Rheology of emulsions stabilized by sodium dodecyl alcohols

Abstract

Liquid paraffin emulsions stabilized by sodium dodecyl sulfate with long-chain alcohols have been examined by microscopy, particle-size analysis, continuous shear rheometry, and creep. The disperse phases were aggregated and emulsions were viscoelastic and thixotropic and developed crystals on storage. Emulsions were firm and rheologically stable when cetostearyl alcohol was used. They were similar but slightly less stable when formulated with (a) a mixture of C16 and C18 alcohols in the ratio present in cetostearyl alcohol and (b) a mixture of C10, C12, C14, C16, and C18 alcohols in similar ratios. Emulsions were less stable when formulated either with C16 or with mixtures of C16 and C18 alcohols in ratios 31, 11, and 13. A more mobile, less stable emulsion was obtained with C18 alone, but a stiff emulsion was formed provided that the ratio of C16 to total alcohol (C16 plus C18) was greater than approximately 0.07. Differences between emulsions were not related to particle-size distribution but to the nature and content of the C18 alcohol, which influenced the strength of the viscoelastic network formed. Trace amounts of unidentified compounds exerted a minor effect.