Recent papers confirm that the interface between air and protein solutions can lead to major errors in viscosity measurements of protein solutions and model synovial fluids!
A series of recent scientific reports indicates that the air/protein-solution interface introduces major errors into viscosity measurements. Traditional viscometers and rheometers require an air/solution interface for viscosity measurements. The protein molecules are adsorbed at the air interface to minimize overall free energy. Protein molecules rearrange at the interface and form a viscoelastic film, which in turn affects the apparent viscosity of the solution. The film leads to erroneously high viscosity measurements of protein solutions by an order of magnitude.
V. Sharma, et. al.,” Rheology of globular proteins: apparent yield stress, high shear rate viscosity
and interfacial viscoelasticity of bovine serum albumin solutions,” Soft. Matt. , 2011
J. Pathak, et. al.,” Do clustering monoclonal antibody solutions really have a concentration
dependence of viscosity?,” Biophys. J., 104, 1 (2013).
Z. Zhang, et. al.,” The role of protein content on the steady and oscillatory shear rheology of model synovial fluids,” Soft Matter, 10, 5965 (2014).