Competitive displacement of beta-lactoglobulin from the air/water interface by sodium dodecyl sulfate

In this work, the displacement of a globular protein from the air/water int erface by sodium dodecyl sulfate (SDS) was fallowed using a combination of the Langmuir-Blodgett method and atomic farce microscopy. The results are c ompared to displacement of the same protein by the nonionic surfactant Twee n 20. The displacement by SDS is characterized by the same orogenic mechani sm but the charge inter actions between the protein and surfactant settled to increase the surface pressure at which displacement occurred. Two types of interfacial film transfer were used in order to check that features seen were not caused by the method of transfer. The displacement was also follo wed using two surface rheological techniques: shear and dilation. The resul ts from the rheological studies are correlated with the data seen with the AFM and show that the mixed film was much weaker than either of the compone nt films. Both surface sheaf and dilation rheology showed similar trends. A lso demonstrated is the appearance of larger circular holes in the protein film during the latter stages of displacement.