Search

Abstract: The characterization of wetting properties (by contact angles) of several undersea artificial (glass plates,) and natural (stones, sand layers, soft-bottom structures, aquatic macrophytes, sediments, and seafloor communities) solid substrata in the Baltic Sea brackish water (Gulf of Gdansk). The studies were performed under laboratory and field conditions using a novel captive bubble air-pipette computer microscope system. A set of the surface wettability parameters: the apparent surface free energy γSV, adhesive layer film pressure Π, work of adhesion WA, and work of spreading WS were determined to quantify the wetting properties of model substrata using the contact angle hysteresis (CAH) approach. The useful technique to measure in situ the contact angle giving reproducible and accurate values of CA turned out to be a captive bubble method, for fully hydrated interfacial layers of highly hydrophilic and porous nature met at seabed (Rodrigues-Valverde et al., 2002). CA measurements revealed mostly hydrophilic nature of the studied solid material (CA<90°) where the presence of adsorbed organic matter layer or crude oil film covering lead to surface hydrophobization (CA↑, γSV ↓,WA↓, WS more negative). The adhesion of biofouling was correlated both with CAH and the dispersive interaction term γSV d of the total γSV. Monitoring of the artificial substrata of the hydrophilic nature with a CA technique can be used to observe the development of the organisms community i.e., microfouling, and to carry out a comprehensive study of surfaces of the submerged macrophytes (Potamogeton lucens in particular). Since aquatic macrophytes can act as bio-indicators of water chemistry their surface wettability may reflect plant surface erosion and organic matter accumulation state being of particular value in biological assessment of ecosystems status. [Copyright &y& Elsevier]

Floating dust-originated solid particles at air-water interfaces will interact with one another and disturb the smoothness of such a composite surface affecting its dilational elasticity. To quantify the effect, surface pressure (II) versus film area (A) isotherm, and stress-relaxation (II-time) measurements were performed for monoparticulate layers of the model hydrophobic material (of µmdiameter and differentiated hydrophobicity corresponding to the water contact angles (CA) ranging from 60 to 140°) deposited at surfaces of surfactant-containing original seawater and were studied with a Langmuir trough system. The composite surface dilational modulus predicted from the theoretical approach, in which natural dust load signatures (particle number flux, daily deposition rate, and diameter spectra) originated from in situ field studies performed along Baltic Sea near-shore line stations, agreed well with the direct experimentally derived data. The presence of seawater surfactants affected wettability of the solid material which was evaluated with different CA techniques applicable to powdered samples. Surface energetics of the particlesubphase interactions was expressed in terms of the particle removal energy, contact cross-sectional areas, collapse energies, and so forth. The hydrophobic particles incorporation at a sea surface film structure increased the elasticity modulus by a factor K (1.29-1.58). The particle-covered seawater revealed a viscoelastic behavior with the characteristic relaxation times ranging from 2.6 to 68.5 sec [ABSTRACT FROM AUTHOR]

Natural surface film experiments in inland waters and shallow offshore regions of the Baltic and Mediterranean Seas were carried out in the time period 1990–1999 under calm sea conditions using a novel device for sampling and force-area studies. The sampler-Langmuir trough-Wilhelmy filter paper plate system ‘cuts out’ an undisturbed film-covered sea area to perform π-A studies without any initial physico-chemical sample processing. The limiting specific area Alim (2.68–31.57 nm2/molecule) and mean molecular mass Mw (0.65–9.7 kDa) of microlayer surfactants were determined from the 2D virial equation of state applied to the isotherms. Enthalpy ΔH and entropy ΔSt of the 2D first-order phase transitions were evaluated using the Clausius-Clapeyron equation applied to the isotherms. Miscibility of film components and film structure evolution is expressed by the scaling exponent y adopting the 2D polymer film 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 organisation relaxation phenomena. The obtained results suggest that natural films are a complex mixture of biomolecules covering a wide range of solubilities, surface activity and molecular masses with an apparent structural organisation exhibiting a spatial and temporal variability. [Copyright &y& Elsevier]

A double-walled submersible sea surface film sampler which ‘‘cuts out’’ an undisturbed film-covered area has been built for force-area isotherm studies of untreated water samples. Preliminary results on static and dynamic surface properties of naturally formed films present in coastal zones of the Baltic Sea are presented and discussed in reference to water samples collected in a bottle (depth of 20 cm) at the same site and time, which in turn significantly differ from each other. The new sampler also allows a few statements of oceanographic relevance on the film homogeneity (i.e., film filling factor) and the energy transfer through surface films from isotherm hysteresis measurements. [ABSTRACT FROM AUTHOR]