Wetting Transition from Lotus Leaf to Rose Petal using Modified Fly Ash

We present a facile and scalable approach to develop lotus leaf as well rose petal like superhydrophobic surfaces using fly ash (an industrial waste obtained from the burning of coal). To achieve this, as-obtained fly ash powder with wide particle size distribution (FA) was processed through sedimentation technique to obtain fly ash powder with narrower particle size distribution (FAS) and modified with two different concentrations of stearic acid (SA) and treated at two different temperatures - one each below and above melting point of SA. All samples showed superhydrophobicity, where, the water contact angle (WCA) increased with an increase in the amount of stearic acid and modification temperature. Interestingly, the water droplets roll-off from the modified FA surfaces at a small tilting angle of 5 degrees similar to the lotus leaf, whereas, the modified FAS surfaces exhibited high adhesion for water droplets even when inverted, as in case of the rose petal. It was seen that drying at temperature lower than melting temperature of stearic acid introduced additional roughness, yet the WCA decreased. This is investigated to understand the effect of topology and substrate nature on WCA in different wetting states.