Measurement of the Surface Elasticity of an Adsorbed Monolayer by Continuous Surface Deformation
The elasticity of a monolayer adsorbed from a surfactant solution is considered by continuous surface deformation. For all kinds surface deformations a single relation between the elasticity and the effective time should be obtained (master curve). This effective time depends on the rate of deformation and on the kind of deformation. The relation between elasticity and effective time was proven experimentally for a decanoic acid solution at a concentration 10(-7) mol cm-3. The following surface deformations are considered: (i) expansion at a constant dilatation rate, (ii) compression at a constant dilatation rate, (iii) linear expansion, (iv) linear compression, and (v, vi) compression and expansion in a some what more complicated way. From these data the Gibbs elasticity and the diffusion relaxation time are obtained. These parameters are also obtained by longitudinal wave method of Lucassen-Van den Tempel. Both set of parameters are comparable. Finally the situation at a growing drop with constant flow rate is considered (Triton X-100) to show that also here the approach is followed.