Stratified patterns from evaporating colloidal dispersions containing binary particles

Stratifying particles based on their size, coupled with evaporation-driven self-assembly, is an energy-efficient path to achieve particle segregation from an engineering and scientific perspective. At the end of evaporation, elegant arrays of deposition patterns emerge. Even though it is well-known that when two dispersions, i.e., with one having particles in the micrometer range while the other one has particles in the sub-micron range, are mixed and dried, the resultant deposition pattern may have particle segregation. Nevertheless, a well-established size ratio combination that will result in an utterly stratified pattern has not been reported. In this work, we have endeavored to achieve particle stratification resulting from evaporating colloidal dispersions at inverted or pendant drop configurations consisting of two different sets of particles (hereafter known as binary particles) that vary only in size and have the same chemical composition and shape. Our findings show that the deposition patterns obtained from dispersions dried at inverted configurations imbued with binary particles show an utterly perfect stratified deposition of particles when the particle size ratio exceeds 100.