Abstract
Spatial and temporal variability of natural surfactant sea surface film structural parameters were evaluated from force-area isotherms, film pressure-temperature isochors, dynamic surface tension-time relations performed on samples collected in Baltic Sea shallow coastal waters. The film structure state was postulated as a 10-D dimensionless vector created from the normalized thermodynamic, adsorptive, and viscoelastic film parameters. The normalization procedure is based on the concept of self-corresponding states known in thermodynamics. The values taken by all the reduced parameters indicated a significant deviation from the reference ideal-2D gas behavior. The exhibited deviations of the surface parameters from the background values of the same thermodynamic state of each film were independent on the film-collecting procedure, sample solvent treatment, and temperature. The structural similarity was expressed quantitatively as a (Cartesian, street, and Czebyszew) distance between two vectors of the analyzed film and the standard one from the database, and appeared to be related to environmental conditions, surface-active organic matter production, and migration in the studied coastal sea region. The most distinctive parameters differing the films were y, Mw and Eisoth, as established from Czebyszew function application. The proposed formalism is of universal concern and could be applied to any natural water surfactant system (seawater, inland water, rain water, and snowmelt water).
Highlights
The sea surface microlayer (SML) is the thin surface layer of the ocean at the ocean-atmosphere interface that has distinctive physical, chemical, and biological properties compared to the underlying water (Zhang et al 2003)
Natural surfactant films exhibit the multicomponent character being a mixture of biopolymeric molecules covering a wide range of solubilities, surface activity, and molecular masses demonstrating a spatial-temporal-seasonal variability which can be quantified with several surface rheology parameters
The presented approach based on the physical states similarity theory provides a universal measure of surface film structure evolution independent on the film-collecting procedure, solvent treatment, and sample temperature applicable to a wide variety of the original films met in natural waters
Summary
The sea surface microlayer (SML) is the thin surface layer of the ocean at the ocean-atmosphere interface that has distinctive physical, chemical, and biological properties compared to the underlying water (Zhang et al 2003). It is of particular interest to make near real-time and on-site measurements of microlayer film signatures using a probing technique that responds to a broad class of organic film-forming components, and that provides specific quantitative information on a thermo-elastically complex, highly heterogeneous interfacial system with internal transition processes of different time scale and origin. Such an experimental film collection technique, theoretical background of interfacial data processing, and comprehensive film signatures classification stand for a complete oceanographic procedure presented here, and tested in a coastal area of the Baltic Sea (Gulf of Gdansk, Poland)
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