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ARTICLE IN PRESS
Colloids and Surfaces A: Physicochem. Eng. Aspects xxx (2010) xxx–xxx

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Colloids and Surfaces A: Physicochemical and Engineering Aspects
journal homepage: www.elsevier.com/locate/colsurfa

Evolution of water-in-oil emulsions stabilized with solid particles Influence of added emulsifier
AudreyDrelich, Francois Gomez, Danièle Clausse, Isabelle Pezron ∗ ¸
Groupe Interfaces et Milieux Divisés, EA 4297 Transformations Intégrées de la Matière Renouvelable, Université de Technologie de Compiègne, BP 20529, 60200 Compiègne Cedex, France

a r t i c l e

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a b s t r a c t
Water-in-oil emulsions made of water droplets dispersed in a continuous paraffin oil phase were prepared andstabilized with hydrophobic silica particles alone. Differential scanning calorimetry (DSC) experiments were carried out to characterize the water droplets freezing transitions and their evolution with time. Water droplet size distribution, oil–water interfacial tension, and rheological stress–strain properties were determined alongside to better understand the role of particles in the formationand stabilization of emulsions. The results obtained were compared to the properties of emulsions prepared with a non-ionic emulsifier, sorbitan monooleate. No interfacial tension reduction was observed at the oil/water interface in presence of particles. As a consequence, the fragmentation of water into droplets required more energy in absence of surface-active emulsifiers. The resulting emulsiondroplet size distribution is polydisperse and contains large droplets. Rheology measurements showed that the stability of the emulsion prepared with particles originates from the formation of a 3D network of particles in the continuous oil phase. In emulsion samples containing sorbitan monooleate, calorimetry experiments revealed a progressive displacement of the water droplet freezing transitiondue to a change in ice nucleation mechanism. The interpretation points out a possible reorganization of the emulsifier film at the water/oil interface, which could modify the conditions of crystallization of dispersed water droplets and affect the emulsion long-term stability. Calorimetry, when used together with other techniques, such as laser light scattering, provides complementary information onthe evolution with time of the structure of the emulsion. © 2010 Elsevier B.V. All rights reserved.

Article history: Received 30 October 2009 Received in revised form 15 January 2010 Accepted 19 January 2010 Available online xxx Keywords: Solid-stabilized water-in-oil emulsions Differential scanning calorimetry Water droplet crystallization Rheology Laser diffraction Droplet size distributionEmulsion stability

1. Introduction Solid-stabilized emulsions have received a lot of attention recently as the replacement of surface-active emulsifiers by solid particles is considered to improve their long-term stability [1–3]. However the mechanism of emulsion stabilization by solid particles, and their interaction with surface-active material is no fully understood [4]. Emulsions are unstablesystems which ultimately evolve towards the separation of the oil and water phases. For manufactured emulsions, the challenge is to control the system stability and avoid its destabilization during storage, for instance when environmental conditions, such as temperature, change. Conversely, for natural emulsions, as petroleum emulsions formed during crudeoil extraction, destabilization of thesystem and separation of the two phases is generally required. With time, the distribution of water droplets in the continuous oil phase of the emulsion will

∗ Corresponding author. Tel.: +33 3 44 23 46 18; fax: +33 3 44 23 19 80. E-mail address: isabelle.pezron@utc.fr (I. Pezron). 0927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.01.042...