Compression and expansion of surfactant adsorption layers at the liquid/air interface studied by a glass funnel method

In this work a funnel method as a technique for investigating dynamic surface properties at the liquid/air interface is used. The experimental set-up consists of a hydrophilic glass funnel with the inclinations 45 and 30°. A counter-body compensates the displaced liquid by moving in the opposite direction to the funnel. The two advantages are the constant phase boundary level of the flat interface and the isotropic area change of the interfacial layer. After moving the funnel into the subphase and subsequently up again desorption/adsorption processes take place, each directed to re-established the equilibrium adsorption state. The relaxation process is monitored by measuring the dynamic surface tension. Studies are performed with the non-ionic model surfactant dodecyl dimethyl phosphine oxide. The data obtained are discussed in terms of the funnel material and the diffusion relaxation theory.