The addition of dodecanethiol to a polydisperse platinum colloidal aqueous solution capped with acrylic acid leads to self-assembled monolayers which not only contain various sizes, but also various shapes of nanoparticles. Assembled monolayers arranged in hcp arrays are achieved for mixed shape-samples. In;the case of the assembly of cubic nanoparticles, cubic closest packing is achieved when the size difference between the nanoparticles is less than 25% (or between 6 and 8 nm). The ccp array is disrupted when the size difference is between 25 and 60% or there is a mixture of shapes. Finally, size segregation is seen in regions where the size difference is more than 60% with the resultant assembly being hcp no matter what the shape.