NONEQUILIBRIUM PROPERTIES OF FLUID INTERFACES - APERIODIC DIFFUSION-CONTROLLED REGIME .2. EXPERIMENTS

We have investigated the surface dilational properties of a submicella r aqueous solution of n-dodecyldimethylphosphine oxide. We compared (a ) the steady-state responses of dynamic surface tension, induced by sm all-amplitude harmonic disturbances of surface equilibrium (at differe nt frequencies), and (b) the transient response induced on the same sa mple by a single trapezoidal-pulse disturbance. Using the equations fo r a diffusive model, we determined the fit parameters from the observe d response values both in the frequency and in the time domains. The r esults enabled us to predict satisfactorily the harmonic dynamic behav iour of the surface, from the relaxation data. The prediction-observat ion agreement supports the theoretical treatment and, in particular, t he assertion that the viscoelastic link, between surface excitation an d response, is a constitutive property of a liquid solution. The exper iments also show the existence of a linearity range and the repeatabil ity of measurements.