The present work shows, for the first time, the use of single-particle Brownian dynamics methodology, followed by optical microscopy, coupled with electrochemistry techniques to evaluate the fluidity of phospholipid films adsorbed at liquid/liquid interfaces. The combination of the two methods allows observing the movement of latex beads at the liquid/liquid interface modified by a phospholipid monolayer, with and without polarization by linear potential scans or potential steps. In this way, the effect of polarization on distearoylphosphatidylglycerol (DSPG), dimyristoylphosphatidylcholine (DMPC), and distearoylphosphatidylcholine (DSPC) monolayers, adsorbed at the water/1,2-dichloroethane interface, could be directly observed and diffusion coefficient values were derived. Lateral motilities of these particles can be correlated with the monolayer fluidity and solid character. A comparison with the behavior of the lipids at air/water interfaces is also included. (c) 2018 Elsevier Ltd. All rights reserved.