Surface potential and film pressure measurements in seawater systems1

Abstract

Surface potential (AV,) and film pressure (rr) measurements of monolayers of standard compounds spread on organic carbon-free seawater were compared to AV, and yf values for natural films. The results suggest that natural seawater films most resemble films composed of proteins, polysaccharides, humic-type material, and waxes. They contain relatively small amounts of free fatty acids, free fatty alcohols, or triglycerides, but the plesence of relatively small amounts of these can strongly affect the resultant surface potential and film pressure of multicomponent films. Films formed very rapidly initially and formation rates decreased with time. Nevertheless, the potential for generating new films in 72-liter natural seawater samples did not markedly decrease with time. Surface films derived from marine phytoplankton cultures had AV, and Yf properties similar to those of naturally occurring sea-surface films. Cultures of marine bacteria contributed much less surface-active material for film formation than did those of phytoplankton.

Biological modification of mechanical properties of the sea surface microlayer, influencing waves, ripples, foam and air-sea fluxes

“…Carbohydrates are dominant in terms of mass, followed by proteins and thirdly by a lipid class comprised of free fatty acids, free fatty alcohols and triglycerides. However, lipids affect the surface electric potential and film pressure of muticomponent films much more strongly than carbohydrates or proteins in relation to their relatively low abundance ( Van Vleet and Williams, 1983). The surface of water or saltwater at an interface with OM-free air possesses surface tension.…”

“…In 3D, particulate, colloidal and dissolved polymers in ocean water, including transparent exopolymeric particles (TEP) and organic aggregates (OAs), produce elasticity and increase viscosity in the bulk phase of both underlying water and in water sampled from the SML. In 2D, by binding electrically to or otherwise associating with the surface film, they produce viscosity in it ( Van Vleet and Williams, 1983) and change its elasticity both in the SML and on the surfaces of bubbles and droplets.…”

“…Using an apparatus similar to those in Figures 3 and 4, a range of workers (e.g., Dragčevic´ et al, 1979;Dragčevic´ andPravdic´, 1980, 1981;Williams et al, 1980Williams et al, , 1986Van Vleet and Williams, 1983;Goldman et al, 1988;Frew and Nelson, 1992a, b;Frew et al, 2006) have compared the 2D rheological properties of both surface "film" samples taken with a stainless steel mesh sampler with samples taken by bottle from depths of 0.5 m and 5m. Oscillation of the wiper (slider) in the apparatus gave Lissajous plots (Ewoldt and McKinley, 2009) of τ 2D vs. γ 2D (not shown), where the strain γ 2D = dA/A is the relative variation of the total area in the experiment.…”

“…A large proportion of this organic matter is polymeric, with complex molecules bearing lipid, amino-acid, carbohydrate and other functional groups ( Van Vleet and Williams, 1983). In the ocean, DOM is partitioned into three relatively distinct pools: one refractory, with half-lives considered to be around 15,000 years; and one semi-labile (tens to hundreds of years), much of which remains in the surface mixed layers, particularly in the tropics, for several months or "a few years".…”

Fluorescently Labeled Phospholipids – New Class of Materials for Chemical Sensors for Environmental Monitoring

“…Natural sea/river/lake films mostly resemble layers composed of proteins, polysaccharides, humic-type materials and long chain alkanoic acid esters (Van Vleet and Williams, 1983). The generally accepted view is that the ubiquitous background of degraded biopolymeric and heterogeopolymeric material in the bulk waters has the potential to generate measurable surface films even in oligotrophic waters.…”