The floating lens of an oil spill on the sea surface can be removed by compressing the oil layer to a sufficient thickness so that it can be incinerated. In chemical herding, surfactant is dispersed as a monolayer onto the sea surface at the periphery of the lens to lower the air/sea surface tension. This causes the lens to contract upon itself. An effective herder is required to significantly lower the tension, and to dampen waves, which can act to break-up the herding monolayer encircling the spill. To dampen surface wave action, the herder monolayer should have a large dilatational surface viscosity, which can dissipate the wave energy. The focus of this research is to develop herders, which have these properties and are ecofriendly (“green”) –a difficult requirement because the marine biota is very sensitive to chemical addition.  We use amphiphilic molecules present in the marine environment to lower the surface tension. To this end, we take advantage of the synergism between glycolipids (particularly MGDG, monogalactosyldiacylglycerol) and phytanic acid (an isoprenoid) which are both present in the thylakoid membrane of the chloroplasts of plants. These two molecules in the membrane form a low tension system through efficient packing. To elevate the dilatational viscosity, we take advantage of the natural polysacharides present in the surface micro-layer underlying the air/sea surface to form a network complex to the head-groups of the marine amphiphiles MGDG and phytanic acid. We use lambda carrageenan, a negatively charged polysaccharide produced by green algae, as representative of the polysaccharides of the sea surface microlayer.  We report measurements of the surface pressure isotherms using a Langmuir trough, and dilatational viscosity using an oscillating pendant drop. We confirm a synergism between MGDG and phytanic acid in mixed monolayers that results in a low tension, and a binding of the polysaccharide to the herding monolayer which results in high dilatational viscosity. Finally we demonstrate pan scale experiments of the efficacy of this herding formulation.

Marine surfactants as chemical herders for maritime oil spill remediation

2019 Fall National Meeting

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