Formation of electrically charged microdroplets in a nonpolar solvent and assembly into patterns on charged substrates

• Electrically charged droplets were dispersed in a nonpolar solvent by electro-emulsification.
• The charged droplets were assembled on a latent electrostatic image in a nonpolar solvent.
• Uniform droplets were obtained by using a double-nozzle configuration with a smooth outer flow.
• The droplet charge was much greater than the charges on ordinary ionized particles.

We developed a method to form microdroplets in a nonpolar solvent and then assemble these droplets in patterns on substrates. An electrical latent image was first formed, onto which the charged droplets were assembled. This process is based on a similar principle as the xerographic process but has been applied to liquids. The electrically charged droplets were dispersed in the nonpolar solvent using electro-emulsification.We used a double-nozzle configuration and flowed the continuous phase in a smooth jet to continuously form uniform droplets. The charged droplets in a nonpolar solvent were assembled on a latent electrostatic image. The droplet charge was estimated using simulations and experiments. The simulated and experimental results were in good agreement, and the droplet charge was found to be much higher than the charges of ordinary ionized particles because the droplet electrical charge was generated by induction between the liquid interface at the nozzle and the electrode.The droplet size was controlled by changing the flow rate of the dispersed phase, and the minimum diameter was 7 μm. The droplets were successfully assembled on the latent images at various latent voltages which produced varying droplet size. Charged 7- and 80-μm droplets were used to form patterns on a 500-μm-wide latent line in a nonpolar solvent using electrostatic forces. The charged droplets were also assembled on a latent image of 400 μm L/S. We plan to extend the use of this method to various applications, including sensors and composite materials.