An instrument for measuring the static and dynamic response to shear at the air/water interface and of insoluble monolayers: some new insights into two-dimensional phases

An apparatus has been designed, assembled, and employed in experiments to determine, as a function of molecular areal density, the viscoelastic behavior of insoluble monolayers spread on water. The apparatus has several unique features: (1) surface tension can be monitored constantly without touching the monolayer; (2) compression of the film is isotropic in an annular space entirely free of obstructions; (3) the stress transducer, located at the geometric center, defines the inner wall of the annulus and the trough wall defines the outer wall of the annulus. A wide range of viscosity and shear modulus can be measured by controlling the stress or strain applied to the film. The apparatus can be used to study the air/water interface of surfactant solutions as well as the surface of water covered by an insoluble monolayer. 14 references, 4 figures.