Goggin, Paul Laurence; (1996) The use of low frequency dielectric spectroscopy in the characterisation of semi-solid emulsions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This study was concerned with the analysis of two cream formulations and their corresponding ternary systems using low frequency dielectric spectroscopy (L.F.D.S.). These systems were Aqueous cream BP (both preserved and unpreserved) and Cetomacrogol cream BP containing a surfactant (sodium lauryl sulphate and cetomacrogol 1000 respectively) and cetostearyl alcohol. The ternary systems contained a fixed quantity of surfactant (sodium lauryl sulphate 0.5% and 1% or cetomacrogol 1% and 2% and cetostearyl alcohol (range 0.25 - 8%) Aqueous creams (hand and mechanicaly mixed) were characterised using flow rheometry, differential interference contrast (D.I.C.) and scanning electron microscopy (S.E.M.). The rheology revealed the preservative (phenoxyethanol) and processing method influences viscoelastic properties. Microscopy revealed hand mixing produces systems of poor quality with a wide oil droplet size range, while high shear mixing ensures a well dispersed oil phase. L.F.D.S. however showed little difference between the samples. The emulsions based on cetomacrogol 1000 were examined using oscillatory rheometry, D.I.C and S.E.M. and the results were compared with L.F.D.S. The nonionic creams employed the same formula but were processed at differing shear and mixing speeds. The flow dynamics of the mixing vessel were altered by the use of a removable baffle system. When examined by oscillatory rheometry and microscopy it was found the systems exhibiting a well developed microstructure showed reduced conductive behaviour. The electrical behaviour of the ternary systems was related to the concentration of cetostearyl alcohol. As this increased there was a corresponding change in both rheological and microscopic behaviour which reflected an increase in the formation of a complex micro structure. The study shows the usefulness of L.F.D.S. in analysing semi-solid systems, and the processing methods and the concentration and ratio of the emulsifying agents affects the electrical, rheological and microscopic behaviour of such systems.

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