SURFACE-DIFFUSION IN MONOMOLECULAR FILMS .1. LATERAL PROFILE SHIFT IN RADIOTRACER METHOD

The lateral shift of the surface concentration profiles was systematically investigated during a study directed at obtaining reliable surface diffusion data for myristic acid monolayers on 0. 01 NHCl subsolutions using the radiotracer technique. Monolayer characterization studies showed that there were no differences between the II- DELTA V-A isotherms of high purity radioactive and nonradioactive myristic acid monomolecular films below the equilibrium spreading pressure. However, film stability measurements indicated that the freshly purified radioactive surfactant undergoes significant decomposition, not only during storage, but also when it is spread on the subsolution surface for monolayer studies. The lateral profile shift, does not arise from temperature-induced Rayleigh instabilities as claimed recently but rather it results from unequal monolayer losses as proposed earlier.