Hydrocarbons on sea water: steady-state spreading signatures determined by an optical method

The spreading properties of several hydrocarbons (vegetable, engine, gear and crude oils) on distilled and artificial sea water were determined under laboratory conditions using a novel optical method. With the aid of Langmuir’s equation, the geometrical signatures of a discrete lens of each hydrocarbon droplet floating on a water tank served to calculate the entering E (31.30–94.18 mN m−1) and spreading S (−3.50 to −57.49 mN m−1) coefficients, and equilibrium thicknesses t∞ (0.20–1.25 cm). They appeared to be in agreement with the values derived from direct interfacial tension measurements (Wilhelmy plate and stalagmometer methods). Empirical relations of the normalized lens radius rL/rdrop and S on the water surface tension γAW were postulated as being of significant value in oil spill assessment studies at sea. The parameters obtained together with the surface properties of a natural surfactant-containing water body represent the principal input data required for modelling the spreading of a surface-tension-gradient-driven oil spill at sea