A new strategy to create well-ordered latex particle monofilms from polydisperse latex solutions was developed. Due to size-dependent segregation, the spherical particles assemble in grains with a uniform sphere size within each grain. The size-dependent segregation process can be deduced from the action of a single force, the lateral capillary force. A strong temperature dependence can be observed, and the process becomes evident when the substrate is cooled. The samples are characterized by scanning force microscopy. Finally, to prove the theoretical model, a computer simulation is performed, supporting the experimental results.