Surface dilational behaviour of aqueous protein solutions: History effects

Aqueous protein solutions have dynamic surface properties that are found to depend on the experimental technique by which they are measured. Especially aqueous solutions of globular proteins have dynamic surface properties that are sensitive for the history of the surface. By means of a Langmuir trough (Lt) technique and an overflowing cylinder (Oc) technique, these differences in surface behaviour can be quantified. It appears that much higher surface dilational viscosities are measured by using the Lt technique than with the Oc technique. These results are interpreted in a qualitative way by taking into account the different histories of the liquid surfaces in the two techniques and the more or less globular nature of the proteins used. The consequence of the observed phenomena for practical application is discussed in view of the behaviour of bubbles in a moving liquid. It is concluded that both techniques, although they give different results, can be applied to different practical situations.