Formation of dimeric carboxylic acid functional groups observed at the film-substrate interface of ethyl acrylate/methacrylic acid (EA/MAA) and butyl acrylate / methyl meth-acrylate / methacrylic acid (BA/MMA/MAA) latex films prepared on a high surface tension substrate, such as liquid mercury, is observed when sodium dioctyl sulfosuccinate (SDOSS) is employed as the synthetic emulsifier. To address the acid species assembled at this interface due to the inability of SDOSS to effectively alleviate interfacial tension and to assess the orientation and spatial configuration of acid groups species at the interface, polarized attenuated total reflectance, Fourier-transform infrared spectroscopy (ATR FT–IR) is employed. It is found that the acid dimer rings adopt an average “on-edge” configuration at the interface with the hydrogen-bonded rings perpendicular to the film-mercury interface. This configuration serves to provide not only the necessary interfacial acid-dimer layer, but also facilitates favorable ring–ring interactions between groups of opposite polarity on adjacent rings. This study indicates that the on-edge configuration may also serve to reduce unfavorable interactions between the polar acid functionality and the less polar components present in the bulk of the coalesced latexes. © 1993 John Wiley & Sons, Inc.