Optical investigation of a wavy ageing interface

As an attempt to develop a sensitive device for biomolecule detection, a micromechanical methodology, based on the rheological change of an air/water interface is put forward [1]. Capillary waves induced from the vertical electrodynamic vibration of a brimfull cylindrical tank, filled with water, stand as a good way to identify dilational elasticity and viscosity of an ageing interface. Of prior interest for us, the complex wave number and the frequency of the waves are obtained through an optical technique, which allow us to recognise accurately the whole interface geometry. These two parameters and a modeling based on a dispersion relation are jointly used to identify the dilational rheology of the interface [2]. The validity of the methodology is assessed making use of palmitic acid as surfactant.