Effect of carrageenans of different chemical structures in biointerfaces: a Langmuir film study. Carrageenans have unique properties in the pharmaceutical and food industries that involve interactions with lipid interfaces, which may be accessed if surface chemistry techniques are employed. The interaction between three different types of carrageenans with dipalmitoylphosphatidylcholine (DPPC) was investigated using Langmuir monolayers as biointerface models. With a combination of data on Surface Pressure-Area Isotherms and Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), the effect of different fractions on DPPC monolayers was compared by considering the chemical and structural differences as well as the anticoagulant activity of each fraction. Thus, a model is proposed in which carrageenans can encompass interactions that are maximized due to geometrical adaptations on behalf of the interactions between polysaccharide sulfate groups and lipid polar heads.