DILATIONAL VISCOELASTICITY OF FLUID INTERFACES - THE DIFFUSION-MODEL FOR TRANSIENT PROCESSES

The functional form of the surface dilational modulus is determined by considering the subsurface concentration changes produced by the diffusion process consequent to a non-periodic (rectangular step) perturbation of surface area (local equilibrium between surface and subsurface is assumed). The mathematical treatment is intended to present a straightforward demonstration that the same (unique) physical quantity, i.e. the dilational modulus, governs both harmonic and transient surface processes. The results definitely show that this modulus is an intrinsic physical property of a diffusive system, independent of the type of surface disturbance (within the linearity approximation).