Static and dynamic properties of surfactant films on natural waters

The paper contains the results of natural surface film surface pressure – area experiments carried out in inland waters and shallow offshore regions of the Baltic and Mediterranean Seas during 1990–99 under calm water conditions using the Langmuir trough – Wilhelmy filter paper plate system, which ‘cuts out’ an undisturbed film-covered sea area without any initial physico-chemical sample processing. The limiting specific area Alim (268–3157 ˚A2/molecule−1) and mean molecular mass (0.65–9.7 kDa) of microlayer surfactants were determined from the 2D virial equation of state applied to the isotherms. Film structure signatures were derived from π − A isotherm hysteresis and application of the 2D polymer scaling theory. The stress-relaxation measurements revealed a two-step relaxation process at the interface with characteristic times τ1 (1.1–2.8) and τ2 (5.6–25.6) seconds suggesting the presence of diffusion-controlled and structural organization relaxation phenomena. The results demonstrate that natural films are a complex mixture of biomolecules covering a wide range of solubilities, surface activity and molecular mass with an apparent structural organization exhibiting a spatial and temporal variability.