During area deformation, the surface tension
The elasticity of a monolayer adsorbed from a surfactant soluis different from its equilibrium value and depends on time: tion is considered by continuous surface deformation. For all kinds s(t). We are merely interested in the jump of the surface surface deformations a single relation between the elasticity and tension s(t) defined as Ds(t) ร
s(t) 0 s e .
the effective time should be obtained (master curve). This effective If the relaxation process of the equilibrium re-establishing time depends on the rate of deformation and on the kind of deforis diffusion, it is plain the diffusion equation must be consid-
mation. The relation between elasticity and effective time was
ered with corresponding boundary conditions. Since the surproven experimentally for a decanoic acid solution at a concentraface is deformed continuously, a convection term must be tion 10 07 mol cm 03 . The following surface deformations are conaccounted for in the diffusion Eq. [1]. In this way the jump sidered: (i) expansion at a constant dilatation rate, (ii) compression at a constant dilatation rate, (iii) linear expansion, (iv) linear in surface tension with time is predicted and the theoretical compression, and (v, vi) compression and expansion in a some curve has to be compared with experimental data. To dewhat more complicated way. From these data the Gibbs elasticity scribe this curve two parameters, the Gibbs elasticity, e 0 , and the diffusion relaxation time are obtained. These parameters and the diffusion relaxation time, t D , are involved. From are also obtained by longitudinal wave method of Lucassen-Van these experiments also the elasticity of the monolayer is den Tempel. Both set of parameters are comparable. Finally the obtained, which depends on time. If the surface deformation situation at a growing drop with constant flow rate is considered is fast, the diffusion process has no time to operate and the (Triton X-100) to show that also here the approach is followed.