SURFACE RHEOLOGICAL PROPERTIES OF MONOSTEARIN AND MONOOLEIN FILMS SPREAD ON THE AIR AQUEOUS-PHASE INTERFACE

The surface viscoelastic properties of monostearin and/or monoolein fi lms spread on the air-aqueous phase interface were studied by sinusoid al oscillation tests performed in a special Langmuir trough with a cyl indrical barrier. The surface rheological parameters - such as surface dilational modulus, elastic and viscous components, and loss angle ta ngent - and the surface tension were measured at 20 degrees C as a fun ction of the time and radial frequency. The concentration of the lipid spread on the interface, the composition of the interface, and the aq ueous phase composition (ethanol, 1 M; sucrose, 0.5 M) were the variab les studied. It can be concluded that the films are essentially elasti c. The surface dilational modulus is higher with monostearin than with monoolein but is not very frequency dependent. The surface rheologica l properties depend on the surface and subphase compositions. In the m onostearin-monoolein mixed films the molecules are not miscible, so th e surface dilational modulus is lower than in an ideal film.