The Effect of Evaporation on Wilhelmy-Type Measurements of Wetting Tension: Is Wetting Equilibrium Reached for Cationic Surfactant Adsorption on Mica?
The effect of lowering of the liquid level by evaporation on the measured values of the advancing wetting tension is calculated and is shown to be able to account for most of the change with time of the advancing wetting tension in an earlier paper (L. G. T. Eriksson et al., J. Colloid Interface Sci. 181, 476 (1996)) concerned with the adsorption of hexadecyltrimethylammonium bromide (CTAB) on mica, using rates of evaporation ( approximately 0.07 mm/h) measured for that setup. With stricter evaporation control, the wetting tension hysteresis is still large after 15 h of equilibration, and it is not possible, on that time scale, to record the approach to equilibrium of the advancing contact angle for the system CTAB/mica.
Eriksson
LGT
Department of Chemistry, Royal Institute of Technology, Stockholm, SE-100 44, Sweden