Microstructural Changes During the Storage of Systems Containing Cetostearyl Alcohol/Polyoxyethylene Alkyl Ether Surfactants

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Abstract
Non-ionic emulsifying wax/water ternary systems composed of water, cetostearyl alcohol and non-ionic polyoxyethylene alkyl ether surfactants (R-(OCH2CH2)AOH with polyoxyethylene (POE) chain lengths, A, varying from 10-30 and R = cetostearyl were examined as they aged for several weeks. The technigues employed included Theological (Ferranti-Shirley cone and plate viscometer), microscopical (brightfield and between crossed polars), thermal (thermogravimetry and D.S.C) and ultracentrifuqation. The rheological properties of the samples were complex. They confirmed, however, that all ternary systems increased in consistency on storage. For each ternary system apparent viscosities (Oapp) increased as the samples aged. In addition, ternary systems prepared with surfactants with long POE chains were generally of a higher consistency than similar ternary systems containing shorter POE chains. Each ternary system was considered to be composed of crystalline and gel (Lβ), phases dispersed in bulk (free) water. The overall consistency of each system was related to the swelling ability and the relative amounts of gel phase present; this in turn depended on the POE chain length of the surfactant. The structural changes on storage were due to the formation of additional gel phase. This occurred because hydration of POE chains to form gel phase was limited at the high temperature of manufacture. On storage at lower temperature (25*) the increased solubility of the POE chains allowed additional gel phase to form. However, this now occurred relatively slowly because of the crystalline nature of the hydrocarbon chains. Microscopical observations support this theory, for the timescale of observed interaction correlated well with the consistency and ‘free’ water changes on storage.

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