Читать книгу Surface Science and Adhesion in Cosmetics - Группа авторов - Страница 20

Adsorption testing of lipsticks provides an understanding of how oil and saliva adsorb onto the lipstick film over a period of time by looking at the spreading and wetting on the formulation sample. Such testing requires the use of a tensiometer, which is a machine used to measure the surface tension of liquids by dropping the liquid of interest (in this case olive oil or saliva) onto the film surface in the form of a sessile drop. This provides us with an idea of how resistant to oil or liquid the formulation may be; if there is a low value for the contact angle (Θ), the film surface is considered to be highly wetting. When the drop placed is water and the formulation has a contact angle greater than 90°, it is hydrophobic; a value less than 90° indicates the formulation has an affinity with water and can be characterized as hydrophilic. A contact angle less than 90° when testing with oil indicates the formulation is lipophilic and has an affinity with silicone.