The contact angle of a sea-water drops on a superhydrophobic surface of steel A40S during evaporation research

Abstract

The work is directed at solving the problem of reducing the efficiency of marine industrial facilities, in particular shipping, due to the harmful effects caused by biological soiling. The technology of superhydrophobic coating is combining economic and environmental criteria for the protection of hulls. However, there are problems for their widespread use, associated with temporary surface degradation and loss of the superhydrophobic state. Therefore, experimental studies, including observations of the behavior of sea-water drops on the superhydrophobic surfaces of materials used in shipbuilding, help to identify the causes of the microstructure disturbance of the layer and the loss of necessary properties.

In this work, the mechanism of evaporation of natural sea water droplets on the superhydrophobic surface of A40S shipbuilding steel is considered. A possibility of loss of a superhydrophobic state with salt concentration increase due to a droplet´s volume decrease, the dependence of the contact angle on the evaporation time was investigated on a specially designed unit. The effect of the force of gravity on the shape of a drop is estimated.

It is shown that in the process of evaporation the contact angle decreases, but before the crystallization process begins, it exceeds 150º, thereby preserving the superhydrophobic properties of the surface. A decrease in volume does not completely eliminate the effect of gravity on the shape of the drop, but reaches its minimum for a value of 0.5 μl.

The obtained results contribute to the further investigation of the properties of superhydrophobic coatings, and expand the possibilities of their application in shipbuilding.