Stress Relaxation Studies on Vinyl Stearate and Poly(vinyl stearate) Monolayers

Stress relaxation studies were performed on vinyl stearate monolayers, films polymerized at the gas-water interface, and films of vinyl stearate polymerized in the bulk and spread at the gas-water interface in order to examine the differences in the mechanical behavior of monomer, bulk polymerized, and in situ polymerized films. Monomer films exhibit a decay in stress as a function of time, while the initial stress remains constant over the time period of the experiment for the bulk polymerized sample. The relaxation response of films polymerized at the gas-water interface demonstrates that residual stresses remain in the film due to the polymerization process. These stresses can be removed by subsequent expansion and recompression of the film. These data illustrate the differences between the morphologies of the three monomolecular films.