Thermoelastic surface properties of seawater in coastal areas of the Baltic Sea

Correlations and data for the thermoelastic surface properties of seawater were determined by means of surface tension-temperature and surface pressure-area isotherm measurements performed in Baltic Sea coastal waters (Gulf of Gdansk, Poland). Thermodynamic surface parameters examined include: surface free energy-gamma, entropy, enthalpy, surface specific heat of air-seawater (AW), air-crude oil (AO) and crude oil-seawater (OW) interfaces, and the surface elasticity was quantified in terms of complex viscoelasticity modules with relaxation times of the transition processes. The spatial and temporal evolution of the parameters differed significantly from the literature data for seawater since the effect of surface active substances of natural and municipal origin was likely to be present in these coastal waters. The seawater surface turned out to have the viscoelastic 2D character as well as other interfacial systems AO and OW where three crude oils in contact with the seawater were studied for comparison. The dilational elasticity modules were found to follow the sequence E-AW > E-OW > E-AO. Composite oil lens-covered seawater exhibited a significant drop of E from E-AW (crude oil free surface) even for low oil coverage fraction F-0. The obtained surface and interfacial tension-temperature dependences allowed to correct the spreading coefficient (S = gamma(AW) - gamma(AO) - gamma(OW))to the desired temperature range, for example. The latter parameter with the sea surface elasticity data allows one to test the modified model of crude oil spreading proposed by the authors (Boniewicz-Szmyt and Pogorzelski, 2008), for spreading kinetics phenomenon at the surface-tension regime. (C) 2015 Institute of Oceanology of the Polish Academy of Sciences.