Oscillatory testing of o/w emulsions containing mixed emulsifiers of the surfactant-long chain alcohol type: self-bodying action

Abstract

Liquid paraffin-in-water emulsions stabilized by cationic (cetrimide) or non-ionic (cetomacrogol) surfactants and cetostearyl alcohol were examined at 25" in oscillatory mode, using the Weissenberg Rheogoniometer with parallel plates coupled to a digital transfer function analyser. Ternary systems, formed by dispersing the mixed emulsifiers in water, were similarly investigated. Each preparation was tested in the linear viscoelastic region, and fundamental rheological parameters, the storage modulus (G) and the real viscosity (7') were derived as functions of frequency over the range 7.91 x to 25 Hz. All ternary systems behaved similarly with respect to frequency. As this increased, G' rose and 7' fell. These trends were related to the viscoelastic nature of the systems. Both mixed emulsifiers exhibited self-bodying mechanisms, so that emulsion consistency increased as the mixed emulsifier concentration rose. This was shown by increases in G' and 7' at each frequency. The shapes of the plots and other rheological properties were related to viscoelastic gel networks formed in the emulsion continuous phases. The ternary system parameters implied that emulsion networks were similar to ternary gels, that is, they formed by the interaction of long chain alcohol and aqueous surfactant solution. The oscillatory data were compared and correlated with creep data derived for similar ionic and non-ionic dispersed systems, previously described.The self-bodying action of mixed emulsifiers of the surfactant-long chain alcohol type is their ability both to stabilize oil-in-water emulsions and to control their consistencies between wide limits. An essential feature of this action is that a significant elastic component is introduced into the rheological behaviour which distinguishes such emulsions from preparations with simple emulsifiers since these do not exhibit a prominent elastic component.Many self-bodied emulsions are semisolid and this phenomenon can be investigated by small strain experiments (e.g. creep or oscillatory techniques). In these the systems are examined in their rheological ground states, and the results are analysed on the basis of linear viscoelastic theory to provide fundamental viscoelastic parameters.Creep experiments provided valuable information about the self-bodying action of various ionic and non-ionic mixed emulsifiers (Barry, 1968;Barry & Saunders, 1970a,b, 1971a,b, 1972a. Transient experiments, however, are restricted by the response time of the apparatus and recording system and by the impossibility of applying a truly instantaneous stress at the beginning of each experiment.* nie Saunders.

Correlation of Viscoelastic Functions for Pharmaceutical Semisolids: Comparison of Creep and Oscillatory Tests for Oil-in-Water Creams Stabilized by Mixed Emulsifiers

“…1-9 are similar to those shown by uncrosslinked viscoelastic polymers (34) and conform with a generalized Maxwell model analogy described previously (20). For both ionic and nonionic preparations, as the mixed emulsifier concentration increased, consistencies rose as coherent viscoelastic networks formed in the continuous phases (1).…”

“…At the other end of the frequency range, oscillatory measure ments involve errors, mainly because of evaporation from the parallel plates during the comparatively long experimental time (20,21). data were transformed from values of J(t) taken within a few seconds of creep.…”

“…Initial tests for linearity were performed (20). The instrument was employed with parallel plates, 7.5 cm.…”

“…These preparations have already been examined in detail by both fundamental methods, and information is available as to the effects of small changes in formulation on each type of viscoelastic function (13,17,20). These preparations have already been examined in detail by both fundamental methods, and information is available as to the effects of small changes in formulation on each type of viscoelastic function (13,17,20).…”

Brian Barry: Innovative Contributions to Transdermal and Topical Drug Delivery

“…He continued to work in colloid science, in particular exploring the rheology of topical formulations and the influence of mixed emulsifiers on semisolid preparations [[2,3,4]. With his first PhD student at Portsmouth, Gill Eccleston (later to become Professor of Pharmaceutics at the University of Strathclyde, Glasgow), Brian published a series of papers showing the influence of long-chain alcohol emulsifiers on oil-in-water creams [5,6,7]; indeed one of these early papers was co-authored with S.S. (Bob) Davis, later Lord Trent Professor of Pharmacy at the University of Nottingham who had studied for his PhD in colloid science alongside Brian under the guidance of Edward Shotton.…”