RHEOKINETIC ANALYSIS OF BOVINE SERUM-ALBUMIN AND TWEEN-20 MIXED FILMSON AQUEOUS-SOLUTIONS

The surface dynamic properties (surface tension and surface dilational properties) of films formed by bovine serum albumin (BSA) and the sur factant Tween 20 were studied using Periodic sinusoidal interfacial co mpression and expansion in a superficial rheometer (ring trough). All measurements were performed at a constant temperature (20 degrees C) a nd at constant BSA concentration in the bulk phase (0.1% w/w). The sur face dynamic properties were dependent on the protein/surfactant ratio in the bulk phase, on the interfacial composition (BSA, Tween 20, and BSA-Tween 20 mixture), and on the aqueous phase composition (i.e., pr esence of ethanol and sucrose). The results show that at higher protei n concentrations in mixed films the surface dilational modulus is high er, which agrees with greater protein-protein interactions. However, l ower superficial dilational modulus was observed at higher surfactant concentrations, which agrees with weaker surfactant-surfactant interac tions. The dynamic surface tension and surface dilational modulus depe nd on subphase composition. The surface dynamic properties were tested by a kinetic model to monitor the unfolding and rearrangements of ads orbed BSA molecules including the existence of BSA-Tween 20 interactio ns.