(623a) Design of Ecofriendly Surfactant Chemical Herders for Maritime Oil Spill Remediation

The floating lens of an oil spill on the seas 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. Our strategy is to use amphiphilic molecules present in the marine environment to lower the surface tension. Second, to elevate the dilatational viscosity, we take advantage of the natural polysaccharides present in the surface microlayer underlying the air/sea surface to form a network complexed to the headgroups of the marine amphiphiles.

In this presentation, we study two specific herding formulations: In the first, a glycolipid, MGDG (monogalactosyldiacylglycerol), the major component of the thylakoid membrane of chloroplasts is used as the amphiphilic species. This glycololipid, which is uncharged, can bind to polysaccharides by hydrogen bonding between sugar residues. We use lambda carrageenan, a negatively charged polysaccharide produced by green algae, as representative of sea polysaccarides.

We report measurements of the surface pressure isotherms of the glycolipid/polysaccharide complex, and their dilatational viscosity using an oscillating pendant drop. We also characterize the surface structure of the monolayer by imaging Langmuir-Blodgett films of the monolayer using atomic force microscopy. The evolution of the MGDG/polysaccharide complex in time is also studied. In a second system, we examine the effect of electrostatic binding between the polysaccharide and the herding amphiphile by replacing MGDG with phytanic acid, an isoprenoid carboxylic acid found in the marine environment. As seawater contains divalent cations (in particular calcium) the polysaccharide and the carboxylate head group of phytanic acid can bridge, resulting in a stronger complex. For the phytanic acid/polysaccharide complex, we measured increased dilatational viscosities relative to the MGDG/polysaccharide complex. Finally, we study mixtures of MGDG and phytanic acid. The unique isoprenoid chain of phytanic acid allows for close packing with the lipid and low surface tensions, which we verify by measuring surface pressure isotherms. The mixed system with high surface tension reduction and large dilatational viscosities represents an optimum herding formulation.