Suppression of the coffee-ring effect by sugar-assisted depinning of contact line.

Inkjet printing is of growing interest due to the attractive technologies for surface patterning. During the printing process, the solutes are transported to the droplet periphery and form a ring-like deposit, which disturbs the fabrication of high-resolution patterns. Thus, controlling the uniformity of particle coating is crucial in the advanced and extensive applications.

Rotary motion of a micro-solid particle under a stationary difference of electric potential.

The periodic rotary motion of spherical sub-millimeter-sized plastic objects is generated under a direct-current electric field in an oil phase containing a small amount of anionic or cationic surfactant. Twin-rotary motion is observed between a pair of counter-electrodes; i.e.

Back-and-forth micromotion of aqueous droplets in a dc electric field.

Recently, it was reported that an aqueous droplet in an oil phase exhibited rhythmic back-and-forth motion under stationary dc voltage on the order of 100 V. Here, we demonstrate that the threshold voltage for inducing such oscillation is successfully decreased to the order of 10 V through downsizing of the experimental system. Notably, the threshold electric field tends to decrease with a nonlinear scaling relationship accompanied by the downsizing.