Comparison of micro-/nano-hierarchical and nano-scale roughness of silica membranes in terms of wetting behavior and transparency

Superhydrophobic membranes with different surface roughness were prepared by dip-coating method. The wetting behavior observed on the micro-/nano-hierarchical and nano-scale structure was the same, which indicated that superhydrophobic membranes could be fabricated without micro-scale structures. The static contact angle is ascribed to the air bubbles trapped in the surface, while contact angle hysteresis is attributed to the discontinuous contact line. The contact line on the micro-/nano-hierarchical asperities is relatively stable with respect to the nano-scale asperities. Membranes with lower roughness show higher light transmittance than the bare substrate and better visual transparency.