Flow Characteristics and Deposit Structure for Particle-laden Rivulets

The structure of the deposit left behind by a nanoparticle-laden rivulet is governed by fluid transport during its evaporation. In this work, we used fluorescent tracers and optical microscopy to measure this evolving flow inside aqueous rivulets printed using inkjet. The use of a chemically treated substrate prevented the breakup of the rivulet by decreasing the receding contact angle close to zero. We investigated the effects of (i) adding small surfactants (sodium dodecyl sulfate) and (ii) using binary (water-alcohol) solvent on the flow characteristics and final deposit structure. The binary mixture created a strong solutal Marangoni flow (i.e. eddies) during evaporation and resulted in a “twin line” deposit. In contrast, the presence of surfactant at high concentrations induced rapid dewetting of the rivulet at the final stages of evaporation to create a “single line” deposit. For mixed binary-surfactant solutions, the particle transport was highly dependent on the presence of alcohol rather than surfactants at the early stages of evaporation. However, during the later stages, surfactant plays a more important role in governing the transport dynamics.