Interfacial tension gradient driven self-assembly of binary colloidal particles for fabrication of superhydrophobic porous films.

Hypothesis: Self-assembly of two types of particles into the binary colloidal crystals (BCCs) leads to the peculiar features which the monocomponent colloidal crystals do not possess. However, the self-assembly methods of the BCCs are still limited.

Experiments: A facile, cost-effective and controllable approach was presented to fabricate the BCCs by directly dripping silica particle suspensions containing water and ethanol into the monodisperse polytetrafluoroethylene (PTFE) colloidal solutions. The BCCs composed of the silica and PTFE particles were formed at the air-liquid interface and picked up using the target substrates, followed by the corrosion of silica particles. Using this strategy, various ordered porous PTFE films including homo-pore-size mono/multilayer and hetero-pore-size bilayer films were prepared. The chemical composition of the porous films was well controlled.

Findings: The dissolution of ethanol resulted in the interfacial tension gradient, and thus the Marangoni convection and the relative movement of the liquid and the particles emerged. The silica particles were trapped at the air-liquid interface and the PTFE particles filled the interstitial spaces between the silica particles. After the porous films were sintered at temperatures above the melting point of PTFE, the PTFE particles were transformed into nanofibers, leading to the transferability, excellent superhydrophobicity and environmental durability.