Improved spreading rates for monolayers applied as emulsions to reduce water evaporation

To be suitable for reducing water evaporation, monolayers need to be easy to apply and also spread quickly across the surface of water. However, the choice of monolayer often involves a compromise between spreading rate and evaporation resistance. Because emulsions of the monolayer material have been suggested as a way to improve spreading, emulsions were made with the long-chain alcohols hexadecanol, octadecanol and eicosanol using the non-ionic surfactants Brij 78 and Tween 60 as emulsifying agents. The emulsions of octadecanol and eicosanol spread faster than the corresponding powder. However there was no improvement in the spreading of hexadecanol emulsion due to a significant amount of the material dispersing into the bulk water instead of spreading at the interface. The choice of emulsifier to stabilise the emulsions is critical for effective evaporation resistance. Whereas the octadecanol emulsion made with Brij 78 showed improved evaporation resistance, the emulsion with Tween 60 had an appreciably lower evaporation resistance than powdered octadecanol. One limitation of the emulsion application method is the poor spreading on surfaces with an already high surface pressure.