Applied Colloids Surfactants

Speeding up the evaluation of emulsion stability during normal storage conditions

T. Sobisch, D. Lerche

LUM

Rudower Chaussee 29 (OWZ) 12489 Berlin / Germany

info@lum-gmbh.de, www.lum-gmbh.com

Abstract

The principle of inclined settling is often used in separation technology to increase capacity and efficiency of settling aggregates. The Boycott effect is also applied in clinical tests to speed-up the evaluation of blood samples.

To answer the question whether this approach can also be used to speed up the evaluation of emulsion stability tests were carried out with colloidal stable emulsions (stable against aggregation and coalescence) and flocculated emulsions.

The LUMiReader instrument (LUM, Germany) can measure space and time resolved extinction (transmission) profiles (STEP technology) in multiple channels using near infrared (NIR) or visible light. This way it measures changes in turbidity and the movement of the boundary towards the supernatant. Even more the angle of inclination can be varied between 0 and 30° from the vertical.

Investigations on creaming as function of angel of inclination were carried out on nonflocculated silicone oil-in-water emulsions varying the oil concentration and on flocculated silicone oil-in-water emulsions at different electrolyte concentration.

The same principle behaviour as in case of monodisperse colloidal stable silica was found for the polydisperse colloidal stable (nonflocculated) emulsion. In this case ‘inclined creaming’ proceeds. At 30° inclination the creaming can be accelerated by a factor of about 9, i.e. the necessary time for stability evaluation can be shortened accordingly.

The creaming rate dependence on inclination is rather unpredictable for flocculated network forming emulsions. A maximum in creaming rate was observed around 25° inclination. In case of the emulsion with 0.5 M NaCl this relates to an enhancement factor of over 25, however, for 0.75 M NaCl it is only slightly higher than 1.

Keywords: enhanced creaming, Boycott effect, emulsion stability, creaming velocity, salt induced flocculation