Dilatational and Shear Elasticity of Gel-like Protein Layers on Air/Water Interface

TLDR: In this article, the authors measured the surface shear elasticity modulus (μ) together with the dilatational modulus of gel-like protein layers on an air/water boundary.

Abstract: We propose a simple new method for measuring the surface shear elasticity modulus (μ) together with the dilatational modulus (K) of gel-like protein layers on an air/water boundary. The stress response to compression/expansion of the interface in a Langmuir trough is measured at two different orientations of a Wilhelmy plate, collateral and perpendicular to the movable barrier in the trough. The interfacial tension is a tensorial quantity, whence the measured values depend on the direction of the length along which the stress acts. The fact that the deformation in the trough is uniaxial, i.e., a combination of dilatation and shear, is used to determine the respective two elastic moduli (K, μ). The experiment demonstrates that adsorbed layers of β-lactoglobulin (BLG), when subjected to small deformations, exhibit a predominantly elastic rheological behavior. This proves the existence of the two-dimensional gel, as a result from partial denaturation and unfolding accompanied with entanglement of the protein...