When the number of nanoparticles introduced over the subphase is exactly equal to what is needed to cover the entire surface, the film tends to be monolayer. With increasing number of nanoparticles over this limit, bi-layer or multilayers form at different locations of the films. Regardless of the subphase used, in air-liquid interfacial assembly procedures, nanoparticles that are synthesized in an aqueous medium have to functionalized with organic ligands to be dispersed in a volatile organic solvent. It stands to reason that the use of a non-polar solvent (e.g., hexane, toluene, chloroform, etc.) as the solvent of the nanoparticle colloid is convenient as the solvent stays separated from the polar subphase (water or glycols) due to the immiscibility. This requires the nanoparticles to be made dispersible in a non-polar phase, for instance via ligand exchange procedures. Usually, all the excess ligands present in the non-polar phase are removed before self-assembly. Griesemer et al.