Micropatterned Surfaces through Moisture-Induced Phase-Separation of Polystyrene−Clay Nanocomposite Particles

We report micropatterned polystyrene−clay nanocomposite (PCN) surfaces with concavities by moisture-induced phase separation of PCN particles. Micropatterned film with concavity size of 800 nm to 1.3 μm and a high number density of 2 × 10⁸ features/cm² was obtained by drop-casting PCN solution (20 mg/mL PCN/THF) under ambient relative humidity of 70−80%. It is proposed that water droplets were channeled through the hydrophilic interfaces between the PCN particles, and the two-dimensional array of concavities was formed by spontaneous phase separation due to the presence of rigid clay platelets. The concavity size and number density can be tuned by varying the solvent for PCN. Micropatterned film with concavity size in the range of 650 nm to 1.1 μm with a number density of 5 × 10⁷ features/cm² was obtained using chloroform as solvent, whereas a concavity size of 150−740 nm and number density of 10⁸ features/cm² were obtained using carbon disulfide.