The influence of fatty alcohols on the structure and stability of creams prepared with polyethylene glycol 1000 monostearate/fatty alcohols.
Synopsis Liquid paraffin in water emulsions stabilized by PEG 1000 monostearate and alcohols cetostearyl (c/s) myristyl (C(14)), cetyl (C(16)) or stearyl (C(18)) and ternary systems prepared by dispersing each fatty alcohol and surfactant in water were examined during 30 days using a Ferranti-Shirley cone and plate viscometer. Microscopical diffusion experiments investigated interaction between PEG 1000 monostearate solution and each alcohol at high and low temperature. The rheological properties of each ternary system and corresponding emulsion were similar. Formulations prepared from pure C(14), C(16) or c/s alcohols were semisolid immediately after preparation. Flow curves were in the form of anticlockwise hysteresis loops with spur points. On ageing for 24 h, structure built-up over a time scale similar to that observed in diffusion experiments, so that apparent viscosities increased. However, on further ageing the pure C(14) and C(16) alcohol systems were not as stable as those prepared with c/s alcohol. In contrast, the pure C(18) systems were mobile liquids and the emulsion cracked within days. This correlated with diffusion experiments where little interaction was observed between stearyl alcohol and PEG 1000 monostearate.
Eccleston
G M
GM
Department of Pharmacy, University of Strathclyde, 204 George Street, Glasgow G1 1XW.