Transient contact angle of evaporating inkjet droplet on trans-parent polymer substrate

For advanced control and optimization of inkjet-printed droplet and line morphologies, this paper seeks to provide insights into characterizing and understanding the transient behavior of the inkjet droplet on different surface conditions and substrate temperatures. The transient behavior of contact angle of tested fluids includes deionised water and glycerol solution is discussed. Fluids with different viscosity and surface tension are deposited by inkjet on polymer substrate in three surface conditions: as-received, plasma treated and hydrophobic coated. The substrates are subjected to various thermal exposures (from room temperature up to 75°C) during the printing process. The induced convective flux within the droplet is dependent on the initial interaction of the droplet and substrate. The impact of the surface temperature to the drying of the droplet is examined. "Stick-slip", a phenomenon of the contact line of impinged droplet remain static for an interval of time and move abruptly toward the centre of the droplet, is observed on specific printing conditions and fluid properties. Video microscopy and digital image analysis techniques are applied to monitor and observe the evaporation of the droplets.