Some observations on the surface wetting relaxation of latex rubbers

The relaxation of dynamic contact angles using distilled water was measured for some elastomeric latex rubbers (unlubricated condoms). These measurements indicated that the wetting force increased with time after the forced motion of the meniscus was stopped. The time variation of the wetting force was analyzed with the help of several models. Neither a simple exponential of the Debye type nor an exponential based on diffusion fitted the data adequately. The experimental data are described best by a stretched exponential. One mechanism for this dependence would be the dispersive motion of the meniscus because of the chemical and physical heterogeneity of the latex rubber surface. A time dependent deformation of the thin rubber sheet due to wetting may also explain the time dependence, but cannot explain all results.