Rigidity in Protein Films, and the Properties of the Force-Area Curves

Abstract

PROTEINS when spread upon aqueous solutions at sufficiently low surface concentrations exhibit the mechanical properties of two-dimensional liquids. A change of state occurs upon compression, the film acquiring marked rigidity in the plane of the surface; upon the slender basis of an analogy with the behaviour of proteins in bulk, the film in this rigid condition has been called a ‘gelâ¹. A consequence of this rigidity is that whereas in the liquid film any change in pressure can be transmitted through a small aperture dividing the film into two portions, this should be no longer possible in the case of the solid film, and the presence of a constriction will result in an uneven distribution of pressures and surface concentrations. We have observed such effects in protein films divided by slits of various widths and have also noted in the liquid-solid transition region a phenomenon resembling thixotropy.