A solution to the slow stabilisation of surface pressure sensors based on the Wilhelmy method

摘要

Dynamic measurement of surface pressure is of particular interest in the field of Langmuirmonolayers, where the change in surface pressure throughout an experiment can provide informationon the properties of the monolayer forming material, or on the reaction kinetics ofthe monolayer’s interaction with other materials. One of the most common methods for themeasurement of dynamic surface pressure is the Wilhelmy plate method. This method measureschanges in the forces acting upon a thin plate of material at the air-water interface; thismeasurement is then converted to surface pressure. One version of this method, which uses filterpaper plates at the air-water interface, is particularly popular due to their relatively low cost.However, it has been seen that the use of filter paper plates attached to a Wilhelmy balance requiresan initial stabilisation period lasting several hours, during which the readings drift fromthe original baseline. Here the cause of this drift is explored, considering how changes in theweight of the plate over time influence the assumptions on which the surface pressure is derivedfrom the measurements made by the Wilhelmy balance. A simple method for preventingthis drift through pre-soaking of the filter paper plates is presented.