Investigation of sea-surface microlayer and phytoplankton culture samples by monolayer techniques and Brewster angle microscopy

Natural samples of sea-surface microlayer and phytoplankton culture samples have been studied by monolayer techniques and by Brewster angle microscopy (BAM). Surface pressure-area (pi-A) and surface potential-area (Delta V-A) isotherms have been measured. Simultaneously BAM video images have been recorded. The pi-A isotherms, as well as BAM images of monolayers of dipalmitoyl phosphatidylcholine (DPPC), dimyristoylphosphatidic acid (DMPA) and dioctadecyldimethyl ammonium bromide (DOMA) spread on an aqueous subphase containing a sample of phytoplankton culture show that surface active substances released by phytoplankton influence molecular organization as well as domain morphology of the lipid monolayers. The sea-surface microlayer sample spread at the air/water interface exhibits the characteristics of a liquid expanded phase without undergoing a phase transition. The BAM images taken from this film depend on surface pressure, showing at low surface pressures liquid condensed domains surrounded by a liquid expanded phase, and at higher surface densities only a liquid condensed phase