We report a simple method to films of CdS nanocrystals at the water-oil interface starting with a polydispersed aqueous sol of crystallites and alkylamines. The optical band gaps of the obtained films are dependent on the chain length of amines, with the smallest chain length amine yielding the largest gap. A systematic increase in particle diameters following adsorption is responsible for the changes in the electronic structure of the films. The films were characterized with X-ray diffraction, transmission and scanning electron microscopy as well as UV-visible spectroscopy. (C) 2012 Elsevier B. V. All rights reserved.