SURFACE VISCOELASTICITY OF PHOSPHOLIPID MONOLAYERS AT THE AIR WATER INTERFACE/

The surface viscoelastic properties of monolayers of two phospholipids DPPC (L-alpha-dipalmitoylphosphatidylcholine) and DMPE (L-alpha-dimyr istoylphosphatidyl-ethanolamin), at the air-water interface have been investigated. Two techniques were used for the investigation. One invo lved use of an interfacial shear rheometer (torsion pendulum apparatus ISR1), to provide measurements of the shear viscosity eta(s) as a fun ction of surface pressure, and the second, a modified LB trough with a n oscillating barrier to generate periodic dilation and compression so as to measure the dilational elastic modulus E as a function of surfa ce area. Results indicate a strong dependence of eta(3) and E upon mon olayer phases. This suggests that the viscoelastic relaxation of monol ayers can be understood as molecular rearrangements, domain exchange a nd molecular reorientations between different monolayer states.