A study of the ageing of the gel structure in a nonionic O/W cream by X-ray diffraction,differential scanning calorimetry and spin-lattice relaxation measurements

The time dependent changes of the lamellar gel structure in a nonionic O/W cream were studied. It appeared that the changes were connected with alterations in the hydrophilic layers of this lamellar gel structure. The structure of the hydrocarbon layers did not change. The alterations were induced by an increasing hydration of the surfactant molecules on cooling from the preparation temperature to room temperature. Ageing of the cream involves a decrease of the thickness of the hydrophilic layers and a change of the distribution of the surfactant molecules, resulting in, among other things, a decrease of the release rate of a hydrophilic drug. Ageing of the cream can be prevented by using the appropriate amount of starting materials or by the use of polymerizable surfactants. In the former case a cream, from which a drug is slowly released, is obtained. On the other hand, creams containing polymerized surfactants can release drugs at a relatively high rate.