Evaporation of an inkjet droplet on a flat substrate

Understanding the evaporation behavior of inkjet droplets has become increasingly important as printed electronic technology develops. In this study, the evaporation phenomena of a 5-6-pL droplet were studied. Four types of non-polar liquid droplets were prepared via the inkjet method and placed on substrates with small contact-angle hystereses. The observed contact radius and contact angle during evaporation were in good agreement with the theoretical model. This model, that of diffusion-controlled evaporation, was obtained based on a microliter droplet or bulk liquid wherein the evaporation was considered to be a quasi-steady state. The square of contact radius R decreased linearly with the evaporation time t, and the gradient of the R-2 vs t plot provided the diffusivity of vapor in the air. The experimentally obtained diffusivity values were helpful for estimating the evaporation speeds and times of droplets at any contact angle. (C) 2017 The Japan Society of Applied Physics