An experimental study of boundary lubricants is described which is based on a surface force apparatus that had been modified to allow an oscillatory shear stress to be imposed. Phospholipid monolayers having different acyl chain lengths and a phospholipid bilayer were deposited onto the mica surfaces using the LB method at relatively high surface pressures in order to achieve close-packing. The storage moduli and loss tangents were measured as a function of the frequency and the contact pressure. They provide a means of monitoring the influence of the contact pressure on the molecular organisation of the lipid layers and also an understanding of the influence of this organisation on the sliding frictional characteristics of the layers.
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