부산대학교 도서관

Ring-like residual deposits are often observed after drying suspension droplets on surfaces. That introducesa crucial defect in practical applications, such as ink-jet printing that requires a uniform deposit. In this study, depositions after drying sessile/pendant droplets with silica/polystyrene particles wereexamined to identify the effect of gravitational sedimentation of particles on self-pinning and depositionpattern. The suspension droplet with larger polystyrene (or silica) particles would trigger the self-pinningat larger (or smaller) particle concentrations. The deposition pattern of pendant drops with silica particlesis hill-like. This is due to the large density difference between silica and water to induce high sedimentationvelocity, and the particles would precipitate and aggregate along the air–liquid interface to form ahollow shell deposit. The depositions for suspensions with bi-dispersed particles, the larger silica particleswould accumulate at the bottom of the deposit due to the higher sedimentation velocity, in contrastto the well-mixed in the deposits for bi-dispersed polystyrene particles. The sedimentation and capillaryflow velocities were calculated and discussed. These new findings reveal that the particle density (gravityeffect) can be used to adjust the sedimentation velocity to control the deposition morphology and particlesize distribution even to suppress the coffee-ring effect.