LINEAR COMPRESSION OF AN ADSORBED MONOLAYER OF A SURFACTANT SOLUTION

The surface of a soluble monolayer (Brij-58 solutions) in equilibrium is compressed with a constant speed, and the surface tension with time is measured, To analyze the experimental data the convective diffusio n equation is integrated and thereafter approximated. The agreement be tween theoretical predictions and experimental data was good, using Gi bbs elasticity and diffusion relaxation time as adjustable parameters, From these data the elasticity of the monolayer as a function of the effective time is obtained, For a micellar system, the bulk region adj oining the surface becomes oversaturated, after threshold micellizatio n sets in, The Gibbs elasticity and the diffusion relaxation time resu lting from experimental data sue compared with those obtained from the adsorption isotherm, The agreement is poor, This is discussed by cons idering that the Gibbs elasticity and the diffusion relaxation time re quire second differentials of the equilibrium surface tension concentr ation curve. (C) 1996 Academic Press, Inc.