increased with pH of the nanohybrid aqueous dispersion decrease. Also, the reduced dynamic interfacial tension predicted the thermodynamically unstable state of the emulsions prepared at high pH values. Most interesting, the paraffin oil-in-water high internal phase emulsions (HIPEs) with a high oil volume fraction of 83.3% were formed when the nanohybrids were heavily flocculated by adding HCl. The HIPEs were pH-responsive and capable of demulsification with the addition of an alkaline solution showing a potential application in the oil industry.