SEARCH Articles Figures Tables Adsorption of surface-active molecules as an orientated monolayer at air-water and oil-water interfaces. The circular part of the molecules represents the hydrophilic polar head group and the rectangular part represents the non-polar hydrocarbon tail. At the air-water interface, the hydrocarbon chains will tend to lie horizontally on top of the water surface at low coverage, but will tend to assume more upright configurations at high coverage [Publishers Imprint]