Structural-dilatational characteristics relationships of monoglyceride monolayers at the air-water interface

We have studied the effect of monolayer structure on dilational characteris tics (surface dilatational modulus and its elastic and viscous components) of monoglyceride monolayers (monoolein and monopalmitin) spread on the air- water interface, at 20 degreesC and at pH 5 and 7. The stress response to c ompression-expansion sinusoidal deformation of the interface in a modified Wilhelmy-type trough with two oscillating barriers was measured as a functi on of deformation amplitude (within the range of 1-20% of the initial area) , frequency (within the range of 1-300 mHz), and superficial density (withi n the range of 1-3.5 mg/m(2)). The same experimental device coupled with Br ewster angle microscopy makes it possible to determine the structure and mo rphology of the monolayer. The monolayer structure and, especially, the con ditions at which the monolayer collapses determine the viscoelastic behavio r of the monolayer and the linear response of the stress to area deformatio n. The nonlinear viscoelastic behavior of the interface has been associated with the monoglyceride monolayer collapse. It was found that the dilatatio nal modulus is not only determined by the interactions between spread molec ules (which depend on the surface density) but that the structure of the sp read monolayer also plays an important role.