Titre / Title: Stability and Behavior of Thin Oil/Water/Oil Films with beta-Lactoglobulin

By means of interference microscopy, we investigate emulsion films stabilized by beta-lactoglobulin (BLG). The films are subjected to capillary pressure in the range 10-50 Pa, which is of the same order of magnitude as the buoyancy in creams and concentrated emulsions. The film lifetime and the thickness are measured. Our aim is to explore in a systematic way how the thin film properties are influenced by pH (in the range 3-8), concentration of NaCl (up to 1 M), ageing of the surfaces before film formation. The film stability is discussed in view of the DLVO theory (interplay of van der Waals attraction and electrostatic repulsion). The electric properties of the BLG-laden o/w interfaces are characterized by measured zeta-potential; the data are used for calculation of the disjoining pressure barrier. With 0.15 M NaCl, the observed trends in the film stability cannot be explained by the DLVO model. When the protein is charged (at pH away from pI), and the aqueous phase contains significant amount of salt, local short-range repulsion between the molecules in lateral direction might be responsible for decreased film stability (e.g., because of hindrance to the formation of a stiff protein layer). The films at the isoelectric pH in the bulk solution, pI=5.2, are very stable. This may be attributed to the existence of mechanically reinforced layer (gel-like network), favored by high salt content. The interfaces adhere strongly, which is manifested as sticking (large contact angle hysteresis). In systems containing 1 M NaCl, wrinkles of