Sol–gel microencapsulation of oil phase with Pickering and nonionic surfactant based emulsions

• Silica shell particles were successfully prepared by sol–gel synthesis.
• 1 wt.-% of silica nano particles allows preparation of highly stable emulsions.
• Utilization of nano particles conduces to smoother and denser particles.
• Both classical surfactant and nano particles lead to satisfying thermal stability.

Sol–gel polycondensation was used to encapsulate two different kinds of core with a silica shell, i.e. castor oil which is considered as a model active agent, and bisphenol A bis(diphenyl phosphate), an insoluble liquid fire retardant. The influence of the nature of the emulsifier was also studied, i.e. Pickering emulsion based on the interface stabilization performed by the organization of solid nanoparticles was compared to a classical emulsion process using a non-ionic surfactant. The influence of both cores and emulsifiers on the stability of emulsion was studied by granulometric analysis, optical microscopy and macroscopic morphology (from nacked-eye observations). The sol–gel encapsulation efficiency was assessed by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. Finally, thermal stability of microcapsules was evaluated by thermogravimetric analysis (TGA). Results show that both Pickering and classical emulsions processing allow successful sol–gel encapsulation of castor oil and bisphenol A bis (diphenyl phosphate) with a satisfying thermal stability for textile application. However, the use of Pickering emulsion with nanoparticles provides more highly stable emulsions and promotes silica shell formation.

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