Adsorption of protein layers at the water/air interface as studied by axisymmetric drop and bubble shape analysis

Experimental studies of dynamic and equilibrium surface tensions of aqueous beta-casein solutions were performed by using the pendent drop and bubble techniques. A comparison of the results shows good agreement at higher prot ein concentrations. However, at low protein concentrations a significant di fference between the data is observed, caused by the loss of protein molecu les from the bulk at the drop surface due to the limited solution reservoir . In bubble experiments the reservoir is larger by more than 2 orders of ma gnitude so that losses become essential at much lower bulk concentrations. Loss of protein and the diffusional transport in the limited reservoir of a small drop lead to the formation of an adsorption layer with properties qu ite different from those obtained at a bubble surface.