Rheology of Surface Films. I. Rheological Characteristics of Monomolecular Films of Ovalbumin and Serum Albumin

Abstract

Abstract A static method of measuring the viscoelasticity of spread monolayers is presented, and the rheological study was carried out with the monolayers of ovalbumin, horse serum albumin, and hemoglobin. The deformation-time relations, obtained under the shear stress, were found to give very detailed information about the structure of films. With ovalbumin films spread on 0.1 N hydrochloric acid, it was found that an instantaneous elasticity, accompanying retarded elasticity, appeared in an unexpectedly large area, i.e., in the area above 5 sq. m. per mg. Surface shear modulus of instantaneous elasticity increased linearly with the decrease of surface area, exhibiting several breaks in the slope. The films of serum albumin and hemoglobin behaved differently from ovalbumin film, as they did not exhibit any viscoelasticity until they were compressed to a considerably small area. Compression down to the area below 1.0 sq. m. per mg., however, makes a simple viscous film and further compression down to the area below 0.8 sq. m. per mg., just rendered the film viscoelastic. Such changes of film state were found to be consistent with the breaks in the compressibility-area curve obtained from the forcearea curve. Discussions of the characterization of these protein films were briefly made in terms of molecules.