Liquid appears to behave differently when in contact with a solid surface under certain conditions. Shape of a liquid droplet over a solid surface, for instance, can be influenced by various parameters, such as wetting properties, surface roughness, viscosity, surface tension, and external forces. The wetting properties, in particular, termed as wettability, is one of the key parameters that affects the shape of droplets on a surface. Furthermore, the wetting properties of a surface can influence other parameters that affect the droplet shape and flow, such as surface roughness, viscosity, and surface tension. Wettability itself can be influenced by several parameters that affect the droplet shape. Surfactants, for instance, are molecules that can change the wettability of the solid surface when added in the liquid. Studies have found that surfactants addition to liquids can change the contact angle of surface droplets, which leads to changes in droplet shape. Furthermore, studies have shown a relation of surfactant concentration and temperature on the spreading kinetics and the final shape of droplet. Most studies have focused on the static interfacial tension and contact angle measurement but very few have focused on dynamic measurements. The goal of this paper is to experimentally investigate the temporal impact of surfactants on the surface wettability and how it affects the shape of the droplet.

The reduction in interfacial tension due to the addition of surfactants can lead to an increase in wettability, leading to the droplet spreading out more on the surface. The effect of surfactants on interfacial tension and wettability is not straightforward and depends on various factors, including surfactant type and concentration, solid surface chemistry, and liquid properties. In this paper, droplet contact angle and interfacial tension will be measured via Droplet Shape Analyzer given different types of surfactant and concentration. Furthermore, the temporal evolution of the contact angle and interfacial tension will be investigated to understand the transport behavior of the surfactant molecules. The expected results here will advance the fundamental understanding of the droplet flow behavior on a surface with various surfactant type and concentrations.

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