A new methodology based on the study of the viscoelastic properties of polymer monolayers was developed. The Maxwell model applied to a viscoelastic bidimensional body correlates with the dynamic behavior of polyvinyl alcohol (PVA) spread or adsorbed at the air/water and dichloromethane (DCM)/water interfaces. Differences in the conformation of the PVA monolayers were observed depending on how the interface was formed and the nature of the hydrophobic phase. For a condensed polymer monolayer (poly(DL-lactide) (PLA50)), the model was no longer valid because of particular properties of the phase, which condenses during the first-order transition of the polymer monolayer. In the mixed PVA/PLA50 monolayer formed at the air/water or DCM/water interface, the presence of PVA in the him allowed us to use the theoretical model. It is concluded that PVA probably strongly interacts with PLA50 in the interfacial region during the preparation of microparticles by an oil-in-water emulsion-based process,