Ljepsa Komunjer

Stability of W/O and W/O/W emulsions as a result of partial solidification

Abstract This communication reviews the drastic modifications that may occur within emulsions when they are submitted to temperature variations during manufacturing, storage, transport and use. Emphasis will be given to the modifications resulting from changes after solidification. Pathways of solidification of W/O and W/O/W emulsions will be presented. Due to the specific structure of the emulsions under study (simple or multiple) only partial solidification may be obtained. This situation, out of thermodynamic equilibrium, may lead to a water transfer across the oil phase. Resulting emulsion transformation and destabilization are examined.

Experimental determination of capillary forces by crushing strength measurements

Mechanisms that lead to powder agglomeration are in many cases controlled by capillary forces. Indeed, in the earliest stage of agglomeration, minute amounts of liquid join solid particles by liquid bridges. Spontaneous formation of the bridge at contact points is caused by capillary condensation. Depending on solid/liquid interactions, particularly contact angle and spreading, liquid bridges may attract or repel individual particles. Undesired agglomeration may appear during storage and is called caking. On the other hand, powder agglomeration process is often required, for example, in enlargement of the particle size, i.e. granulation. A simple experimental device, designed from usual caking tests, was developed in order to estimate capillary forces transmitted by attracting liquid bridges joining particles. Crushing strength of wet cylindrical agglomerates was estimated. Influence of the low saturations of the void space (0<S<25%) and the surface tension of a liquid have been investigated. A normalised force which does not depend on the surface tension contribution has been calculated from experimental measurements and compared to Rumpfs model. It is possible to roughly estimate the solid/liquid contact angle by comparison with the model.

Phosphorylation of Mono- or Di-octadienyl-D-xylosides. Influence towards Surfactant Properties

Abstract Phosphorylation of mono- or dioctadienyl-D-xylosides has been studied and led to mono- or dioctadienyl-D-xylosides phosphate derivatives. Comparison between monooctadienyl-D-xylosides and monooctadienyl-D-xyloside phosphate derivatives are not easy because of the complexity of having pure forms and corresponding data. However, comparison of dioctadienyl-D-xyloside diethoxyphosphate derivatives to dioctadienyl-D-xylosides indicates similar cmc values and surface activity. Dioctadienyl-D-xyloside phosphate derivatives, on the other hand, are characterized by a high hydrophilicity and a poor surface activity. Mostly, it was found that the introduction of these ethoxylated or non-ethoxylated phosphate groups influences the solubility and the surfactant properties of the mono- or dioctadienyl-D-xylosides.

Interfacial properties of a silicone copolymer demulsifier at the air/water interfacePresented at the 17th Conference of the European Colloid & Interface Science Society, Firenze, Italy, September 21?26, 2003.

Crude oil/water emulsion stability is one of the major obstacles to efficient off-shore separation of undesired aqueous phase. Chemical demulsifiers based on polysiloxanes have been successfully tested as accelerators of phase separation but the mechanism of coalescence is not fully understood. Better understanding of interfacial properties in the presence of demulsifier should give better insight in their mode of action. Comprehensive study of the interfacial properties of small water-soluble PEO–(PDMS)–PEO triblock copolymer is presented in this paper. Insoluble monolayers are formed by deposition of dissolved polymer at the air/water interface but also by adsorption from aqueous solution of the polymer. High affinity of the polymer molecule for the interface i.e. too high the energy needed to remove the molecules from the interface is at the origin of such behaviour. The elastic moduli are function of the surface pressure in the film and are very similar in both Gibbs and Langmuir monolayers.