Characterization of adsorbed microlayer thickness on an oceanic glass plate sampler

Abstract

The thickness of solution layers adsorbed onto rotating glass plates designed for use on an oceanic glass plate sampler was investigated in laboratory experiments using optical techniques. Using the Beer‐Lambert Law, light attenuation measurements were used to calculate the thickness of adsorbed solution layers on a rotating glass disk with and without salt and surfactants. The observations have shown that the adsorbed film thickness can vary between 80 and 40 µm for glass rotation speeds between 4 and 16 cm s−1, depending on salinity and surfactant concentrations. For example, the thickness of a film of water with 40 ppt of salt and 5 cm s−1 rotation speed was in the range of 80 µm. The adsorbed layer thickness increases with increasing salt concentration and with increasing concentrations of surface active substances. These results are comparable to results obtained by vertically dipping a glass plate and determining film thickness from the collected volume of water. Because the glass disk rotational speed significantly influences the thickness of the adsorbed solution layer, it is important that the speed is maintained at a value for which the adsorbed thickness has been calibrated. At typical oceanic salinities, the dependence of the adsorbed film thickness on rotation speed was limited. However, even small changes in surface active substances resulted in significant thickness changes.