Spreading dynamics of liquid droplets

The spreading dynamics of liquid droplets has been widely studied due to its importance in many technological applications. Studies have found that spreading is governed by a spreading coefficient, which is dependent on the competition between the cohesion energy of the liquid itself and the adhesion energy between the solid and the liquid. The liquid’s surface tension is an important factor that affects both cohesion and adhesion energies, hence it can influence spreading behaviours. It is also useful to study the effects of surface roughness since most real surfaces have defects.This project aims to examine the effects of surface tension and surface roughness on the spreading dynamics of liquid droplets on solid surfaces, quantified in terms of the degree and rate of wetting. This was done by varying the liquid’s surface tension by using different surfactant concentrations and varying the solid’s surface roughness by using sandpapers of different grit sizes. Samples of the sandpaper were coated with varying levels of surfactant, and liquid droplets were deposited on its surface to observe their spreading behaviours. The spreading behaviour of the liquid droplets was found to be dependent on both the liquid’s surface tension and the solid’s surface roughness. The results suggest a critical surfactant concentration, dependent on the surface roughness, which determines the effectiveness of the surfactant’s influence on spreading behaviours of liquids. Results also show that rougher surfaces also potentially reduced the wettability of the solid surface during the early phase of spreading.Bachelor of Engineering (Mechanical Engineering