A challenging problem in the biophysics of cell membranes is the characterization of the lateral organization of their domains. These are made up of lipids in an ordered phase and are dispersed in a more disordered continuous phase. A widely used experimental model to study these systems are the lipid monolayers at the water-air interface. Based on these experiments and using Brownian simulations, in this talk we will see how the dipolar interaction between domains and the polydispersity in sizes affect the structure of monolayers with phase coexistence and the dynamics of their domains. We will also present a new way to estimate the dipole repulsion directly from the experimental results.