Disjoining Pressure vs Thickness Isotherms of Thin Emulsion Films Stabilized by Proteins

Abstract

In the present paper, we report measurements of the disjoining pressure vs thickness isotherms of emulsion films stabilized by proteins. A novel variant of the Mysels−Bergeron thin liquid film setup was constructed and further employed in the investigation of foam and emulsions films. The films are formed in a porous glass plate immersed in the corresponding oil phase. The disjoining pressure is directly measured by means of a pressure transducer, and the thickness is determined via light interferometry. The disjoining pressure vs thickness isotherms show different features in respect to the stabilizing protein. When the films are stabilized by bovine serum albumin (BSA) and β-lactoglobulin (BLG), a steric-like interaction comes into play being differently pronounced in the two cases. In contrast, the films stabilized with β-casein exhibit classical Derjaguin−Landau−Verwey−Overbeek (DLVO) behavior. The disjoining pressure was converted to force adopting the Derjaguin approximation, and the result is compared with force−distance laws obtained employing magnetic chaining technique (MCT); there is an excellent agreement. Similar comparison with data obtained in a surface force apparatus (SFA) experiment reveals substantial discrepancies due to the different physical state of the proteins adsorbed at a liquid−liquid and a solid interface. The experiment reported here demonstrates one important possibility for realistic modeling of the interaction between emulsion droplets.