Formation of coffee-stain patterns at the nanoscale: The role of nanoparticle solubility and solvent evaporation rate.
When droplets of nanoparticle suspension evaporate from surfaces, they leave behind a deposit of nanoparticles. The mechanism of evaporation-induced pattern formation in the deposit is studied by molecular dynamics simulations for sessile nanodroplets. The influence of the interaction between nanoparticles and liquid molecules and the influence of the evaporation rate on the final deposition pattern are addressed. When the nanoparticle-liquid interaction is weaker than the liquid-liquid interaction, an interaction-driven or evaporation-induced layer of nanoparticles appears at the liquid-vapor interface and eventually collapses onto the solid surface to form a uniform deposit independently of the evaporation rate. When the nanoparticle-liquid and liquid-liquid interactions are comparable, the nanoparticles are dispersed inside the droplet and evaporation takes place with the contact line pinned at a surface defect. In such a case, a pattern with an approximate ring-like shape is found with fast evaporation, while a more uniform distribution is observed with slower evaporation. When the liquid-nanoparticle interaction is stronger than the liquid-liquid interaction, evaporation always occurs with receding contact line. The final deposition pattern changes from volcano-like to pancake-like with decreasing evaporation rate. These findings might help to design nanoscale structures like nanopatterns or nanowires on surface through controlled solvent evaporation.
Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermo-Fluids & Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Straße 8, D-64287 Darmstadt, Germany.
Jianguo
J
Zhang
Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermo-Fluids & Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Straße 8, D-64287 Darmstadt, Germany.
Jasmin
J
Milzetti
Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermo-Fluids & Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Straße 8, D-64287 Darmstadt, Germany.
Frédéric
0000000284705811
F
Leroy
Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermo-Fluids & Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Straße 8, D-64287 Darmstadt, Germany.
Florian
F
Müller-Plathe