Effect of the hydrophobicity of fumed silica particles and the nature of oil on the structure and rheological behavior of Pickering emulsions

Abstract

We studied the efficiency of Aerosil® fumed silica particles to emulsify oils with water. Pickering emulsions were prepared using 1%wt of particles displaying different degrees of hydrophobicity. 0.1 Pa^.s polydimethylsiloxane and paraffin oils were used to investigate the effect of the oil polarity and a 0.02 Pa^.s polydimethylsiloxane was used to check the effect of the viscosity on the structure and the rheological behavior. Macroscopic stability and emulsion composition were studied by visual observations. The emulsion structure and particle localization at the droplet interface were observed by confocal laser scanning microscopy (CLSM). Rheological properties of particle suspensions and emulsions were studied.

More hydrophobic particles led to water-in-oil emulsions with a lower elastic modulus and a lower emulsified volume fraction that decreased with the oil viscosity regardless the particles hydrophobicity. CSLM shows a particles localization at the droplet interface and evidences a network of particles in the continuous phase. The emulsion features are discussed in terms of the physicochemical characteristics of the particles, their ability to disperse in the oil phase and the viscosity of the latter. In addition, we show that the rheology of the particle suspensions is a relevant indication for their affinity with the liquid phases.

Graphical Abstract

Keywords:

• Emulsions
• Pickering emulsions
• silica particles
• rheology

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Brazilian funding agency CNPq (Conselho Nacional de Pesquisa) process no. 246416/2012-2.